[meteorite-list] Herschel Links Juipiter's Water To Comet Shoemaker-Levy 9 Impact

[Ron Baalke]

http://www.esa.int/Our_Activities/Space_Science/Herschel/Herschel_links_Jupiter_s_water_to_comet_impact

Herschel Links Juipiter's Water To Comet Shoemaker-Levy 9 Impact
European Sapce Agency
23 April 2013

ESA's Herschel space observatory has solved a long-standing 
mystery as to the origin of water in the upper atmosphere of Jupiter, 
finding conclusive evidence that it was delivered by the dramatic impact 
of comet Shoemaker-Levy 9 in July 1994.

During the spectacular week-long collision, a string of 21 comet fragments 
pounded into the southern hemisphere of Jupiter, leaving dark scars in the 
planet's atmosphere that persisted for several weeks.

The remarkable event was the first direct observation 
of an extraterrestrial collision in the Solar System. It was followed 
worldwide by amateur and professional astronomers with many ground-based 
telescopes and the NASA/ESA Hubble Space Telescope.

ESA's Infrared Space Observatory was launched in 1995 and was the first to 
detect and study water in Jupiter's upper atmosphere. It was widely speculated 
that comet Shoemaker-Levy 9 may have been the origin of this water, but direct 
proof was missing.

Scientists were able to exclude an internal source, such as water rising from 
deeper within the planet's atmosphere, because it is not possible for water 
vapour to pass through the "cold trap" that separates the stratosphere from the 
visible cloud deck in the troposphere below.

Thus the water in Jupiter's stratosphere must have been delivered 
from outside. But determining its origin had to wait more than 15 years, 
until Herschel used its sensitive infrared eyes to map the vertical and 
horizontal distribution of water's chemical signature.

Herschel's observations found that there was 2-3 times more water in the southern 
hemisphere of Jupiter than in the northern hemisphere, with most of it concentrated 
around the sites of the 1994 comet impact. Additionally, it is only found 
at high altitudes.

"Only Herschel was able to provide the sensitive spectral imaging needed to find the 
missing link between Jupiter's water and the 1994 impact of comet Shoemaker-Levy 9," 
says Thibault Cavalie of the Laboratoire d'Astrophysique de Bordeaux, lead author of 
the paper published in Astronomy and Astrophysics.

"According to our models, as much as 95% of the water in the stratosphere is due to the 
comet impact."

Another possible source of water would be a steady rain of small interplanetary dust 
particles onto Jupiter. But, in this case, the water should be uniformly distributed 
across the whole planet and should have filtered down to lower altitudes.

Also, one of Jupiter's icy moons could deliver water to the planet via a giant 
vapour torus, as Herschel has seen from Saturn's moon Enceladus, but this 
too has been ruled out. None of Jupiter's large moons is in the right 
place to deliver water to the locations observed.

Finally, the scientists were able to rule out any significant contributions from 
recent small impacts spotted by amateur astronomers in 2009 and 2010, along with 
local variations in the temperature of Jupiter's atmosphere.

Shoemaker-Levy 9 is the only likely culprit.

"All four giant planets in the outer Solar System have water in their atmospheres, but 
there may be four different scenarios for how they got it," says Dr Cavalie "For Jupiter, 
it is clear that Shoemaker-Levy 9 is by far the dominant source, even if other external 
sources may contribute also."

"Thanks to Herschel's observations, we have now linked a unique comet impact - one that 
was followed in real time and which captured the public's imagination - to Jupiter's water, 
finally solving a mystery that has been open for nearly two decades," adds Goran Pilbratt, 
ESA's Herschel project scientist.

The observations made in this study foreshadow those planned for ESA's future Jupiter Icy 
moons Explorer mission launching towards the Jovian system in 2022, where 
it will map the distribution of Jupiter's atmospheric ingredients in even 
greater detail.

Notes for Editors

"The spatial distribution of water in the stratosphere of Jupiter from Herschel-HIFI and 
-PACS observations," by T. Cavalie et al. is published in Astronomy & Astrophysics, 553, A21, 
May 2013.

The observations were obtained under the Herschel Guaranteed 
Time Key Programme ""Water and related chemistry in the Solar System". 
HIFI observations were taken in July 2010 and PACS observations were made 
in October 2009 and December 2010.  The results were complemented with 
data on the stratospheric temperature of Jupiter taken at NASA's Infrared 
Telescope Facility taken during the same period.

Herschel is an ESA space observatory with science instruments provided by European-led 
Principal Investigator consortia and with important participation from NASA.

For further information, please contact:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer at esa.int

Thibault Cavalie
Laboratoire d'Astrophysique de Bordeaux (joint research unit of the CNRS-INSU and University Bordeaux, 
France)
Tel: +33 5 57 77 61 24
Email: cavalie at obs.u-bordeaux1.fr

Goran Pilbratt
ESA Herschel Project Scientist
Tel: +31 71 565 3621
Email: gpilbratt at rssd.esa.int