Asteroids, even small ones, are deadly on Mars or the Moon, but harmless on Earth.

(Images from NASA)
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The circles shown for scale on the NASA images are 12 km across. If you ran around the circles, you run a distance of 37.699 km. A Marathon run has been set at 26 miles 385 yards which is 42.195 km, so running around one of these circles would get you almost 90% of an Olympic run.

Of course, at the surface of Mars the gravitational pull of the planet is 37.9% of the pull of the Earth's gravity, a little more than a third. And with Mars, it's a reason the "air" is so thin an object the size of a football made of rock likely makes it all the way to the surface. Well made rocks, the size of a quarter also can reach Mars surface. A steel ball bearing that size would have a very good chance of making it through to the surface, depending on velocity and angle of traverse through the thin Martian atmosphere.

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It's all about the air, there.
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Your Great-Great-Great Grand children, those few living on Mars will know exactly what this image is about. On Earth it would have been a fireball, a bright meteor. It would probably have burned up at 50 to 60 miles overhead; halfway to low earth orbit; halfway to space. Even if it made it into the thick atmosphere at the tops of the Earth's highest mountains, it is likely it would never make it the surface intact.

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On Mars it also can streak and burn, but if it starts its journey being a rock the size of a football, it makes it all the way through the Martian atmosphere and impacts on the surface.

It never occurred to early investigators that they would be able to see as many as twenty asteroidal impacts in a relatively small area of Mars, but they have their before and after impact images, like the ones shown here.

The eventual count of impacts over the entire Martian surface will refine the estimation of impacts on the Moon as well -- another small world we will have humans living upon before the end of the century.

Anywhere on Mars after a lifetime there, you would likely to have been close enough to see, hear or feel them. And be thankful one missed you.
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http://www.nasa.gov/vision/universe/solarsystem

Use the link above and explore, or pickup the 8 December 2006 issue of SCIENCE (at your school, your library, or institution of higher learning. )

These are Meteors Hitting the MOON

After initially seeing what asteroids and anything moving in the 10 to 15 km/second range impacting Mars can do, it was easy to further push home the point that walking around on the Moon or Mars for a lifetime increases the likelihood of getting smacked and these hunks of a comet suffice to show that even comet-ice and dust can make a visible impact on the Moon. That is, visible from Earth.

In this case with every meteor shower the Earth experiences, THE MOON gets hit too. These 'hits,' on the Moon are not asteroids; these are chunks of rock or hunks of ices and dust strewn off of Comet Tempel-Tuttle (55P, the number means 55th periodic comet in a close orbit around the Sun.) Images of some recent impacts of the Leonid's Meteor Shower were captured. This is not a new thing, Amateurs see them often but are usually looking for the close ones, the ones in Earth's air!

According to NASA scientists, the meteoroids are smashing into the Moon more often than anyone expected. These meteoroids are in a tube shaped volume of space and retain much of the original comets orbital momentum, so are still circling the Sun in roughly the same place every year, until they run into Earth or the Moon.

Each red dot denotes a meteoroid impact observed since Nov. 2005 by members of the NASA Meteoroid Environment Office.

If correct, this conclusion could influence planning for future moon missions. But first, the Leonids:

Bill Cooke, head of NASA's Meteoroid Environment Office, says, after his team "observed" two Leonids hitting the Moon on Nov. 17, 2006 they were ready to let the recording equipment take over. "We've seen 11 and possibly 12 lunar impacts since we started monitoring the Moon a year ago, and that's about four times more hits than our computer models predicted."

Last month, Earth passed through the "minefield" of debris from Comet 55P/Tempel-Tuttle. This happens every year in mid-November and results in the annual Leonid meteor shower. From Nov. 17th to Nov. 19th both Earth and the Moon were peppered with meteoroids.

Meteoroids that hit Earth's blanket of air disintegrate harmlessly (and beautifully) in the atmosphere. But the Moon has no atmosphere to protect it, so meteoroids don't stop in the sky. They hit the ground.

A very few of these Leonids would also make it through an atmosphere like Mars' atmosphere -- if they are big enough.

But these are the debris of a comet, not chunks of rock out of the asteroid belt.

The vast majority of the Leonids are dust-sized, and their impacts are hardly felt, though in past meteor showers astronomers have recorded enough hits on the Moon to see gasses vanishing to space after impacts on the Moon's surface. Bigger debris can gouge a crater in the lunar surface and explode in a flash of heat and light. Some flashes can be seen from Earth.

During the passage through Comet Tempel-Tuttle's debris field, Cooke's team trained two 14-inch reflectors located at the Marshall Space Flight Center to image the dark surface of the Moon. On Nov. 17th, after less than four hours of watching, they video-recorded two impacts: a 9th magnitude flash in Oceanus Procellarum (the Ocean of Storms) and a brighter 8th magnitude flash in the lunar highlands near crater Gauss.

"The flashes we saw were caused by Leonid meteoroids 2 to 3 inches (5 to 8 cm) in diameter," says Cooke. "They hit with energies between 0.3 and 0.6 Giga-Joules." In plain language, that's 150 to 300 pounds of TNT.

Most of the Leonids are too small to make it through Mars weak thin atmosphere. Of the two Cooke mention's likely only one would make it to Mars' surface.

But the Moon has NO atmospheric protection!

http://science.nasa.gov/headlines/y2006/01dec_lunarleonid.htm

Unlike Mars, where we have orbiters constantly watching the surface, we do not have lunar orbiting spacecraft of comparable ability -- or none of this would be a surprise to NASA's scientists. Observational data trumps theory everytime. Yes, we need a capable imaging satellite orbiting the Moon, not two telescopes in the yard at Marshall. (Those are nice telescopes however.)

Now there would be some improvement in information before we go to the Moon again, and definitely before we go there to build a Moonbase.
Visit the NASA site; check it out.