UVIS Input to Cassini
Quarterly Report
L.W. Esposito
April 26, 2006
(For Feb - April 2006)
UVIS Accomplishments
• Science Highlights
–
New calculations indicate the opacity of the A ring is up to 35 percent higher than previously
reported.
–
Monte Carlo Simulations of the water vapor plume on Enceladus.
New calculations indicate the opacity of the A ring is up to 35 percent
higher than previously reported
Saturn's B Ring (center) and A Ring (right), separated by the Cassini Division. The bright horizontal
streak is created by a series of time lapse images of the star 26 Taurus taken over a nine-hour period
as it shines through the two rings. The opacity of the outer A ring is most pronounced on its inner edge,
indicating more ring debris is present there. The Enke Gap, much smaller than the Cassini Division, is
visible near the outer edge of the A Ring. The B Ring is significantly more opaque than the A ring,
indicating a greater density of ring material when imaged from above.
Monte Carlo Simulations of the water vapor plume on Enceladus
Monte Carlo simulations show that the July 14, 2005 UVIS stellar occultation observations of the water
vapor plume on Enceladus can be best explained by water molecules ejected at vertical surface
velocity 300-500 m/s along the “Tiger Stripes” in the south polar region of Enceladus. The high surface
velocity suggests that the plume on Enceladus originates from some depth beneath the surface. The
total escape rate of water molecules is 4-6x1027 s-1, consistent with previous analysis, and more than
1000 times the estimated escape rate for ice particles. The average deposition rate in the South Polar
region is in the order of 1011 cm-2s-1. The globally averaged deposition rate of water molecules is about
one order of magnitude lower. The resurfacing rate in the South Polar region can be as high as 10-4
cm/yr.
The solid linear features mark the positions of the “Tiger Stripes” in the south polar region of Enceladus. The stripes are numbered S1 to S4
accordingly. The dotted lines represent the lines of sight of the UVIS stellar occultation observations on July 14, 2005. The rightmost line of
sight line is for UVIS time record #33. The dashed curve and the asterisks represent the footprints of Cassini spacecraft. The diamonds
represent the positions where the distances between the lines of sight and the surface of the satellite are the smallest.
UVIS Accomplishments (Continued)
• Scientific Publications
–
–
Published February - April 2006:
2006 to date:
3
3
(From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
–
–
–
Entire mission:
Submitted February - April 2006:
Submitted in 2006
(From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
23
4
4
UVIS Accomplishments (Continued)
• Science Presentations - February — April 2006
–
4 Science Seminars
–
2 Presentations at Scientific Meetings
UVIS Accomplishments (Continued)
• Public Outreach
–
Press releases
• 1 February - April 2006
• 1 2006 YTD (From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
–
Press conferences
• 1+ February - April 2006
• 1+ 2006 YTD (From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
–
EPO: Talks to school children, teachers and public
• 6 February - April 2006
• 6 2006 YTD (From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
UVIS Plans (May - July 2006)
• Upcoming Science Activities (for next quarter)
–
–
T14 and T15 EUV/FUV limb-to-limb scans to probe haze optical properties, atmospheric
nitrogen emissions and hydrocarbon absorption, and absorption by methane of the Lymanalpha interplanetary background which helps us understand the distribution of methane in the
thermosphere of Titan.
T16 Stellar Occultation to determine temperature of the thermosphere, and vertical profiles of
N, N2, and other hydrocarbons at many latitudes.
• Publications in the works this quarter
–
1 paper to be submitted around May ("Ultraviolet Observations of Phoebe from Cassini
UVIS," by Hendrix and Hansen)
• EPO in the works (for next quarter)
–
None
• Upcoming Science Presentations and Seminars (for next
quarter)
– XVIIIth Rencontres de Blois Enceladus, May 28-June 2, Planetary Science: Challenges and
Discoveries (Hansen)
– Spring AGU - Baltimore, May 22-26 (Esposito, Pryor, Larsen)
Backup Material
UVIS April 18, 2006
UVIS Publications: Published 2006
(From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
•
•
•
Hansen, C., J. Colwell, L.W. Esposito, A.R. Hendrix, W. Pryor, D. E. Shemansky, A.I.F. Stewart,
R.A. West. (2006) Enceladus’ Water Vapor Plume. Science. 311. no.5766. 1422-1425. (Published
March 10, 2006.)
