Astronomy/Objects that have impacted the earth...
Greetings! I have a relatively simple question but have been unable to find the answer after searching the internet. Part of my problem is knowing how to formulate a search, so I thought I would go the old "ask a human route" :) Basically I am just curious if humans have ever tracked a foreign space body that has hit earth. Obviously we are able to track NEO's and of course there are plenty of objects that have impacted the earth but Have we ever been able to track one? I am aware that we have been able to track Man made objects (satellites, rocket boosters etc.) reentering the atmosphere but I am not aware of any foreign object. Of course small objects hit earth every day that are likely too small to see but have we ever? I suppose another way of putting the question is has an object (not man made) ever impacted earth that we saw coming? Thanks!
The ability to track objects that are potential impactors is extremely limited and I know of no cases where we've successfully managed to do that, say from their point of origin (e.g. asteroid belt) This is why Rusty Schweickart, who flew on Apollo 9 in 1969, and helped establish the planet-protecting B612 Foundation, believes we need to move seriously on it with a group of contributors - including gov't.
Here's the current skinny: Scientists think there are 500,000 to 1 million "near-Earth" asteroids comparable in size to DA14 or bigger out there (DA 14 was three times the size of the Chelyabinsk object and made a heart stopping close pass to Earth) . But less than 1 percent have been spotted. Astronomers have catalogued 9,600 of them, of which nearly 1,300 are bigger than 0.6 miles long. That means they are at least of mass extinction level.
Earth's atmosphere gets hit with 100 tons of junk every day, most of it the size of sand and most of it burning up before it reaches the ground, according to NASA. And also, there may be many bolides such as exploded over Siberia, but many will do that over oceans or other areas where few human observers live.
As NASA's Jim Green, director of planetary science, puts it, regarding the Russian event:
"These fireballs happen about once a day or so, but we just don't see them because many of them fall over the ocean or in remote areas. This one was an exception,"
Former Astronaut Schweickart observed:
"The chances of Earth getting hit without warning by one of the big ones are extremely low, so low that it's ridiculous. But the smaller ones are quite different."
This is true, but the probabilities for the monster rocks smacking us ought not be readily dismissed, because one never knows what sort of gravitational perturbations can affect existing orbits. We already know, for example, that an estimated 1,000 asteroids are perturbed from the asteroid belt each year to become Earth-crossers. We call these "Apollo asteroids". We need to keep track of them, because they are the ones that are among the planet killing or mass extinction scales. The smaller ones? Yes, they are nuisances, but we can deal with them if we have some long range planning wherewithal combined with alert observers.
The problem is in the details and mechanics of tracing with high efficacy. Alas, a lot of that depends on decent funding and so far our congress critters have not ben exactly generous. Schweickart and others meanwhile, have advised that NASA launch a $250 million-a-year program to survey asteroids and work up a deflection plan. The latter would be most effective for the lesser objects but may also help with the larger ones, of at least mass extinction scale.