Astronomy Picture of the Day 2-21-03

Explanation: Tantalizing images of gullies on Mars have offered striking evidence for recent flows of liquid water. But Mars is too cold and its atmosphere too thin for liquid water to exist on the surface. Still a new and compelling explanation for gullies carved by liquid water was inspired by this recently released image from the Mars Odyssey spacecraft. Pictured is a section of what is likely a snow covered crater in the Martian southern hemisphere. North is at the top and the scene, illuminated from the left, is about 16 kilometers wide. Patches of smooth snow pack remain along the northern crater wall, while structures resembling the famous Martian gullies appear to be emerging as the snow cover gradually disappears, and are exposed along the crater's western (left) wall. Melting snow, running underneath the snow pack and down the crater walls would be protected from the extreme surface conditions, remaining liquid and eroding the gullies over time. Could life exist in a liquid water environment beneath the Martian snow?

1) What is THEMIS?

THEMIS is a thermal emission imaging system. It contains two independent multi-spectal imaging sub-systems: a 10-band thermal infrared imager (IR), and a 5-band visible imager (VIS).

2) What's the resolution of THEMIS images?

The IR subsystem has a resolution of 100m/pixel.
The VIS subsystem has a resolution of 19m/pixel.

3) What bands does THEMIS use?

The IR bands used by THEMIS are centered at: 6.78 microns, 6.78 microns, 7.93 microns, 8.56 microns, 9.35 microns,10.21 microns, 11.04 microns, 11.79 microns, 12.57 microns and 14.88 microns.
The visible bands are centered at: 0.425 microns, 0.540 microns, 0.654 microns, 0.749 microns and 0.860 microns.

4) Why is the 6.78 micron band listed twice?

There are 10 different filters on THEMIS, however the first two filters have the same spectral center.

5) What's up with the 14.88 micron band? It doesn't look like the others.

At 14.88 microns, the atmosphere of mars is opaque, so THEMIS cannot see the surface of the planet.

6) Who built THEMIS?

The infrared-wavelength imaging portion of THEMIS was fabricated at Raytheon/Hughes Santa Barbara Remote Sensing of Goleta, California.

The visible-wavelength camera portion of THEMIS was provided by Malin Space Science Systems of San Diego, California.

The THEMIS telescope was manufactured by Axsys Technologies.
THEMIS is controlled and operated from the Arizona State University campus in Tempe, Arizona.

7) Can THEMIS detect water or ice?

Yes. Both water and ice are strongly absorbing in the IR wavelength bands THEMIS uses.

8) Can THEMIS see through dust?

THEMIS can see through a small amount of atmospheric dust, but even a thin layer of surface dust (~100um) will obscure any underlying thermal IR signatures. Diurnal thermal conductivity can occur through several centimeters of dust, but will only increase or decrease the temperature of the dust on top.

9) When will the public get access to the THEMIS data?

The THEMIS team will be releasing images to the Planetary Data System on 3-month intervals, beginning in October, 2002.

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