###### Abstract

While there have been far fewer missions to the outer Solar System than to the
inner Solar System, spacecraft destined for the giant planets have conducted a
wide range of fundamental investigations, returning data that continues to
reshape our understanding of these complex systems, sometimes decades after
the data were acquired. These data are preserved and accessible from national
and international planetary science archives. For all NASA planetary missions
and instruments the data are available from the science discipline nodes of
the NASA Planetary Data System (PDS). Looking ahead, the PDS will be the
primary repository for giant planets data from several upcoming missions and
derived datasets, as well as supporting research conducted to aid in the
interpretation of the remotely sensed giant planets data already archived in
the PDS.

###### keywords:

giant planets; planetary atmospheres; planetary interiors; magnetospheres;
data archiving; Jupiter; Saturn; Uranus; Neptune; Planetary Data System

1 1 0 Academic Editors: Imke de Pater and Yamila Miguel 31 October 2022 20
November 2022 https://doi.org/ Giant Planet Observations in NASA’s Planetary
Data System Giant Planet Observations in NASA’s Planetary Data System Nancy J.
Chanover 1,∗, James M. Bauer 2, John J. Blalock 3, Mitchell K. Gordon 4, Lyle
F. Huber 1, Mia J. T. Mace 4, Lynn D. V. Neakrase 1, Matthew S. Tiscareno 4
and Raymond J. Walker 5 Nancy J. Chanover, James M. Bauer, John J. Blalock,
Mitchell K. Gordon, Lyle F. Huber, Mia J. T. Mace, Lynn D. V. Neakrase,
Matthew S. Tiscareno and Ray J. Walker Chanover, N.J.; Bauer, J.M.; Blalock
J.J.; Gordon, M.K.; Huber, L.F.; Mace, M.J.T.; Neakrase, L.D.V.; Tiscareno,
M.S.; Walker, R.J. Correspondence<EMAIL_ADDRESS>Tel.: +1-575-646-2567

##  1 Introduction

Spacecraft exploration of the outer Solar System began with the arrival of
Pioneer 10 at Jupiter in 1973, and continues to the present day with the Juno
spacecraft in orbit around Jupiter. Unlike the more frequent orbiter and
lander missions to destinations in closer proximity to Earth (e.g., the Moon
or Mars), missions to the outer Solar System have been more scarce due to
cost, power, and travel time constraints. Nevertheless, spacecraft destined
for the giant planets have conducted a wide range of fundamental
investigations, returning data that continues to reshape our understanding of
these complex systems, sometimes decades after the data were acquired.

Early in the history of NASA’s planetary missions, data archiving was somewhat
unregulated: data were typically delivered from missions to Principal
Investigators (PIs), who were individually responsible to clean, process, and
document the data, and then to deposit them with the National Space Science
Data Center Archive (NSSDCA) for permanent storage and public access. However,
there was a realization in the late 1980s that careful stewardship of data was
required to ensure both its accessibility and its usability for future
generations of researchers. Not only were the data degrading (whether stored
on analog media such as photographic film or scan tapes, or on digital media
such as magnetic tapes), but subsequent attempts by others to use the data
were failing despite conscientious efforts on the part of the PIs to provide
sufficient documentation. It was recognized that these remote sensing (and
also in situ) data represent a national treasure and a significant investment
that must be preserved and maintained indefinitely.

NASA’s Planetary Data System (PDS) was established with this aim in mind,
following recommendations made by the Committee on Data Management and
Computation (CODMAC) on behalf of the Space Science Board, National Academy of
Sciences (Bernstein et al., 1982; Arvidson et al., 1986), with the PDS being
one of a series of data systems recommended (the others covering other
scientific disciplines such as Heliophysics and Astrophysics). CODMAC reviewed
several archiving approaches and concluded that planetary datasets should
reside at research institutions associated with the relevant scientific
community, ensuring that scientists with direct experience in working with the
data are closely involved in the archiving and curation process as well as the
development of tools for data search, analysis, visualization, and planning
observations.

To that end, the PDS is structured as a federated system of six Discipline
Nodes (DNs) that provide unique expertise in various sub-disciplines of
planetary science (Figure 1) PDS (2017). Of these DNs, all but the Geosciences
Node archive key remote sensing data sets related to the giant planets
(specific examples are given in Section 2):

  * •

The Atmospheres Node (ATM, https://pds-atmospheres.nmsu.edu, accessed on 30
October 2022) archives all non-imaging atmospheric data from planetary
missions (excluding Earth observations), ground-based observations, and
planetary analog, laboratory and field measurements.

  * •

The Cartography and Imaging Sciences Node (IMG, https://pds-
imaging.jpl.nasa.gov, accessed on 30 October 2022) archives digital image
collections from planetary missions, and supports cartographic and geospatial
data analysis.

  * •

The Geosciences Node (GEO, https://pds-geosciences.wustl.edu, accessed on 30
October 2022) archives and distributes digital data related to the study of
the surfaces and interiors of terrestrial planetary bodies.

  * •

The Planetary Plasma Interactions Node (PPI, https://pds-ppi.igpp.ucla.edu,
accessed on 30 October 2022) archives data related to the study of the
interaction between the solar wind and planetary winds with planetary
magnetospheres, ionospheres and surfaces.

  * •

The Ring-Moon Systems Node (RMS, https://pds-rings.seti.org, accessed on 30
October 2022) archives data relevant to outer planetary systems, with a focus
on individual data products within their original context. This includes
remote sensing data (images, imaging spectrometer, and occultations) for
systems beyond the asteroid belt (that is, Jupiter through Pluto). RMS also
hosts the Radio Science Sub-Node (RSSN), which assists all of PDS with the
ingestion and curation of radio science data, including gravity science and
occultations.

  * •

The Small Bodies Node (SBN, https://pds-smallbodies.astro.umd.edu, accessed on
30 October 2022) archives mission, ground-based, and laboratory data for
objects generally described as comets, asteroids and interplanetary dust. This
includes dwarf planets, objects in the Kuiper Belt and the Oort cloud,
Centaurs, and small planetary satellites, as well as observations of the giant
planets acquired en route to small body targets.

Data standards, i.e., the technical specifications used to describe data
storage, sharing, and interpretation, are crucial for information transfer and
interoperability. PDS standards ensure consistent description of planetary
science data so that data providers, programmers, and end-users all know what
to expect when creating and working with PDS files Data Design Working Group
(2021). Historically, the PDS Requirements Review Arvidson et al. (1986) laid
out an ambitious design for preserving, cataloging, and distributing planetary
datasets to users, all during a time that predated the widespread use of the
internet. It consisted of a proposed three-stage rollout:

  * •

PDS version 1.0: Focused on software infrastructure and catalog design (1990)

  * •

PDS version 2.0: Basic operations in the central cataloging and distribution
node, with two selected DNs being brought up to full operational status as
test cases (1992–1993)

  * •

PDS version 3.0: “Final” release with all DNs fully operational and user
support in place (1994–1995)

Figure 1: Organizational structure of the PDS. The Discipline Nodes are shown
in blue boxes. The support nodes, shown in gold boxes, contain experts in
areas that cover numerous missions. The Radio Science Subnode, currently at
RMS, supports data providers and users with the specialized needs of radio
science data.

By the mid-1990s, following feedback from users and data preparers, two major
changes were implemented, resulting in what came to be known as PDS3 data
standards (referring to v3.0 in the list above). First, major simplifications
were made to the catalog file structures in order to streamline the process
for users to locate and order datasets, and second, an attempt was made to
rationalize and standardize the keywords used in labels by imposing some
minimal metadata requirements.

Fifteen years following the introduction of PDS3, the process of developing
and implementing new standards (PDS4) began, based on lessons learned during
twenty years of archiving, current information systems concepts, and the
capabilities inherent in the modern internet. PDS4 ensures more consistent
standardization, better long-term preservation, and improved automation
support Prockter et al. (2021). Currently, all new datasets submitted to PDS
comply with the PDS4 standards, and all existing PDS3 datasets are in the
process of being migrated to PDS4. Further details of the history and data
standards of the PDS are provided in Raugh and Hughes (2021).

