Auroral Update
UVIS Meeting Jan 2006
UVIS auroral tasks completed
• Jupiter auroral papers (Ajello, Pryor et al.) out in Icarus
• Saturn Auroral image, spectra in Esposito’s Science
publication
• Newer Saturn image in JPL press release (and CU alumni
magazine)
• Time-series campaign (GO WEST) manuscript is in rough
draft form
• Hubble/VIMS/UVIS campaign completed
• VIMS reports first auroral images/spectra
• Auroral talks at MOP and fall AGU by Pryor et al.
• EUV/FUV auroral modeling presented at DPS by Jacques
Gustin et al.
• Latest image Dec. 23-24 2005 looks ok
Upcoming tasks
• Future HST campaigns? - Cycle 15 due Jan 27
• Cycle 15 runs July 2006 to June 2007
• J. Clarke is proposing 50 HST orbit Saturn campaign near
Feb 2007 (before opposition) (Overlaps with 2007-034
Saturn EUVFUV?)
• Extended mission planning- add to WIKI
• Can we coordinate better with VIMS? (are we riding along
on their stuff, and vice versa?)
• GO WEST paper to co-authors, then GRL
• Jacques Gustin to visit Arizona in Feb. to learn more about
UVIS spectra
• Spring AGU poster- Lyman-alpha trends
• My summer plans: auroral and heliosphere work at LASP
with Ajello, Stewart, Esposito, Jouchoux, McClintock, etc.
Saturn’s Auroras from the Cassini Ultraviolet Imaging
Spectrograph (UVIS) and Visual Infrared Mapping
Spectrometer (VIMS)
Wayne Pryor
Kevin Baines
Pierre Drossart
Robert West
Joseph Ajello
Candice Hansen
Ian Stewart
Larry Esposito
Joshua Colwell
William McClintock
Alain Jouchoux
Don Shemansky
Janet Tew Hallett
Frank Crary
John Steinberg
William Kurth
John Clarke
Jacques Gustin
Denis Grodent
Jean-Claude Gerard
Emma Bunce
Presented at Fall AGU, 2005 ref # 1888 pin 3329
Saturn auroral emissions
• UV aurora (N and S) observed by
– Pioneer 11 (Judge et al. 1980)
– Voyager UV spectrometer (Broadfoot et al, 1981)
– IUE (Clarke et al. 1981)
– HST/FOC (Gérard et al, 1995, Trauger et al, 1998)
– HST/STIS (Cowley et al. 2004; Prangé et al, 2004)
– Cassini/UVIS (Colwell et al., DPS 2005)
=> Auroral oval observed ~ 70-80dg latitude / variations morningafternoon / correlation with Solar activity
• Saturn Kilometric Radio emission
– Voyager (Desch, 1982)
• Infrared aurora
– H3+ spectroscopic observations : (Geballe et al 1993, Stallard et al
1999) ~ 100 times lower than Jupiter
UVIS and VIMS are on the
Cassini Orbiter
VIMS Instrument
VIMS
Visible channel:
0.35-1.03 mm
96 pixels
Infrared channel :
0.88-5.1 mm
256 pixels –
16nm spectral width
(R~200 @ 3.5 mm)
Spatial resolution :
0.5mrad
CH4 and H3+ emissions from
Cassini/VIMS Jupiter observations
Spectral image of 19 November 2000
Spectrum of South auroral zone
compared to synthetic pure H3+ spectrum
(Trot = 1000 K)
VIMS Saturn spectra: auroral vs. nonauroral
(April 23, 2005, phase angle 40 deg., 1500 km/pixel)
H3+ (thermal)
Auroral
Non auroral
CH4
(fluorescence)
Wavelength (mm)
Wavelength (mm)
+
Processed H3 Saturn images
April 23, 2005
(phase angle 40 deg., 1500 km/pixel)
Images at 3 wavelengths : 3.33, 3.53, 3.7 mm
H3+
emission
Composite
Solar reflected comp. CH4 fluorescence
VIMS Conclusions
• Oval-like emission of H3+ observed April 23, 2005
• Latitude ~78 degrees South (+/- 4 degrees):
– comparable to previous UV emission (between 70-80 degrees )
• Absolute intensity : faint ! (< 0.1 Jupiter)
• Intensity variations in H3+ along the oval
• (No UVIS observations that day)
UVIS long-slit spectroscopy
EUV channel 56.3-118. 2 nm
FUV channel 111.5-191.3 nm
64 spatial x 1024 spectral pixels
Spectral imaging is done
by spacecraft slews
Saturn’s emissions:
H Lyman-a and H2 bands
from auroras and dayglow.
