An Asteroid Could Smash Us
Edward M. Sion is a Professor of Astronomy and Astrophysics at Villanova University. He received a B.A. in Astronomy from the University of Kansas in 1968, an M.A. in Astronomy from the University of Kansas in 1969, and a PhD in Astronomy from the University of Pennsylvania in 1975. His primary research interests include the formation and evolution of white dwarf stars, the physics and evolution of cataclysmic variable stars, and theoretical studies of accretion physics.
Question: What hazards exist in outer space that could pose a grave threat to Earth?
Ed Sion: Well one of the scenarios is the one regarding what our press release was about, concerning T Pyxidis. But I think that most scenarios now, for example, trying to account for the mass extinctions that have occurred throughout geological history that the, for example, the gamma ray burst. A burst of gamma rays from a very massive star that collapses on itself with a prompt formation of a black hole, and then with gamma ray jets that, if they’re oriented just right, the gamma ray burst will be directed at Earth. These could be potentially devastating, the gamma ray bursts.
In addition to that, there is a lot of debris in our solar system that was part of the fundamental building blocks of the solar system. Primordial matter is what we call it. Pristine chemical composition. There’s been no chemical alteration. The comets are good examples of that. And some of the asteroids are pretty primitive, that is they have a composition that is very pristine and primordial. It has been altered by geological evolution. That is, they haven’t been incorporated in large bodies that undergo geological evolution. So, these are the basic building blocks. Well, these building blocks, they’re out there and of course they can potentially collide with the planets, including Earth. And in fact this is how we think the moon originated.
The most widely held theory for the origin of the moon is the giant impacter theory where billions of years ago, after Earth had developed an iron core, after it had what we call it differentiation, where the heavy elements sink to the center of a newly formed planet and the lighter elements float to the surface because of their different density, that Earth once it differentiated early in the history of the solar system when collisions with other bodies was more frequent, earth was struck by a Mars-sized intruder body. That then liquefied a large portion of the Earth’s mantel at the collision site and ejected this liquid rock out into space. This liquid rock then cooled and solidified and then reassembled itself by gravity and that’s what we have now, according to this theory as the present day moon. It eventually then suffered other collisions, the moon suffered other collisions. That gives us the Man in the Moon appearance. The lunar seas, for example, those blue patches are actually gigantic impact basins that have been flooded with lava, with liquid rock during lunar volcanism, during volcanic activity in lunar history.
So, these collisions happened much more frequently in the past, but that doesn’t rule out that they can’t happen now. So, I think it’s an area that is really deserving of a lot of exploration as is being done now.
Question: How do you rate the danger of an asteroid or comet impact happening within our lifetimes?
Ed Sion: Well, within the human lifespan, it’s a very, very low probability. But on the other hand, one cannot rule it out. There are three families of asteroids that actually have the potential of colliding with Earth, the Amore Asteroids, the Apollo Asteroids, and the Aten Asteroids.
The Apollo Asteroids actually have orbits that are internal to Earth’s orbit and they’re perhaps the most likely, the Apollo Asteroids. And they are being monitored very carefully by telescopic patrol observatories that have been set up. And if one of the Apollo Asteroids were to enter into collision course with Earth, hopefully we’d have enough warning, but we do in fact have the technology now and in the future to intercept and possibly deflect such a body. But during the span of a human lifetime, it’s not likely. It’s rather improbable that something large enough to do a great deal of devastation of the globe would happen.
Now, there was an event in 1908, the Tunguska event, that appears to be a porous primitive asteroid that detonated, that exploded above the ground and this leveled an entire forest in central Siberia near the Tunguska River. But fortunately the area was very sparsely populated and there were no recorded human fatalities. But if that event had happened a few hours before, in other words, if it had happened – if the detonation had happened over the ocean, that could have generated tidal waves, tsunamis, and that could have had a devastating effect on the coast lines. So, it was really a lucky thing that the Tunguska even occurred over central Siberia and not over a populated area. Like for example in Western Europe.
Question: What would actually happen if an asteroid or comet threatened us in the near future?
Ed Sion: Well, I presume that our leadership would meet with NASA officials and plan to intercept such a body with either a kinetic energy device, a missile that would ram into it, but they would have to be very careful because you don’t want to fragment it too much. You don’t want to fragment it in such a way that the fragments themselves would enhance the devastation. So, you want to make sure it has to be carefully calculated. But I think this kind of scenario has been anticipated and I think that both with our space program, with other space programs, the Russian space program, the Chinese, I think there are plans in case of such an event. And of course you would want to avoid worldwide panic and that kind of thing. I think the details remain to be seen, but such plans have been in the works in case of, for example, an Apollo Asteroid being perturbed into a collision with us, with Earth.
Recorded on January 20, 2010
Interviewed by Austin Allen
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