The release of the Memorandum from the President’s Office of Science and
Technology Policy entitled “Increasing Access to the Results of Federally
Funded Scientific Research” in 2013 led to the development of the NASA Plan
for Increasing Access to the Results of Scientific Research in 2014, the NASA
Science Mission Directorate’s Strategy for Data Management and Computing for
Groundbreaking Science 2019–2024, and the NASA Science Mission Directorate’s
Policy Document SPD-41: Scientific Information Policy in 2021. Taken together,
these documents codify the requirements surrounding the accessibility and
preservation of digital data produced by NASA missions, instruments, and
projects. The PDS has played a central role in serving as a publicly
accessible and appropriate repository for archiving planetary data. The
strength of the PDS lies in its long-term stability and the fact that all data
are peer reviewed, both to ensure that they conform to the PDS standards and
to confirm that they are well-documented and will be usable by future
researchers. The PDS is an archive guided by the FAIR principles for
scientific data management and stewardship, namely that the data should be
findable, accessible, interoperable, and reusable.

After nearly five decades exploring the giant planets of our Solar System, the
PDS is now responsible for the curation, preservation, and distribution of a
wealth of remote sensing data on the outer planets. This includes data
covering a wide range of wavelengths, instrumentation, acquisition modalities,
targets, and physical processes. In this paper, we describe examples of such
data in Section 2, discuss the modes through which these data can be accessed
in Section 3, highlight anticipated future giant planets data and their
application to both Solar System and exoplanetary science investigations in
Section 4, and provide conclusions in Section 5.

##  2 Giant Planets Data in the PDS

Remote sensing data relevant to numerous science questions about the giant
planets can be found across the PDS, illustrative of both the breadth and
depth of the existing giant planets data. With the current PDS4 standards it
should be immaterial where the data are actually located since they should be
discoverable from any search within the PDS. However, the DNs still play an
important and active role in working with and advising new and experienced
data providers, data users, and tool developers who interact with data in the
PDS.

In the following subsections we provide representative examples of giant
planets data that are available from the PDS, organized by science area. This
is by no means an exhaustive list. Rather, it is intended to showcase the
aforementioned breadth of data and the physical processes they probe. Many
instances of giant planet observations in the PDS archive were obtained when
the planet was not encountered by the spacecraft, i.e., at distances where the
planet is poorly resolved or unresolved by imaging instruments. We highlight
here only datasets where the spacecraft was in the vicinity of the giant
planet and conducted scientific observations during a flyby, or the planet was
the subject of a prolonged orbiter mission. We also provide examples of Earth-
based observations of the giant planets that are archived in the PDS.

###  2.1 Atmospheric Science

The most widely recognized attribute of the giant planets is their dynamic
atmospheres, including the presence of latitudinally confined cloud bands,
long-lasting vortices, discrete convective cloud features, auroral emissions,
and evidence of bolide impacts. The PDS archives a broad range of observations
that support investigations of these phenomena, including some with temporal
coverage spanning several decades that enable studies of seasonal changes in
the giant planet atmospheres and comparative studies between the four giant
planets of our Solar System.

####  2.1.1 Atmospheric Composition

The chemical composition of gas giant atmospheres can yield critical insights
into both their formation and evolution as well as dynamical processes taking
place below the cloud tops. Abundance measurements for the most ubiquitous
elements (helium, carbon, nitrogen, and sulfur) as compared to the
corresponding solar values provide constraints on different planetary
formation scenarios Owen and Encrenaz (2006). Global abundances and the
spatial distribution of disequilibrium species (e.g., PH3, CO) provide
linkages between the atmospheric thermochemistry and the vertical convective
motions, which also probes the heat balance of the deep atmosphere.

Several long-wave infrared (LWIR) spectrometers have flown on NASA missions to
the outer planets, including the Infrared Interferometer Spectrometer and
Radiometer (IRIS) instrument on Voyagers 1 and 2 and the Composite Infrared
Spectrometer (CIRS) on Cassini. The flyby nature of the Voyager missions
resulted in the same instruments being used to probe similar phenomena across
all four of the giant planets, which can enable comparative studies. For
example, data from the IRIS instruments were used to determine the helium
abundance of Jupiter Gautier et al. (1981); Conrath et al. (1984), Saturn
Conrath et al. (1984); Conrath and Gautier (2000), Uranus Conrath et al.
(1987), and Neptune Conrath et al. (1991) (Figure 2). The 13 year duration of
the Cassini mission enabled studies of seasonal variation in Saturn’s
atmospheric composition and chemistry using the CIRS data Fouchet et al.
(2009); Fletcher et al. (2010, 2018). (Both the raw and calibrated CIRS data
are archived in the PDS and are accessible from
https://atmos.nmsu.edu/data_and_services/atmospheres_data/Cassini/inst-
cirs.html and https://pds-rings.seti.org/cassini/cirs/index.html, both
accessed on 30 October 2022).

Figure 2: Helium abundances of Jupiter Conrath et al. (1984), Saturn Conrath
and Gautier (2000), Uranus Conrath et al. (1987), and Neptune Conrath et al.
(1991) derived from Voyager 1 and 2 IRIS observations.

####  2.1.2 Global Dynamics

Every mission to the giant planets was equipped with some form of an imaging
camera (Table 1), resulting in a wealth of data in the PDS that can be used
for studies of giant planet atmospheric dynamics. The Voyager flybys revealed
the large-scale zonal structure of the atmospheric circulations of Jupiter
Smith et al. (1979a, b), Saturn Smith et al. (1981, 1982), Uranus Smith et al.
(1986), and Neptune Smith et al. (1989), with the Galileo and Cassini orbiters
revealing time-dependence and small-scale structure in the wind fields on
Jupiter Vasavada et al. (1998) and Saturn Porco et al. (2005); García-Melendo
et al. (2011) , respectively. There were also valuable secondary imaging
science opportunities during gravity assist flybys as conducted during Jupiter
flybys by Cassini Porco et al. (2003); Li et al. (2006) and New Horizons Simon
et al. (2015).

The large-scale zonal and meridional wind speeds of the giant planets can be
inferred through cloud-tracking techniques. This requires images with
appropriate temporal spacing of ideally one to several hours: a time
separation that is too small will not yield measurable motion, whereas a time
separation that is too large increases the likelihood that the feature(s)
being tracked will evolve and lose their fidelity. Cloud tracking techniques
also are optimized when using images of high spatial resolution, which
increases the number of features that can be tracked.

Table 1: Optical and near-infrared imagers used for remote sensing of Jupiter
(J), Saturn (S), Uranus (U) and Neptune (N), and the Digital Object
Identifiers (DOIs) for accessing the data. All links in this table were
accessed on 30 October 2022.

Spacecraft |  Instrument |  Target |  Access DOIs
---|---|---|---
Pioneer 10, 11 |  Imaging Photopolarimeter (IPP) |  J, S |  not available *
Voyager 1 |  Imaging Science Subsystem (ISS) |  J |  https://doi.org/10.17189/1520214
|  |  S |  https://doi.org/10.17189/1520304
Voyager 2 |  ISS |  J |  https://doi.org/10.17189/1520214
|  |  S |  https://doi.org/10.17189/1520304
|  |  U |  https://doi.org/10.17189/1520365
|  |  N |  https://doi.org/10.17189/1520412
Galileo |  Solid State Imager (SSI) |  J |  https://doi.org/10.17189/1520425
|  Near Infrared Mapping Spectrometer (NIMS) |  J |  https://doi.org/10.17189/1520293
Cassini |  Imaging Science Subsystem (ISS) |  J |  https://doi.org/10.17189/1520210
|  |  S |  https://doi.org/10.17189/1520177
|  Visual and Infrared Mapping Spectrometer (VIMS) |  J, S |  https://doi.org/10.17189/1520275
New Horizons |  Long Range Reconnaissance Imager (LORRI) |  J |  https://doi.org/10.26007/tcne-cm20
|  Multispectral Visible Imaging Camera (MVIC) |  |  https://doi.org/10.26007/xmy5-zx84
Juno |  JunoCam |  J |  https://doi.org/10.17189/1520191

* Pioneer 11 imaging data can be obtained from NSSDC, but not from the PDS.

