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Cheap Astronomy
2009-Aug-02, 08:23 PM
I understand the late heavy bombardment is theorised to have left it's mark on the Moon due to the absence of much surface geology - while its mark is erased from Earth (plate tectonics) and Venus (volcanic resurfacing).

How does Mars fit then? It doesn't show signs of heavy bombardment does it? And if not, why not?

Thanks

Caglow
2009-Aug-02, 08:41 PM
Off the top of my head, I'll have to say that Mars has its wind which can wear away things...

slang
2009-Aug-02, 09:40 PM
Funny how a search for your post topic (http://www.google.nl/search?q=Late+heavy+bombardment+on+Mars) returns this thread as first result in Google. It does give a bunch of other results though. Check 'm out and report back. :)

stu
2009-Aug-03, 05:19 AM
I'll get back to you in 2 years when I actually finish this research project.

Simona
2009-Aug-03, 05:55 AM
I'm guessing it used to have more geology than it has now. There might have been some plate tectonics before it lost its internal heat, maybe water. And the wind certainly helped with the erosion processes as well.

stu
2009-Aug-03, 06:27 AM
Sorry for my flippant answer (though a real one, I'm actually working on Mars' cratering and a side project is to date very large craters to see if there is a spike (see below) that would be a signature of the late heavy bombardment). Mars shows significant evidence of heavy cratering, just like the moon does. The only major difference is the crustal dichotomy between the northern and southern hemispheres, though there are very large and still-visible buried craters up north. The LHB actually happening is generally agreed upon, but there is still significant debate.

What you should NOT equate it with is the "early" heavy bombardment, ~4.3ish-4.5 Gya which was the general clearing of the solar system of debris from its formation. This left its mark on everything (though that has been erased on many solid bodies), and it is when the majority of very large basins on the moon, Mars, and Mercury formed (though of course there are always exceptions). The LHB is effectively a "spike" in cratering around 3.8-4.1 Gya that could have been caused by Jupiter and Saturn dancing about.

Simona - saying that something has "more geology" is like saying that some air is "more gaseous" -- it really doesn't make sense when you're comparing two solid bodies. It's a nitpick as I'm sure what you meant to say was "more active geology." In addition, there is no accepted evidence that Mars ever had plate tectonics. There was one paper that I know of a few years ago, but the problem is that they looked at a map of Mars under a poor projection (Mercator vs. polar for where they were looking) and when looking at it under a correct one, the effect went away.

Simona
2009-Aug-03, 06:48 AM
Simona - saying that something has "more geology" is like saying that some air is "more gaseous" -- it really doesn't make sense when you're comparing two solid bodies. It's a nitpick as I'm sure what you meant to say was "more active geology."

Well, I don't write scientific papers so my terminology is poor and English is my third language so I guess I sometimes don't express myself clearly. But thanks for showing understanding. Yes, I meant more active geology in the past. :)


In addition, there is no accepted evidence that Mars ever had plate tectonics. There was one paper that I know of a few years ago, but the problem is that they looked at a map of Mars under a poor projection (Mercator vs. polar for where they were looking) and when looking at it under a correct one, the effect went away.

Good to know that. I was under the impression that they're speculating about it. Do you have enough evidence for water flow by now?

astromark
2009-Aug-03, 07:17 AM
Welcome Simona., and do not let your language skills stop your questions... We all learn from them still.
I will attempt to explain the 'No sign of water riddle' The atmospheric pressure on the surface of Mars is only a small fraction of that found on Earth. At that low bar pressure water can not exist as a liquid. It can be formed as ice and may as a very saline solution ( salty ) be found as condensed droplets of condensation. Water as we know it would simply evaporate into the atmosphere of Mars. As thin as it is, Mars does have high velocity wind storms which from time to time have been witnessed to sweep across much of Mars. Effectively covering and changing the landscape constantly. The flow you speak of is more likened to a mud flow. Per ma frost like mud.

stu
2009-Aug-03, 07:19 AM
Oh yes, there's plenty of past water flow evidence. There are at least 50 river deltas identified, over 40,000 valley networks, and fresh gullies in the sides of craters.

Cheap Astronomy
2009-Aug-03, 10:17 AM
Thanks everyone - nice to stumble across a question that doesn't have a bleedingly obvious answer (yet).

I was thinking it was probably a case of more geology ;-)

Simona
2009-Aug-03, 02:14 PM
Thanks for the informative posts, guys. That's what I wanted to know!