# The TEMPO Survey II: Science Cases Leveraged from a Proposed 30-Day Time
Domain Survey of the Orion Nebula with the Nancy Grace Roman Space Telescope

Melinda Soares-Furtado 1,2 0000-0001-7493-7419 Mary Anne Limbach 3
0000-0002-9521-9798 Andrew Vanderburg 2 0000-0001-7246-5438 John Bally 4
0000-0001-8135-6612 Juliette Becker 1 0000-0002-7733-4522 Anna L. Rosen 5,6
0000-0003-4423-0660 Luke G. Bouma 7 0000-0002-0514-5538 Johanna M. Vos 8
0000-0003-0489-1528 Steve B. Howell 9 0000-0002-2532-2853 Thomas G. Beatty 1
0000-0002-9539-4203 William M. J. Best 10 0000-0003-0562-1511 Anne Marie Cody
11 0000-0002-3656-6706 Adam Distler 1 0009-0006-4294-6760 Elena D’Onghia 1
0000-0003-2676-8344 René Heller 12 0000-0002-9831-0984 Brandon S. Hensley 13
0000-0001-7449-4638 Natalie R. Hinkel 14 0000-0003-0595-5132 Brian Jackson 15
0000-0002-9495-9700 Marina Kounkel 16 0000-0002-5365-1267 Adam Kraus 10
0000-0001-9811-568X Andrew W. Mann 17 0000-0003-3654-1602 Nicholas T. Marston
1 0009-0007-1123-0038 Massimo Robberto 18,19 0000-0002-9573-3199 Joseph E.
Rodriguez 20 0000-0001-8812-0565 Jason H. Steffen 21 0000-0003-2202-3847
Johanna K. Teske 22 0009-0008-2801-5040 Richard Townsend 1 0000-0002-2522-8605
Ricardo Yarza 23,24 0000-0003-0381-1039 Allison Youngblood 25
0000-0002-1176-3391 1Department of Astronomy, University of Wisconsin-Madison,
475 N. Charter St., Madison, WI 53706, USA  2Department of Physics & Kavli
Institute for Astrophysics and Space Research,
Massachusetts Institute of Technology, Cambridge, MA 02139, USA  3Department
of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA  4Center for
Astrophysics and Space Astronomy,
Astrophysical and Planetary Sciences Department, University of Colorado,
Boulder, CO 80389, USA  5Department of Astronomy, San Diego State University,
San Diego, CA 92182, USA  6Computational Science Research Center, San Diego
State University, San Diego, CA 92182, USA  7Department of Astronomy, MC
249-17, California Institute of Technology, Pasadena, CA 91125, USA  8School
of Physics, Trinity College Dublin, The University of Dublin, Dublin 2,
Ireland  9NASA Ames Research Center, Moffett Field, CA 94035, USA
10Department of Astronomy, The University of Texas at Austin, Austin, TX
78712, USA  11SETI Institute, 189 N. Bernardo Ave #200, Mountain View, CA
94043, USA  12Max Planck Institute for Solar System Research, Justus-von-
Liebig-Weg 3, 37077 Göttingen, Germany  13Jet Propulsion Laboratory,
California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109,
USA  14Physics & Astronomy Department, Louisiana State University, Baton
Rouge, LA 70803, USA  15Department of Physics, Boise State University, Boise
ID 83725-1570, USA  16Department of Physics & Astronomy, Vanderbilt
University, Nashville, TN 37235, USA  17Department of Physics & Astronomy, The
University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA
18Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD
21218, USA  19Johns Hopkins University, 3400 N. Charles St., Baltimore, MD
21218, USA  20Center for Data Intensive and Time Domain Astronomy, Department
of Physics and Astronomy, Michigan State University, East Lansing, MI 48824,
USA  21University of Nevada, Las Vegas & Nevada Center for Astrophysics, 4505
S Maryland Pkwy, Las Vegas, NV 89154, USA  22Earth and Planets Laboratory,
Carnegie Institution for Science, 5241 Broad Branch Rd NW, Washington, DC
20015, USA  23Department of Astronomy and Astrophysics, University of
California, Santa Cruz, CA 95064, USA  24Texas Advanced Computing Center,
University of Texas, Austin, TX 78759, USA  25Exoplanets and Stellar
Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD
20771, USA  Corresponding author<EMAIL_ADDRESS>
###### Abstract

The TEMPO (Transiting Exosatellites, Moons, and Planets in Orion) Survey is a
proposed 30-day observational campaign using the Nancy Grace Roman Space
Telescope. By providing deep, high-resolution, short-cadence infrared
photometry of a dynamic star-forming region, TEMPO will investigate the
demographics of exosatellites orbiting free-floating planets and brown dwarfs
— a largely unexplored discovery space. Here, we present the simulated
detection yields of three populations: extrasolar moon analogs orbiting free-
floating planets, exosatellites orbiting brown dwarfs, and exoplanets orbiting
young stars. Additionally, we outline a comprehensive range of anticipated
scientific outcomes accompanying such a survey. These science drivers include:
obtaining observational constraints to test prevailing theories of moon,
planet, and star formation; directly detecting widely separated exoplanets
orbiting young stars; investigating the variability of young stars and brown
dwarfs; constraining the low-mass end of the stellar initial mass function;
constructing the distribution of dust in the Orion Nebula and mapping
evolution in the near-infrared extinction law; mapping emission features that
trace the shocked gas in the region; constructing a dynamical map of Orion
members using proper motions; and searching for extragalactic sources and
transients via deep extragalactic observations reaching a limiting magnitude
of $m_{\mathrm{AB}}=29.7$ mag (F146 filter).

###### keywords:

Brown Dwarfs (185) — Natural satellites (Extrasolar) (483) — Exoplanets (498)
— Free floating planets (549) — Surveys (1671) — Young star clusters (1833)

##  1 Introduction

Time-domain surveys have provided valuable insights into the diverse and
evolving phenomena that emerge at the early stages of star and planet
formation. Variability analyses of these regions have informed our knowledge
on topics such as (sub)stellar mass accretion (Bell & Lin, 1994; D’Angelo &
Spruit, 2010; Venuti et al., 2017; Cody & Hillenbrand, 2018; Sabbi et al.,
2020), rotational velocities of young brown dwarfs and pre-main-sequence stars
(Hartmann, 2002; Marilli et al., 2007), and circumstellar disk evolution
(Hillenbrand, 2002). While optical transit surveys have yielded a wealth of
knowledge about exoplanets orbiting main sequence (MS) stars (e.g., Pepper et
al., 2007; Collier Cameron et al., 2007; Dressing & Charbonneau, 2013;
Sanchis-Ojeda et al., 2014; Winn & Fabrycky, 2015; Zhu et al., 2018; Petigura
et al., 2018; Hardegree-Ullman et al., 2019; Vanderspek et al., 2019; Uzsoy et
al., 2021), our understanding of exosatellite populations remains
comparatively sparse (e.g., Hippke, 2015; He et al., 2017; Teachey & Kipping,
2018; Vanderburg & Rodriguez, 2021; Tamburo et al., 2022a; Limbach et al.,
2024).

The forthcoming Nancy Grace Roman Space Telescope (formerly known as the Wide
Field Infrared Survey Telescope; hereafter Roman) presents the potential to
drastically advance our understanding of this untapped discovery space. More
specifically, high-precision near-infrared (NIR) photometric transit searches
among free-floating planets (FFPs; also known as “isolated planetary-mass
objects” or “rogue” planets) and brown dwarfs is an emerging method to detect
exosatellites111Following a precedent established in the literature, we use
the term “exosatellite” to refer to a companion orbiting an FFP, brown dwarf,
or late M dwarf (Kenworthy & Mamajek, 2015; Muirhead et al., 2019). (e.g., He
et al., 2017; Tamburo & Muirhead, 2019; Tamburo et al., 2022b, a; Limbach et
al., 2021, 2023, 2024). This technique is particularly effective when applied
to young FFPs and brown dwarfs that are still self-luminous at
$1-2\,\mathrm{\mu m}$.

In this paper, we present the broad scientific outcomes that will accompany
the proposed Transiting Exosatellites, Moons, and Planets in Orion (TEMPO)
Survey — a 30-day time domain investigation of the Orion Nebula Cluster (ONC)
and surrounding regions using Roman. Limbach et al. (2023) found that the ONC
— a young star cluster located in the Orion Molecular Cloud Complex — serves
as the optimal location for the TEMPO survey, due to its young age (1–3 Myr;
Jeffries 2007), proximity ($390\pm 2$ pc; Maíz Apellániz et al. 2022) and
dense stellar population (central density ${\sim}10^{4.7}$ stars/pc3;
McCaughrean & Stauffer 1994; Hillenbrand & Hartmann 1998). Roman’s instrument
specifications, particularly its large field of view and IR bandpass, will
facilitate the concurrent monitoring of thousands of young, luminous targets.
We refer the reader to Table 1 in Limbach et al. (2023) for a breakdown of the
estimated number of monitored sources grouped by host type. Moreover, this
survey offers the sensitivity required to detect Titan-sized worlds transiting
brown dwarfs and FFPs (Limbach et al., 2023).

In addition to probing exosatellite demographics, TEMPO presents an
opportunity to investigate a wide range of astrophysical phenomena. In this
work, we outline the anticipated scientific outcomes enabled by such an
investigation. In Section 2, we present a summary of the TEMPO survey design
specifications. Section 3 details the primary scientific objectives shaping
the design of the proposed survey, as well as the simulated survey
exosatellite yield. In Section 4, we present the broad scientific outcomes
enabled by the TEMPO survey. Subsequent subsections delve into specialized
topics, including: probing the planetary-mass regime of the Initial Mass
Function (Section 4.1); ONC membership analysis of substellar targets (Section
4.2); direct imaging detections of substellar targets (Section 4.3);
gyrochronological investigations (Section 4.4); investigations of stellar
formation, evolution, variability, and multiplicity (Section 4.5); the
generation of regional dust maps (Section 4.6.1); investigations of the nature
and origin of the Radcliffe Wave (Section 4.6.2); and extragalactic source
detection (Section 4.6.3). We conclude in Section 5 with final remarks.

