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 morning-afternoon / 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 VIMS Saturn spectra: auroral vs. non-auroral (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 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 ratio 1st/2nd 1328-1426 wavelengths (A) 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, 1251-1255, 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 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 2005-087T07:46:00..UVIS_005SA_EUVFUV001_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) 2007-034T12:10:00..UVIS_038SA_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 3 4 S/N < 10 some artifacts due to imperfect dark subtraction Strongest contrast in polar features observed in #2 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 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!) -18:45 -14:59 <-East-West-> EUV FUV

VIMS observations Sequence of observation S10 – 23 April 2005 (CIRS ride along observations) List of observations and characteristics Phase angle : ~40 degrees Spatial resolution : ~1500 km/pixel 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

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+