Tuesday, August 30, 2005

"Enceladus Eruptions" CHARM presentation

Today's CHARM talk covered the UVIS results at Enceladus from the flyby last month. I've linked to the PDF file with the slides from the talk above. This talk fit nicely with the press briefing today since it perfectly covered many of the discoveries announced at the talk plus providing more in-depth analysis of the data as well as...more graphs. UVIS detected an atmosphere on ingress of the gamma Orionis occultation in July but failed to detect an atmosphere during the occultation in February. The path of the occultation allowed for measurements at a far southern latitude on ingress, allowing UVIS to measure the patchy atmosphere measured by MAG and INMS. UVIS was able to detect the atmosphere starting at an altitude of 155 km above the surface of Enceladus using the High Speed Photometer (HSP) on UVIS. Compositionally, UVIS found that the atmosphere/plume was made primarily of water vapor with no detection of CO (thus placing an upper limit on CO at 2x1014 cm-2. This is important because INMS detected a species at mass 28 which can either be CO or N2. N2 could be a disassociative product of ammonia in Enceladus' patchy, slushy interior.

In addition to the UVIS data, the talk, by Larry Esposito the UVIS Principle Investigator, also has data from INMS, with a plot of their data from below 500 km. The plot shows a high number of counts from H2O and less amounts from a species at mass 28 as well as hydrogen and maybe methane. The detection at mass 44 is a mix of background noise and CO2. The presentation also has plot from the simulation the CDA team ran to show that their data was consistent with a spread out source near the south pole.

Esposito concludes by stating that the composition of the atmosphere is mostly water vapor with a near surface abundance of 1.5 x 1016 cm-2 with an upper limit on CO at 2% the water vapor density. The atmosphere is not global and has only been found near the south pole. Finally, and here is the kicker as I will go into with more detail later today, "The water vapor escaping from Enceladus is adequate to supply the atomic oxygen in the Saturn system detected by UVIS, and to re-supply Saturn's E ring."

Update 12:45 pm: The detection at mass 44 is a mix of background noise and CO2. Not sure what the mix is, but is less than the detection at mass 28...


Blogger Bruce Moomaw said...

More news from "The "Independent" ( http://news.independent.co.uk/world/science_technology/article309205.ece ):

(1) "An analysis of its atmosphere revealed it was about 91 per cent water vapour, 3 per cent carbon dioxide, 4 per cent nitrogen or carbon monoxide and about 2 per cent organic molecules."

(2) "Candy Hansen, a NASA scientist working on Cassini's ultraviolet instruments, said that half a ton of material a second was ejected from Enceladus's south pole, which would, over the four billion-year lifetime of the solar system, amount to a loss of 5 per cent of the moon's original mass." Could many of the strange surface features on Enceladus thus be wrinkle ridges?

8/31/2005 03:58:00 PM  
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