Liu, X., and D. E. Shemansky. (2006) Analysis of electron impact ionization properties of methane,
J. Geophys. Res., 111, A04303, doi:10.1029/2005JA011454, (Published April 2006.)
Colwell, J.E., L. W. Esposito, and M. Sremcevic. (2006) Self-gravity wakes in Saturn’s A ring
measured by stellar occultations from Cassini. GRL. 33, L07201, doi:10.1029/2005GL025163
(Published in April 2006)
UVIS Publications: Submitted 2006
(From Q1’s start of Feb. 2006- through Q4’s end of Jan. 2007)
•
•
•
•
Parkinson, C. D., M. C. Liang, H. Hartman, C. J. Hansen, G. Tinetti, V. Meadows and Y. L. Yung.
(2006) Enceladus: Cassini Observations and Implications for the Search for Life" Submitted to
Astrophys. J. Lett. (Submitted February 2006.)
Hallett, J.T., D. E. Shemansky, X. Liu. (2006) Rotational-level hydrogen chemistry model of the
Cassini UVIS observed Saturn dayglow. J. Geophys. Res., (Submitted March 2006, in review.)
Tian, F., A.I.F. Stewart, Owen B. Toon, Kristopher Larsen, Larry W. Esposito. (2006) Monte Carlo
Simulations of the water vapor plume on Enceladus. Icarus. (Submitted April 2006.)
Liu, X., and D. E. Shemansky. (2006) A simple model for N2 line oscillator strengths of
the
bands, Atrophys. J., 645, July 10, doi:
10.1086/’504465’, 2006. (Accepted for publication March 2006.)
UVIS Science Presentations:
February - April 2006
•
Science Seminars
–
–
–
–
•
Enceladus: Spewing Water into the Saturn System, UCLA, undergraduate and graduate
students and faculty in Earth and Space Sciences Department, February 2 (Hansen)
UVIS observations of Enceladus' Water Vapor Plume, Cal Tech, February 21 (Hansen)
The Icy Saturnian Satellites as Seen by the Cassini UVIS., CalTech, March 7 (Hendrix)
Cassini Observations of Saturn's Icy Moons. UC Santa Cruz IGPP/CODEP, April 28
(Hendrix)
Presentations at Scientific Meetings
–
–
2 EGU - April 2-7 (Esposito: Invited talk on ring history, Sremcevic: Self-gravity wakes)
1 Lunar and Planetary Science Conference. March. Talk on density waves in UVIS data
(Colwell).
UVIS Outreach: February - April 2006
• Press Releases
–
Press release from University of Colorado, New Cassini Image at Saturn Shows “A” Ring
Contains More Debris Than Once Believed. April 6. Resulting articles: on Physorg.com - April
6; Boulder Daily Camera - April 7.
• Press Conferences
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Numerous interviews associated with the publication of Enceladus paper in Science
(Hansen)
• Talks to School teachers Children and Public
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–
–
–
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Answered weekly questions about planetary science and exploration. October, 2005 - March,
2006: Waitman Barbe Elementary in Morgantown, West Virginia. NASA Pluto Pen Pals
program. (Larsen)
Cassini UVIS Observations of Saturn’s Icy Moons, Cal Tech, March 7 (Hendrix)
General Cassini overview talk - March 18. Brideun School in Lafayette, CO. Approximately
150 students, teachers, and parents. Event was the 5-year anniversary of the school's
founding. (Larsen)
Two planetarium shows on Cassini for University of Colorado. April. (Colwell)
CHARM Telecon at JPL Saturn’s Rings. April 25 (Colwell)
Update on Cassini Results at Saturn- April 28, Central Arizona College observatory in
Coolidge, AZ. (Pryor)