Parameter | Value
---|---
Field of View | 0.28 deg2
Duration | Two observation windows of 15 days each, separated by one year
Spectral Band | F146, 0.93–2.00 $\mathrm{\mu m}$
Exposure Time | 18 s (6 reads at 3 s each)
Limiting Magnitude (1 month) | 29.7 magAB
Photometric Precision (1 hr, F146 = 17 magAB) | 125 ppm
Photometric Precision (1 hr, F146 = 21 magAB) | 850 ppm

Table 1: Observational parameters for the proposed TEMPO survey, utilizing the
Roman WFI/F146 filter.

##  2 TEMPO Survey Design Summary

Currently set to launch in 2027, Roman will be stationed at the second
Lagrange point and will have a primary mission lifetime of five years (Green
et al., 2012; Spergel et al., 2013, 2015). Roman’s main science goals
encompass censuses of high redshift galaxies and a microlensing survey of the
inner Milky Way. Roman has two main scientific instruments: the Coronagraph
Instrument and the Wide Field Instrument (WFI). The proposed TEMPO survey aims
to harness the WFI—a high-spatial-resolution (0.11” per pixel), wide-field
($0.28\,\mathrm{deg}^{2}$) camera. The instrument covers a wavelength range
spanning $0.48$–$2.3$ $\mathrm{\mu m}$, enabling NIR observations. Drawing
from the findings of Limbach et al. (2023) and Tamburo et al. (2022b), TEMPO
will employ the WFI/F146 filter. Future work will explore the benefits of
alternating between the WFI/F146 and WFI/F213 filters as a method of
disentangling color-dependent host variability from achromatic transit
signatures.

The observational parameters of the proposed TEMPO survey are provided in
Table 1. This table includes the survey field of view, proposed duration,
spectral band limits, exposure time, limiting magnitudes, and expected
photometric precision. Comprehensive information on the survey’s design
specifications and potential noise sources can be found in Limbach et al.
(2023). Notably, TEMPO will be near-photon-noise-limited for ONC members of
0.2 $\rm M_{\odot}$ down to 1 $\rm M_{\mathrm{J}}$, corresponding magnitude
range of $17$–$23$ $\mathrm{mag_{AB}}$.

Prior successes, such as the Hubble Space Telescope (HST) F130N/F139M
discovery of 320 brown dwarfs and 220 FFPs (with masses as low as 5 $\rm
M_{\mathrm{J}}$) within a tiled FOV (13 arcmin2; Gennaro & Robberto 2020),
suggest promising outcomes for TEMPO. Further, the TEMPO footprint offers more
than twice the FOV obtained by prior tiled surveys of the ONC (Drass et al.,
2016; Robberto et al., 2020; Gennaro & Robberto, 2020). The TEMPO footprint is
illustrated as the white outline in Figure 1. The core of the ONC, known as
the Trapezium cluster, is the brightest region in the figure.

Figure 1: Illustration of the proposed TEMPO survey’s field of view, focusing
on the Orion Nebula Cluster (ONC) which has an age range of 1–3 Myr. The ONC
is a region of intense star formation and offers a valuable window into the
early stages of stellar and planetary evolution. Credit: ESO/H. Drass et al.

TEMPO couples Roman’s larger FOV with an orientation optimized for maximum
stellar density, allowing us to monitor $1.75\times$ the number of $17$–$21$
$\mathrm{mag_{AB}}$ sources observed by Gennaro & Robberto (2020). Within the
ONC alone, TEMPO will study 2,000 young stars, 560 brown dwarfs, and 400 FFPs
(Limbach et al., 2023). An additional 5,000 field stars of varying ages will
also be monitored during the survey.

TEMPO can probe sources below the mass limit of the Gennaro & Robberto (2020)
investigation, therefore, our estimate for the number of FFPs in our survey is
likely to be on the conservative side. In addition, an investigation of the
Trapezium Cluster using the James Webb Space Telescope (JWST) Near Infrared
Camera (NIRCam) instrument reported the detection of 540 FFPs down to 0.6 $\rm
M_{\mathrm{J}}$ (Pearson & McCaughrean, 2023). These sources were identified
within an $11\arcmin{}\times 7.5$ ($1.2$ pc $\times$ $0.8$ pc) FOV, which is
slightly larger than a single Roman tile. If we were to extrapolate from these
findings, TEMPO will monitor as many as ${\sim}5,000$ FFPs, however, our
reported yields remain conservative until there is further follow up of the
JWST results.

The TEMPO survey will observe the ONC and surrounding regions for 720 hours in
two 15-day intervals separated by one year. The expected photometric
precisions range from 125 ppm (for 17 $\mathrm{mag_{AB}}$ stars) to 850 ppm
(for 21 $\mathrm{mag_{AB}}$ stars). Continuous 18-s exposures will be employed
to minimize detector saturation, providing unsaturated photometry for stars as
bright as 17 $\mathrm{mag_{AB}}$. Furthermore, we can obtain photometric
measurements of the brighter, saturated stars by employing advanced analysis
techniques, such as halo photometry (White et al., 2017). To assess cluster
membership of dimmer sources, which fall below the faintness limit imposed by
the Gaia space observatory (Gaia Collaboration et al., 2023), TEMPO proposes
to measure kinematic (proper motion) by splitting the observation window into
two 360-hour segments separated by one year. This science case is discussed in
more detail in Section 4.1.1. The one-year temporal gap in the observations
also helps with vetting transit candidates, as transits are strictly periodic,
while (sub)stellar variability is expected to evolve with time (Limbach et
al., 2023).

##  3 TEMPO Primary Science Outcomes

Figure 2: Distribution of host-companion separation (AU) as a function of host
mass ($\rm M_{\odot}$) for the simulated TEMPO survey detections (circles),
Solar System moons and planets (blue squares) and select habitable exoplanets
(red diamonds). Simulated TEMPO satellites and exoplanets: size of the circle
corresponds to the satellite or planet mass. Open circles are gas giants ($>5$
$\rm M_{\oplus}$), gray circles are Earths or super-Earths (1-5 $\rm
M_{\oplus}$) and black circles are super-Titans ($\mathrm{M_{Titan}}$-$\rm
M_{\oplus}$). The light-blue region is the habitable zone for main sequence
stars from Kopparapu et al. (2013).

###  3.1 Anticipated TEMPO Detection Yields

In the first TEMPO paper, our team developed simulation code to calculate the
expected yield from the TEMPO survey based on a wide variety of input
parameters (satellite occurrence rates, radius-mass relations, ONC extinction,
etc), and taking into account several possible instrumental configurations and
measurement systematics (instrument spectral band, host variability, etc). In
this section, we leverage that code to calculate the expected detections.
Figures 2 and 3 illustrate the estimated TEMPO survey exosatellite detection
yields within the parameter space of orbital separation and host mass. These
figures incorporate two distinct sets of simulations: For the substellar
hosts, the default parameters provided in Table 3 of Limbach et al. (2023) are
used to calculate yield (settings used for this simulation are in bold font).
For the stellar hosts, we leverage known occurrence rates around more massive
stars (see distribution in Section 5.2.1 of Limbach et al. (2023). The abrupt
predicted increase in the detection of large ($>$sub-Neptune) exoplanets just
above the stellar/sub-stellar boundary is an artifact that arises due to a
change in the methods employed for yield calculations. This shift is due to
the assumptions inherent in these calculations, which are subject to the
various caveats and limitations detailed in Limbach et al. (2023).

Also plotted are select Solar System moons and planets (blue squares), as well
as several well-known habitable zone (HZ) exoplanets (red diamonds). In both
figures, we illustrate exosatellites in the following way: open circles
indicate sub-Neptune to Jovian gas giant companions ($>5$ $\rm M_{\oplus}$),
gray circles indicate 1-5 $\rm M_{\oplus}$ companions, and black circles
indicate super-Titan ($M_{\rm Titan}$-$\rm M_{\oplus}$) companions. The size
of the circles scales with satellite mass. The detection of companions of low-
mass stars and high-mass brown dwarfs provide an opportunity to study
extraordinary young counterparts to the currently known exoplanet population,
while the detections of companions orbiting lower-mass brown dwarfs and
planetary-mass hosts will constitute a critical discovery space, for which
very little is currently known.

Figure 3: Distribution of host-companion separation (AU) as a function of host
mass ($\rm M_{\odot}$) for the simulated TEMPO survey detections (circles),
Solar System moons and planets (blue squares), and select habitable exoplanets
(red diamonds)—same as Figure 2, but zoomed in on the HZ. Simulated TEMPO
exoplanets: circle size corresponds to exoplanet mass. Open circles are gas
giants ($>5$ $\rm M_{\oplus}$), gray circles are Earths or super-Earths (1-5
$\rm M_{\oplus}$) and black circles are super-Titans
($\mathrm{M_{Titan}}$-$\rm M_{\oplus}$). The light-blue region is the HZ for
main sequence stars from Kopparapu et al. (2013). TEMPO is expected to detect
approximately ten proto-habitable zone terrestrial ($<5$ $\rm M_{\oplus}$)
exoplanets around low-mass stars (mid to late M-dwarfs), similar to the
Trappist-1 exoplanets and Proxima Centauri b.

