The Undiscovered Country of Small Bodies

What We can Learn from Near Earth Objects

This radar image of asteroid 2005 YU55 was obtained on Nov. 7, 2011, at 11:45 a.m. PST (2:45 p.m. EST/1945 UTC), when the space rock was at 3.6 lunar distances, which is about 860,000 miles, or 1.38 million kilometers, from Earth. Credit: NASA/JPL-Caltech (Click to enlarge.)

A couple of weeks ago many people were startled to learn that a space rock—an asteroid called 2005 YU55—was about to pass just inside of our Moon’s orbit. This tumbling piece of debris is big enough that a decent-sized ocean liner could fit inside it, and its 1.22-year orbit occasionally brings it close to Earth. This time, we were in no danger of an impact from it during the November 8th flyby.

Scientists took the opportunity to study the asteroid in great detail. The radio astronomy community was all over it. The Arecibo radio telescope, the Very Long Baseline Array, the Green Bank Telescope, and the Goldstone telescopes all focused on 2005 YU55. The Herschel Space Telescope also looked at the asteroid in far-infrared light, which helps us understand the temperature of the asteroid and what it’s made of.

In particular, astronomers used the Goldstone Deep Space Antenna to bounce radar signals off the asteroid and then examine the data to see what this baby looked like. The movie below shows a series of the highest resolution radar “images” ever taken of a near-Earth object. The movie consists of six frames made from 20 minutes of radar data, and is a work in progress. Word is there will be another, more detailed movie released here after astronomers get through analyzing all the data—perhaps in a week or two.

2005 YU55  rotates on its axis once every 18 hours, so what you see below is five repetitions of the same loop, and the loop shows the rotation faster than in real time.

What About NEOs?

So, I’ve had people ask me what NEOs mean. The close passage of this one raised concerns again about what we would do if such a rock were headed straight toward our planet. Obviously if it had hit Earth, 2005 YU55 would have dug out a crater about six kilometers across (nearly four miles) if it had impacted on solid ground. The consequences could have been pretty severe. Of course, the asteroid didn’t hit, for which we all breathed a sigh of relief.

But, that’s not to say that Earth is safe from a collision with one of these orbiting space rocks. It turns out the solar system is peppered with them, and in particular, the region we inhabit (the inner solar system) has a good-sized population of these rocks. They’ve BEEN around since the earliest history of the solar system. In fact, populations of such objects were spread out across much of the proto-solar nebula. They were the precursor “worldlets” that combined and collided to form the larger bodies such as Earth, the Moon, and so on. What we have now are the ones that didn’t participate in that early solar system tango to create worlds. They still zip around in their own orbits, and occasionally get close enough to another world (like Earth) to pose a collision threat.

There are communities of scientists who track these objects (once they’re discovered) and do a good job of assessing the chances of impact, near misses, and close encounters. You can read their work at the Web page for NASA’s Near Earth Object Program , the Minor Planets Center , and at the European Space Agency’s NEO’s pages here and here.

There are a number of search programs called asteroid surveys that constantly watch the sky and catalog just about everything that moves. They are scattered around the world, and you can see a list of the major ones here.  These surveys aim to find as many NEOs as possible, down to the limits of what they can see. Planned future surveys will need to use ever-more sensitive detectors to find smaller and dimmer objects with orbits intersecting Earth’s.

So, what can we learn about these NEOs as they whiz by? The radar imaging you saw in the movie here tells scientists something about the surface characteristics of an object. That is, is it cratered, does it have other surface features like hills or outcrops? What is its shape? Sometimes they can figure out what its surface is made of—that is, the minerals that make up a rocky asteroid, for example. And, by sussing out the composition and “look and feel” of these asteroids, we learn more about the raw materials that made up Earth and other worlds. We find out what conditions were like in various parts of the solar system during the early days when these types of objects were forming, colliding, and contributing themselves to build larger worlds. So, in a sense, these asteroids are historical treasure troves that give us a look at the early history of the solar system. In another sense, the ongoing discovery of NEOs also tells us about their distribution—that is, how many of them there are and WHERE their orbits are in the inner solar system.

NEOs have always been there, folks. As I mentioned above, the solar system was born with an inventory of these guys, and over time they collide with planets and Sun. The inner solar system’s collection of NEOs is constantly being replaced by asteroids that migrate from the main Asteroid Belt, or from objects that are bumped from their orbits out near Jupiter and Saturn and sent inward toward the Sun.

Currently we’ve discovered most of the larger ones. In recent decades, we’ve developed much better detectors to find the smaller near-Earth objects (the size of city blocks, for example). Most are so small and so dim (their surfaces can be as dark as charcoal, which makes them hard to spot, particularly when they’re little guys).

Once a NEO is discovered, scientists have to make many observations of it to pin down its orbit very accurately. This is like watching a plane land: the more observations you have of that plane, the more accurately you can figure out its path to its landing site. In the days after a NEO discovery, scientists are very careful to point out that their calculations of the object’s orbit and trajectory are preliminary AND that the orbital parameters will change as more observations come in. This is completely normal and nothing to worry about. Yet, I often see people, particularly in the media or as part of the conspiracy theory crowd ignoring that fact and getting all upset because they think scientists are hiding information or aren’t telling the truth.

The truth is that calculating orbits, particularly when you want to figure out whether or not something will impact us, requires observations over a long period of time, and those observations should be very precise. It’s not an overnight job— it’s like any other quality work—it reflects the amount of time and effort put into it. We pay our scientists well to do their jobs, and so it’s only fair to LET them DO their jobs without having people screech about it.

I’ve also seen a lot of nonsense on the Web about how NEOs can change our magnetic fields or shift our polar axes or how they are being hidden by NASA/ESA/whoever. Such speculations are the work of people who either don’t know much about the reality of NEOs (or about the laws of physics for that matter) or don’t care to know because they can get more attention by making stuff up and then posting their “fantasies” on the Web. That’s the politest way I can term such nonsense. There’s good, solid science behind the discovery and characterization of NEOs, and I wish people would pay more attention to THAT. The universe is always much more fascinating and wondrous than our imaginations can dream up.

So, to sum up: NEOs are fascinating rocks from space. Sure, they can pose a threat, and we should be looking for ways to mitigate that threat. But, in the larger sense, NEOs hand us a unique chance to learn more about our neck of the woods, by giving us a look at what was once the undiscovered country of small bodies of the solar system.

(Special thanks to Dr. Paul Chodas at NASA/JPL for his insights on these NEOs. If you want to read more commentary about NEOs, check out David Ropeik’s discussion of impact risks here , and Alan Boyle’s comments on CosmicLog at MSNBC. Both of their blog entries were written after a workshop about communicating risks of NEO impacts, sponsored by the Secure World Foundation that I and a number of other scientists and writers attended this past week.)

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