“Vermin of the Skies”

The JPL scientist in charge of tracking incoming asteroids tells us if we should be worried.

Artist's conception of asteroid 2012 DA14 passing through the Earth-moon system on Feb. 15, 2013. (NASA/JPL-Caltech)

Don Yeomans is a senior research scientist at NASA’s Jet Propulsion Laboratory, where he manages the Near-Earth Object Program Office. His latest book, Near-Earth Objects: Finding Them Before They Find Us, briefly chronicles the major asteroid strikes on our planet and the ongoing search to find others that might be headed our way. A review of his book will be published in an upcoming issue of Air & Space. Yeomans spoke with associate editor Heather Goss about the search for near-Earth objects.

Air & Space: You explain in the book that this concept of “rocks from space” is relatively new, and that the astronomers who first encountered them called them “vermin of the skies.”

Yeomans: Oh yeah, that’s great.

Can you explain how our awareness of asteroids evolved, especially in the last couple of decades?

The first asteroid was discovered on January 1, 1801. They were expecting to find a planet between Mars and Jupiter, because there’s a bit of a gap and people were convinced there should be a planet there. When they found it they said, “Ah! We were right, there is an extra planet there.” It was called a planet for a while but then a few years later they found another one, and then a few years later yet another, and it became obvious pretty soon that there wasn’t just one “planet” between Mars and Jupiter, but several.

Even so, it was slow going for a long time. The first near-Earth asteroid was discovered in 1898 – Eros – and that was considered a bit of an oddity because back in the 1900s it was thought that the inner solar system was void of any [asteroid] material. Then, I think it was 1932, a couple of near-Earth asteroids were discovered one after another, Apollo and Amor, and so it was obvious that there are a few asteroids near Earth.

That was an era when they were using photography, and that really isn’t the most efficient way to find these objects. When astrophysicists were looking primarily at stars or galaxies, they would see these streaks of light that would be printed on their photographic film when they were taking long exposures, and they would curse them as the “vermin of the sky” because they disrupted their observations.

The discovery of near-Earth objects didn’t really take off until the 1990s, because that’s when [film] photography was replaced by CCD chips, very much like the chips that are in your camera or your cell phone. It wasn’t until the late 1990s that [the era of rapid near-Earth object discovery began when] NASA-supported observatories began using wide-field CCD-equipped cameras.

What is one of the most interesting things we’ve learned from the study of asteroids?

One thing they found is that some asteroids and all comets have organic material – carbon-based material. Comets [and some asteroids] have water-ice, and a lot of asteroids have hydrated minerals. So it’s very likely that the water and organic carbon-based materials that were resident on the early Earth and allowed life to form were probably delivered by impacts of these near-Earth asteroids and comets. Subsequent impacts by these objects, at a much reduced rate, punctuated evolutions, allowing only the most adaptable species to progress further, like mammals, so in a sense we owe our very origin and our position at the top of the food chain to these objects impacting the Earth a few billion years ago.

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