The detection yields can be summarized as follows:

  * $\circ$

12 Super-Titan ($\mathrm{M_{Titan}}$-$\rm M_{\oplus}$) exosatellites orbiting
FFPs

  * $\circ$

2 $>1.0$ $\rm M_{\oplus}$ exosatellites orbiting FFPs

  * $\circ$

34 Super-Titan exosatellites orbiting brown dwarf hosts

  * $\circ$

20 $>1.0$ $\rm M_{\oplus}$ exosatellites orbiting brown dwarf hosts

  * $\circ$

21 Earth-sized ($<5$ $\rm M_{\oplus}$) exoplanets orbiting young Orion stars

  * $\circ$

122 $>5.0$ $\rm M_{\oplus}$ exoplanets orbiting young Orion stars

  * $\circ$

20 exoplanets around older main sequence field stars

###  3.2 A Discussion of Critical Questions Addressed by TEMPO Transiting
Companion Detections

While the initial TEMPO paper concentrated on creating the code that allowed
us to estimate the expected yield of transiting companions (illustrated in the
previous section), this manuscript will shift its focus to discussing
critically important questions that can be addressed using the anticipated
detected population.

####  3.2.1 Detection of the First Population of Exosatellite Companions

While the community has confirmed more than 5,500 exoplanets, we have yet to
confirm the detection of a single exomoon/exosatellite. The literature reports
approximately a dozen signals from candidate exomoons. These signals were
identified through various methods, including gravitational microlensing
(Bennett et al., 2014; Miyazaki et al., 2018), features observed in transit
spectra (Oza et al., 2019; Gebek & Oza, 2020), gaps within circumplanetary
rings (Kenworthy & Mamajek, 2015), transit-timing variations (TTVs)
accompanied by exomoon transits of the host star (Teachey et al., 2018;
Teachey & Kipping, 2018; Rodenbeck et al., 2018; Kreidberg et al., 2019;
Teachey et al., 2020), TTVs alone (Fox & Wiegert, 2020; Kipping, 2020), direct
imaging (Lazzoni et al., 2020), the detection of gas absorption possibly
associated with an orbiting moon (Ben-Jaffel & Ballester, 2014), and
exosatellites transiting FFPs (Limbach et al., 2021) or more massive brown
dwarfs (Miles-Paez et al., 2019; Tamburo et al., 2022a).

A critical next step for the astronomical community is the detection,
confirmation, and characterization of exosatellite companions to substellar
hosts. Of particular interest are the exosatellites of FFPs with masses
similar to that of Jupiter. The TEMPO survey will enable the detection of
exomoons/exosatellites in nearby, well-constrained environments, including the
ONC and surrounding regions. This enhances our ability to interpret population
demographics in these regions. The smallest exosatellites the TEMPO Survey is
capable of detecting are $R\approx 0.35$ $\rm R_{\Earth}$ companions on short
orbits (approximately 8 hr) around 10-30 $\rm M_{\mathrm{J}}$ hosts. This
corresponds to predicted transit detections of exosatellites comparable in
size to Titan, Ganymede, and Callisto, orbiting hosts with masses between
10-30 $\rm M_{\mathrm{J}}$ (Limbach et al., 2023). Additionally, the survey
will detect “Super-Titans” (exosatellites ranging from Titan to Earth-sized)
transiting within all the Orion molecular clouds. The proposed 720-hour
observational window will allow for the detection of multiple companion
transits at close orbital separations ($<0.1$ AU). This outcome is crucial, as
it provides an opportunity to distinguish between signatures of (sub)stellar
variability and those of transiting companions (e.g., Rizzuto et al., 2017;
Mann et al., 2017, 2018; Rizzuto et al., 2020; Limbach et al., 2021; Ment et
al., 2021).

Identifying exosatellites bridges the knowledge gap between the population
demographics of low-mass stellar systems, such as TRAPPIST-1, and the moon
systems of the Solar System giant planets. Previous comparisons between
compact Kepler systems and the moons around giant planets in the Solar System
by Kane et al. (2013) have revealed similarities in system architectures,
despite the host masses varying by several orders of magnitudes. TEMPO will
enable comparative studies of companion architecture extending down to the
planetary-mass host regime, several orders of magnitude lower than previously
explored.

####  3.2.2 Constraining Exosatellite Formation Theories

The projected detection yields of the TEMPO survey vary significantly based on
the selected assumptions in our simulations. By comparing the actual measured
yield with the diverse outcomes predicted by our simulations, we can use the
TEMPO results to determine which models align with observations. The TEMPO
survey data will thus provide observational constraints to test prevailing
theories of exomoon/exosatellite formation and evolution (e.g., Canup & Ward,
2006; Heller & Pudritz, 2015; Barr, 2016; Miguel & Ida, 2016; Moraes et al.,
2018; Cilibrasi et al., 2018; Ronnet & Johansen, 2020; Inderbitzi et al.,
2020; Cilibrasi et al., 2020; Nakajima et al., 2022), which predict differing
rates of companion occurrences and orbital periods. Additionally, it will
provide constraints on other models related to young worlds, like the
existence of H/He envelopes at an early stage in the formation of terrestrial
worlds, as discussed in section 3.2.3.

TEMPO observations may also enable constraints on the formation location of
the substellar hosts. Numerical simulations indicate that it is possible for
exomoons to remain gravitationally bound to their rogue hosts out to orbital
separations of $0.1$ AU (orbital period of $12$ days) (Rabago & Steffen, 2018;
Hong et al., 2018). Finding more distantly separated satellite systems around
free floating planets may offer clues as to whether these worlds formed in-
situ or were ejected after forming in a circumstellar disk.

In addition, it may be possible to understand how the composition of
exomoons/exosatellites compares with the exoplanet, which could indicate
formation scenarios for both. For example, there appears to be a correlation
between elements within stars and their planets (e.g., Bond et al., 2010;
Thiabaud et al., 2015; Adibekyan et al., 2021), a relationship that is
particularly true for refractory elements such as Mg, Si, and Fe (McDonough,
2003; Unterborn et al., 2023). Given that stars, planets, and their satellites
are all formed around the same time and from similar material, the composition
of exomoons/exosatellites may mirror the host star.

####  3.2.3 Capture and Loss of H/He Envelopes

Theoretical models based on the current understanding of the known exoplanet
population and the Solar System’s terrestrial planets indicate that young
rocky bodies with masses $>0.1$ $\rm M_{\oplus}$ (greater than the mass of
Mars) are likely to possess gaseous envelopes composed of hydrogen and helium
(Hayashi et al., 1979). The H/He envelope capture and dissipation models have
far-reaching scientific implications, impacting the critical core mass for gas
giant formation (Hori & Ikoma, 2011), the composition of the secondary
atmosphere (Misener & Schlichting, 2021), and even the potential for the
planet’s future habitability (e.g., Owen & Mohanty, 2016).

H/He envelope capture and loss timescales are the largest driver in the
expected yield of exosatellite and exoplanet yield for the TEMPO survey, as
envelopes can significantly increase the sizes of these objects (Lammer et
al., 2020; Scherf & Lammer, 2021; Wordsworth & Kreidberg, 2021; Hayashi et
al., 1979; Erkaev et al., 2014; Stökl et al., 2015, 2016, e.g.,). Limbach et
al. (2023) demonstrate that transit detection yields vary by nearly an order
of magnitude depending on the implemented H/He envelope capture and loss
model.

To date, there are no known systems that are young enough to constrain
prevailing models of envelope capture and loss of terrestrial ($\sim$Earth-
mass) worlds. However, TEMPO will be capable of detecting a population of
young, nearby exosatellites and exoplanets predicted to possess H/He envelopes
(Rogers & Owen, 2021). Transit detection from the TEMPO survey alone will not
be capable of distinguishing between low-mass proto-terrestrial worlds in
possession of an envelope and more typical sub-Neptunes of similar radii (but
much higher density). In some cases, follow-up transmission spectroscopy via
the HST and/or JWST is possible for targets brighter than F146 $\gtrsim 16$
$\mathrm{mag_{AB}}$.

Such follow-up observations will offer the means to explore several
significant questions that are presently challenging the field. This includes
an opportunity to precisely constrain the exosatellite’s mass, enabling
differentiation between higher mass sub-Neptunes and proto-terrestrial worlds
with H/He envelopes. Such observations will also constrain the atmospheric
composition, including C/O ratios and overall metal abundances. The presence
of an extended envelope (i.e., large atmospheric scale height) enables such
follow-up observations potentially down to Earth-mass companions. This will
offer an unprecedented opportunity to examine the atmospheres of companions
similar to early-Earth.

Figure 4: The transmission spectra for a Neptune-analog (blue dashed line) and
a 3 M${}_{\Earth}$ proto-terrestrial world with a H/He envelope (red line).
Also shown is simulated JWST NIRSpec prism data of the proto-terrestrial world
(error bars) assuming three hours of observations during transit(s) on a 16.1
mag, 52 MJup brown dwarf host. In this simulation, the extended envelope of
the proto-terrestrial world is easily detected, however, cloud cover may
impede detectability (see discussion in text).

Figure 4 illustrates the simulated transmission spectra for a Neptune-analog
with a clear atmosphere and a 3 M${}_{\Earth}$ proto-terrestrial world with a
H/He envelope transiting a young 52 MJup brown dwarf host. Both exosatellites
have a radius of about 4 $R_{\Earth}$ due to the presence of a very extended
the H/He envelope on the proto-terrestrial world. Both exosatellites are
modeled using clear atmospheres in Exo-Transmit (Kempton et al., 2017). The
simulated JWST data (black/gray error bars) of a 3 M${}_{\Earth}$ proto-
terrestrial world illustrates its low-density atmosphere. The presence of
thick clouds may make the atmosphere undetectable and/or degenerate with the
Neptune-analog.

