Water From Comet in Jupiter's Atmosphere
Date: Spring 2013
Astronomers have finally found direct proof that almost all water present in Jupiter's stratosphere, an intermediate atmospheric layer, was delivered by comet Shoemaker-Levy 9, which struck the planet in 1994. How were they able to determine the presence of the water? Was it liquid, solid, or gas? How did they know it was from Shoemaker-Levy 9?
Very good question on your part. Substantial water was detected spectroscopically during the impact week, Although it was not as much as predicted before the impacts. This water was confirmed a year later by the Galileo satellite as it dropped its atmosphere probe into Jupiter.
Yesterday (23.April.2013), astronomers studying data from the Herschel Space Observatory, concluded that there is a north-south asymmetry in how the water is distributed. The results indicate that at least 95% of the water that they observed on Jupiter comes from the comet.
David H. Levy
Thanks for the question. One can determine the presence of water (and its physical state) by using looking at the infrared spectrum. Water emits infrared light of known energy. By using analyzing the infrared light that is emitted, one can determine whether water is present and if so, whether it is in the solid, liquid, or gas form. By looking in the direction of the Shoemaker-Levy 9 comet, they can tell whether it comes from that source or someplace else.
I hope this helps. Please let me know if you have more questions.
What you relate is a proposal set forth by T. Cavalie, et al; A&A 553 A21 (2013); http://dx.doi.org/10.1051/0004-6361/201220797. As a bit of background, the Herschel Space Observatory is an ESA collaboration effort. Herschel is the first telescope having detectors capable with the high spectral/spatial resolution necessary to resolve water differences, if any, on Jupiter.
These researchers looked at water specific spectral lines from two detectors; the Far Infared Spectrometer and the Photodetector Array Camera and Spectrometer on board the Herschel. These water spectral lines are highly specific, the background used was by mapping emission spectral lines of methane from NASA Infrared Telescope Facility. By a highly technical "overlay" of these maps, the location of the water could be detailed.
The researchers found that the water was limited to a narrow belt in the southern Jupiter stratosphere, approximately where comet Shoemaker-Levy 9(SL9) was absorbed. This finding is quite different from what one might expect if the water was the result from dust particulates - dust would be expected to be relatively uniform in distribution. Therefore they have proposed that SL9 is the source of the water in that band of Jupiter's stratosphere.
Hoping this helps! Peter E. Hughes, Ph.D. Milford, NH
Click here to return to the Astronomy Archives
Update: December 2011