PDA

View Full Version : Moon impacts

Silent Knight
2004-Sep-09, 05:59 AM
We hear a lot about people who are worried that an asteroid will hit Earth, but what if one hits the moon? Would that have an effect on Earth?

ngc3314
2004-Sep-09, 12:47 PM
We hear a lot about people who are worried that an asteroid will hit Earth, but what if one hits the moon? Would that have an effect on Earth?

Maybe... A big impact could produce enough ejecta near lunar escape velocity that some of it could find its way to Earth. Orbital mechanics would make this a curved thread of debris, which is why it was popular for a while to attribute tektite fields to lunar impacts. (As I understand it, most people who actually know about such things favor fallback from terrestrial impacts more these days). The odd thing, though, based on numerical simulations, is that (lunar escape velocity being pretty low and Earth-escape velocity at that distance also low), the odds of Earth impact are non-negligible only on the first pass, which may explain why we actually find about as many Martian meteorites as lunar.

Russ
2004-Sep-09, 01:01 PM
We hear a lot about people who are worried that an asteroid will hit Earth, but what if one hits the moon? Would that have an effect on Earth?

It depends on several variables:

1) Size/mass of impactor
2) Velocity at impact
3) Composition of impactor, nickle/Iron, silicate, carbonatious, etc.
4) Impact location on Moon.
5) Composition of location on Moon
6) Angle of incidence
7) There's more but you get the picture.

The bigger the mass, the higher the velocity, the denser, the stronger, the more rubble it excavates, etc.,etc.. the greater the possibility that some of the rubble will attain lunar escape velocity, attain an intercepting orbit with Earth and survive to impact on said Earth.

There is a site here (http://www.lpl.arizona.edu/impacteffects/) which lets you estimate the amount of damage caused by impactors. It's kind of rough cut but fun to use.

ToSeek
2004-Sep-09, 02:00 PM
Another impact estimater is here (http://janus.astro.umd.edu/astro/impact/).

Cougar
2004-Sep-09, 04:52 PM
We hear a lot about people who are worried that an asteroid will hit Earth, but what if one hits the moon? Would that have an effect on Earth?
With no water or atmosphere, the moon retains a record of every impact that has occurred there for the past several billion years. These craters have actually been counted and categorized. Generally spaking, there are millions of tiny ones, 100,000s of small ones, 10,000s of medium-small ones, 1,000s of medium ones, 100s of medium-large ones, 10s of large ones, and only a few monstrous ones. That's over the past few billion years. This very regular pattern gives us a good idea of impact probabilities on ours as well as the other planets, regardless of how well surface activity has covered up the record. In its history, the moon has taken some big hits. It's still there, and we're still here.

Silent Knight
2004-Sep-11, 04:19 PM
Are astronomers watching for asteroids that could hit the moon?
Is there a website that lists the stats (composition, velocity, etc) of known asteroids?
Can you give me an example of an asteroid that would shoot debris off of the moon?

ToSeek
2004-Sep-11, 06:15 PM
Are astronomers watching for asteroids that could hit the moon?
Is there a website that lists the stats (composition, velocity, etc) of known asteroids?
Can you give me an example of an asteroid that would shoot debris off of the moon?

There are various lists accessible here (http://cfa-www.harvard.edu/iau/lists/Unusual.html), but it's kind of technical.

EDIT: And here (http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects_list:0;main).

Captain Kidd
2004-Sep-11, 07:26 PM
and only a few monstrous ones.Boy what I wouldn't give to have a clear night and great view of one of those happening.

Tom Mazanec
2004-Sep-12, 10:14 AM
Captain Kidd Posted: Sat Sep 11, 2004 7:26 pm Post subject: Re: Moon impacts

--------------------------------------------------------------------------------

Cougar wrote:
and only a few monstrous ones.
Boy what I wouldn't give to have a clear night and great view of one of those happening.

Just imagine the Mare Imbrium impact...especially as the Moon was somewhat closer!