The simulation provided here is meant to illustrate the potential
detectability of proto-terrestrial worlds discovered with TEMPO, however, we
caution that further modeling beyond the scope of this paper will be required
to fully and accurately model the atmosphere of a proto-terrestiral world.
Here, we have made the simple assumption that Exo-Transmit can be used to
model transmission spectra of any exoplanet with a H/He envelope. However, in
low surface gravities, Exo-Transmit works under the assumption that the
surface gravity is constant through the entire modeled portion of the
atmosphere. This is a fine assumption if the atmospheric thickness is much
smaller than the planetary radius. In the case of a low-$g$ extended envelope
around a proto-terrestrial world, it will underestimate the transmission
spectrum amplitude since, in this low surface gravity case, $g$ decreases
significantly throughout the atmosphere. We recommend further modeling beyond
the scope of this paper to explore this in more detail.

Probing the atmospheres of Earth-mass exoplanets will help to constrain the
lower mass limit for the capture and loss of planetary envelopes. These data
will provide an opportunity to test our understanding of terrestrial planet
formation, as well as prevailing theories of Earth’s formation (e.g., Hayashi
et al., 1979; Rogers et al., 2011; Mordasini et al., 2012; Stökl et al.,
2016). TEMPO data may show that young exoplanets around low-mass stars have
begun to lose their envelopes on timescales of a few Myr. This will help
differentiate between viable envelope dissipation mechanisms, such as
photoevaporation via high-energy (XUV) radiation from the stellar host (e.g.,
Mordasini, 2020), core-powered mass-loss (e.g., Ginzburg et al., 2018; Gupta &
Schlichting, 2019; Rogers et al., 2021), and an initial boil-off stage (Owen &
Wu, 2016; Owen, 2020).

TEMPO data can be used to test theories of the underlying mechanism driving
the observed “radius gap” near 1.7 $\rm R_{\Earth}$ — a theorized loss of H/He
envelopes among less massive substellar bodies (e.g., Lopez & Fortney, 2014;
Fulton et al., 2017; Owen & Wu, 2017; Owen, 2020; Misener & Schlichting,
2021). More specifically, it will be possible to probe 0.1-4 $\rm M_{\oplus}$
proto-terrestrial ONC exoplanets for the presence of H/He envelopes to
determine if this radius gap is observed at these extremely early stages of
evolution.

####  3.2.4 Habitable & Pre-Habitable Worlds

We refer to systems in the light-blue region in Figures 2 and 3 as “proto-
habitable zone” systems, as they indicate the location of the HZ once stellar
hosts reach the main sequence (Kopparapu et al., 2013). This is not to be
confused with the location of the HZ at early timescales of 1-3 Myr. In Figure
3, we provide a zoom-in of “proto-habitable zone” systems . TEMPO is expected
to detect approximately ten proto-habitable zone terrestrial ($<5$ $\rm
M_{\oplus}$) exoplanets orbiting mid to late M-dwarfs. While a large fraction
of the exosatellite detection yield extends to lower mass hosts, the majority
of our expected TEMPO transit detections consist of systems similar to Proxima
Cen b and Trappist-1 (but much younger). Unlike stellar hosts, the brown
dwarfs and FFPs will continuously cool, therefore never providing a long-lived
stable HZ (Barnes & Heller, 2013). While we do not illustrate the HZ for FFP
and brown dwarf hosts, it may be possible that detected exosatellites orbiting
FFPs and brown dwarfs occupy a “transient” HZ, which in some cases may persist
over gigayear timescales (Barnes & Heller, 2013).

HZ exoplanets orbiting main sequence stars have very low transit
probabilities: 2% for M-dwarf hosts and $<0.5$% for sun-like hosts. While
substellar worlds harbor a transient HZ, Limbach et al. (2021) showed that the
transiting companions of young FFPs and brown dwarf hosts are far more likely
to orbit within the HZ. This is the result of two factors: the HZ of young
FFPs and brown dwarfs is very close to the host star, and because these hosts
have large radii at young ages. The typical transit probability of a HZ
exosatellite in the TEMPO survey is approximately $10\%$. TEMPO will offer an
opportunity to help constrain the number of expected habitable exomoons and
exoplanets, which in turn helps to quantify the total number of habitable
worlds where we might expect to find life.

The known population of detected exoplanets does not contain sources that are
both $<100$ Myr and $<1.8$ $\rm R_{\Earth}$. Therefore, there are no known
proto-terrestrial worlds — barring cases that may undergo substantial loss of
extended atmospheres. The dozens of young exoplanets expected to be detected
by the proposed TEMPO survey will provide the first window into the properties
of young terrestrial worlds. As discussed in Section 3.2.3, a young
exoplanet’s large scale height — resulting from existing, but temporary, H/He
envelopes — will enable observations of follow-up transmission spectroscopy.
If a proto-terrestrial world is detected around a sufficiently bright host
star, it may be possible to characterize the proto-habitable-zone of
“primordial-Earth” exoplanets. Such studies may offer a rare opportunity to
place temporal constraints on the timescales for the formation of conditions
favorable to the emergence of life. Under reasonable assumptions, we estimate
the detection of about ten proto-habitable zone worlds transiting low-mass
stars. Such systems will be young analogs to the 7 Gyr Trappist-1 system, but
at a much younger age ($\lesssim$3 Myr).

Additionally, it has been proposed that some exomoons could harbor conditions
that support liquid water — and potentially life. It is not a requirement for
an exoplanet (or FFP) to be in the habitable zone in order for the
exomoon/exosatellite to be conducive to life, since the moon could receive
thermal radiation from the planet (e.g., Scharf, 2006; Hinkel & Kane, 2013;
Heller & Barnes, 2013; Ávila et al., 2021). The tidal interactions among moons
and planets can heat the moon interiors to produce liquid water (e.g., Dobos &
Turner, 2015; Roccetti et al., 2023) — as is seen with Europa. These necessary
conditions can survive the planet’s ejection (Rabago & Steffen, 2018) and can
persist for billions of years.

####  3.2.5 Constraining Exoplanet Formation Timescales

A long-standing conundrum is how short-period gaseous planets reach orbital
periods of a few days or shorter. The discovery of the very first exoplanet
around a Sun-like star, 51 Peg b (Mayor & Queloz, 1995), inaugurated this open
question, and it remains unresolved. Three main avenues for the origination of
these puzzling planets have emerged (Dawson & Johnson, 2018): in situ
formation – the gas giants formed in or near their current orbits; disk
migration – gravitational interactions between the nascent planets and their
parental gas disks rapidly move the planets from where they form several AU
from their host stars into their current orbits; and high-eccentricity tidal
migration — some flavor of gravitational perturbation excites their orbital
eccentricities high enough that tidal interactions with their host stars
circularize and shrink the orbits.

No one explanation seems consistent with all available evidence, but a key
diagnostic that may help distinguish between the different scenarios is the
timescale required for migration. For in situ formation, short-period gaseous
planets will be found in short-period orbits from the very earliest stages of
planet formation, perhaps only $10^{5}-10^{6}\,{\rm yr}$ after the system
originated (Dawson & Johnson, 2018). It is likely that disk migration occurs
early in the system’s history, certainly before the protoplanetary disk is
dissipated (Kennedy & Kenyon, 2009). The migration itself likely occurs faster
than the formation of the plane — perhaps several times $10^{5}\,{\rm yr}$,
depending on the planet’s mass and the disk properties (Dürmann & Kley, 2015).
High-eccentricity tidal migration, by contrast, may act at any stellar age and
should lead to a time-dependant hot Jupiter occurrence rate (Miyazaki &
Masuda, 2023). The ONC is sufficiently young (1-3 Myr) that the detection of
hot Jupiters with a similar occurrence rate to that which is seen around main
sequence stars will provide evidence in favor of the first two theories, while
a significantly lower occurrence rate in these young systems may place limits
on the fraction of systems assembled by the last mechanism.

While current observational evidence (gleaned from measured orbital parameters
such as orbital geometries and planetary eccentricities) suggests that tidal
migration is the dominant pathway to form hot Jupiter systems (Rodriguez et
al., 2023; Zink & Howard, 2023), it is clear that not all hot Jupiter systems
form in this way (e.g., Becker et al., 2015; Cañas et al., 2019; Huang et al.,
2020; Hord et al., 2022; Sha et al., 2023; Maciejewski et al., 2023). The next
step to understanding how hot Jupiters form is to refine the relative
frequencies with which each of these three scenarios operate. TEMPO will
provide a valuable constraint towards this goal because it will refine the hot
Jupiter occurrence rate for the youngest stars, a diagnostic of exactly how
important post-disk phase evolution is in shaping the hot Jupiter population
we observe. TEMPO thus, through measurement of this occurrence rate, has the
potential to provide a valuable additional constraint in the efforts to map
out the relative importance of each hot Jupiter formation mechanism. The TEMPO
constraint on occurrence rate in the young ONC, combined with constraints
derived from surveys like TESS, will paint a more complete picture of hot
Jupiter formation across all timescales.

##  4 Additional Science Outcomes

While the design of the survey is optimized for the detection of Orion
exosatellites, TEMPO has the potential to make contributions to many other
astrophysical contributions. We summarize those science cases in this section.

###  4.1 Probing the Planetary-Mass Regime of the Initial Mass Function

Studying the planetary-mass regime of the Initial Mass Function (IMF) is
crucial to refining theoretical models of star and planet formation. Do
planets frequently form like stars, via core collapse and turbulent
fragmentation? This formation channel will be an unusually low mass outcome of
the normal star-forming process, as the mass of a planet is $100\times$
smaller than the average Jeans mass in star-forming clouds (Boss, 1997). Yet,
if planets are expected to form through the accretion of material in a
circumstellar disk, this will indicate that the relatively large populations
of FFPs observed in star-forming regions (e.g., Gennaro & Robberto, 2020;
Robberto et al., 2020; Pearson & McCaughrean, 2023) are likely “rogue” planets
that have been ejected from their host stars. Is this supported by kinematic
measurements?