####  2.1.3 Vortices

In addition to enabling the study of global dynamics of the giant planets, the
imaging instruments described in Section 2.1.2 have also been used for
detailed studies of discrete vortices. Long-lived storms like Jupiter’s Great
Red Spot have been characterized in terms of their chemistry and dynamics
using observations from several instruments with data archived in the PDS
Simon et al. (2014); Sanchez-Lavega et al. (2018). In a more recent NASA
mission, Juno’s polar orbit has provided unprecedented access to the polar
regions of Jupiter, and data from the JIRAM instrument (https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/JUNO/jiram.html,
accessed on 30 October 2022), as shown in Figure 3, revealed new insights into
the formation, evolution, and vertical extent of polar vortex crystals.

Figure 3: Six cyclones in Jupiter’s south polar region as revealed by a
Juno/JIRAM image taken on February 2, 2017, at a wavelength of roughly 5
microns. Image Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM (NASA PIA23556).

####  2.1.4 Vertical Profiles

The variation of atmospheric temperature as well as molecular mole fractions
with depth (or pressure) can be inferred by radio or stellar occultations. In
the former, the S or X band (or both) radio signals from the spacecraft are
the source, and the reduction in signal as it passes from the spacecraft
through a giant planet atmosphere to be received on Earth by the Deep Space
Network can be analyzed to produce pressure-temperature profiles as well as
vertical abundance profiles. For stellar occultations, a star is the source,
and the dimming of starlight as measured by remote sensing instruments on
board a spacecraft (or on Earth) can yield vertical profiles for atmospheric
constituents Elliot and Olkin (1996), particularly when components of the
occultation data are spectroscopic Greathouse et al. (2010). The radio science
and UV and IR spectroscopic remote sensing instruments on board Voyager 1 and
2, Galileo, Cassini, New Horizons, and Juno have all been used to extract
information about the behavior of the giant planet atmospheres with depth. A
quick-look view of the types of data archived in the PDS for each giant planet
is available through the Integrated Archive pages at the PDS Atmospheres Node.
(For example, the Integrated Jupiter Data Archive page (https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/JUPITER/matrices.html,
accessed on 30 October 2022) provides a summary of the remote sensing
instruments on board the spacecraft that flew by or orbited Jupiter.)
Additionally, the RMS Node hosts 53 bundles of Earth-based, stellar
occultations of the Uranian system (https://pds-
rings.seti.org/pds4/bundles/uranus_occs_earthbased, accessed on 30 October
2022). Approximately half of these observations include atmospheric
occultations by Uranus. They are presented as time series data, in units of
counts-per-time, and are available for users who wish to further analyze them
to generate vertical profiles of the Uranian atmosphere.

Other than occultations, the microwave observations from Juno’s Microwave
Radiometer (MWR) instrument are sensitive to deeper regions of the Jovian
atmosphere (from 0.5 bar to hundreds of bars of pressure) than any previously
flown giant planet remote sensing instrument. These data, which are available
from the PDS Atmospheres Node (https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/JUNO/microwave.html,
accessed on 30 October 2022), are comprised of brightness temperatures in six
different radiometric channels. The combination of data from MWR as well as
instruments sensitive to Jupiter’s upper troposphere (e.g., JIRAM or JunoCam)
is a powerful approach for exploring the depths to which atmospheric phenomena
such as waves or storms extend Fletcher et al. (2020).

Atmospheric entry probes are the most direct way to gain information about the
vertical structure of the giant planet atmospheres. To date, only the Galileo
mission to Jupiter was equipped with a dedicated probe, which entered
Jupiter’s atmosphere on 7 December 1995. Key science results from the Galileo
probe include the findings that Jupiter’s zonal winds increased with depth and
remained high (and constant) from 4 to 21 bars Atkinson et al. (1997), the
relatively cloud-free Jovian “hot spot” where the probe entered the atmosphere
had an anomalously low water abundance Niemann et al. (1998), and the probe
detected radio signals attributed to the existence of Jovian lightning Rinnert
et al. (1998). Additionally, at Saturn, when Cassini approached and plunged
into the atmosphere, Cassini Radio Science was actively following the
spacecraft with multiple Deep Space Network (DSN) receivers until the signal
was lost. These in situ data, the Galileo Probe and the End-of-Mission raw
Cassini radio science data, are archived in the PDS Atmospheres Node
(https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/Galileo/galileo.html
and https://atmos.nmsu.edu/data_and_services/atmospheres_data/Cassini/inst-
rss.html, both accessed on 30 October 2022).

####  2.1.5 Upper Atmospheres and Aurora

Many of the spacecraft destined for the giant planets have been equipped with
remote sensing instruments that enable the study of the neutral upper
atmospheres, ionospheres, and auroral emissions. The ultraviolet spectrometers
listed in Table 2 detected Lyα emission from the giant planets, revealing the
complex interactions between each planet’s magnetic field and the solar wind
and more local sources of charged particles. The Cassini Ultraviolet Imaging
Spectrograph (UVIS) provided the most extensive dataset of a giant planet
upper atmosphere to date. The UVIS observations of Saturn included solar and
stellar occultations in the extreme ultraviolet (EUV) and far ultraviolet
(FUV), dayglow spectral images, and images of the magnetosphere that show the
vertical profile of neutral hydrogen escaping from Saturn’s atmosphere Nagy et
al. (2009). As shown in Figure 4, the Grand Finale phase of the Cassini
mission enabled views of Saturn’s polar regions of unprecedented detail,
revealing a complex structure of Saturn’s aurora that relates to the quiet or
disturbed nature of the nearby plasma Bader et al. (2020).

In addition to the auroral processes probed by the ultraviolet instruments,
the Jovian Infrared Auroral Mapper (JIRAM) instrument on board the Juno
spacecraft is sensitive to the 3.3–3.6 $\upmu$m emissions from H${}_{3}^{+}$,
which are used to characterize the morphology of the aurora and the conditions
in the magnetosphere that lead to auroral emissions. The JIRAM nadir and limb
observations of the H${}_{3}^{+}$ emissions (https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/JUNO/jiram.html,
accessed on 30 October 2022) reveal complex morphology in Jupiter’s auroral
ovals and an anti-correlation between derived thermospheric temperatures and
the H${}_{3}^{+}$ density, reinforcing that H${}_{3}^{+}$ emission is an
atmospheric cooling mechanism Dinelli et al. (2019).

Table 2: Ultraviolet spectrometers used for remote sensing of Jupiter (J),
Saturn (S), Uranus (U) and Neptune (N), and the DOIs for accessing the data.
All links in this table were accessed on 30 October 2022.

Spacecraft |  Instrument |  Target |  Access DOIs
---|---|---|---
Voyager 1 |  Ultraviolet Spectrometer (UVS) |  J |  https://doi.org/10.17189/4p9r-gc87
|  |  S |  https://doi.org/10.17189/8ads-fr53
Voyager 2 |  UVS |  J |  https://doi.org/10.17189/0w47-dq75
|  |  S |  https://doi.org/10.17189/emh4-v313
|  |  U |  https://doi.org/10.17189/fec9-4c64
|  |  N |  https://doi.org/10.17189/2e17-9r73
Galileo |  UVS |  J |  https://doi.org/10.17189/dv1z-cx79
|  |  |  https://doi.org/10.17189/8n8q-xf47
Cassini |  Ultraviolet Imaging Spectrograph (UVIS) |  J, S |  https://doi.org/10.17189/4be3-xq57
|  |  |  https://doi.org/10.17189/zzgw-f046
|  |  |  https://doi.org/10.17189/kthj-r777
New |  Alice Ultraviolet Imaging Spectrograph |  J |  https://doi.org/10.26007/qfvg-5k41
Horizons |  Linear Etalon Imaging Spectral Array (LEISA) |  J |  https://doi.org/10.26007/0cc7-4a49
Juno |  Ultraviolet Spectrograph (UVS) |  J |  https://doi.org/10.17189/b29k-pv96
|  |  |  https://doi.org/10.17189/c32j-7r56

Figure 4: UVIS observations of Saturn’s northern (a–d) and southern (e,f)
auroral ovals during the Grand Finale phase of the Cassini mission. Figure
reproduced from Bader et al. (2020).

