Spaceguard Near Earth Asteroid (NEA) Report

SpaceRef ^ | 05/27/2004

[cogitator]

At the end of 2003, there were 2600 known Near Earth Asteroids (NEAs), and of these 691 are brighter than absolute magnitude H=18, which is taken to correspond to 1 km diameter. Of these, 131 are classed as PHAs (potentially hazardous asteroids) larger than 1 km. These data from Alan Chamberlin are posted on the JPL/NASA NEO Program Office website .

For comparison, there are estimated to be a total of 1100 +/- 100 NEAs larger than 1 km. Thus at the end of 2003 we had found 63 percent of these NEAs.

Recently there appears to have been a modest slow-down in the discovery rate of NEAs larger than 1 km, perhaps reflecting the fact that we have already discovered nearly 2/3 of this population group. For the most recent three complete years (2001, 2002, and 2003), the numbers discovered are: 89, 95, and 67, respectively. We can check this effect by noting that the total discovery rate of all NEAs has not changed much, remaining at about 450/yr. Previously, improvements in the search systems more than compensated for the declining number of unknown asteroids bigger than 1 km waiting to be discovered.

The Spaceguard Goal is 90 percent completeness by the end of 2008. This corresponds to discovery of 990 NEAs brighter than H=18 for the nominal population. The survey passed its halfway mark of 495 in mid-2000 (see NEO News, 08/01/00). The 75 percent objective is 742 NEAs larger than 1 km. If we anticipate 50 discoveries during 2004, then the survey should reach this milestone at the end of this year.

This leaves 4 more years to increase the number of known large NEAs from roughly 750 to 1000. To meet this goal, the current (2003) discovery rate of about 50/yr will need to be maintained by improvements in the system to compensate for a shrinking pool of undiscovered objects. Stay tuned to see if this is accomplished.

The 2003 NASA study of sub-kilometer NEAS (NEO News, 07/23/03) focused on PHAs rather than NEAs. The estimated population of PHAs larger than 1 km is 258 (from the NASA SDT Report, pg 21), leading to a reformulated Spaceguard Goal of discovering 232 large PHAs by the end of 2008. The number of 131 PHAs (discovered as of the end of 2003) is 56 percent of the way to meeting the Spaceguard goal. Please note that conversions between NEAs and PHAs, as well as the total numbers above the 1 km size, vary because the assumptions about such things as the conversion from magnitude to diameter are not exactly the same in different studies.

The Spaceguard Survey is healthy and continuing toward meeting its 90 percent goal sometime between 2008 and 2010. However, the discovery rate of large NEAs has apparently gone thought its peak. Larger aperture survey telescopes now under design (at Lowell Observatory and the University of Hawaii), of course, can be used in the future to accelerate the discovery rate and push into the sub-kilometer size range.

David Morrison

[cogitator]

The one they need to find is the one that's going to hit the Earth...

[hchutch]

We've reached the point where all we REALLY nead is enough lead time on the discovery.

That, folks, is the hard part.

We've done most of the rest of the work thanks to the NEAR-Shoemaker probe, which LANDED on Eros and was still in contact for 16 days after the landing. If we can land a spacecraft with a scientific instruments on an asteroid, we could land a spacecraft with what the Air Force calls a "physics package" consisting of a "special store" on an asteroid.

Landing on the asteroid and then sending the signal to activate the physics package should solve the problem.

[JOAT]

Paging Bruce Willis...

What a boondoggle. "Will Fearmonger For Tax Dollars"

[darth]

About 10,000 years ago a large asteroid body entered at a shallow angle over South America. It broke up and the multiple impacts released over 1000 MEGATONS of energy. A similar impact today would kill hundreds of millions of people. Study of celestial threats is just as important as study of other natural threats such as hurricanes, floods, lightning, etc. Study of such common threats is as much a proper role for the Federal Government as national defense against earthbound enemies. Science is not a boondoggle; without scientific knowledge humanity would still be living in the Dark Ages. Our society spends way more on cosmetics than we spend on science.