To probe this topic further, it is necessary to perform additional
investigations of star-forming regions in the NIR. Recent observations of the
Orion Nebula and Trapezium Cluster using the Near Infrared Camera (NIRCam) on
the NASA/ESA/CSA James Webb Space Telescope (JWST) revealed 540 planetary-mass
objects with masses down to 0.6 $\rm M_{\mathrm{J}}$ (Pearson & McCaughrean,
2023). Is it reasonable to expect such a large population of rogue planets in
extremely young star-forming systems? This discovery further challenges
existing theories of planet formation, as 9% of these detections consisted of
planetary-mass objects (0.7-13 $\rm M_{\mathrm{J}}$) in wide, weakly-bound
binaries. If these are rogue binary planets, how did such weakly bound system
survive the ejection process?

Figure 5: Illustrated is the stellar initial mass function in terms of the
number of stars formed per logarithmic interval in stellar mass (normalized to
$M=1M_{\odot}$). Overplotted is the IMF as described by Kroupa 2001 and
Chabrier 2003, as well as mass limits for the onset of hydrogen-burning and
deuterium burning. The mass completeness limit of a low-mass IMF investigation
of the ONC Gennaro & Robberto (2020) is also indicated. TEMPO will be
sensitive to probing objects down to sub-Saturn masses (illustrated by the
pink-hued panel).

TEMPO has the ability to revisit this region, conducting a deeper, wide field,
time series investigation. More specifically, with a limiting magnitude of
29.7 $\mathrm{mag_{AB}}$ TEMPO can directly image FFPs with the following
lower bound characteristics: $T_{\mathrm{eff}}\approx 410$ K and $R\approx
1.4$ $\rm R_{\mathrm{J}}$, corresponding to a $50$ $\rm M_{\oplus}$ ($0.15$
$\rm M_{\mathrm{J}}$) exoplanet at an age of 1 Myr (Linder et al., 2019). The
ability to directly image sub-Saturn mass FFPs will provide the lowest mass
investigation of the IMF to date — roughly one order of magnitude smaller than
the FFPs that have been used as constraints in the past (Gennaro & Robberto,
2020). Below several Jupiter masses, theory predicts that objects can no
longer form via the normal star-formation process. Therefore, TEMPO will probe
a mass region where the majority of the objects below ${\sim}3$ $\rm
M_{\mathrm{J}}$ are expected to be rogue exoplanets. While the number of
objects found in this mass regime is poorly constrained, TEMPO’s findings will
have major implications for our understanding of the planet formation process.
Note that recent investigations have explored the low-mass end of the IMF of
the ONC region down to 0.005 $M_{\odot}$ (Gennaro & Robberto, 2020). The
underexplored region of the substellar IMF is depicted as the pink-hued region
in Figure 5. The low-mass end of this pink-hued region is the lowest-mass FFP
that TEMPO will be capable of observing ($50$ $\rm M_{\oplus}$).

Building upon prior investigations, TEMPO will also have the opportunity to
update the astrometric positions of detected FFPs, enabling kinematic
investigations to compare the motion of FFPs with that of low-mass stellar
members in the region. Kinematic measurements offer critical insights into the
origins of these planets. While members of a stellar moving group generally
follow a common spatial trajectory, the kinematics of an ejected planet should
diverge from this shared trajectory. Comparing the motion of FFPs to the
motion of the cluster members will tell us the relative importance of the two
formation pathways.

####  4.1.1 Constraining FFP Formation Pathways With Exosatellite Demographics

The formation mechanism of FFPs also has important implications for the
corresponding exosatellite demographics. The dynamical encounters responsible
for planetary ejection events have the potential to disrupt the orbital
stability of the exosatellites, either causing the companion to collide with
its host or supplying yet another rogue body to the surrounding environment as
the exosatellite is stripped from the system (Hong et al., 2018).
Exosatellites that are weakly bound are particularly at risk of undergoing
destabilization.

N-body investigations performed by Hong et al. 2018 and Rabago & Steffen 2018
indicate that FFPs with close-orbiting Io-like exosatellites are far more
likely to survive dynamical scattering events. These studies show that the FFP
exosatellites that have survived dynamical scattering processes are more
likely to be on short-period, eccentric orbits. This offers predictions for
the orbital configuration of exosatellites orbiting rogue planets, providing
useful constraints on the viability of this potential FFP formation pathway.
This, in turn, offers further constraints on the planetary-mass regime of the
IMF.

While it remains outside the scope of this work, Rabago & Steffen 2018 went on
to show that it is possible for the Galilean-like exosatellites on eccentric
orbits about FFPs to undergo significant tidal heating. This is an exciting
result, which suggests that these exosatellites may be geologically active,
with the potential to host subterranean oceans heated by a mechanism that
could persist for billions of years.

###  4.2 Cluster Membership of Brown Dwarfs and Planetary-Mass Targets

The current census of known members of the ONC is largely complete down to the
spectral type of M5 (McBride & Kounkel, 2019), thanks in large part to a
number of spectroscopic surveys that are able to confirm the youth of stars,
and the Gaia mission which enabled identification of members via kinematic
analysis. As these stars have only recently formed, not to mention their
association with a dense cluster, their velocities tend to be similar to
within a few km s-1. Unfortunately, the census of cooler stars is limited
(e.g., De Furio et al., 2021): only a few of the brown dwarfs have been
confirmed as members: since they are extremely faint, they are inaccessible to
most surveys. A deeper survey that can establish membership of brown dwarfs
and free-floating planets is imperative in order to fully sample the IMF in
such a notable young cluster. TEMPO will be a significant step towards
providing this outcome.

Combining TEMPO astrometric measurements with existing HST and Keck II NIRC2
observations of the ONC (Kim et al., 2019) will significantly improve proper
motion measurements of the red ONC stars that are too faint for astrometric
analysis with Gaia. For reference, the faintness limit of the Gaia survey is
approximately 21 $\mathrm{mag_{AB}}$, while TEMPO will achieve a faintness
limit of 29.7 $\mathrm{mag_{AB}}$. Such proper motions are required for a
detailed analysis of stellar dynamics within the cluster (Getman et al.,
2019).

Typical proper motions of stars within Orion are approximately 2 mas year-1.
Previous HST observations of young stars in the ONC achieved a positional
accuracy of 2-3 mas down to the limiting magnitude of 24.7 mag in F775W band
(Platais et al., 2020). With a similar pixel scale, but observing at longer
wavelengths, we expect to reach positional accuracy of approximately 5 mas.
This means that over a temporal baseline of one year, we expect to obtain
precision in proper motions of approximately 5 mas year-1, or approximately 10
km s-1 at the distance of Orion. While such precision will not be sufficient
for characterizing intracluster dynamics on its own (coupled with a large
degree of extinction for stars behind the cloud), it will facilitate the
identification of a number of low-mass members of the ONC from a significant
number of field stars. It will also help to identify high-velocity runaways
among already confirmed members (McBride & Kounkel, 2019), such as, e.g, among
dusty young stellar objects (YSOs) that have been primarily been detected in
near-IR observations (Megeath et al., 2012).

More importantly, TEMPO observations will act as a crucial anchor that will
help to refine proper motions for these faint stars at subsequent observations
of the cluster several years down the line. Indeed, combining TEMPO data with
archival data, such as from HST observations that have been carried out from
2004–2015 (Kim et al., 2019; Platais et al., 2020), will double the temporal
baseline, extending it to approximately 20 years, enabling a precision $<$0.2
mas year-1. While such a degree of precision is only possible for sources
observed by both surveys (excluding sources fainter than 24.7 mag and those
outside the HST footprint), this underscores the importance of such legacy
datasets, which TEMPO will be poised to become in the future.

###  4.3 Imaging Free Floating Planets and Widely-Separated Exoplanets

Co-adding the full set of observations will permit the direct-image detection
of FFPs with sub-Saturn masses (50 $\rm M_{\oplus}$ at 1 Myr; Linder et al.
2019). In addition, TEMPO will enable the investigation of a population of
faint companions at wide separations using the advanced point spread function
subtraction techniques based on Karhunen-Loeve Image Processing (KLIP) (Pueyo,
2016). These techniques were recently applied to HST imaging data of the Orion
Nebula (Strampelli, 2021). Sub-Saturn mass planets at separations beyond $10$
AU are largely an unexplored parameter space, yet characterizing these worlds
remains critical to building a comprehensive framework of the overall
architectures of planetary systems.

The detection of sub-Saturn planets requires the infrared sensitivity of an
instrument like JWST or Roman — albeit Roman enables the monitoring of a much
larger field of view. As described in Section 4.1, these observations also
enable TEMPO to probe the low-mass-end of the IMF down to a largely untapped
mass range.

###  4.4 Investigating Substellar Variability

TEMPO will enable a large survey for substellar variability that will shed
crucial light on the dependence of that variability on mass and spectral type
in a young, coeval sample. Rotation periods for substellar objects at the age
of the ONC are typically less than $\sim 100$ hr (e.g., see compilations by
Moore et al., 2019; Vos et al., 2022), so multiple rotation periods will be
covered in each TEMPO window, placing robust constraints on the rotational
periods of the sample. This provides a unique opportunity to extend current
gyrochronology studies into the substellar regime and to probe the angular
momentum evolution of substellar objects as a function of mass at young ages.
Planets within our Solar System show a clear trend between their rotational
velocity and mass, and initial measurements of a small number of directly
imaged exoplanets, FFPs, and brown dwarfs appear to follow this trend (Snellen
et al., 2014; Allers et al., 2016; Scholz et al., 2018). Rotation period
measurements by TEMPO survey will provide the first statistical sample to test
this relation beyond our Solar System.