####  2.1.6 Impacts and Convective Outbursts

Impact events are ubiquitous throughout the Solar System, but they are
challenging to observe without monitoring a target of interest night after
night since they are signatures of a stochastic process. However, in the case
of Comet Shoemaker-Levy 9 (SL9), whose 21 fragments impacted the Jovian
atmosphere, observers had more than a year of advanced warning between the
time the comet was discovered in March 1993 and the dates on which the
fragments were predicted to impact Jupiter (July 1994). Numerous ground-based
and space-based assets were used to observe the impacts, deriving information
about the chemical composition of both the Jovian atmosphere and the comet
fragments, the propagation of waves through the Jovian atmosphere, and the
interaction of charged particles with both the magnetosphere and upper
atmosphere of Jupiter. The spacecraft data from Galileo and Hubble Space
Telescope are archived in the PDS Imaging Node and Atmospheres Node,
respectively, and some ground-based observations of the SL9 impacts are also
archived in the PDS Atmospheres Node (https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/catalog.htm#Jupiter,
accessed on 30 October 2022).

In addition to impacts, convective outbursts are another episodic phenomenon
that can be used to probe vertical transport and moist convection in giant
planet atmospheres. Although generally there is little indication _a priori_
of when such a storm will take place, fortunately these events are often so
energetic that their effects are visible for weeks or months after the initial
outburst. Such was the case for the Saturn storm of 2010–2011, which was first
detected in December 2010 and whose aftermath was detected through August
2011. The Cassini spacecraft was well positioned to acquire observations of
the storm with its instrument suite (Figure 5), revealing new insights into
Saturn’s atmospheric structure, wind field, tropospheric cloud composition,
stratospheric thermal structure and trace gas composition, ammonia vapor
distribution, and associated lightning discharges Sanchez-Lavega et al.
(2018). These data are archived in the PDS Imaging (ISS and VIMS), Atmospheres
(CIRS), RMS (ISS, VIMS and CIRS) and PPI (RPWS) nodes.

Figure 5: Cassini ISS image of the 2010 Saturn storm acquired on 24 December
2010. This image was downloaded from the PDS using the RMS OPUS tool (Section
3.1); the tint of this browse image is indicative of the wavelength range of
the ISS filter through which the image was acquired (in this case, 429–492
nm).

####  2.1.7 Ground-Based Photometric Monitoring

Studies of seasonal changes in the atmospheres of the giant planets are by
necessity long-term endeavors, given the orbital periods of the gas giants
(approximately 12, 29, 84, and 164 years for Jupiter, Saturn, Uranus, and
Neptune, respectively). There are few facilities that have been operating
continuously and collecting data in a self-consistent manner that would enable
long-term studies of the giant planets; the 21-inch telescope at Lowell
Observatory is one such example. Disk-integrated albedos of Uranus and Neptune
in the Strömgren b and y filters spanning the period 1972–2016 (Figure 6)
Lockwood (2019a) are archived in the PDS Lockwood (2019b). They reveal
seasonal changes in the integrated brightness of the ice giant planets as well
as short-term brightness changes that are likely due to the appearance and
fading of large, discrete atmospheric features.

Figure 6: Disk integrated light curves of Uranus (left) and Neptune (right) in
the Strömgren b (blue points) and y (green points) filters from 1972 to 2016.

###  2.2 Particles and Fields

Radio frequency emissions from Jupiter are very strong, at times even stronger
than those of the Sun. Radio frequency observations at decametric wavelengths
($\sim$22 MHz) were used to determine that Jupiter had an intrinsic magnetic
field Burke and Franklin (1955) before the first in situ observations by
Pioneer 10. Other Jovian emissions include decametric radiation from
synchrotron emissions of trapped electrons in Jovian radiation belts. The
first spacecraft to make radio frequency observations were Voyager 1 and 2 in
1979. Both Voyager 1 and Voyager 2 carried a Planetary Radio Astronomy (PRA)
experiment and a Plasma Wave Subsystem that measures electric and magnetic
field waves in the range of Hz to 10 s of KHz. The radio and plasma wave
investigations have probed the strong interaction between the moon Io and the
upper atmosphere of Jupiter and have been used to determine the rotation rate
of Jupiter. Plasma wave observations have been used to determine the electron
density at Jupiter.

Since Voyager 1 and Voyager 2, the radio or plasma (or both) wave experiments
have been flown on four subsequent missions to Jupiter. Table 3 gives the
spacecraft and instruments, and the Digital Object Identifiers (DOIs) through
which the data can be accessed directly from the PDS. The PDS is in the
process of migrating all data holdings that were originally archived using the
PDS3 metadata standard to the PDS4 standard, which provides a more modern
archive structure and richer metadata. In cases where both PDS3 and PDS4
versions of the data are available, we list in Table 3 the access DOIs to the
PDS4 data.

Figure 7 shows the radio spectra at the giant planets as well as that from
Earth. As is the case for Jupiter, electromagnetic wave observations at Saturn
have provided insight into the planetary rotation. However, at Saturn the
period obtained called planetary period oscillations (PPO) is not the rotation
period of the planet. The PPO period drifts over a time scale of years and is
different for sources in the north and south (e.g., Gurnett et al. (2007)).
Its origin remains an area of intense study. Table 3 lists the radio astronomy
and plasma wave data that are available from Saturn.

Figure 7: The radio spectra observed at Jupiter, Saturn, Earth, Uranus, and
Neptune Zarka (1998).

The Magnetospheric Imaging Instrument (MIMI) on Cassini provided a form of
remote sensing of Saturn’s magnetosphere not available for the other outer
planets. The coexistence of trapped energetic ions and neutral gases in
Saturn’s magnetosphere allows the process of charge exchange to take place, in
which an energetic particle takes an electron from a neutral particle, turning
the ion into a neutral particle that is no longer magnetically trapped. The
neutral particles can be imaged, providing a picture of the source energetic
ion population, in a process called Energetic Neutral Atom (ENA) imaging. The
Ion and Neutral Camera (INCA), was part of Cassini’s MIMI package. The INCA
camera data are available from the PDS (Table 3), including processed images
and movies of the ENA that are included as browse files. In Figure 8, we show
a sequence of four ENA images in the magnetosphere along with auroral EUV
images in the ionosphere. The images show the injection of ions and the
corresponding aurora. Note, the images of the ions map along magnetic field
lines to Saturn’s aurora and both rotate with Saturn.

Figure 8: ENA images of Saturn’s magnetospheric ions and auroral EUV emissions
during an particle acceleration event on 8 May 2008 ((A) 0749–0849UT, (B)
0919–1019UT (C) 1043–1143UT, (D) 1141–1149UT). Currents along the magnetic
field accelerate the particles producing the aurora. (Figure courtesy of
Donald Mitchell, a movie of the ENA images can be found at
%MDPI:␣Another␣)␣missed?␣Please␣add␣it.%%␣NJC:␣added␣ithttps://doi.org/10.17189/1519607,
accessed on 30 October 2022.)

Only Voyager 2 has visited Uranus and Neptune. Both the Planetary Radio
Astronomy and the Plasma Wave Subsystem instruments returned data; these are
also listed in Table 3.

Recently, all of the Voyager Plasma Wave Subsystem data have been made
available in bundles covering the entire mission by using the PDS4 standard.
The newly submitted PDS4 Voyager data are available in the NASA Common Data
Format (CDF) format. PDS4 was designed to allow translation from the formats
used in the archive to other formats. In space plasma research, the CDF format
is widely used in research. PDS developed a version of CDF (called CDF-A) that
adheres to PDS4 archival standards. A large number of research tools are
available for data archived in CDF-A. The PPI Node is currently translating
most of the PDS4 data in the archive into PDS4 documented CDF-A. Both the
original PDS4 data and the translated data will be made available to users.
Researchers wanting to use data translated into CDF-A can find the CDF-A
standards documents and user guides at https://pds-
ppi.igpp.ucla.edu/doc/index.jsp (accessed on 30 October 2022).

