Asteroid Detection ....?

Question

I understand that through NEO detecting we have a basic understanding of the orbits of both small and big asteroids. However, if a verylarge asteroid that we have not discovered yet were bound to hit earth, would we know about it before it hit? Is this still true for small asteroids or are they much harder to see? What is the latest we would find out about a world-threatening asteroid before it hit the earth?

Answer 1

Your questions are fascinating.Let me give you some brief,

>>If a very large asteroid that we have not discovered yet were bound to hit earth, would we know about it before it hit?< impact well in advance -- enough time to devise a defensive strategy.
However, though the odds are good, they are not 100%. A very large
asteroid could, conceivably, sneak through our observation net.



>>Is this still true for small asteroids or are they much harder to see?<<

The ease with which we can see an asteroid depends largely on its
brightness. A very large, very distant asteroid might have the sameoverall brightness as a much smaller, much closer asteroid. So...inone sense...both asteroids are equally easy to see. However, we would
be able to see the larger asteroid years or decades before any
potential impact. But for the smaller ones, they may only be spotted
months -- or even only days -- prior to their intercept with Earth.



>>What is the latest we would find out about a world-threatening
asteroid before it hit the earth?<<

An event like this is extremely rare. Presumably, the last time itmay have occurred on Earth was when the dinosaurs became extinct 65 million years ago. In all likeliehood, we would be alerted to the possibility of a collision course with a very large object many years or decades ahead of any actual impact. However, there is always a chance -- however small -- that a large asteroid could remain undetected in its approach to Earth, finally to be seen with only a few months advanced warning.




No one really denies the possible destructive power of an asteroid collision, up to the possibility that a large enough impact couldpretty much wipe out human life on the planet. At the same time, the odds of something this catastrophic occuring are remote in the extreme...what the scientists, with their gift for understatement,have dubbed a "Low Probability, High Consequence Event".

As I said earlier, it's been at least 65 million years since the last such event may have taken place, and could easily be tens or hundreds of millions years before the next one.


You're much better off taking care of yourself by looking both ways before crossing the street, as that's where the real,everyday dangers lie.

Answer 2

Good question. The answer is that it depends on a number of factors--but yes, we COULD get "blindsided."--though its unlikely and becoming less likely every year as our knowledge of what's out there improves.

There's really two cases: a relatively small object and 2) a "biggie"

Small objects (whether an asteroid or leftover bit o fan old comet, etc) is harder to detect. Consequently, there's a lot of them (current estimates, several hundred small Near-Earth Asteroids) wwe haven't found yet. If one of these headed toward us on a collision course, we might not spot it ahead of time--or perhaps only a few days or even hours ahead.

A bigger object would most likely be a comet--whe pretty much have found all the bigger Near-Earth asteroids. But we'd have at least some warning--a few weeks , months, even a couple of years. Comets are a lot easier to spot, after all, and they have long orbits.

None of which will do us one bit of good until we start taking space travel seriously again. Besides the other benefits, advanced spacecraft woudl enable us to divert such objects. But right now, all we could do is stock up on supplies and hope a really big one didn't wipe us out completely, like the one that wiped out the dinosaurs 65 million years ago.

Answer 3

Asteroids are dark, and thus small ones are difficult to detect. However, any asteroid that would be of significant enough size to pose an extinction level threat would most likely be detectable. As a general rule, although predictions of impact potential can be made many years prior to a potential impact, the final trajectory wouldn't be known until the asteroid will no longer interact with any other object's gravity. In fact, there is one object "2003 QQ47" being tracked currently that has a fairly small chance of impacting in 2014. A greater issue would be a comet impact from something perturbing the orbit of one of the many comets in the oort cloud and hurtling it back in towards earth.

Answer 4

Depends a bit on what you mean by "a very large asteroid". (433) Eros is one of the largest NEAs and is about 30 km long along its largest axis. It was discovered in1898 and has been tracked extensively. It has been visited by the NEAR Shoemaker spacecraft and you could track it using relatively low-end amateur equipment. The last time we discovered an NEA brighter than magnitude 13 was in 1990 when (4954) Eric was found. The last time an asteroid brighter than magnitude 14 was found was in 2001. We are still discovering the odd asteroid around magnitude 15, which is roughly 5 km in diameter and quite big enough to cause a global catastrophe (at least for human civilization).

Current estimates put the number of objects brighter than magnitude 18, around 1 km in diameter, at about 1100 to 1200. So far we have seen about 800 and around 740 of those we have seen more than once so were getting to know where they are quite well. We only found about 30 in 2006 whereas we had been finding more than 50 a year since 1998 when the major surveys such as LINEAR got going.

Going still fainter, there are estimated to be around 100,000 objects brighter than magnitude 22 (around 100 to 150 meters across) and 20,000 of those are thought to be "potentially hazardous" i.e. their present orbits can bring them within 7.5 million km of the Earth if everything aligns right. We don't know many of these, only a little over 2500 after you take out the larger ones we already know and only 1000 of these have reasonably well-known orbits. These objects are probably capable of causing destruction on the scale of Hurricane Katrina in the US or the Indian Ocean tsunami of 2004. It takes a lot more effort to find and track these. We find a trickle at the moment with mostly 1-m class survey telescopes and they are mostly beyond the follow-up capabilities of amateurs with equipment costing around US$10,000. The recent NASA report suggested a budget of US$1 billion to go after them more seriously.

The JPL site mentioned below has a lot of worthwhile links

Answer 5

Asteroids orbit in a limited region, between the orbits of Mars and Jupiter. Therefore, it is most likely that we know about the orbits of all large asteroids, since they are not far away. I think your concern is not about asteroids, but about comets. Comets can enter the solar system from afar. It is possible for a large distant comet to enter the solar system and approach the earth on a collision course, without being discovered until a few weeks or months before impact

Answer 6

Hi. This is a bit scary but most of the close approaches come form the direction of the Sun. We may have literally no warning because the governments probably think 'ignorance is bliss (or at least not panic)'.

Answer 7

It would already be on the ground before we spotted it.