J/ApJS/263/15 Cassini Visual & IR obs. of Saturn & Jupiter (Coulter+, 2022)
Jupiter and Saturn as spectral analogs for extrasolar gas giants and brown
dwarfs.
Coulter D.J., Barnes J.W., Fortney J.J.
<Astrophys. J. Suppl. Ser., 263, 15 (2022)>
=2022ApJS..263...15C 2022ApJS..263...15C
ADC_Keywords: Planets; Spectra, infrared; Optical
Keywords: Jupiter ; Saturn ; Extrasolar gaseous planets ; Brown dwarfs ;
Direct imaging
Abstract:
With the advent of direct-imaging spectroscopy, the number of spectra
from brown dwarfs and extrasolar gas giants is growing rapidly. Many
brown dwarfs and extrasolar gas giants exhibit spectroscopic and
photometric variability, which is likely the result of weather
patterns. However, for the foreseeable future, point-source
observations will be the only viable method to extract brown dwarf and
exoplanet spectra. Models have been able to reproduce the observed
variability, but ground-truth observations are required to verify
their results. To that end, we provide visual and near-infrared
spectra of Jupiter and Saturn obtained from the Cassini VIMS
instrument. We disk-integrate the VIMS spectral cubes to simulate the
spectra of Jupiter and Saturn as if they were directly imaged
exoplanets or brown dwarfs. We present six empirical disk-integrated
spectra for both Jupiter and Saturn with phase coverage of
1.°7-133.°5 and 39.°6-110.°2, respectively. To
understand the constituents of these disk-integrated spectra, we also
provide end-member (single-feature) spectra for permutations of
illumination and cloud density, as well as for Saturn's rings. In
tandem, these disk-integrated and end-member spectra provide the
ground truth needed to analyze point-source spectra from extrasolar
gas giants and brown dwarfs. Lastly, we discuss the impact that icy
rings, such as Saturn's, have on disk-integrated spectra and consider
the feasibility of inferring the presence of rings from direct-
imaging spectra.
Description:
Spectral data comes from the Cassini Visual and Infrared Mapping
Spectrometer (VIMS) instrument, which acquired individual point
spectra with 352 spectral channels between 0.35 and 5.2um.
Cassini VIMS obtained over 14,000 cubes during its flyby of Jupiter
and over 550,000 cubes of Saturn's disk during its 13yr in orbit.
In the end, six cubes each were selected for Jupiter and Saturn so
that they provided the most complete phase-angle coverage possible for
each planet and for the two combined. Color images of the cubes
selected for this study are shown in Figure 1 and important
observational data can be found in Table 1.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 56 12 *Cassini VIMS spectral cubes selected for this study
(see Figure 1)
fig3.dat 30 330 Signal to noise ratio as a function of wavelength
for both Jupiter and Saturn
fig4.dat 37 1980 Disk-integrated spectra of Jupiter for six phase
angles
fig5.dat 32 1320 Jupiter end member spectra obtained from
cube V1357335218 1
fig6.dat 37 1980 Disk-integrated spectra of Saturn for six phase
angles
fig7.dat 32 1980 Saturn end member spectra obtained from
cube V1469259344 1
--------------------------------------------------------------------------------
Note on table1.dat: All data presented here were retrieved from the NASA
Planetary Data System (PDS) archive, except the resolution values
marked with an asterisk, which were not available in PDS and we
calculated ourselves. Color images created from each cube can be found
in Figure 1.
--------------------------------------------------------------------------------
See also:
J/ApJ/564/421 : Spectra of T dwarfs. I. (Burgasser+, 2002)
J/ApJ/818/176 : HST/WFC3 NIR photometry of 2M1207b (Zhou+, 2016)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Target Planet name ("Saturn" or "Jupiter")
9- 21 A13 --- FileName Cube name
23- 33 A11 "Y/M/D" Date Acquisition date (UT)
35- 38 I4 s ExpVIS [640/2560] VIS exposure duration
40- 42 I3 s ExpIR [20/120] IR exposure duration
44- 48 I5 km/pix Res Resolution
49 A1 --- f_Res [*] * = not available in PDS; calculated here
51- 56 F6.2 deg Angle [1.6/133.6] Phase angle
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.6 um lambda [0.35/5.2] Wavelength
10- 19 F10.6 --- Jupiter [-1.5/242.4] Jupiter's signal-to-Noise ratio
21- 30 F10.6 --- Saturn [1.2/632.7] Saturn's signal-to-Noise ratio
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig[46].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 deg Phase [1.6/133.6] Phase angle
8- 15 F8.6 um lambda [0.35/5.2] Wavelength
17- 27 F11.6 uW/cm2/sr/um Flux [-0.07/1091.4] Spectral flux radiance
29- 37 F9.6 --- I/F [-0.008/1.9] Apparent reflectance
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig[57].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Type Member spectra type code (1)
3- 10 F8.6 um lambda [0.35/5.2] Wavelength
12- 22 F11.6 uW/cm2/sr/um Flux [-109/8480.2] Spectral flux radiance
24- 32 F9.6 --- I/F [-0.008/6.6] Apparent reflectance
--------------------------------------------------------------------------------
Note (1): Code as follows:
a = dayside, cloudy;
b = dayside, clear;
c = nightside, cloudy;
d = nightside, clear.
e = A ring;
f = B ring.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Nov-2022