Table 3: Radio astronomy, plasma wave, and particle data for Jupiter (J),
Saturn (S), Uranus (U) and Neptune (N) available in the PDS, and the DOIs for
accessing the data. Several of the investigations listed have multiple data
sets; in those cases, the range of sequential DOIs is given. All links in this
table were accessed on 30 October 2022.

Spacecraft |  Instrument |  Target |  Access DOIs
---|---|---|---
Voyager 1 |  Planetary Radio Astronomy Receiver (PRA) |  J |  https://doi.org/10.17189/1522972
|  |  S |  https://doi.org/10.17189/1522966
|  Plasma Wave Spectrometer (PWS) |  J |  https://doi.org/10.17189/1519900 – https://doi.org/10.17189/1519905
|  |  S |  https://doi.org/10.17189/1519905
|  |  |  https://doi.org/10.17189/1519927 – https://doi.org/10.17189/1519928
|  |  J, S |  https://doi.org/10.17189/wp0z-1c51 – https://doi.org/10.17189/g5fy-rz59
Voyager 2 |  PRA |  J |  https://doi.org/10.17189/1519955
|  |  S |  https://doi.org/10.17189/1520011
|  |  U |  https://doi.org/10.17189/1520041 – https://doi.org/10.17189/1520043
|  |  N |  https://doi.org/10.17189/1519984 – https://doi.org/10.17189/1519986
|  PWS |  J |  https://doi.org/10.17189/1519957 – https://doi.org/10.17189/1519962
|  |  S |  https://doi.org/10.17189/1519960 – https://doi.org/10.17189/1519962
|  |  U |  https://doi.org/10.17189/1519960 – https://doi.org/10.17189/1519962
|  |  |  https://doi.org/10.17189/1520044 – https://doi.org/10.17189/1520046
|  |  N |  https://doi.org/10.17189/1519987– https://doi.org/10.17189/1519989
|  |  J,S,U,N |  https://doi.org/10.17189/86sw-jn08 – https://doi.org/10.17189/bwn5-bs17
Ulysses |  Unified Radio and Plasma Wave Experiment (URAP) |  J |  https://doi.org/10.17189/1519865 – https://doi.org/10.17189/1519873
Galileo |  PWS |  J |  https://doi.org/10.17189/1519678 – https://doi.org/10.17189/1519684
Cassini |  Radio and Plasma Wave Science (RPWS) |  J |  https://doi.org/10.17189/1519614 – https://doi.org/10.17189/1519617
|  |  S |  https://doi.org/10.17189/1519610 – https://doi.org/10.17189/1519617
|  Magnetospheric Imaging Instrument (MIMI) Imaging Neutral Camera (INCA) |  S |  https://doi.org/10.17189/1519607
New Horizons |  Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) |  J |  https://doi.org/10.26007/v0m7-pw47; https://doi.org/10.26007/hggb-f658
|  Radio Science Experiment (REX) |  J |  https://doi.org/10.26007/61tf-4r89; https://doi.org/10.26007/f0cb-zn89
|  Solar Wind Around Pluto (SWAP) |  J |  https://doi.org/10.26007/dfhh-kn63; https://doi.org/10.26007/q952-d227
|  Student Dust Counter (SDC) |  J |  https://doi.org/10.26007/02b6-rm36; https://doi.org/10.26007/ke28-ke10
Juno |  RPWS |  J |  https://doi.org/10.17189/1519708 – https://doi.org/10.17189/1520498
Radio Jove (Earth-based) |  Radio Telescope |  J |  https://doi.org/10.17189/1520498 – https://doi.org/10.17189/1522500

In addition to the spacecraft observations of the giant planets, Jupiter can
be readily observed from Earth’s surface. In recent years, a worldwide program
of continuous monitoring of Jovian radio waves has been maintained. In
cooperation with the International Planetary Data Alliance (IPDA), PDS has
archived and made available data from the Radio Jove project. The data are
available in the archival version of the CDF-A format and in their native
format used at radio observatories. The data from Radio Jove are also listed
in Table 3. A unique aspect of the Radio Jove program is that it includes
contributions from both professional and amateur observers. An inexpensive
receiver that can detect the Jovian emissions is available through the NASA
Radio Jove web site (https://radiojove.gsfc.nasa.gov/, accessed on 30 October
2022).

Planetary particles and fields data are of interest to scientists in both the
astronomy and heliophysics communities. In addition to direct access from PPI,
the data are being made available through the International Virtual
Observatory Alliance’s (IVOA) protocol (EPN-TAP) and the Heliophysics API
(HAPI). These will enable users in those communities to stream the data using
the protocol with which they are familiar. At this writing, all of the Voyager
and Cassini data are available through EPN-TAP and the Voyager, Cassini and
Galileo data are available through the HAPI server. In addition, PPI supports
the TOPCAT (Tool for OPerations on Catalogs And Tables) display system for
data using EPN-TAP and Autoplot for data accessed through HAPI.

###  2.3 Interiors

The deep atmospheres and interior structure of the giant planets can be probed
through gravity measurements, whereby the returned radio signal from the
spacecraft is used to quantify slight deviations in its orbit due to the
gravitational influence of the planet on the spacecraft. The Doppler shifts of
the signals from the radio science instruments on board Voyager 1 and 2,
Cassini, and Juno were measured by the Deep Space Network to probe the gravity
fields of the giant planets. For example, recent analyses of measurements made
by the Juno Gravity instrument revealed new insights into the depth limits of
Jupiter’s zonal winds Kaspi et al. (2020) and Jupiter’s asymmetric gravity
field Iess et al. (2018). The radio science data for the giant planets are
archived in the PDS at the PPI Node (Voyager and Galileo), the Atmospheres
Node (Cassini and Juno) and the Small Bodies Node (New Horizons). The Radio
Science subnode, housed at the Ring-Moon Systems Node, serves all of the PDS
and provides expertise on working with radio science data.

Additionally, certain waves in Saturn’s rings have been used as records of
processes originating in Saturn’s interior, similar to the information
provided by a terrestrial seismometer (Hedman et al. (2022) and references
therein). The data facilitating this research is primarily the derived
occultation profiles taken from Cassini VIMS (https://pds-
rings.seti.org/viewmaster/volumes/COVIMS_8xxx, accessed on 30 October 2022)
and RSS (https://pds-rings.seti.org/viewmaster/volumes/CORSS_8xxx, accessed on
30 October 2022).

##  3 Data Discoverability and Usability

Given the diversity of giant planets data in the PDS, examples of which are
described in Section 2, accessing and making use of those data might seem like
a task that requires advanced knowledge of data processing and visualization,
file manipulation, or data engineering. Here we discuss various methods
already implemented – some across the PDS and some at specific Discipline
Nodes – to aid in giant planets data search and discovery.

A new user to the PDS, or an experienced user who is interested in exploring
the PDS holdings rather than conducting a focused search for something
specific, should start at the PDS homepage (https://pds.nasa.gov, accessed on
30 October 2022). From there, the Data Search function enables users to search
by Target (e.g., Uranus System) or Mission (e.g., Voyager). In each case the
search returns links to (a) specific search tools – including those described
in the following subsections – that are most appropriate for finding the data
of interest, and (b) resource pages containing more information about the PDS
holdings in the area of interest.

Experienced PDS users, or those who know more specifically what kind of giant
planets data they are searching for, may wish to begin their search at the
relevant DN. There users can make use of sophisticated tools developed by the
DNs that enable searching on parameters such as observing geometry, positional
information, or science theme. Examples of such tools are described in the
following subsections.

###  3.1 OPUS and Viewmaster: Search and Browse the RMS Archive

An enhanced data browser is provided by Viewmaster (https://pds-
rings.seti.org/viewmaster/volumes, accessed on 30 October 2022), which allows
users to see every data volume in the RMS archive within an intuitively
designed framework so that corresponding preview images, diagrams, indices,
and documentation are listed in parallel to each data product, and related
files can be found straightforwardly. The process of finding and using PDS
data archived by the RMS Node is illustrated in Figure 9 by an example of how
a user can generate a spectrum of Saturn’s aurora.

