Earth could be blindsided by asteroids, panel warns

[Sam Fraser]

Existing sky surveys miss many asteroids smaller than 1 kilometre across, leaving the door open to damaging impacts on Earth with little or no warning, a panel of scientists reports.

http://www.newscientist.com/article/dn17599-earth-could-be-blindsided-by-asteroids-panel-warns.html

It's important not to hype the impactor threat, but we've had a few recent close calls:

http://en.wikipedia.org/wiki/DD45_2009 (passed within 5 Earth diameters March 2, 2009)
http://en.wikipedia.org/wiki/2004_FH (passed within 3.4 Earth diameters March 18, 2004)
http://en.wikipedia.org/wiki/2004_FU162 (passed within 0.5 Earth diameters March 31, 2004)
http://en.wikipedia.org/wiki/2008_TC3 (detected 20 hours before atmospheric entry October 7, 2008)

More here:

http://www.cfa.harvard.edu/iau/lists/Closest.html (measuring close Earth approaches in AU gives no sense of scale and seems rather useless)

[JohnHunt]

Here's the diameters of each of those asteroids:
- 2004_FH - 30 metres
- 2004_FU162 - 6 meters
- 2008_TC3 - 2 to 5 meters
- DD45_2009 - 6 meters

>1,000 meter asteroids would be far more easily seen as they approach the Earth. We won't be blindsided. There will be time to evacuate an area or give warning to evacuate coasts. We had 20 hours warning with 2008_TC3. A 1,000 meter asteroid is at least 200 times the size and so we'd expect much more warning.

Also, we currently know of something like 85% of the >1km asteroids. Within a few years we'll know about close to 100% of them and with new whole-sky surveys we'll be aware of most of the asteroids down to tens of meters or so. The residual risk (risk from unknown asteroids) to human life is quickly decreasing.

Risk from the development of self-replicating technology is, in my opinion, far greater than the risk from asteroids.

[joertexas]

Here's the diameters of each of those asteroids:
- 2004_FH - 30 metres
- 2004_FU162 - 6 meters
- 2008_TC3 - 2 to 5 meters
- DD45_2009 - 6 meters

>1,000 meter asteroids would be far more easily seen as they approach the Earth. We won't be blindsided. There will be time to evacuate an area or give warning to evacuate coasts. We had 20 hours warning with 2008_TC3. A 1,000 meter asteroid is at least 200 times the size and so we'd expect much more warning.

Also, we currently know of something like 85% of the >1km asteroids. Within a few years we'll know about close to 100% of them and with new whole-sky surveys we'll be aware of most of the asteroids down to tens of meters or so. The residual risk (risk from unknown asteroids) to human life is quickly decreasing.

Risk from the development of self-replicating technology is, in my opinion, far greater than the risk from asteroids.

As far as I know, there is no system in place to continously sweep all sectors of the sky for asteroids. Until we have enough space based telescopes to cover the sky, I'm pretty skeptical of our ability to see all potential threats.

JR

[JohnHunt]

Hi Sam,

> Existing sky surveys miss many asteroids smaller than 1 kilometre across, leaving the door open to damaging impacts on Earth with little or no warning, a panel of scientists reports.

Yes, but the key phrase here is "smaller than 1 km". That's a vague statement. How much smaller than 1 km?

Notice the table on this page:
http://www.spaceobs.com/perso/recherche/NEA2002/NEA2002.htm
It shows that the specific number is 500m in terms of 50% known. And, I presume that that % is going up and the diameter (for 50% known) is going down each year.

It is important to note that we are routinely detecting much smaller asteroids before they pass us by at some distance. It is also important to note that you probably need an asteroid larger than the Yucatan peninsula in order to cause humanity to go extinct and it's really quite unreasonable to believe that an asteroid that size would catch us unawares until after it impacted. We would know about such a large asteroid for many months before it hit giving plenty of time for mass evacuation, stockpiling supplies, etc.

We shouldn't overhype nor underhype the risk. Rather, we should be honest about the probable death toll given rate of impact per size, our increasing knowledge of location of NEAs, the likely heads-up time for NEAs of various size, and the likelihood of evacuation.

Also, sky surveys do not cover the entire sky. But NEAs tend to move around within a year and so might come into and out of a survey's view during the course of a survey. Also, I'm guessing that NEAs have a bias towards the ecliptic which can be seen by both the northern and southern hemispheres. I seem to recall a couple of years ago looking at a catalogue of NEAs and noticing that very few get above 60 degrees above the ecliptic.

