Rock crashes into the Moon

[glenc (Glen)]

A 40-kilogram space rock has slammed into the Moon at about 90,000 kilometres per hour, creating a bright flash of light as it exploded with a force of five tonnes of TNT, according to NASA.
An automated telescope captured the images of the March 17 explosion, the biggest seen since NASA began watching the Moon for meteoroid impacts about eight years ago.
The United States space agency says the flash was so bright that anyone looking at the Moon at the moment of impact could have seen it without a telescope.

http://www.abc.net.au/news/2013-05-1...n-moon/4697932

[Matt Wastell (Matt)]

Thanks for this - I was unaware!

[multiweb (Marc)]

That's amazing they can detect this kind of thing. 40kg doesn't seem big but it certainly packs a punch at that speed. If we ever build a moon base it's going to have some serious shielding. Underground's got my vote.

[asimov (John)]

Originally Posted by multiweb

Underground's got my vote.

[space oddity]

E= 1/2 mv squared. v is a rather large number. On earth, typically 90% would be ablated (leaving 4kg) and the cosmic velocity of a meteoroid this size would all be lost, resulting in the last few miles in free fall at terminal velocity of only 250 m/s. The bolide would more than likely break up first into smaller pieces in our atmosphere. It would give a spectacular fireball but probably never be found. A lunar colony would need a solid rock equivalent roof thickness of at least 15 metres to survive and an air tight inner layer. The depth of the crater itself would be about 8 metres. Realistically, tunnelling in to a mountain is how the lunar colony would have to be built.

[Zaps]

The odds of a strike versus the cost of excavation.

Originally Posted by space oddity

Realistically, tunnelling in to a mountain is how the lunar colony would have to be built.

[glenc (Glen)]

http://www.guardian.co.uk/science/vi...ce-flash-video

[MattT]

Thanks Glen, always wondered if an impact on the Moon could be seen and now I know. 40kg is not a large rock....I'll be looking at the Moon a bit more often, well as often as a Melbourne winter will allow.
Matt

[Wavytone]

Originally Posted by MattT

wondered if an impact on the Moon could be seen

yes an impact can be seen. In 1979 in the middle of a total lunar eclipse there was one in the crater Copernicus, quite a few saw it telescopically and it appears in a photo of that eclipse as a bright spot that normally isn't present in that crater.

In those days they were called "Transient Lunar Phenomena", it was a good bet they were impacts but no-one was really sure.