Alongside Viewmaster, seamless cross-mission cross-instrument search for
spacecraft and ground-based remote sensing observations is provided by the RMS
Node’s Outer Planet Unified Search (OPUS) tool (https://opus.pds-
rings.seti.org, accessed on 30 October 2022). OPUS uses extensive metadata
generated by the RMS Node using the most current SPICE kernels for enhanced
search capabilities and provides preview images for an enhanced browsing
experience, so users can easily filter down through the available holdings to
reach the desired data products. Figure 10 illustrates how a user could search
through OPUS to obtain the same data (and find additional metadata) used to
plot the spectrum described in Figure 9. OPUS supports full geometric search
of the giant planets for Voyager ISS, Cassini CIRS, ISS, UVIS, and VIMS, and
New Horizons LORRI.

Visit RMS Viewmaster and navigate to the COUVIS_0xxx volumes: https://pds-
rings.seti.org/viewmaster/volumes/COUVIS_0xxx Select COUVIS_0011, which
contains the Cassini UVIS Saturn observations taken between 2005-04-01 and
2005-06-30 Within COUVIS_0011, select DATA and then D2005_172, and search for
data with observation time close to 03:35 Click on the thumbnail image to the
left of the filename to open a detailed page for the data product. Scroll down
to obtain information from the PDS3 label (EUV2005_172_03_35.LBL), including
the structure of the data (dimensionality, binning, and windowing) Users are
free to write their own programs to read and analyze the data. Sum over all
the sample data from lines 2 to 61 of the data file (EUV2005_172_03_35.DAT) to
generate a spectrum https://pds-rings.seti.org/viewmaster/volumes/COUVIS_0xxx/
https://pds-
rings.seti.org/viewmaster/volumes/COUVIS_0xxx/COUVIS_0011/DATA/D2005_172/
https://pds-
rings.seti.org/viewmaster/volumes/COUVIS_0xxx/COUVIS_0011/DATA/D2005_172/EUV2005_172_03_35.DAT

Figure 9: Step-by-step instructions on how to find and obtain UVIS data from
the PDS via RMS Viewmaster for an observation of Saturn’s aurora carried out
around 03:35 on day 172 of year 2005. All links in this figure were accessed
on 30 October 2022.

Visit RMS OPUS: https://opus.pds-rings.seti.org Choose “Cassini UVIS” under
“Instrument Name [General]”, then select “Observation Time” in the left menu
under “General Constraints” and enter an observation time range from midnight
to 4am on day 172 of year 2005 OPUS uses a RESTful API, so that the search is
encoded in the following URL:
https://opus.pds-
rings.seti.org/#/instrument=Cassini+UVIS&time1=2005-06-21T00:00:00.000&time2=2005-06-21T04:00:00.000&qtype-
time=any&unit-
time=ymdhms&cols=opusid,instrument,planet,target,time1,observationduration&widgets=time,instrument&order=time1,opusid&view=browse&browse=data&cart_browse=gallery&startobs=1&cart_startobs=1&detail=
Navigate to the “Browse Results” tab (which has both table and gallery view
options) Users can select the data product of interest, e.g. the observation
with OPUS ID co-uvis-euv2005_172_03_35 and click through to show further
details The raw data and metadata, including the PDS3 .LBL files can be
downloaded and used as described in Figure 9

Figure 10: Step-by-step instructions on how to find and obtain UVIS data from
the PDS via RMS OPUS for an observation of Saturn’s aurora carried out around
03:35 on day 172 of year 2005. All links in this figure were accessed on 30
October 2022.

###  3.2 Ephemeris Tools

RMS also maintains a suite of tools to assist planetary scientists in the
planning, acquisition and interpretation of observations (https://pds-
rings.seti.org/tools, accessed on 30 October 2022). These tools help users to
understand the context of observations, by generating ephemerides for a planet
or any of its moons as a function of time, or diagrams of a planetary system
at specified times from various viewpoints, or diagrams tracking moons:

  * •

Planet Viewer generates a diagram showing the appearance of a planetary system
at a specified time. Bodies and rings are rendered with terminators and
shadows as appropriate. The viewpoint can be Earth’s center, a particular
Earth-based observatory, JWST, HST, or a specific planetary spacecraft. Figure
11 shows diagrams from the Jupiter Viewer tool for the same approximate times
of Galileo’s observations of Jupiter and its four large moons in 1610.

Figure 11: Galileo Galilei’s observations Galilei (1610) on the nights of 21
and 22 January 1610 (left) and the corresponding diagrams from the RMS Node’s
Jupiter Viewer tool (right) for the same approximate observing times.

  * •

Moon Tracker generates a diagram showing the apparent east–west motion of one
or more moons relative to the disk of a planet, within a specified time
period.

  * •

Ephemeris Generator generates a table listing of useful information about the
viewing geometry for a planet or any of its moons as a function of time. Users
are free to specify which of a variety of useful quantities to tabulate (e.g.,
RA and dec, phase angle, ring opening angle, distance, lunar phase, etc.)

The tools are supported for many missions, including Juno, New Horizons,
Cassini, Europa Clipper, JUICE, HST, and JWST, and offer temporal coverage
between the years 1550 and 2650.

###  3.3 User-Directed Classification via Self-Supervised Learning

As useful as OPUS and Viewmaster are, the system requires the user to already
have knowledge about what data they wish to obtain. The RMS Node is developing
a pilot project in self-supervised learning (Hastie et al., 2009), which we
hope will eventually result in the ability to add search and classification
capabilities based on features in the data. For example, users could identify
similarities across objects, instruments, or wavelengths to focus on
characteristics of interest to their investigations. This is one way in which
machine learning methods can speed up the searching process and aid in
discovery of relevant data sets.

###  3.4 Mission Pages

The PDS Discipline Nodes host a variety of mission-specific pages to help
users access all data from individual missions. Legacy data from missions that
were archived using the PDS3 standards are currently being migrated to the new
PDS4 archive standard. Experienced users who are familiar with these missions
may be better served by accessing the node pages directly; however, new users
should start with the mission pages contain a wealth of background and
contextual information that will aid them as they begin working with the
mission data. Most mission pages serve as portals to instrument-specific data
located at the DNs and cross-referenced through these mission pages.

An example set of detailed mission pages are those created for the Cassini
mission, which generated 635 GB of science data from 12 instruments while
orbiting Saturn for more than 13 years (2004–2017). Near the end of the
mission, the Cassini Project in partnership with the PDS developed a set of
mission web pages that organized the data by science discipline and included
support data and tools to ensure long-term access to the Cassini data by
future generations of researchers Edgington et al. (2019). Mission data
archived in the PDS are generally presented to the users by mission, and then
organized by instrument. The Cassini web pages maintained by the Atmospheres
Node (https://atmos.nmsu.edu/data_and_services/atmospheres_data/Cassini/sci-
saturn.html, accessed on 30 October 2022) go beyond this structure to also
provide a science-based thematic organization that contains numerous resources
for accessing data concerning Saturn’s interior and atmosphere. Additional
mission pages for Cassini are maintained by the other relevant DNs (RMS
(https://pds-rings.seti.org/cassini), accessed on 30 October 2022), SBN, IMG,
and PPI).

The Juno mission is an example of an active mission (at the time of this
writing), with accumulating datasets that continue to provide a wealth of new
observations of the Jovian system. ATM serves as the lead PDS node for the
Juno mission and coordinates the archiving of Juno data, which are distributed
through the mission web page (https://pds-
atmospheres.nmsu.edu/data_and_services/atmospheres_data/JUNO/juno.html,
accessed on 30 October 2022). Links to the various instruments take users to
corresponding pages at other nodes (e.g., IMG and PPI). These pages are
designed to provide information about the mission and instruments to help
users find and make use of Juno data.

