Posted on 05/28/2004 7:30:14 AM PDT by 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
As long as we catch it far enough out, we won't need too much of a "physics package" to push it out of our way. I read something recently about the matter, and was surprised at how little of a nudge these would need far enough out, but it makes perfect sense, considering that we aren't talking about one object on a simple X/Y axis.
Well, if "physics package" is a euphemism for a B-O-M-B, an uncontrolled explosion might be more dangerous. As you note NEAR, I think that it wouldn't be difficult at all to land a ion propulsion engine and nudge a potentially dangerous object into a non-dangerous orbit. But you have to have lead time for this to work.
Beat me to it! I said the same thing in response 22.
I think we should honor prominent DemocRATs by naming NEA after them, because their goal is to make us weak so our enemies can destroy us.
Keep in mind, I'm thinking a B83's "physics package" - we're talking eighty (80) times the power of the bomb that was used in Hiroshima.
At point-blank range on a 1000 meter-wide asteroid - part of it would be vaporized.
Considering something is trotted out every decade to scare us into submission to more government, I'll stick with my boondoggle angle, thanks.
(Global cooling, then global warming, water shortages, oil shortages, overpopulation, now underpopulation of western society..ad nauseum)
I agree. What I said above.
And my response #9 :-)
And it would probably affect the trajectory a bit, too.
If we were faced with a near-certain impact, and not enough lead time to implement nudging orbital corrections (but enough lead time to do something other than confirming that our salvation plan is in order), more drastic/risky/uncertain outcome plans would certainly be considered and perhaps tried.
Did you ever read "The Cold Equations" or see the fairly recent Sci-Fi channel movie? Not necessarily the greatest story (it was written in the 1950s, after all), but if an asteroid is discovered on collision course with Earth, all of us will learn about the implacability of "the cold equations" soon enough.
I hope we never have to face that situation. But I think that it's worthwhile to keep thinking about what might be done if we do.
Again.. an asteriod on the smaller end of the scale will "burn up" in the atmosphere causing no damage. One on the larger scale would end up creating a ton of mini bombs if you will. But an asteriod of that size would be an Earth killer anyways.
Acknowledged, sir! Great, er, good minds think similarly.
NASA did it with the "ozone hole" a decade or so ago.
Then, they migrated to "global warming".
Now, its a perfectly natural occurance that they want to mess with...
"Painting" it white or black will speed up/down the velocity too.
(I always get confused which does what)
Siderites don't burn up in the atmosphere unless they are tiny. Aerolites can burn up in the atmosphere whether they are broken into pieces or not, even if they are large enough to cause major damage. The Tunguska object--apparently an aerolite--burned up entirely before hitting the ground, and it still devastated a vast area.
So smashing a small object doesn't help.
One on the larger scale would end up creating a ton of mini bombs if you will. But an asteriod of that size would be an Earth killer anyways.
If it hits the Earth, yes. But if it remains intact, it can be steered away from its collision course.
So smashing a big object doesn't help.
NASA atmospheric observations only confirmed the ground-based measurements of stratospheric ozone depletion over Antarctica in the southern hemisphere spring (October). In fact, the data analysts originally thought the data was erroneous -- they had to get the ground-based measurements to confirm that the satellite data wasn't wrong.
That's not how I remember it being "sold". I don't doubt that the science is valid for that particular "snapshot", but
NASA went overboard in pimping itself as envirowacko for funding - the Algorists.
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