[joertexas]

Also, sky surveys do not cover the entire sky. But NEAs tend to move around within a year and so might come into and out of a survey's view during the course of a survey. Also, I'm guessing that NEAs have a bias towards the ecliptic which can be seen by both the northern and southern hemispheres. I seem to recall a couple of years ago looking at a catalogue of NEAs and noticing that very few get above 60 degrees above the ecliptic.

There is a full sky survey satellite up right now - NASA's Wide Field Infrared Survey Explorer (WISE). They've found a new 1km asteroid, with much more to come :-)

JR

[JohnHunt]

> There is a full sky survey satellite up right now - NASA's Wide Field Infrared Survey Explorer (WISE). They've found a new 1km asteroid, with much more to come :-)

Great. Within 6 months WISE ought to find practically all of the remaining >= 1km NEAs. Correct? The odds that any one of them will be on a collision course (at any reasonable length in time) should be << 10%, Correct? So in 6 months it is likely that we'll be confident that humanity won't be threatened with extinction from asteroids. Or am I missing something?

If they estimate that WISE will detect 100,000 asteroids then when I look at the chart (1) it means that it will detect all of the asteroids down to about 120m diameter. Granted, there'll be a sigmoid-shaped taper off at that point so let's say that WISE will detect 50% of asteroids at 120m and so will pick up some smaller and will miss some larger.

Still, 120m would equal about 100 megaton? explosion which would still be really devastating. Double the power of the Tsar Bomba.

(1) http://www.spaceobs.com/perso/recherche/NEA2002/NEA2002.htm
(2) http://geology.com/articles/asteroid-impact/asteroid-impact-frequency.gif <-- I'm getting an order of magnitude conflicting information compared with other web sources.

[joertexas]

Great. Within 6 months WISE ought to find practically all of the remaining >= 1km NEAs. Correct? The odds that any one of them will be on a collision course (at any reasonable length in time) should be << 10%, Correct? So in 6 months it is likely that we'll be confident that humanity won't be threatened with extinction from asteroids. Or am I missing something?




Well, WISE doesn't have the coolant to do more than 1 1/2 full sky scans. I don't know what their camera resolution is, so I'm not sure how small of an object it can find. Even so, it should dramatically increase our asteroid list - we may even find a juicy new target to add to our mining wish list.

JR

[Rhyshaelkan]

Aye, while they are looking for threats, we can use such data for finding prospective asteroids to send a probe to. And then later a mining mission.

Orbital periods, inclination to solar equator, mass, density, possible makeup. All good data.

[JohnHunt]

Previously we have found asteroids by seeing if they move compared to a previous picture. If WISE can do only 1.5 full sky scans then I would be worried that maybe it wouldn't be able to understand what it is seeing. But it seems as though WISE distinguishes asteroids differently than Earth-based cameras. They show up as infrared objects. Is there any way that we could tell if an infrared object is an asteroid and not a brown dwarf for the remaining 1/2 of the sky that's not scanned the second time?

[joertexas]

Previously we have found asteroids by seeing if they move compared to a previous picture. If WISE can do only 1.5 full sky scans then I would be worried that maybe it wouldn't be able to understand what it is seeing. But it seems as though WISE distinguishes asteroids differently than Earth-based cameras. They show up as infrared objects. Is there any way that we could tell if an infrared object is an asteroid and not a brown dwarf for the remaining 1/2 of the sky that's not scanned the second time?

Actually, the WISE team is handing off their finds to ground based observers. Otherwise, the asteroids they find will be lost again.

JR

[JohnHunt]

So Joe, Isn't the purpose of WISE to detect infrared objects which cannot be detected on the ground? If WISE hands off new finds to the ground telescopes, will they even be able to confirm them?

[joertexas]

So Joe, Isn't the purpose of WISE to detect infrared objects which cannot be detected on the ground? If WISE hands off new finds to the ground telescopes, will they even be able to confirm them?

Yes, WISE is supposed to detect objects we cannot see. But, many of the asteroids can be seen, if the ground obsevers know precisely where to look. The other objects in question are dwarf stars and more distant (and slower moving, in relative terms) objects that can be plotted either with WISE's observations, or in conjunction with other space telescopes.

The asteroids are moving too qucikly for WISE to plot their orbits, ergo the need for oher observers to take up the slack. I don't know if every single asteroid will be visible from the ground, but they should be able to add quite a few entries to the catalog over the next few months.

JR

JR