NASA Images Suggest Water Still Flows on Mars Options

[Guest_Sunspot_*]

Dec. 4, 2006

Dwayne Brown/Erica Hupp
Headquarters, Washington
202-358-1726/1237

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278

MEDIA ADVISORY: M06-186

NASA SCHEDULES BRIEFING TO ANNOUNCE SIGNIFICANT FIND ON MARS

WASHINGTON - NASA hosts a news briefing at 1 p.m. EST, Wednesday, Dec.
6, to present new science results from the Mars Global Surveyor. The
briefing will take place in the NASA Headquarters auditorium located
at 300 E Street, S.W. in Washington and carried live on NASA
Television and www.nasa.gov.

The agency last week announced the spacecraft's mission may be at its
end. Mars Global Surveyor has served the longest and been the most
productive of any spacecraft ever sent to the red planet. Data
gathered from the mission will continue to be analyzed by scientists.


Panelists include:
- Michael Meyer -- Lead Scientist, Mars Exploration Program, NASA
Headquarters, Washington
- Michael Malin -- President and Chief Scientist, Malin Space Science
Systems, San Diego, Calif.
- Kenneth Edgett -- Scientist, Malin Space Science Systems
- Philip Christensen -- Professor, Arizona State University, Tempe,
Ariz.

[John M. Dollan]

Considering the rate that the Earth intercepts meteors, and adding to that Mars' thinner atmopshere, would it not stand to reason that impacts would reach the surface much, much more often?

And if that is true, what does it say about those regions that are relatively crater-free? Could there be some active geology involved, or are Martian aeolian forces enough to erase some of these smaller craters?

...John, curious as always...

[helvick]

Considering the rate that the Earth intercepts meteors, and adding to that Mars' thinner atmopshere, would it not stand to reason that impacts would reach the surface much, much more often?

The rate is higher but it's not as high as you might think given the difference in densities at the surface. The martian atmosphere is extremely thin and at the surface is comparable to the Earth's at around 35KM but because of the lower martian gravity it's scale height is higher (~11km vs ~6km for earth) it is remarkably similar in density to the Earth's atmosphere once you get above 75km or so if I remember correctly. For the most part it filters out a similar amount of "stuff". By similar I'd guess we're talking about a similar order of magnitude here but I'd have to do some digging to get a number I'd be willing to defend.

The percentage that reaches the ground is higher for another reason that could well be as important - the average atmospheric impact speed at mars orbit is slightly slower (5-10km/sec slower) and so there is less energy to dissipate. For asteroidal debris this is quite significant as the impact speed can be as low as 7km/sec at mars (vs ~17km/sec typically for Earth) so only about 17% of the energy needs to be disipated. Cometary and retrograde impacts are a different animal and the difference at Mars for these (compared to earth) is 80% and 50% respectively.

The main reason there are more apparent craters on Mars is that the surface is (for the most part) really and truly ancient and erosion rates are many orders of magnitude slower than on earth.