Reflected sunlight spectrum:
Rayleigh scattering in H2
and acetylene absorption bands
UV Saturn image July 13, 2004
H Lyman-a
H2 bands
Saturn Auroral Spectrum
June 21 (Day 172), 2005
• N-S-N UVIS scan
• Slit E-W
• Auroral oval imaged
twice
• Images deconvolved
• Blue H2, H emission
• Orange reflected
sunlight
• Aurora changes over
~1 hour
• Oval 70-75S
Polar Dark Spot (2005 day 172)
1738-1816 1816-1894
wavelengths (A)
ratio 1st/2nd 1328-1426
Spot in 1st image is gone at longer wavelengths (2nd image)
Localized small hydrocarbons? (spectrum is noisy)
Polar convergence & downwelling?
50 day time-series moving away
from Saturn near phase angle 90...
^ shock
^ shock
Color Ratio Trend
(1.16= no overlying hydrocarbons)
Hubble Auroral Campaign Feb 17, 2005
• J. Clarke, J.-C. Gerard PI’s:
• Day-side S auroras by HST ACS in UV (5 orbits)
•
Night-side N auroras by Cassini VIMS and UVIS
• Cassini VIMS_003SA_THRCYLMAP001_UVIS_FOV
• Started 2005-048 T23:08:00 GMT, ran 8 h 22 m
• Cassini at ~800,000 km range
• Aurora was weak that day
HST Campaign ACS Images: Feb 17, 2005
16:20-16:58
17:53-18:33
19:29-20:09
21:04-21:45
22:40-23:21
HST Campaign UVIS Geometry
VIMS_003SA_THRCYLMAP001
UVIS dark-side spectrum
color ratio 1.9
EUV aurora data (black)
Model w/o self-absorption (dashed brown)
Model fit (solid brown) for H2 = 5x1020 cm-2 & T=500K
Relative
Intensity
Wavelength (Ångstroms)
UVIS Saturn Conclusions
Saturn has extended H, O clouds
Small polar dark spot (hydrocarbons?) near 1750 ± 75 Å
Linked to IR polar warm spot?
Polar auroras vary over ~1 hour time scale
Auroral brightness varies by ~3
Daily-averaged auroral counts vary with SKR (RPWS)
Auroras brighten after solar wind shocks ( MAG & CAPS)
Auroras brightest during (and after) shock 2004 d 207 19:30
Auroral spectrum like Jupiter’s, with CH4 absorption
Auroral color ratio (1550-1620 Å/1230-1300 Å) steady, near ~2.5±0.2
(1.9 in HST campaign) : ~15 keV primary electrons
Saturn’s 3.53 mm H3+
auroral emission
Oval Latitude
~ 78 degrees
composite
References
•
Esposito, L. W., et al., The Cassini Ultraviolet Imaging Spectrograph Investigation.
Space Sci. Reviews, 115, 299-361, 2004.
•
Esposito, L. W., et al., UVIS shows an active Saturnian system, Science, 307, 12511255, 2005.
•
Ajello, J. M., et al., The Cassini Campaign Observations of the Jupiter Aurora by the
Ultraviolet Imaging Spectrograph and the Space Telescope Imaging Spectrograph,
Icarus 178, 327-345, 2005.
•
Pryor, W. R., et al., Cassini UVIS Observations of Jupiter’s Auroral Variability, Icarus
178, 312-326, 2005.
Future Work
• Auroral time-dependence, longitude-dependence
• Auroral studies from higher inclinations
• High-latitude absorber studies (acetylene, haze, ?)