BTW, has anyone seen a meteoroid impact on the Moon? Just a little one?

jt-3d
2004-Sep-12, 10:22 AM
The best I've done is seeing two satellites pass in front of the moon. Both times were just as I swung on it. The first time I just went "Huh?!". The second time I tried to track it but I had the scope on slew so naturally it went too far, too fast.
I keep waiting to see the moon get smacked. I really need to get a moon filter. Next time I'll try some sunglasses. Too bad I didn't think of that before.

frogesque
2004-Sep-12, 05:24 PM
Lunar meteor impact has been recorded on video and was confirmed by an independant observer. Stills of the event here. (http://iota.jhuapl.edu/lunar_leonid/index2.html)

BAD Astronomy note. They talk about viewing the faintly Earthlit dark side of the moon. I take it these observations were of the Lunar surface in shadow, not the face of the moon facing away from Earth.

2004-Sep-12, 06:27 PM
dark side of the moon

Dark side? :wink:

rleyland
2004-Sep-12, 08:41 PM
"Dark Side" is, of course, the side facing away from the sun :-)

In the last couple of years there have been a several attempts to capture images, on video, of lunar impacts during meteor showers.

There have been a couple of reported sucesses. See IMO and AMS websites http://www.imo.net and http://www.amsmeteors.org/

cheers,
Robbo

Cougar
2004-Sep-12, 09:59 PM
"Dark Side" is, of course, the side facing away from the sun :-)
So that could be the side facing us. I'm not sure if you make it clear that you get that this is one of the BA's Bad Astronomy Misconceptions. (http://www.badastronomy.com/bad/misc/dark_side.html) The side of the moon facing away from earth gets well lit by the sun every month. (Sorry if you're saying to yourself, "I knew that!")

frogesque
2004-Sep-12, 10:37 PM
I think my post above may be responsible for the confusion. The site link I gave to Lunar meteor impacts includes several references to the dark side of the moon. In the context of what is being described it is clear they are talking about impacts observed as a small flash of light that can be seen against the shadowed part of the Moon's surface that is very faintly illuminated by reflected light from the Earth.

I was perhaps being pedantic in my comment but I belong to the grey haired generation and the expression "dark side of the moon" was prety well synonymous for the far side of the moon; that is the side that always faces away from Earth which of course cannot be seen by an Earth bound observer. Libration (http://www.minervatech.u-net.com/moon/not_libr_ac.htm) not withstanding. (nice graphic of libration from that page)

Lunar meteor impacts are probably one area of astronomy where usefull data and discovery can be made by backyard amatures. Moon terrain is well documented and mapped and the only real equipment need besides a telescope is a realtime camcorder with an accurate datestamp hooked up to the eyepiece.

2004-Sep-13, 06:06 AM
I have a quick question - were the maria formed either directly or indirectly by asteroid impacts?

Tom Mazanec
2004-Sep-13, 03:08 PM
I believe it was indirectly, by lava "bleeding" into the busted up terrain.
I could be wrong, however.

kucharek
2004-Sep-13, 03:15 PM
AFAIK, the basins created by the impacts were filled with lava many, many million years after their creation.

rleyland
2004-Sep-13, 11:04 PM
"Dark Side" is, of course, the side facing away from the sun :-)
So that could be the side facing us. I'm not sure if you make it clear that you get that this is one of the BA's Bad Astronomy Misconceptions. (http://www.badastronomy.com/bad/misc/dark_side.html) The side of the moon facing away from earth gets well lit by the sun every month. (Sorry if you're saying to yourself, "I knew that!")

Hi Cougar,

I was trying to be precise, but clearly I was not precise enough, perhaps I should have added "Not the side facing away from the earth".

If you look at the descriptions of what the amateur astronomers are trying to do, the meaning is pretty obvious (frogesque pointed this out).

By using video, and timing signals they can verify that they are recording actual impacts (and not glitches in their viedo systems). Quite impressie stuff.

cheers,
Robbo.