TEMPO also enables a unique investigation of how light curve properties vary
across spectral type and mass. For older FFPs and brown dwarfs, near-IR
amplitudes depend on parameters including spectral type (Radigan et al., 2014;
Metchev et al., 2015), surface gravity (Metchev et al., 2015; Vos et al.,
2022; Liu et al., 2023) and viewing angle (Vos et al., 2017). The small number
of long-term monitoring studies of brown dwarfs and FFPs have shown that the
light curves of variable objects evolve dramatically both on rotational and
yearly timescales (e.g., Apai et al., 2017; Zhou et al., 2022). However, with
relatively small sample sizes and samples that differ across ages, it is
necessary that these trends are studied with a larger sample at constant age.
TEMPO will enable investigations of the variability properties of substellar
atmospheres in a uniform, coeval sample on a variety of timescales.

###  4.5 Star Formation, Evolution, Variability, and Multiplicity

####  4.5.1 Investigating Star Formation

The ONC and Orion Molecular clouds are among the most well-studied star
formation regions in the Milky Way, exhibiting both low- and high-mass star
formation. TEMPO Survey observations will permit a high spatial resolution
investigation to map the dust distribution and examine stellar clustering. The
data can be leveraged to investigate the presence of disk dispersal via
stellar feedback — the injection of energy and momentum by young stars in the
interstellar medium (ISM) — and the presence of protoplanetary disks that may
be actively undergoing planet formation. TEMPO’s spatial resolution (30 AU)
permits the mapping of the dense star-forming gas—including the presence of
pillars, proplyds, and globules that are shaped by stellar feedback by young
stars and are actively undergoing star and planet formation (Hopkins et al.,
2021). The presence of protoplanetary disks is supported by prior
investigations, including a 3-year submillimeter investigation of the ONC,
which found 42 individual protoplanetary disks (0.003-0.07 $\rm M_{\odot}$)
(Mann & Williams, 2010). Protoplanetary disks can be perturbed and/or
truncated via stellar feedback from nearby young stars or dynamical effects in
clustered environments like the ONC. For example, Otter et al. (2021) used
ALMA data to investigate 127 protoplanetary discs in the ONC and surrounding
regions. Of this sample, 72 were spatially resolved (3 mm) and the disk sizes
were smaller than expected — likely a result of photoevaporation from nearby
massive Trapezium stars.

Additionally, by mapping the density distribution of this region, we will
determine the density PDF to compare to star formation models and determine
how feedback shapes the ISM, drives turbulence, and may trigger star formation
in star-forming environments (Burkhart, 2018; Rosen et al., 2020; Menon et
al., 2021).

####  4.5.2 Rotation Rate Dispersion & the Role of Disk Locking

Disk locking is an important mechanism driving the angular momentum evolution
of stars during the first few million years ($\lesssim 3$ Myr) (e.g., Edwards
et al., 1993; Barnes, 2003). Driven by magnetic interactions between young
stars and their surrounding circumstellar disks, it is theorized that disk
locking is responsible for the observed rotation rate dispersion among members
within a young stellar cluster. At later stages, when circumstellar disks have
been sufficiently dissipated, stars contracting onto the main sequence begin
to spin more rapidly. At this stage, the rotation rates of cluster sources are
seen to converge, forming a tight period-mass-age relation (e.g., Hartman et
al., 2009; Meibom et al., 2015; Curtis et al., 2020).

While precise circumstellar disk dispersal timescales are dependent on stellar
mass, the surrounding radiation field, disk viscosity, and dust evolution,
observations indicate that disk dispersal generally takes place within a few
million years (e.g., Lissauer, 1993; Alexander et al., 2006). The 3 Myr ONC
members targeted by TEMPO will offer an important opportunity to investigate
the effects of disk locking on the rotational dispersion of an extremely young
stellar population, while also probing the corresponding circumstellar disk
dispersal timescales.

####  4.5.3 Investigating Pulsational Variability

TEMPO will monitor approximately 10,000 targets for variability. This includes
young stellar members in the ONC and surrounding Orion molecular clouds and
approximately 5,000 field stars that fall within the TEMPO FOV, as shown in
Figure 1. Taking into account the photometric precision limits of the TEMPO
survey (provided in Table 1), as well as the minimum integration time (18-s)
and full 30-day observation window, the survey will be sensitive to the
detection of a wide range of main sequence, subgiant, giant, and compact
pulsational variables. This includes both gravity and pressure mode
pulsational variables of the following classes: Solar-like pulsators, $\alpha$
Cyg, $\beta$ Cephei, Cepheids, $\delta$ Scuti, p-mode sdBVs (EC 14026 and V361
Hya), g-mode SdBVs (PG1716+426, lpsdBV), pulsating Be (SPBe), pre-MS pulsators
(pulsating T Tauri stars, pulsating Herbig Ae/Be stars), $\gamma$ Doradus, GW
Vir, PG1716, roAp, RR Lyrae, SPB (53 Per), V777 Her, W Vir, ZZ Ceti, PNNV, and
GW Vir.

####  4.5.4 Stellar Flares

TEMPO Survey stars (both young and field stars) are expected to flare. Flares
are sudden releases of energy that occurs when a star’s magnetic field
rearranges itself or reconnects (Benz & Güdel, 2010), causing brightness
variations on minutes-to-hours timescales characterized by a sharp rise and
gradual decay phase (e.g., Tovar Mendoza et al. 2022). Flares are commonly
observed in time-series data at all wavelengths (Caramazza et al., 2007; Loyd
et al., 2018; MacGregor et al., 2018; Howard et al., 2019). Our knowledge of
the energies and frequencies of stellar flares at infrared wavelengths is
scarce (Davenport, 2017; Howard et al., 2023).

More specifically, the study of how flaring impacts the infrared spectra for
M-dwarfs is particularly necessary to measure accurate stellar abundances and
exoplanet transmission spectra. In order to measure the composition of M-dwarf
stars, which is difficult to accomplish on the ground due to the telluric
interference of Earth’s atmosphere, M-dwarfs must be observed in the infrared.
One key issue affecting the determination of stellar abundances is the
signature of flares filling elemental or molecular absorption lines. While
this might be less important for early type (0-4) M-dwarfs which have a low
flare occurrence rate (Hilton et al., 2010), it is an important factor to
understand for the more active late-type (5-9) M-dwarfs (Kowalski et al.,
2009; Davenport et al., 2012; Davenport, 2016; Davenport et al., 2019). In
addition, measuring the influence of flares on stellar spectra further into
the infrared – i.e. beyond the 2.5um threshold achieved by some of the most
recent infrared surveys (Schmidt et al., 2012) – will allow the community to
determine signatures of flares beyond the lower order Paschen and Brackett
lines.

Flares are also a nuisance in the interpretation of exoplanet transmission
spectra with JWST (Lim et al., 2023). Transit experiments generally rely on
the assumption that stars are homogeneous and stable over time in order to
isolate planetary spectral features from stellar features. However, stellar
surface heterogeneity and time variability can imprint stellar spectral
features in the resulting planetary spectra that are challenging to detect or
remove (Rackham et al., 2018). Dedicated investigations into stellar flare
properties at infrared wavelengths are required to mitigate their
contamination of transit spectra (Howard et al., 2023).

Understanding M-dwarf flares is critical not just for planetary detection, but
for characterizing the planetary system and potential habitability, which is
of importance to upcoming missions that are focusing on M-dwarf planets.
Fortunately, Roman will make huge strides in this area (Tovar Mendoza et al.,
2023), as Kepler/K2 did for stellar flares at visible wavelengths (Shibayama
et al., 2013; Hawley et al., 2014). Probing the flaring statistics of M-dwarfs
and coeval populations of stars with Roman will contribute to the growing body
of research on the flaring evolution of cool stars (Ilin et al., 2021).

####  4.5.5 Investigating Stellar Outflows

The TEMPO survey will make significant contributions to studies of stellar
jets and outflows. The depth of the TEMPO images will be unprecedented. In the
F146 filter, shocks emitting in the 1.27 and 1.46 $\mathrm{\mu}$m [FeII]
emission lines, and in the Paschen series of H-recombination lines will be
clearly seen. We will be able to use the F146 image, along with longer-
wavelength images from JWST and the ground to remove stars and extended
nebulosity. The F146 filter traces ionized plasma from the Nebula and ionized
by strong shocks and rendered visible in the Paschen series of H-recombination
lines. Comparing TEMPO data to that of prior surveys — including ground-based,
HST, Gaia measurements, and JWST images — will allow the measurement of proper
motions of both stars and shocks with unprecedented precision. Further, the
inclusion of the F213 filter images will detect protostellar outflow shocks
with unprecedented sensitivity.

Research has shown that the study of jets and outflows from young stars that
the 2.12 $\mathrm{\mu}$m line of H2 is the optimal tracer of shock-waves
propagating into molecular media (e.g, Reipurth & Bally, 2001; Bally, 2016).
JWST has shown that both the 2.12 $\mathrm{\mu}$m v=1-0 S(1) line in the
spectrum of molecular hydrogen is easily detected in both JWST’s broad- and
narrow-band filters in addition to the F212N narrow band filters. The Integral
Shaped Filament (ISF; the northern, densest portion of the Orion A cloud)
located immediately behind the Orion Nebula extends approximately 30’ South to
30’ North of the Orion Nebula. The ISF is one of the richest regions of
ongoing star formation, filled with jets and outflows best traced by the 2.12
$\mathrm{\mu}$m line. TEMPO will enable investigations of the shock-waves
propagating in this region, offering a new epoch to prior studies. There are
hundreds of H2 shocks from dozens of jets and outflows already known in the
Orion A ISF. Summing the 30 days of data in the F213 filter will provide the
deepest image of these flows. Comparison with the exiting data will yield
proper motions of the outflow shocks radiating in H2. Even if only 10% of the
time was devoted to the F213 filter, the resulting mosaic will be the deepest
image of shock-excited (and fluorescent) molecular hydrogen emission in the
ISF ever obtained.