###  3.5 Planetary Image Locator Tool (PILOT)

The Planetary Image Locator Tool (PILOT) (http://pilot.wr.usgs.gov, accessed
on 30 October 2022) is a web-based interface Bailen et al. (2013) that
provides access to a search tool for several PDS orbital image catalogs
indexed by the Unified Planetary Coordinates (UPC) database Akins et al.
(2009). The UPC database contains improved geometric, photometric, and
positional information about planetary orbital image data, computed using a
uniform coordinate system and the most up-to-date SPICE kernels. These
improvements result in enhanced image metadata and enable the user’s ability
to identify desired images, extending beyond those provided by the PDS.
Precise searches can be performed within PILOT on individual metadata fields
stored in the UPC database. In addition, PILOT has access to browse images,
links to the raw images, and label information that can help scientists and
cartographers perform further investigations on the images. Although all data
in the UPC and PILOT must be supported by a camera model that describes
detailed instrument and target geometric behavior during image acquisition,
together these services address $\sim$90% of the orbital image data for which
Imaging node is responsible to the PDS. PILOT not only allows users to
download select images either individually or through provided scripts to pull
large sets of images, it also provides direct access to the Map Projection on
the Web (POW) online tool. PILOT was developed and is maintained by the
Cartography and Imaging Sciences Node to complement other node delivery
services.

###  3.6 Map Projection on the Web (POW)

The Map Projection on the Web (POW) (https://astrocloud.wr.usgs.gov/, accessed
on 30 October 2022) service Hare et al. (2013); Akins et al. (2015) allows
users to convert raw PDS images to science-ready, map-projected products. POW
integrates PILOT Bailen et al. (2013) and the UPC Akins et al. (2009), the
Integrated Software for Imagers and Spectrometers (ISIS) package
(https://isis.astrogeology.usgs.gov/, accessed on 30 October 2022) Sides et
al. (2017), Geospatial Data Abstraction Library (GDAL) (https://gdal.org/,
accessed on 30 October 2022) Hare and Plesea (2008), and the Astrogeology
cluster for its processing and delivery needs. POW provides users with
calibrated cartographic images that can be used readily for analysis of
atmospheric dynamics, cloud morphology and change detection, merging of
dissimilar instrument images, analysis in a Geographic Image System (GIS) and
use in a host of other scientific applications (e.g., ArcMAP, ENVI, Matlab,
JMARS, QGIS, etc.). POW allows researchers to make use of a wealth of PDS
science data without having to install or learn how to run ISIS and to benefit
from a recommended processing pipeline as defined by USGS and the instrument
teams. This service can also be used as a learning tool or an introduction to
ISIS for those who would like to run it locally because the ISIS commands will
be logged and delivered to the user. Using the POW front-end, a user is
allowed to (1) select and submit a list of up to 250 PDS raw images, (2)
define an output map projection and its parameters (e.g., Polar Stereographic,
Sinusoidal), (3) define the output bit type (8, 16, or 32 bit), and (4) select
an ISIS or PDS output format or a more standardized geospatial format such as
GeoTiff, PNG, or JPEG. Conversion to the various supported image formats will
be completed using the GDAL, which passes all cartographic information into
the output format.

###  3.7 Planetary Image Atlas

The Atlas (https://pds-imaging.jpl.nasa.gov/Atlas, accessed on 30 October
2022) Padams et al. (2017) provides access to the full collection of PDS-IMG
data available in online holdings and data node catalogs. The Atlas uses
faceted navigation to support searches on common search criteria such as
mission name, instrument name, target, product type, observation/illumination
geometry metadata, geographic coordinates, time constraints, etc. The Atlas
also allows users to search images based on their “content” (i.e., moons,
rings, clouds) through the use of deep convolutional neural networks to
classify images Altinok et al. (2014); Stanboli et al. (2017).

##  4 Discussion

Looking forward, the PDS will be the primary repository for giant planets data
from several upcoming missions and derived datasets, as well as supporting
research conducted to aid in the interpretation of the remotely sensed giant
planets data already archived in the PDS.

###  4.1 Future Mission Data

Juno began its extended mission phase in July 2021. The prime mission data,
along with the accumulating data from the extended phase, will continue to be
available from the PDS ATM, RMS, PPI, and IMG nodes. Higher order data
products resulting from the end of the prime mission such as gravity model
harmonic coefficients, auroral UV maps, auroral H${}_{3}^{+}$ maps, magnetic
field models among other products will also be available from the
aforementioned nodes as they complete the peer review process and become
ingested into the archive.

Beyond Juno, NASA’s Europa Clipper and ESA’s JUpiter ICy moons Explorer
(JUICE) missions will conduct detailed investigations of several of Jupiter’s
icy satellites. If observations of Jupiter are also made, those data will be
archived in the PDS in the relevant node(s) (or linked to from the PDS in the
case of the JUICE data, whose primary archive will be ESA’s Planetary Science
Archive).

###  4.2 Data Derived from Analysis of Remote Sensing Observations

The scientific impact of giant planets remote sensing data in the PDS is felt
long after the end of a mission. In some cases the data themselves are used
for investigations long after their acquisition, making use of new analysis
techniques, tools, or interpretations. In other cases the data are used to
inspire new, related projects that enhance the interpretation of the original
data. In these cases, the resulting data are often referred to as derived
data, and ideally they should also be archived in the PDS to optimize their
discoverability and usability.

There are numerous examples of derived data relevant to the giant planets that
are archived in the PDS, for example, Saturn zonal wind profiles derived from
Cassini ISS observations García-Melendo and Sánchez-Lavega (2011) and vertical
profiles of Saturn’s thermospheric temperature and H2 densities derived from
the analysis of Cassini UVIS and CIRS stellar occultation observations
Koskinen (2018). With the greater demand for archiving derived data products
now being placed on researchers funded by NASA’s Research and Analysis
programs, the PDS expects to receive and archive numerous additional derived
data products relevant to the giant planets. Both future data users as well as
data proposers are encouraged to turn to the PDS as a logical repository for
their derived data archiving needs.

###  4.3 Data Generated in Support of Giant Planet Studies

Laboratory experiments involving gases at or near conditions appropriate for
the giant planets are required for the interpretation of remote sensing
observations of the giant planets. For example, interest in hydrocarbons in
the upper atmospheres of Jupiter and Saturn (and Titan) drove the need for
better chemistry data to understand the behavior of these species in such
extreme conditions Bernath (2022). The PDS archives laboratory data alongside
the relevant mission and ground-based observatory data to aid in the
advancement of the science of atmospheric chemistry in the outer Solar System.

Computational models and simulations are another critical tool used for the
interpretation of remotely sensed giant planets data. Although model outputs
are generally not archived in the PDS as they do not conform to PDS standards,
several PDS nodes have implemented – or are now implementing – annex-style
repositories to meet the data accessibility of the planetary modeling
communities Newman et al. (2021). For example, the PPI Node maintains an annex
(https://pds-ppi.igpp.ucla.edu/search/annex/, accessed on 30 October 2022) for
models describing the Jovian current sheet and the global magnetic field of
Saturn. The Atmospheres Node is in the process of implementing an atmospheric
modeling annex that will be used to preserve outputs from atmospheric
dynamical models, including those relevant to the giant planets.

###  4.4 Connections to Other Archives

In 2020 NASA chartered the Planetary Data Ecosystem (PDE) Independent Review
Board (IRB) to provide a holistic evaluation of the planetary science
community’s access to and use of planetary data. The PDE IRB report provided
scores of findings and recommendations aimed at fostering the development of
the ecosystem and addressing barriers to data preservation and the use of
planetary data PDE (2021). The recognition that there is an entire ecosystem
surrounding access to and use of planetary data was a critical outcome of the
PDE IRB effort, as well as the need to improve the connectivity of the
different elements of the ecosystem.

For example, data from the Hubble Space Telescope (HST) have led to many
significant discoveries related to the giant planets during its 32-year (and
counting) mission. These include the appearance and disappearance of dark
vortices in the atmospheres of Uranus and Neptune Hsu et al. (2019), the
unique nature of Saturn’s aurorae Clarke et al. (2005), the long-term studies
of the shrinking of Jupiter’s Great Red Spot Simon et al. (2014), and the
changes in Jupiter’s zonal wind profile Tollefson et al. (2017). The HST data,
which are archived at the Mikulski Archive for Space Telescopes (MAST,
https://archive.stsci.edu/hlsp/search.php, accessed on 30 October 2022),
contains thousands of observations of the giant planets, but they are not
integrated into PDS and are not easily searchable by planetary scientists.

