[ Oran/NASAChatHost - 6 - 11:02:09 ]
David Morrison is responsible for managing basic and applied research programs in the space, life, and Earth sciences, with emphasis on astrobiology -- the study of the living universe.

[ DavidMorrison/ARC - 11 - 11:12:06 ]
RE: [Oran/NASAChatHost] David, we've seen depictions of catastrophes that would result from a large meteor strike on Earth. Would all life really be destroyed, or would some humans and animals be able to survive such an event?
The damage depends entirely on large the impact is. Early in Earth's history there may have been impacts that killed everything, sterilizing the planet. But today impacts are much smaller, and indeed most damage is local only.

[ Oran/NASAChatHost - 13 - 11:13:58 ]
Once again, David Morrison is online and ready to take your questions. So please send them in!

[ DavidMorrison/ARC - 15 - 11:15:04 ]
RE: [Oran/NASAChatHost] David, could you please tell us approximately how many times a year the Earth is "visited" by meteors/meteorites?
Meteors (shooting stars) and even meteorites happen all the time -- millions of meteors per day, in fact. Fortunately, impacts that do damage are very rare, however.

[ DavidMorrison/ARC - 16 - 11:17:06 ]
RE: [Oran/NASAChatHost] David, what is the likelihood the Earth will be struck by a large meteor? How much warning would we have on Earth?
How large to you mean? For an impact with the energy of a big hydrogen bomb (tens of megatons), it is once every few hundred years.

[ Oran/NASAChatHost - 17 - 11:19:53 ]
RE: [DavidMorrison/ARC] How large to you mean? For an impact with the energy of a big hydrogen bomb (tens of megatons), it is once every few hundred years.
OK, where are we on the timeline then, far as being struck by a "big hydrogen bomb"-like meteor? When was the last strike of that magnitude, and how was the environnment affected?

[ DavidMorrison/ARC - 18 - 11:21:58 ]
RE: [Oran/NASAChatHost] OK, where are we on the timeline then, far as being struck by a "big hydrogen bomb"-like meteor? When was the last strike of that magnitude, and how was the environnment affected?
Ther is no way to tell where we are on the timeline. We don't know when the next hit will come. It could be today. It is likely not to be, however. And for impacts this size, the probable warning time is zero.

[ DavidMorrison/ARC - 21 - 11:26:16 ]
RE: [Geoffrey] Dr. Morrison, Is there any data still being used from the Apollo equipment on the moon which can tell us on average how often the moon gets struck by meteorites?
The Apollo monitoring equipment was turned off more than 30 years ago (unfortunately). But we do use the numbers of lunar craters to estimate the average rate at which both the Moon and Earth are hit.

[ DavidMorrison/ARC - 22 - 11:29:01 ]
RE: [DavidMorrison/ARC] The Apollo monitoring equipment was turned off more than 30 years ago (unfortunately). But we do use the numbers of lunar craters to estimate the average rate at which both the Moon and Earth are hit.
I should have said 25 years ago, not 30!

[ DavidMorrison/ARC - 25 - 11:35:59 ]
RE: [Geoffrey/MtnView] Since I would assume most of the smaller meteorities burn up when entering the Earth's Atmosphere, where the moon does not have that magnitude of protection, are the numbers of meteorites approaching great enough of a danger when looking at establishing any sort of long term lunar base?
Good point -- the small stuff will be a problem on the Moon. A lunar base will either have to be built mostly underground or else have a shield against high-speed cosmic dust.

[ DavidMorrison/ARC - 28 - 11:46:25 ]
RE: [Geoffrey/MtnView-Geoffrey] Do meteorites ever become an issue (perhaps a saftey issue) in space travel, such as when NASA is looking at long term missions to Mars?
Right on again! Ther has not yet been any problem of pucturing a spacecraft or spacesuit, but that is a possiblity that worries people.

[ Oran/NASAQuest - 29 - 11:57:24 ]
At this time, we will be ending our chat with David Morrison. We would like to thank david for joining us today, and sharing his career experience and expertise with us. THANK YOU, David!

[ Oran/NASAQuest - 30 - 11:58:20 ]
Be sure to visit our NASA Quest events page at http://quest.nasa.gov/common/events for information about our upcoming chats.

[ Oran/NASAQuest - 31 - 11:58:50 ]
Thank you for joining us, and have a great day!