Ron makes a great point here. It follows that almost all meteorites on
Mars should produce some kind of crater and most would be vaporized...
Does anyone out there know what the terminal velocity ratio is for Mars?
CharlyV
Bad question, CharlyV. The bad answer is 5. You are assuming free fall terminal velocity is reached by Mars impacting meteorites, so it's a loaded question. And from the way I see it, loaded the wrong way. The question ain't so much what free fall terminal velocity "ratio" is. (Anyhow, that depends on object height and planet atmospheric scale height, just like on Earth, so it ain't a linear factor from what I would theorize Charly, ask a skydiver or better yet Captain K who did the big jump in the 1950's or so and some say did and some say did and others didn't break the sound barrier. He didn't but he was real close. That would be six times a typical terminal velocity at sea level. on Earth. And he just jumped off a gondola at 100,000 feet or so (Same thiness as Mars at ground zero, how coincidental:)
For the kind of meteoric stuff falling in the Sahara I get a factor of about 5 times faster, from a crap load of assumptions, even if I consider it a bad question, I picked an answer to please (based on pizza sized assumptions). And there were plenty of assumptions which while you can have a simple number really isn't very useful, because:
You want to know IF it slows to free fall terminal velocity, and the answer is probably NO, except for pretty small stuff, not big crater stuff anyway. I'll leave you to do the cross sectional area and mass for that calculation to see exactly how small. Then the reality may really depend on the initial velocity and angle of incidence of the meteorite to see how much it is slowed. Oh...there the bolides won't be exploding at 20 km high like here on Earth, which handily increased the braked by multing cross sectional area hugely. The SURFACE of Mars has similar density to Earth at something around 30 km height (100,000 feet = 20 miles), so if it explodes too much below that on Earth, it won't explode at all on Mars. The density is just not there. So expect big flaming rocks to smash Mars and make craters, unless the incredible Hulk is there to play ball.
The calculations to the 5 times factor were:
Just by assuming the martian g force to be 3.7 m/s/s and Earth's 9.8 m/s/s (Mars' g force is only about 38% ours) causing a slower free fall velocity. Also, if Mars is mainly carbon dioxide (molecular wt. is 44) and we nitrogen (molecular wt. 28), there will be an additional density about 50% greater 44/28, as well as an increased density of another 30% extra because Mars is colder (300K/230K) absolute temperature ratio based on PV=RT, and finally molecular concentrations at ground level, the famous less than 1%, more accurately factor of about 0.8%.
In summary, it's a g force is proportional to velocity squared, so g-velocity factor: sqrt(0.38) and inversely proportion of atmospheric density to velocity squared, sqrt((1.5)(1.3)(0.01)) So if terminal velocity is reached Mars is loaded with puzzle meteorites, sometimes with thousands of itsy bitsy pieces.
Solving, sqrt(0.38/1.5/1.3/0.008) = 4.9 times Earth terminal velocity, for a pizza sized cross sectional area. Call it an even five. And that's for igneous, not iron. Iron would be 2 to 3 times as fast. But as already stated...the atmosphere is real thin to damp all that momentum in most cases.
My thoughts Charly. They are not guaranteed, but good enough for government work.
Saludos,
Doug Dawn
Mexico
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Ron
Baalke
Sent: Wednesday, January 07, 2004 4:39 PM
To: Meteorite Mailing List
Subject: Re: [meteorite-list] Meteorites on Mars
>1. Mars' thinner atmosphere means more
>meteorites survive the fall though it
>than on Earth.
There are a number of factors to consider. Mars is smaller
than Earth, so has less gravity to pull in meteoroids.
However, Mars is closer to the asteroid belt, so is more
likely to encounter meteoroids than Earth. The thinner atmosphere means
it is more likely a meteorite will reach the surface, but it
also means it is more likely to impact at hypervelocity
speeds, and hypervelocity impacts tends to totally
vaporize meteorites.
Ron Baalke
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