Lunar Impact Options

[Guest_Sunspot_*]

http://science.nasa.gov/headlines/y2005/22...lunartaurid.htm

NASA scientists have observed an explosion on the moon. The blast, equal in energy to about 70 kg of TNT, occurred near the edge of Mare Imbrium (the Sea of Rains) on Nov. 7, 2005, when a 12-centimeter-wide meteoroid slammed into the ground traveling 27 km/s.

[Toma B]

Cooke estimates that the impact gouged a crater in the moon's surface "about 3 meters wide and 0.4 meters deep." As moon craters go, that's small. "Even the Hubble Space Telescope couldn't see it," notes Cooke. The moon is 384,400 km away. At that distance, the smallest things Hubble can distinguish are about 60 meters wide.

That wouldn’t be a problem for Lunar Reconnaissance Orbiters cameras with resolution of .5 meters especially considering that there would be some bright ejecta scattered around…if they can pinpoint location of that impact crater.
They should find more fresh impacts like this…

"The flash we saw," says Suggs, "was about as bright as a 7th magnitude star." That's two and a half times dimmer than the faintest star a person can see with their unaided eye, but it was an easy catch for the group's 10-inch telescope.

This isn't the first time meteoroids have been seen hitting the moon. During the Leonid meteor storms of 1999 and 2001, amateur and professional astronomers witnessed at least half-a-dozen flashes ranging in brightness from 7th to 3rd magnitude. Many of the explosions were photographed simultaneously by widely separated observers.

Does anybody knows how big crater would be one that was seen as 3rt magnitude flash?

[helvick]

Does anybody knows how big crater would be one that was seen as 3rt magnitude flash?

using the data given.
12 cm diameter (6cm radius) object impacting the moon at 27km/sec produces a 3mx0.4m crater. The impact energy released is given as 70kg of TNT and this produced a 7th magnitude flash.

Assume that the flash brightness will be directly proportional to the energy released.
A 3rd magnitude flash is approximately 40x as bright as a 7th magnitude flash.
Quick back of the envelope calc.
Since the energy released is closely approximated by the kinetic energy of the object (mass x vel^2) and the mass of the object is proportional to the cube of the radius (4/3 x pi x radius^3) then the radius of an object that would cause a 3rd magnitude flash is approximately 6cm times the cube root of 40, ie ~20.5cm. Assuming identical materials.

Using The LPL Crater Size page to check this I can approximately reproduce the 70kg of TNT value for a 12cm diameter icy body impacting at 45 degrees into loose sand (that yields 78kg of TNT). Increasing the impactor diameter to 41cm I get a yield of 3140kg of TNT which is ~40x the original.
This calculator doesn't quite agree with the crater size given in the article - I get a 5.6m diameter crater for the original and a 15m diameter crater for the impact that would yield a 3rd magnitude flash.