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NASA Images Suggest Water Still Flows on Mars
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post Dec 4 2006, 09:25 PM
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Dec. 4, 2006

Dwayne Brown/Erica Hupp
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Guy Webster
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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.
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John M. Dollan
post Dec 6 2006, 08:27 PM
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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...


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"To make an apple pie from scratch, you must first create the universe..."
-- Carl Sagan
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helvick
post Dec 6 2006, 11:23 PM
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QUOTE (John M. Dollan @ Dec 6 2006, 08:27 PM) *
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.
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John M. Dollan
post Dec 6 2006, 11:31 PM
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QUOTE (helvick @ Dec 6 2006, 04:23 PM) *
The rate is higher but it's not as high as you might think...


Thanks for that clarification. It definitely helped me with an off-list discussion.

...John...


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Posts in this topic
- Sunspot   NASA Images Suggest Water Still Flows on Mars   Dec 4 2006, 09:25 PM
- - monitorlizard   The presence of Philip Christensen (PI for TES) on...   Dec 4 2006, 10:08 PM
|- - AlexBlackwell   QUOTE (monitorlizard @ Dec 4 2006, 12:08 ...   Dec 5 2006, 04:14 PM
- - Tesheiner   I just found this while reading NASA Watch; perhap...   Dec 5 2006, 09:22 AM
- - djellison   It's impossible to know where smoke ends and f...   Dec 5 2006, 09:51 AM
|- - AlexBlackwell   QUOTE (djellison @ Dec 4 2006, 11:51 PM) ...   Dec 5 2006, 04:10 PM
- - Sunspot   Gullies   Dec 5 2006, 04:52 PM
- - tglotch   A few points: 1) Remember that a TES "pixel...   Dec 5 2006, 05:53 PM
|- - AlexBlackwell   QUOTE (tglotch @ Dec 5 2006, 07:53 AM) 2)...   Dec 5 2006, 06:08 PM
|- - ugordan   This definitely sounds like it belongs to a separa...   Dec 5 2006, 06:29 PM
- - AlexBlackwell   Per Gordan's suggestion, I'll start a new ...   Dec 5 2006, 08:00 PM
- - AlexBlackwell   Leonard David has a brief blurb in his blog.   Dec 5 2006, 08:24 PM
- - volcanopele   Maybe a gully seen recently but not seen in older ...   Dec 5 2006, 08:31 PM
|- - AlexBlackwell   QUOTE (volcanopele @ Dec 5 2006, 10:31 AM...   Dec 6 2006, 01:03 AM
|- - JonClarke   QUOTE (AlexBlackwell @ Dec 6 2006, 01:03 ...   Dec 6 2006, 06:47 AM
|- - AlexBlackwell   QUOTE (JonClarke @ Dec 5 2006, 08:47 PM) ...   Dec 6 2006, 04:21 PM
- - MizarKey   I know that this group is usually great about post...   Dec 6 2006, 04:30 PM
- - AlexBlackwell   It looks like the story is leaking out, no pun int...   Dec 6 2006, 04:54 PM
|- - ugordan   The Daily Mail: QUOTE Earlier this week the MOC to...   Dec 6 2006, 05:08 PM
|- - tuvas   QUOTE (AlexBlackwell @ Dec 6 2006, 09:54 ...   Dec 6 2006, 05:16 PM
|- - Stu   QUOTE (tuvas @ Dec 6 2006, 05:16 PM) Is S...   Dec 6 2006, 05:17 PM
|- - tuvas   QUOTE (Stu @ Dec 6 2006, 10:17 AM) ...   Dec 6 2006, 05:22 PM
- - Stu   Good old Daily Mail... can't be Michael Hanlon...   Dec 6 2006, 05:10 PM
|- - imipak   QUOTE (Stu @ Dec 6 2006, 05:10 PM) Earlie...   Dec 6 2006, 05:17 PM
|- - Stu   Sorry, I didn't insert a "sarcastic g*t...   Dec 6 2006, 05:20 PM
|- - imipak   QUOTE (Stu @ Dec 6 2006, 05:20 PM) Sorry,...   Dec 6 2006, 05:40 PM
- - Stu   More details... Martian find raises chances of l...   Dec 6 2006, 05:16 PM
- - elakdawalla   You probably thought he was American because his v...   Dec 6 2006, 05:42 PM
|- - AlexBlackwell   QUOTE (elakdawalla @ Dec 6 2006, 07:42 AM...   Dec 6 2006, 05:45 PM
