Near Mars Object

Victoria Crater on Mars, similar in size to the crater the
near-Mars asteroid 2007 WD 5 would have produced.
Credit: NASA/Mars Reconnaissance Orbiter

The possibility that a sizable asteroid would strike the planet Mars on January 30th temporarily raised the excitement level in the astronomical community to a pretty high level in the last couple of months. We were even toying with the idea of having a 3:00 AM Mars Bashing Party at Chabot that morning.

At one point astronomers had given odds of 1 in 25 that asteroid 2007 WD 5, newly discovered in November, would collide with Mars--which are astronomically great odds for this sort of thing. Alas, further observations refined our knowledge of the big rock’s trajectory, and the probability declined, hitting rock bottom (0.0%) by January 9th.

Why blog about a non-event? I see it as an opportunity to talk about big rocks bashing planets in general--specifically, the Earth.

While we haven't witnessed an event like this one (a big impact on a solid, Earth-like planet), we have examined the remains of past events, on Earth as well as other planets and moons—such as the hole in the Arizona desert called "Meteor Crater," an impact basin roughly the size of what might have been gouged out on Mars by 2007 WD 5. And compared to the asteroid that is believed to have caused the extinction of the dinosaurs, the Meteor Crater impact was a pipsqueak!

Smaller objects hit the Earth, or its atmosphere, all the time: meteors and meteorites. Fortunately we haven’t experienced a larger impact for a very long time. There was a significant impact of some kind in 1908, over Siberia--but luckily that wasn't a major catastrophe.

Nevertheless, the possibility of a big impact on Earth is something to take seriously. NASA certainly does. They even have a program for it: the Near Earth Object Program, whose goal is to detect and track Near Earth Objects (NEOs) in order to warn of those that might eventually collide with the Earth. A NEO is defined as an asteroid or comet whose orbit carries it close to Earth. The program searches for NEOs that are 1 kilometer in size or larger--objects that would cause catastrophic local devastation and "severe global consequences."

Thus far, over 5,000 NEOs have been found, almost 800 of them 1 kilometer across or larger--and it is expected that there are plenty more out there that we haven't found.

So, is this a good idea? Do we really want to know that the end of the world is going to occur on such and such a date in the near future--or would it be better not to know, living our daily lives in blissful ignorance right up to the last, Earth-shattering day?

Well, whatever your philosophical approach to that question might be, there is a practical side to the NEO Program. If we can predict a NEO collision with enough advance warning, there may be something we can do to avert disaster. For example, we could send Bruce Willis out to destroy it... .

Seriously, though, NASA is working on methods of diverting the course of a NEO, possibly with a spaceship that acts as a sort of tug boat, gently nudging the NEO off course far enough in advance of the impact to make it eventually miss the Earth.

This month, however, Mars 1, asteroid 0. The Martians are quite relieved...

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.

latitude: 37.8768, longitude: -122.251