The jets and outflows traced out by 2.12 $\mathrm{\mu}$m H2 emission can be
seen in Figures 6 and 7, which consists of a 1.2 degree field of the ISF, as
observed by the Calar Astro 3.5-meter telescope in Spain (Stanke et al.,
2002). Both images contain significant overlap with the TEMPO field. Figure 6
illustrates the Northern field, while Figure 7 illustrates the Southern field.
The Northern field shows the M43 cavity, and a host of molecular outflows and
jets emerging from OMC2 and OMC3. The very bright emission in the Southern
field is the Orion Nebula. This field contains the OMC1 and OMC4 regions.

Figure 6: Illustration of 2.12 $\mathrm{\mu}$m H2 emission, tracing jets and
outflows in the Northern field of the Integral Shaped Filament, immediately
behind the Orion Nebula. These data were obtained by the Calar Astro 3.5-meter
telescope in Spain (Stanke et al., 2002). Figure 7: Illustration of 2.12
$\mathrm{\mu}$m H2 emission, tracing jets and outflows in the Northern field
of the Integral Shaped Filament, immediately behind the Orion Nebula. These
data were obtained by the Calar Astro 3.5-meter telescope in Spain (Stanke et
al., 2002).

Additionally, the nearest group of currently forming massive stars (embedded
in Orion OMC1, 0.1 pc behind the Nebula) power the ”Orion Fingers” of shock-
excited H2 material, believed to have been formed by a protostellar merger
(Bally et al., 2020). The expansion of the fingers as revealed by proper
motions are critical to better understanding the evolution of these structures
and TEMPO will offer a new epoch to the community.

####  4.5.6 Investigating Young Stellar Variability

Young stellar objects (YSOs) exhibit wide-ranging photometric variability,
which includes short-term near- or mid-IR fluctuations in brightness. Prior IR
investigations of the Orion region include the Spitzer GO6 Exploration Science
program known as YSOVAR (Young Stellar Object Variability), which provided
mid-IR (3.6 and 4.5 $\mathrm{\mu}$m) photometric variability survey of YSOs in
a 0.9 square degree region centered on the Trapezium cluster (Morales-Calderón
et al., 2012). This survey generated light curves for over more than 1,000
YSOs with a cadence of 2 epochs per day for 40 days.

This cadence enabled precise measurements of YSO spin periods driven by star-
spot modulation, which are generally are on the order of 2-10 days. However,
shorter cadence data is required for investigations of flares. YSOs are active
flare stars with strong magnetic fields and X-ray emission with flare
durations ranging between minutes to hours, making short cadence
investigations incredibly useful. TEMPO will provide unprecedented short
cadence investigations, high photometric precision, and a long temporal
baseline. As such, TEMPO will be sensitive to detecting and characterizing
continuum, Paschen-alpha, and Paschen-beta flares. Incorporating the Roman
F213 filter for near-simultaneous imaging will permit the ability to
distinguish continuum flares from those dominated by H-recombination lines.

Fischer et al. 2019 combined Spitzer and WISE observations to search for YSO
outbursts, constraining their occurrence rate in the ONC. The team found that
such events are far more common at earlier stages of evolution, occurring
every $10^{3}-10^{4}$ yr. They also highlighted the ability of Roman (then
referred to as WFIRST) to contribute to further analysis of eruptive YSOs.
Given the fact that thousands of YSOs will be present in the TEMPO field of
view, it is feasible to search for far more luminous, but rare, accretion
bursts similar to those witnessed in McNeil’s Nebula, or akin to EX Ori and FU
Ori outbursts (e.g., Hartmann & Kenyon, 1996; Briceño et al., 2004; Aspin et
al., 2009). Further, many embedded YSOs also produce compact, near-IR
reflection nebulae, whose illumination varies on time-scales ranging from
hours to weeks, thereby also requiring short cadence observations. The time
scale in this case correspond with the orbital periods of clumps within the
accretions disks (e.g., Muzerolle et al., 2013; Balog et al., 2014). It will
also be possible to leverage observational synergies with the Vera C. Rubin
Observatory Legacy Survey of Space and Time (hereafter Rubin). More
specifically, Rubin will offer complementary deep, wide-field, multi-band
optical observations at a several-day cadence over an expected decade-long
baseline (Gezari et al., 2022). Rubin will sample both short-term (hours to
days) and long-term (months to years) variability, identifying more YSOs than
ever before (Bonito et al., 2023). Yet, it will be difficult to pinpoint the
specific star responsible for these signatures without a synergy such as
Roman’s spatially-resolved NIR observations. Further, Roman data would also
offer the opportunity to further characterize the target when it is active
and/or quiescent.

A particularly important class of YSOs are dipper stars — young stars that
exhibit photometric dips in brightness lasting 0.5-2 days with depths of up to
50%. Nearly one thousand dipper stars have been observed to date (e.g.,
Ansdell et al., 2016; Rodriguez et al., 2017; Ansdell et al., 2018; Hedges et
al., 2018; Bredall et al., 2020; Capistrant et al., 2022; Moulton et al.,
2023). One possible mechanism driving the brightness variations is the
obscuration and accretion of material in the surrounding circumstellar disk,
orbiting near the co-rotation radius (e.g., Ansdell et al., 2016; Bodman et
al., 2017). If this suggested underlying mechanism is truly at play, the
photometric dips observed by the Roman F146 IR spectral band will be
statistically weaker than prior dipper detections performed in the optical, as
NIR investigations penetrate through dust and gas much more effectively than
visible light. Therefore, TEMPO provides a valuable opportunity to test this
theory, while also characterizing the variability using short cadence
integration. Furthermore, the ONC is an ideal location to test such a theory,
as the ages of the stars is this region coincides with the peak age of the
dipper star age distribution, as determined by Capistrant et al. (2022).
Furthermore, the ONC is already well known to be rich with test cases. For
example, a three-year Submillimeter Array (SMA) survey found 42 protoplanetary
disks (0.003-0.07 $\rm M_{\odot}$) in the ONC (Mann & Williams, 2010). While
signs of photoevaporation were observed in the outer regions of the observed
protoplanetary disks, the team found that 18% of these disks had masses
greater than 0.01 $\rm M_{\odot}$ within 60 AU.

One relatively novel class of young variable star is the complex periodic
variable, which are understood based on the sharpness and duration of their
variability to be explained by clumps of circumstellar material located at the
stellar corotation radius (e.g., Stauffer et al., 2017; Bouma et al., 2023).
The origin of the material is not known, but it is likely composed of either
gas or dust. The approximately 100 known instances of these stars are all
young ($<200$ Myr), rapidly-rotating ($P\lesssim 2$ d), low-mass ($M<0.4$ $\rm
M_{\odot}$) M dwarfs (e.g., Rebull et al., 2016; Stauffer et al., 2017, 2018;
Zhan et al., 2019; Günther et al., 2022; Bouma et al., 2023; Popinchalk et
al., 2023). They are distinct from dippers in that they can be a factor of ten
older, and they do not show any infrared excess, imposing a limit on the
amount of warm dust that can be present near the star. Spectroscopically, they
are weak-lined T Tauris, indicating no evidence for active accretion. The
light curves themselves are also periodic over hundreds of cycles, rather than
stochastic over just a few cycles (Bouma et al., 2023).

In their survey of the $\sim$3 Myr Taurus association, Rebull et al. (2020)
found that 3% of Taurus members show highly structured and periodic optical
light curves. The TEMPO survey plans to observe roughly 2,000 young stars
(plus an additional 5,000 stars in the field). We therefore expect to discover
60 complex periodic variables, if the occurrence rate from Taurus translates
to Orion. This will be important for two reasons. First, the lower mass limit
for CPVs is not currently known. The lowest stellar masses currently known to
exhibit this phenomenon are $\approx$0.12$M_{\odot}$ (Bouma et al., 2023). The
TEMPO survey will extend our sensitivity to lower-mass objects and, in
particular, show whether brown dwarfs can be CPVs. Second, a larger CPV sample
will clarify a potentially important source of false positives for transiting
exoplanets. PTFO 8-8695, a candidate 7–10 Myr hot Jupiter in Orion (van Eyken
et al., 2012), has been argued to be a binary system in which one component is
a complex periodic variable (Bouma et al., 2020). If true, the saga of that
object’s discovery and follow-up suggests that care in light curve
classification will be paramount, particularly for candidate exoplanets with
orbital periods near their host star’s rotation period.

There are also important filter considerations in this subdomain. In addition
to the ONC, the OMC1, OMC2, and OMC3 clumps in the ISF have been shown to host
hundreds of embedded YSOs. While most are not visible in the optical bands,
they many do appear on 2-micron K-band surveys. The F213 filter will
characterize these YSOs better than the F146 filter, allowing the TEMPO survey
to investigate a younger sub-population of forming stars and planetary systems
than the ONC.

####  4.5.7 Stellar Multiplicity: Eclipsing Binaries and Stellar Companions

TEMPO will yield insight into binary stars on multiple fronts. There are $>40$
known double-lined spectroscopic binaries (SB2s) within the ONC (Kounkel et
al., 2019). Although no eclipses have been detected among these systems to
date with surveys such as TESS, higher resolution and higher sensitivity data
from TEMPO may change that. Additionally, independent detection of eclipsing
binaries (such as six systems detected in Spitzer light curves, Morales-
Calderón et al., 2012) will also allow for subsequent radial velocity follow
up observations of these systems. The identification of young eclipsing SB2s
will allow for direct dynamical determination of both masses and radii of
these stars, which is a prerequisite for testing pre-main sequence
evolutionary models.