- - elakdawalla   It's typically more efficient for me to wait u...   Dec 6 2006, 05:55 PM
|- - ustrax   "MARS Recent Activity Revealed" That...   Dec 6 2006, 05:57 PM
|- - AlexBlackwell   QUOTE (elakdawalla @ Dec 6 2006, 07:55 AM...   Dec 6 2006, 05:57 PM
|- - AlexBlackwell   QUOTE (AlexBlackwell @ Dec 6 2006, 07:57 ...   Dec 6 2006, 10:33 PM
- - ElkGroveDan   We now have a new unit of measure; Swimming Pools.   Dec 6 2006, 06:12 PM
|- - climber   QUOTE (ElkGroveDan @ Dec 6 2006, 07:12 PM...   Dec 6 2006, 08:30 PM
- - remcook   very nice summaries on the msss page. Something el...   Dec 6 2006, 06:15 PM
|- - tuvas   QUOTE (remcook @ Dec 6 2006, 11:15 AM) ve...   Dec 6 2006, 06:23 PM
|- - Steve   QUOTE (tuvas @ Dec 6 2006, 01:23 PM) I...   Dec 6 2006, 07:21 PM
|- - volcanopele   QUOTE (Steve @ Dec 6 2006, 12:21 PM) I...   Dec 6 2006, 07:29 PM
||- - AlexBlackwell   QUOTE (volcanopele @ Dec 6 2006, 09:29 AM...   Dec 6 2006, 07:42 PM
|- - tglotch   QUOTE (Steve @ Dec 6 2006, 07:21 PM) I...   Dec 6 2006, 07:56 PM
|- - exoplanet   QUOTE (Steve @ Dec 6 2006, 07:21 PM) ...   Dec 7 2006, 12:33 AM
|- - jamescanvin   QUOTE (exoplanet @ Dec 7 2006, 11:33 AM) ...   Dec 7 2006, 01:00 AM
|- - exoplanet   QUOTE (jamescanvin @ Dec 7 2006, 01:00 AM...   Dec 7 2006, 02:24 AM
|- - jamescanvin   QUOTE (exoplanet @ Dec 7 2006, 01:24 PM) ...   Dec 7 2006, 02:50 AM
|- - Steve   QUOTE (exoplanet @ Dec 6 2006, 09:24 PM) ...   Dec 7 2006, 02:51 AM
- - Analyst   A very good press confernce, good questions. I ha...   Dec 6 2006, 07:09 PM
|- - volcanopele   QUOTE (Analyst @ Dec 6 2006, 12:09 PM) fr...   Dec 6 2006, 07:15 PM
||- - AlexBlackwell   QUOTE (volcanopele @ Dec 6 2006, 09:15 AM...   Dec 6 2006, 08:03 PM
|- - centsworth_II   QUOTE (Analyst @ Dec 6 2006, 02:09 PM) .....   Dec 6 2006, 07:16 PM
- - um3k   I recorded the NASA TV internet stream of the enti...   Dec 6 2006, 07:18 PM
- - AlexBlackwell   NASA Images Suggest Water Still Flows in Brief Spu...   Dec 6 2006, 07:39 PM
- - vmcgregor   Additional multimedia products (video, podcast, sl...   Dec 6 2006, 07:53 PM
|- - ElkGroveDan   QUOTE (vmcgregor @ Dec 6 2006, 11:53 AM) ...   Dec 6 2006, 08:03 PM
- - John M. Dollan   Considering the rate that the Earth intercepts met...   Dec 6 2006, 08:27 PM
|- - helvick   QUOTE (John M. Dollan @ Dec 6 2006, 08:27...   Dec 6 2006, 11:23 PM
|- - AlexBlackwell   QUOTE (helvick @ Dec 6 2006, 01:23 PM) Th...   Dec 6 2006, 11:29 PM
|- - John M. Dollan   QUOTE (helvick @ Dec 6 2006, 04:23 PM) Th...   Dec 6 2006, 11:31 PM
- - Paolo   Are artillery projectile-probes like these http://...   Dec 6 2006, 08:29 PM
- - climber   While listening to the show, a question crossed m...   Dec 6 2006, 08:38 PM
- - Stu   "Interesting"? "INTERESTING?...   Dec 6 2006, 08:40 PM
|- - imipak   QUOTE (Stu @ Dec 6 2006, 08:40 PM) ...   Dec 6 2006, 09:38 PM
- - John M. Dollan   Stu... Where did you find that image? It is abso...   Dec 6 2006, 08:46 PM
- - volcanopele   I'm not tuvas. I'm not a vulcan, either, ...   Dec 6 2006, 08:48 PM
|- - AlexBlackwell   QUOTE (volcanopele @ Dec 6 2006, 10:48 AM...   Dec 6 2006, 08:57 PM
|- - climber   QUOTE (volcanopele @ Dec 6 2006, 09:48 PM...   Dec 6 2006, 09:07 PM
|- - Stu   QUOTE (volcanopele @ Dec 6 2006, 08:48 PM...   Dec 6 2006, 09:10 PM
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||- - mhoward   QUOTE (Stu @ Dec 6 2006, 09:10 PM) That ...   Dec 6 2006, 10:50 PM
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|- - AlexBlackwell   QUOTE (ngunn @ Dec 6 2006, 12:13 PM) Than...   Dec 6 2006, 10:17 PM
- - deglr6328   It should be noted that IF this is water (I want t...   Dec 6 2006, 10:29 PM
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- - AndyG   A question! What's a likely figure for th...   Dec 7 2006, 11:43 AM
- - ustrax   What triggers my imagination in this great discove...   Dec 7 2006, 12:24 PM
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