• H cloud variability (source(s): rings + moons (Enceladus) + hot H
from sunlit Saturn due to photoelectron impact on H2)
• Comparison with Saturn atmosphere models
Upcoming UVIS Auroras
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2004-196T06:26:00..UVIS_000SA_AURORAB001_PRIME
2004-197T02:21:00..UVIS_000SA_AURORAA002_PRIME
2004-198T16:16:00...UVIS_000SA_AURORAA003_PRIME
2004-199T07:41:00...UVIS_000SA_AURORAB002_PRIME
2007-096T00:33:00..UVIS_042SA_NAURMOV001_PRIME
2007-145T09:10:00..UVIS_045SA_NAURMOV001_PRIME
2007-350T23:31:00..UVIS_054SA_EUVFUV001_PRIME
2008-002T15:18:00..UVIS_055SA_NAURMOV001_PRIME
2008-037T05:36:00..UVIS_058SA_NAURMOV001_PRIME
2008-109T08:18:00..UVIS_065SA_NAURMOV001_PRIME
2008-129T06:30:00..UVIS_067SA_NAURMOV001_PRIME
Saturn EUVFUV’S
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2005-087T07:46:00..UVIS_005SA_EUVFUV001_PRIME
2005-125T08:10:00..UVIS_007SA_EUVFUV002_PRIME
2005-172T03:30:00..UVIS_010SA_EUVFUV003_PRIME (the oval pictures)
2005-179T01:00:00..UVIS_010SA_EUVFUV002_PRIME
2005-197T21:15:00..UVIS_011SA_EUVFUV002_PRIME
2005-212T05:50:00..UVIS_012SA_EUVFUV001_PRIME
2005-283T20:27:00..UVIS_016SA_EUVFUV001_PRIME
2005-289T17:48:00..UVIS_016SA_EUVFUV003_PRIME
2005-362T16:57:00..UVIS_019SA_EUVFUV004_PRIME
2006-012T13:13:00..UVIS_020SA_EUVFUV003_PRIME
2006-020T15:28:00..UVIS_020SA_EUVFUV004_PRIME
2006-063T10:36:00..UVIS_021SA_EUVFUV005_PRIME
2006-083T16:05:00..UVIS_022SA_EUVFUV003_PRIME
2006-084T07:49:00..UVIS_022SA_EUVFUV005_PRIME
2006-138T06:11:00..UVIS_024SA_EUVFUV005_PRIME
2006-143T20:41:00..UVIS_024SA_EUVFUV002_PRIME
2006-178T02:37:00..UVIS_025SA_EUVFUV002_PRIME
2006-187T01:06:00..UVIS_025SA_EUVFUV005_PRIME
2006-200T00:21:00..UVIS_026SA_EUVFUV007_PRIME
2006-208T23:56:00..UVIS_026SA_EUVFUV006_PRIME
2006-227T01:51:00..UVIS_027SA_EUVFUV003_PRIME
2006-231T01:36:00..UVIS_027SA_EUVFUV002_PRIME
2006-233T00:16:00..UVIS_027SA_EUVFUV006_PRIME
2006-303T18:27:00..UVIS_031SA_EUVFUV003_PRIME
2006-314T21:03:00..UVIS_032SA_EUVFUV003_PRIME
Saturn EUVFUV’s (2)
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2007-034T12:10:00..UVIS_038SA_EUVFUV001_PRIME
2007-122T05:00:00..UVIS_043SA_EUVFUV003_PRIME
2007-137T21:30:00..UVIS_044SA_EUVFUV003_PRIME
2007-168T03:09:00..UVIS_046SA_EUVFUV003_PRIME
2007-177T05:38:00..UVIS_047SA_EUVFUV001_PRIME
2007-245T22:55:00..UVIS_049SA_EUVFUV003_PRIME
2007-276T23:52:00..UVIS_050SA_EUVFUV003_PRIME
2007-277T20:52:00..UVIS_050SA_EUVFUV001_PRIME
2007-290T20:08:00..UVIS_051SA_EUVFUV003_PRIME
2007-316T19:26:00..UVIS_052SA_EUVFUV004_PRIME
2007-342T10:00:00..UVIS_053SA_EUVFUV004_PRIME
2007-357T10:32:00..UVIS_054SA_EUVFUV003_PRIME
2008-041T19:36:00..UVIS_058SA_EUVFUV001_PRIME
2008-104T08:18:00..UVIS_064SA_EUVFUV001_PRIME
Saturn Day 172, 2005
• Limb-fitting puts auroral oval in 70-75 S range
ISS south pole methane, uv3
images
HST campaign UVIS map projection
Red=aurora
Green=no aurora
Auroras ~75 N
• Mostly UVIS slit was too far south, but…
UVIS auroral time-series as Cassini recedes
from Saturn…
EUV, SKR, CAPS solar wind
Abstract
Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed a year of study of
Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain
EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels
along each slit are combined with slit motion to build up spectral images of Saturn, with
sufficient spatial resolution to reveal Saturn's auroral oval. Saturn images include
evidence for rapid auroral variations and polar UV-dark regions mostly inside the auroral
ovals. Absorption bands of acetylene are clearly seen in the reflected sunlight spectrum.