Furthermore, given a resolution of 0.105” in the F146 band (point spread
function at the full width at half maximum), it will be possible to resolve
widely separated binaries down to separations of $<30$ AU (De Furio et al.,
2019), which provides a crucial test of universality of the binary function in
young clusters, and the role of the environment on binary formation. ONC, and
other young star-forming regions, have previously been suggested to have
multiplicity fraction highly discrepant at these separations relative to the
field (Duchêne et al., 2018; De Furio et al., 2021), particularly for lower
mass stars. Moreover, it has been noted that dissimilar binary populations may
be present in dense high-mass clusters like the ONC (Tokovinin & Briceño,
2020). However, as the current census of stars in the ONC that can be resolved
down to these separations is still low, the larger sample that TEMPO will
offer will yield tighter constraints on the multiplicity fraction that could
allow to more definitively examine the evolution of currently young binaries
with respect to the field.

Binary star formation remains an unsolved problem. Raghavan et al. 2010
performed the often used definitive study of stellar binarity in solar-age
field stars. These authors found that the mass ratio distribution peaks near
$M_{2}/M_{1}=q=1$ and is flat to smaller values with the binaries having a
mean separation of 50 AU. However, binary stars harboring planets seem not to
follow this paradigm having mean separations near 100 AU and $q$ values which
seem flat (Ziegler et al., 2020; Lester et al., 2021; Howell et al., 2021).
Solar-like stars (F,G,K types) have a binary fraction near 50%, while M type
stars have lower a binary fraction, near 25% (Winters et al., 2019; Offner et
al., 2023). Field M star binaries tend to favor higher $q$ values and show a
mean separation near 20 AU (Winters et al., 2019), while those hosting
exoplanets show a flat or increasing number toward smaller $q$ values and a
mean separation near 60 AU (Matson et al., 2024, submitted). These differences
in field binaries with no detected planets versus the binaries with detected
planets are being attributed to planet formation and planetary orbital
evolution and dynamics within the star systems, but the exact mechanisms at
work are yet to be discovered. An analysis of spatial correlations is
warranted. For example, if disk truncation is dominated by photo-evaporation
from the massive stars in the ONC, we would expect to see mores instances of
this effect at closer distances to the Trapezium stars. If, on the other hand,
dynamics are the driving mechanism, we would expect to see a correlation with
stellar number density.

A study of both young stars and sub-stellar mass objects in Orion with the
contemporaneous study of surrounding field stars will provide ideal and
uniform comparison samples between early formation time binaries/planetary
systems and old, solar-age field stars. TEMPO will collect the first large
low-mass/sub-stellar sample by which we can explore when and how planets form
in binary systems and when and how they affect the mass ratios of the binary
and their orbital separation.

###  4.6 TEMPO Outcomes on Galactic and Extragalactic Scales

####  4.6.1 Dust Analysis of Orion

The TEMPO survey, in conjunction with simultaneous ancillary multi-band
imaging, will facilitate the generation of an ensemble of NIR extinction
curves, charting the evolution of grain size and composition in Orion as a
function of column density. These data will help unveil how the grain size
distribution in a protostellar cloud is connected to that of dust in a more
diffuse media. Indeed, there is evidence in Orion for a systematically
different extinction law in regions most affected by stellar feedback
(Meingast et al., 2018). Detailed stellar modeling coupled with the known
distance to Orion allows the absolute extinction law to be measured. The true
steepness of the NIR extinction law remains a major uncertainty in the
Galactic extinction curve (Maíz Apellániz et al., 2020; Hensley & Draine,
2021; Decleir et al., 2022; Butler & Salim, 2023). Orion, with its wide range
of environmental conditions and proximity, provides an ideal laboratory to
understand it.

Switching between Roman filters is beneficial in this subdomain, as it enables
a pixel-by-pixel determination of extinction. Modulation of the light curves
by occulting structures in circumstellar environments is likely dominated by
dust in the inner disks and envelopes. A near simultaneous measurement of
colors using F146 + F213 filters will distinguish between small particles
(particle size $<$ the wavelength in the Rayleigh and Mie regimes) and large
particles (particle size $>$ the wavelength in the shadowing regime222The
regime when the grains are much larger than the wavelength so that grains cast
shadows.). The non-variable component of extinction will trace the properties
of the foreground dust.

####  4.6.2 Investigating the Nature and Origin of the Radcliffe Wave

The Radcliffe Wave (RW) is a recently discovered coherent structure in the
disk of the Milky Way (Alves et al., 2020). The wave is 2.7 kpc long and is
believed to have been formed by young star-forming regions in the solar
neighborhood. The molecular clouds in this region align themselves to form a
damped sinusoidal wave-like structure with a maximum vertical displacement of
approximately 160 pc. The Orion star-forming region is part of this wave
structure, however, the nature and origin of this feature found in the dense
gas remains elusive.

Recent work used the proper motions of upper Main Sequence (UMS) stars from
the Gaia mission (Poggio et al., 2021; Zari et al., 2021) to study whether
these stars are part of the vertical oscillation (Swiggum et al., 2022). By
tracing the young stellar counterpart of the RW kinematics, it was discovered
that the spatial oscillation is accompanied by a wave-like motion in velocity
space, resembling a harmonic oscillator with vertical motions extending well
beyond the RW itself (Thulasidharan et al., 2022). In particular, the data
showed a small-scale vertical mode in the kinematics of young stars, with the
amplitude of the oscillation correlating with the age of the stars. However,
the dust extinction significantly limited this analysis.

The IR data from TEMPO is needed to measure the kinematics of stars in the RW,
which are not observable in the optical band. These measurements, combined
with the radial velocity and chemical abundances of the data inferred from
SDSS-V in the the same region, will help to determine whether the RW is a
bending wave induced by the passage of a satellite galaxy or a feature created
by gas instability.

####  4.6.3 Detection of Extragalactic Sources

TEMPO’s observations will achieve a faintness limit on par with that of the
Hubble eXtreme Deep Field, which reached a typical depth of
$m_{\mathrm{AB}}=30$ mag (Illingworth et al., 2013). More specifically,
TEMPO’s proposed FOV offers observations with very little extinction in two
out of the 18 H4RG photodiode arrays that compose the Roman WFI detector focal
plane. In addition, at +5 hr right ascension, there are few other
extragalactic deep fields. Therefore, with a limiting mag of 29.7
$\mathrm{mag_{AB}}$, TEMPO is capable of discovering extragalactic sources
that will be ideal for follow-up with forthcoming 20-30 meter class
telescopes.

##  5 Conclusion

In this paper, we have outlined the ways in which the TEMPO survey has the
potential to address a wide range of scientific open questions with a single,
coherent dataset, thereby enabling scientific investigations across multiple
astrophysical subdomains. The survey will enable observations with deep near-
infrared magnitude limits, wide field coverage, high cadence, and a long
temporal baseline, producing a dataset of lasting scientific value. The key
science drivers addressed by this program include the ability to: constrain
prevailing theories of the formation and evolution of stars, planets, and
moons; discover widely-separated exoplanets to better under the census
demographics of these systems; investigate the variability of young stars and
brown dwarfs; trace the evolution of stellar jets and outflows; and constrain
the low-mass end of the stellar IMF.

The duration of the TEMPO survey is the equivalent to 475 HST orbits, a
baseline that cannot be requested through the standard Telescope Allocation
Committee calls. However, TEMPO will be well poised to be an impactful Roman
Treasury Program. TEMPO’s deep coverage and broad band imaging enables the
detection of objects one hundred times fainter than prior treasury programs in
the ONC (Limbach et al., 2023). In addition to exploring new discovery spaces,
TEMPO will build upon prior efforts, including The HST survey of the Orion
Nebula Cluster (GO10246, 104 orbits; Robberto et al. 2013) and The Orion
Nebula Cluster as a Paradigm of Star Formation (GO13826, 52 orbits; Robberto
et al. 2020) — both Hubble Space Telescope Treasury Programs. Furthermore,
Roman attains HST survey depth in significantly less time. To illustrate,
while HST required approximately 35 hours to map a 0.135 square degree area,
Roman achieves equivalent photometric precision in a field double the size
within 45 minutes. A 30-day Roman survey will be comparable to conducting an
HST survey nearly 1000 times. Pushing the boundaries of efficiency and depth,
TEMPO is poised to leave a lasting legacy in our exploration of the cosmos.

###### Acknowledgements.

The authors will like to acknowledge helpful discussions with Morgan MacLeod,
Snežana Stanimirović, and Anne Noer Kolborg. MSF gratefully acknowledges the
generous support provided by NASA through Hubble Fellowship grant HST-
HF2-51493.001-A awarded by the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy, In.,
for NASA, under the contract NAS 5-26555. This work was carried out in part at
the Jet Propulsion Laboratory, California Institute of Technology, under a
contract with the National Aeronautics and Space Administration. RY is
grateful for support from a Doctoral Fellowship from the University of
California Institute for Mexico and the United States (UCMEXUS) and CONACyT, a
Texas Advanced Computing Center (TACC) Frontera Computational Science
Fellowship, and a NASA FINESST award (21-ASTRO21-0068). J. M. V. acknowledges
support from a Royal Society - Science Foundation Ireland University Research
Fellowship (URF$\backslash$1$\backslash$221932). R. H. acknowledges support
from the German Aerospace Agency (Deutsches Zentrum für Luft- und Raumfahrt)
under PLATO Data Center grant 50OO1501.

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