Would we see a human extinction threatening asteroid coming?

I’m mainly wondering if we could detect such an object (asteroid/comet/whatever) before it crashed into Earth and if so, how long before impact? Assume a worst case scenario of a space object just large enough to obliterate the Earth’s habitability (thus being harder to detect due to its lower size), hurling at the Earth at one of the highest possible speeds for such an object.

This is what NASA has to say:

From here: http://impact.arc.nasa.gov/intro_faq.cfm

Comforting thought either way. We could either all die at any moment from a catastrophic collision, or have decades to think about it and probably not be able to do anything about it.

Or a star could go supernova and send a massive gamma-ray burst towards us that would instantly vaporize all life, and all water, on the planet. Sweet dreams.

At least if that happens, I know where I’m going when I die.

Beggin’ you pardon, but it’s a big ass sky.

And we are a very tiny target.

Given enough warning time, I believe a mission to said asteroid placing and igniting a rocket motor on it will easily alter its course enough to ensure a miss (IIRC such missions are on the drawing board).

Sounds like I’m not the only one who caught Deep Impact on cable last week :smiley:

We’re just little tiny specks about the size of Mickey Rooney.

But there are a lot of PHAs (Potentially hazardous asteroids) out there:

There’s the oft-quoted statistic from Bill Bryson’s “A History of Nearly Everything”, or whatever it’s called, that there are more people working in your local McDonald’s than there are in the whole world working on detecting dangerous asteroids. I wouldn’t take his word as gospel, but it wouldn’t surprise me too much if he were right in this case.

Even if that’s true, I’d bet there’s a lot more computer power dedicated to finding NEO’s than there is serving us Big Macs. :wink:

I’m not even sure if this is true. It seems that every McDonald’s cash register is a computer.

some would claim he is a big star.

Thanks for all the replies.

The Earth has had smaller impacts before though, so I don’t think it’s that infeasible.

Thanks, this website talks about impacts of asteroids that are orbiting closely to Earth, but what about the possibility of impact from extra-solar system objects?

I have often wonder about this too.

Also, what about the possibility for the solar system to pass through a large asteroid field, thus bombarding all planets with many asteroids?

We are much more likely to be hit by something in a similar orbit to earths than by something from outside the solar system (as noted above, big sky, small planet). There are some meteors (a small percentage) that have very high velocities (based on track data). These may be extrasolar material, but are tiny (grain of sand sized, probably). Scientists do examine meteorites to see if any are extrasolar, but I cannot find a reference to any that can be identified as such. There have been some inclusions in meteorites that may qualify as extrasolar, but the evidence is not strong.

If we only spot a few extrasolar grains of material, then the likelihood of a major impactor is vanishingly low.


That is also unlikely - without a star to provide a gravitational center, the field will either disperse to a low density, or start clumping and break down into dust or fuse into a planetoid.

It is more likely that the solar system could hit an interstellar dust field - this would not bombard the planet, but would reduce the solar density hitting the atmosphere, causing the planet to freeze. This could be one cause of “snowball earth” events, but is this is only one theory.

Another possibility is that another star moves past close to the sun (like Gliese 710). This will perturb the Oort cloud, and will produce an increase (estimated to be about 5%) in the number of comets and meteors. These, however, will not be extrasolar, and will mostly be icy chunks.


We’ll be able to see a star coming a long ways away. In fact, the example you give is the only known star that will come close to the Sun in the next 10 million years or so. And it probaby won’t come any closer than about a light year or so.
A spectral class Y brown dwarf could sneak up on us, since their temperatures are quite cool and thus hard to detect. The coolest Y-class so far discovered is just under 300 K (roughly room temperature). The chances of a brown dwarf entering the solar system are no better than that of a random star, i.e. quite low. It’s not something you really need to worry about. (And besides, the danger from them is not crashing into the Earth, but rather snatching the Earth away from the Sun)