The auroral emission spectrum is similar to that of Jupiter, showing H2 band emission
and H Lyman-alpha emission. Saturn's auroral, dayglow, and nightglow spectra show
significant differences. Saturn's aurora is observed to vary in brightness by at least a
factor of four. The brightest auroral emissions seen so far occurred after 2004 day 207
19:30 when Cassini CAPS and MAG recorded passage of a solar wind shock. The
enhanced auroral brightness persisted for days, and is seen at both poles of Saturn.
Cassini RPWS observed enhanced auroral kilometric emissions during several auroral
brightening events seen by UVIS. A campaign of Hubble Space Telescope UV imaging
with ACS (Advanced Camera for Surveys) of Saturn's dayside southern auroral zone
took place on 2005 February 17. Cassini UVIS and VIMS observed Saturn's nightside
northern aurora during this period. The UVIS long slit was aligned with lines of latitude
on Saturn, providing information about intensity and spectral variations along the auroral
oval. Cassini VIMS has now obtained an initial H3+ image of Saturn’s auroral oval.
UVIS, RPWS and MAG trends
EUV, SKR, CAPS solar wind
Future VIMS observations
Wanted ! long integration time for VIMS (1sec or more) =>
implies saturation for some wavelengths
• North Pole observations (night side)
• Diurnal rotation sequence
• Time sequence : search for temporal variations
• Combination ground-based/Cassini observations required
for temperature/column density/spatial distribution
VIMS at Saturn
Saturn observations
with VIMS at T0
CM_1465912440_1
Sequence of Saturn
VIMS images from
1 to 5 mm
Images at 3.56 micron
Images of VIMS from the four different cubes
• S/N < 10
• some artifacts
due to imperfect dark
subtraction
• Strongest contrast
in polar features
observed in #2
3
4
1 2
Mapping Saturn’s Aurora in the Near-Infrared with VIMS
First Maps of H3+ Achieved at 3.53 mm at South Pole
Requires Long VIMS exposures (1 second)
Require Sub-S/C Latitude Away from Equator
Sample Saturn Spectral Images
EUV
FUV
Saturn H Lyman-a
Saturn Oxygen image 130 nm (peaks
~2 Rayleighs, cloud has 1012 grams of O)
HST Campaign UVIS spatial images
-22:44
-18:45
<-East-West->
EUV
-14:59
FUV
• Time increases
upwards
• VIMS mosaic:
repeated UVIS
passes near oval
• UV brightest at
Feb 17, 18:45
• VIMS:
Non-detection
(they’ve seen
auroras more
recently!)
VIMS observations
• Sequence of observation S10 – 23 April 2005
(CIRS ride along observations)
• List of observations and characteristics
Number
Observation ID
Date/Time
CML/SSP
1
CM1492933856_3
2005/113_07:23:56
38.90
2
CM1492954267_1
2005/113_13:04:06
230.40
3
CM1493011617_8
2005/114_04:59:56
48.51
4
CM1493032028_8
2005/114_10:40:06
240.01
• Phase angle : ~40 degrees
• Spatial resolution : ~1500 km/pixel
VIMS observations April 23, 2005
(phase angle 40 deg., 1500 km/pixel)
• Image at 3.53 mm : strongest contrast in
polar features
Spectra limb/center
H3+