[Shryke]

Question for you. How would a nuclear weapon break up a nickel (or high metallic content) asteroid 1km wide?

[Walkingfeather]

It wouldnt need to destroy it, it would just need to bump it out of its present tragectory. Done far enough out, it wouldnt take much of a course correction if it was a million miles out.

[hchutch]

If the lead time is sufficient, the trick is to deflect it.

Although if the guts of a B83 are used, we're talking something 80 times as powerful as the bomb that wiped out Hiroshima...

1.2 megatons ought to knock it off course, at the very least.

[Shryke]

If far enough out, sure. But close in? I think we need to develop Space Sharks w/Laserbeam technology.

[RadioAstronomer]

Question for you. How would a nuclear weapon break up a nickel (or high metallic content) asteroid 1km wide?

You would be better off using a thruster of some type to accomplish a delta-v. I don think a nudet would accomplish this. A continuous thrust ion engine or the like would be a better solution IMHO.

[Physicist]

Question for you. How would a nuclear weapon break up a nickel (or high metallic content) asteroid 1km wide?

It wouldn't, nor would you want it to. All that would give you is a mass of fragments on a collision course with Earth, rather than one big one. You'd actually amplify the effects of the impact.

What you want to put on the asteroid is a solar sail or an ion engine. With enough lead time, a very gentle (but sustained) push can avert its upcoming collision, or even put it permanently into an orbit that does not intersect with Earth's.

The first thing you'd want to land on the asteroid is a beacon. Then you'd be able to measure very accurately how great the risk is, and what sort of delta-v you would need to avert it.

[RightWhale]

We couldn't stop an impactor even if we had ten years lead time. All physics is good for is funding centers.

[El Gato]

What a boondoggle. "Will Fearmonger For Tax Dollars"

If the dinosaurs were still around, you could ask them if they thought it might be a good investment. But they aren't because they couldn't do it, and one of those asteroids got them.

[mrsmith]

The one they need to find is the one that's full of the goodies we need in spce.

Then we can build lots of spacecraft and settlements for people who will live off Earth and keep an eye out for impactors in their spare time from working and living and, most importantly, making babies.

[El Gato]

I don think a nudet would accomplish this. A continuous thrust ion engine or the like would be a better solution IMHO.

Either will work, but the nuke might work better if the rock was closer. The ion engine could take a lot of time to change the course. The Orion project demonstrated that we could, if we chose, build a spacecraft powered by nuclear detonations.

They even build a scale model prototype. It flew, and here it is, (Now in the Smithsonian)

http://www-spof.gsfc.nasa.gov/stargaze/Snucfly.htm http://www.space.com/spacelibrary/books/library_projectorion_020709.html

http://www.angelfire.com/stars2/projectorion/

http://www.islandone.org/Propulsion/ProjectOrion.html

Another possibility would be a NERVA type nuclear rocket. Again, probably better if time is short, as compared to the ion engine.

[MissAmericanPie]

Revelation says we suffer an ocean impact, from a chunk of rock the size of a small mountain, that destroys ships and fish. The reason for this impact seems to be to preserve life in general, as future events on the sun, some type of heating up, causes men to be scorched, and darkness is needed to preserve life during the tribulation period.

[RightWhale]

A nuke might do nothing at all. If they bury it a few feet below the surface they would get some reaction mass, but otherwise they will get a bright flash and not much more.

[RightWhale]

A nuke might do nothing at all. If they bury it a few feet below the surface they would get some reaction mass, but otherwise they will get a bright flash and not much more.

[RightWhale]

Two times nothing is still nothing.

[Almondjoy]

Not neccessarily... The more surface area that is created for the asteroid the more of it will burn up in the atmosphere.

[Physicist]

That would be a bad thing. Why do you think that nuclear warheads are designed for an air burst, rather than to explode on impact?