View Full Version : Podcast: Asteroids Make Bad Neighbours

2007-Mar-27, 04:17 AM
This week we’re talking about asteroids. And not just any asteroids, but Near Earth Objects. How do astronomers find these things, why are they buzzing around the Earth, what are the chances we’ll actually get hit, and what would happen if we did get hit? ...

Read the full blog entry (http://www.universetoday.com/2007/03/26/podcast-asteroids-make-bad-neighbours/)

2007-Mar-28, 01:44 PM
Great headline - title. As they say, it is all about location.

2007-Mar-30, 09:25 AM
Hi, Fraser. Nice podcast. I always enjoy talks on NEOs.

I'm confused about something, though. Dr. Gay states that "If you knock the asteroid into 10,000 little pieces, all of those pieces are going to hit the planet," causing "total destruction of the planet Earth."

Why? This assumes that the pieces, as they spread out, will always stay withing a few hundred km of each other. If they spread out by even a few thousand kilometers, with the Earth being only a few thousand kilometers wide, we'd be missed by at least a few. But why would the fragments stay so close together? They won't have enough gravity to halt their spreading. If they did, they would fall back together and reform the original asteroid. They should continue spreading out from each other indefinately. Once their average spacing exceeds 1 Earth diameter, we can rest comfortable that most of them will miss the Earth.

Of course this requires that we "nuke" the asteroid far in advance. If we nuke it hours before it is about to hit the Earth, like in the movies, then I would agree with Dr. Gay. But all her proposals, such as the gravity tractor, pushing it with space ship, etc. must be done far in advance as well.

If we were to discover today that Apophis would hit us in 2029, nuking it "into 10,000 little pieces" would have a huge advantage. We can do it now. We've already developed nuclear weapons. We've already hit a comet with a projectile. And the 20 years the fragments have to spread out in their orbits would create a low probability that we would get hit by any of them. But we'd be hard pressed to design, build, and test a gravity tractor in time. And the gravity tractor works best for avoiding a possible 2036 hit by pulling Apophis a little off course before its 2029 close encounter to magnify the orbit-altering effect the 2029 Earth passage will have on this asteroid.

Another advantage of "nuking it" is that we don't have to worry about the error bars on our orbit calculations. Since the "nudging" methods work best a few decades in advance, and we might not know to a precision of a few thousand kilometers where this asteroid might be 20 years in the future, we might accidentally be "nudging" it from a near-miss trajectory to a collision trajectory. But waiting long enough to precisely plot its orbit might cost us the time we need for our nudge to have an appreciable effect. But nuking something that is on course to hit Earth, and nuking something that is on a near-miss trajectory both result in not being hit.

You asked Dr. Gay if blowing up an asteroid would be creating a situation "sort of like the Shoemaker-Levy 9 collision with Jupiter." She responded "Exactly". But there's a huge difference. SL9 was in orbit around Jupiter when it was fragemented by passing within Jupiter's Roche limit. And it remained in orbit around Jupiter until its demise. The fragments had no chance to spread out in their solar orbit because their primary orbit was around Jupiter. This could only be analgous to a NEO if we found one that was actually orbiting Earth. But there are no asteroids orbiting Earth. If there were, then I'd agree that nuking it would be a bad idea.

Terry Gush
2007-Apr-03, 02:38 AM
One day after this podcast came academic tussel, http://news.bbc.co.uk/2/hi/science/nature/6503543.stm

There is no way to tell for sure if these nine huge undersea basins are craters without taking core samples and testing for traces of Iridium (common in asteriods but not common on Earth's surface) right?

2007-Apr-24, 08:38 AM
Hi, I don't have the greatest understanding of astronomy, so hopefully someone has a simplified answer for me. I thought this article really explained many aspects of asteroid studies quite well and understandably too. My questions concerns whether all >1km asteroids will be found if they are outside the plane of the ecliptic. From the article she says:
"Nowadays there are multiple telescopes set up around the planet that scan each part of the sky along the ecliptic five times in a given night. They're constantly going through processing, looking for things and discovering new things on a regular basis and calculating the orbits in rapid fire"
"There's a bunch of different programs that go out and take picture after picture after picture of areas specifically along the ecliptic in the sky. This is the area in the sky that the sun travels through and where we see all the planets. More or less, the majority of the asteroids and comets confine themselves to the ecliptic. There are some exceptions, things get thrown around through gravitational interactions and to find asteroids and comets, they look for things that move in their pictures"
So what about the other areas of the sky not on the ecliptic-Are systems in place that cover those others areas too? Thanks...

2007-Jun-07, 04:23 AM
This really dosent bother me all that much, the earth getting hit by a NEO. I think that this would be the way to...die i guess is the best word for it. I think that it would be cool to watch a meterorite come through the atmosphere right at you...i mean you wouldent feel any pain, it would be fast and iv always wanted to die from something from space. But thats just my opinion.

2007-Jun-09, 08:06 PM
All asteroids will pass through the ecliptic. We ambush them there.