The RMS Node is nearing completion of a pipeline to fully incorporate HST data
identified as relevant to the Solar System into PDS4, with fully searchable
OPUS metadata. The RMS pipeline can automatically query MAST, identify Solar
System observations by a variety of attributes, retrieve the relevant files,
and construct a corresponding PDS4 bundle that includes planetary metadata.
When this project is complete, OPUS users will be able to access HST data
based on a full set of Solar System-focused search attributes. In the
meantime, RMS currently maintains a large collection of “placeholder” HST
volumes (in PDS3 format). These contain browse products and metadata, but they
redirect users to MAST to retrieve the actual data files. The foundation laid
by this project will also enable the PDS to give similar treatment to JWST
data.

In an effort to further improve interoperability, the PDS has played a major
role in the development of the International Planetary Data Alliance (IPDA,
https://planetarydata.org, accessed on 30 October 2022), whose goal is to
facilitate access to and the exchange of planetary science data that are
managed by a number of international space agencies. Enabling broad,
international access to planetary data requires the use of common standards
across the archives of different agencies (PDS4 has been adopted as the
current standard for IPDA) and clear linkages among the data archives.
Although the giant planets have yet to be explored by spacecraft managed by
agencies other than NASA, that will change with ESA’s JUICE mission, and the
PDS will play a key role in ensuring transparent access to the JUICE data from
the PDS.

Finally, with the discovery of thousands of giant planets in exoplanetary
systems, there has been a tremendous increase in the number of studies that
treat the giant planets of our Solar System as analogs for advancing our
understanding of exoplanets. Current and future data in the PDS are vital to
such studies, including for example full disk albedos of the giant planets
Karkoschka (1994, 1998), full-disk images of the giant planets acquired at a
wide range of phase angles Mayorga et al. (2016), and laboratory measurements
made at giant planet and exoplanetary analog conditions Bernath (2022).
Efforts are currently underway within NASA’s Science Mission Directorate to
enhance interoperability across the archives of the Astrophysics,
Heliophysics, Planetary Science, and Earth Science Divisions. Exoplanet
studies, which are heavily interdisciplinary in nature, are a motivating
driver for such efforts and potential use cases are currently being explored.

##  5 Conclusions

The giant planets data within the PDS represent a record of an incredible
human achievement: spacecraft exploration of the outer Solar System aimed at
answering fundamental science questions concerning the origin and evolution of
planets. The data also serve as the scientific legacy of numerous researchers
who have contributed data they collected, analyzed, and used to generate new
knowledge about the workings of the giant planets.

The data in the PDS are preserved using state-of-the-art information
technology, with tools available to aid in their discoverability and
usability. The fact that data from NASA’s earliest days of giant planet
exploration are still being used today to obtain new insights about the
workings of the gas giants Gupta et al. (2022) demonstrates their long-lasting
utility and benefit to science. The PDS will continue to uphold its role as
NASA’s preeminent archive for giant planets data while evolving to meet modern
data archiving challenges and the changing needs of its user base.

Conceptualization, N.J.C., M.S.T., R.J.W. and M.K.G.; writing—original draft
preparation, N.J.C., M.S.T., M.J.T.M., R.J.W., L.F.H., L.D.V.N., J.J.B.,
J.M.B.; writing—review and editing, M.K.G.; visualization, N.J.C., M.J.T.M.,
R.J.W., M.K.G. All authors have read and agreed to the published version of
the manuscript.

This research was funded by the Planetary Science Division of NASA’s Science
Mission Directorate through award numbers 80NSSC22M0020 (ATM), 80NSSC22M0022
(RMS), 80NSSC22M0023 (PPI), 80HQTR22TA003 (IMG), and 80NSSC22M0024 (SBN).

All of the data described in this paper are publicly available through the
NASA Planetary Data System (https://pds.nasa.gov, accessed on 30 October
2022).

###### Acknowledgements.

Any use of trade, firm, or product names is for descriptive purposes only and
does not imply endorsement by the U.S. Government. The authors thank R. Beebe
for a pre-submission review of the manuscript. The authors declare no conflict
of interest. The funders had no role in the design of the study; in the
collection, analyses, or interpretation of data; in the writing of the
manuscript, or in the decision to publish the results. Abbreviations The
following abbreviations are used in this manuscript:
API | Application Programming Interface
---|---
ATM | Atmospheres Node
CDF | Common Data Format
CDF-A | Common Data Format Archival
CIRS | Composite Infrared Spectrometer (Cassini)
CODMAC | Committee on Data Management and Computation
Dec | Declination
DN | Discipline Node
DOI | Digital Object Identifier
DSN | Deep Space Network
ENA | Energetic Neutral Atom
EPN-TAP | EuroPlaNet Table Access Protocol
ESA | European Space Agency
EUV | Extreme Ultraviolet spectrographic channel of the UVIS instrument (Cassini)
FAIR | Findability, Accessibility, Interoperability, and Reuse of digital assets
FUV | Far Ultraviolet spectrographic channel of the UVIS instrument (Cassini)
GDAL | Geospatial Data Abstraction Library
GeoTiff | a standard geospatial format
GIS | Geographic Information System
HAPI | Heliophysics Application Programming Interface
HST | Hubble Space Telescope
IMG | Cartography and Imaging Sciences Node
INCA | Ion and Neutral Camera (Cassini)
IPDA | International Planetary Data Alliance
IPP | Imaging Photopolarimeter (Pioneer 10, 11)
IR | Infrared
IRB | Independent Review Board
IRIS | Infrared Interferometer Spectrometer and Radiometer (Voyager 1,2)
ISS | Imaging Science Subsystem (Cassini, Voyager 1, 2)
IVOA | International Virtual Observatory Alliance
JIRAM | Jovian Infrared Auroral Mapper (Juno)
JPEG | a common image format developed by the Joint Photographic Experts Group
JUICE | JUpiter ICy moons Explorer (European Space Agency mission)
JWST | James Webb Space Telescope
ISIS | Integrated Software for Imagers and Spectrometers
LORRI | Long Range Reconnaissance Imager (New Horizons)
LWIR | Long-Wave Infrared Spectrometer (several missions)
MAST | Mikulski Archive for Space Telescopes
MIMI | Magnetospheric Imaging Instrument (Cassini)
MVIC | Multispectral Visible Imaging Camera (New Horizons)
MWR | MicroWave Radiometer (Juno)
NASA | National Aeronautics and Space Administration
NIMS | Near Infrared Mapping Spectrometer
NSSDC | National Space Science Data Center
OPUS | Outer Planet Unified Search
PDE | Planetary Data Ecosystem
PDS | Planetary Data System
PDS3 | Governing standards of the PDS from the mid-1990s until the adoption of PDS4.
PDS4 | Current governing standards of the PDS, adopted in 2005
PI | Principal Investigator
PILOT | Planetary Image Locator Tool
PNG | Portable Network Graphic, a common image format
POW | Map Projection on the Web
PPI | Planetary Plasma Interactions Node
PPO | Planetary Period Oscillations
---|---
PRA | Planetary Radio Astronomy (Voyager 1, 2)
PWS | Plasma Wave Subsystem (Voyager 1, 2)
RA | Right Ascension
RMS | Ring-Moon Systems Node
RSS | Radio Science Subsystem (Cassini)
RSSN | Radio Science Sub-Node
RPWS | Radio and Plasma Wave Science (Cassini)
SBN | Small Bodies Node
SL9 | Comet Shoemaker-Levy 9
SPICE | Observation geometry information system for planetary spacecraft
SSI | Solid State Imager (Galileo)
TOPCAT | Tool for OPerations on Catalogs And Tables
UPC | Unified Planetary Coordinates
URAP | Unified Radio and Plasma Experiment
USGS | United States Geological Survey
UV | Ultraviolet
UVIS | Ultraviolet Imaging Spectrograph (Cassini)
VIMS | Visual and Infrared Mapping Spectrometer (Cassini)
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