Asteroid 2005 YU55 photographed in passing…Credit: NASA

November 9, 2011: It was a reminder for the neighborhood (Earth and Moon) that strangers pass in the night. Night being metaphorical in this case because the asteroid 2005 YU55 actually took about three days to orbit through the vicinity of the Earth and Moon. As asteroids go, YU55 is fairly large, about 400 meters (1300 ft) wide, what Americans would call a city block. If it collided with Earth it would make a helluva bang, on the order of many megatons of TNT, roughly a nuclear bomb that would make a crater 6.4 km (4 miles) across and 518 meters (1700 ft) deep. Of course, it didn’t this time and probably won’t collide with the Earth in the future; so it serves as a reminder that such asteroids are around and collisions can happen. In fact, because 2005 YU55 also passes close to Venus and Mars during its long orbit, it is subject to gravitational and other forces that can alter its path. Current calculations indicate that despite changes caused by Mars or Venus, the asteroid still will not be anywhere near collision course with Earth when it comes back around 2041, however, there is a margin of error.

First seen in 2005 (hence the provisional name, 2005 YU55), this particular asteroid passes between the Earth and Moon with 319,000 kilometers (198,000 miles) to spare at its closest point to the Earth. It’s too far away and too small to be seen by the naked eye, but professional and amateur astronomers will have a day in the field spotting, tracking and studying the relatively infrequent event. The next such ‘near miss’ (to put it with as much dramatic spin as possible) will be in 2028 when asteroid 2001 WN5 swings by for a passing visit.

These passing asteroids, part of a group known as the Near Earth Asteroids are also the subject of a NASA mandate for a human landing. 2005 YU55 might, in fact, be a candidate. Asteroids present an interesting opportunity to ‘hitch a ride’ through the solar system, while at the same time extracting metals and minerals too heavy to be lifted in quantity from Earth. Since asteroids have negligible gravity, it would in theory be easier to ship heavy material from them than to fight the gravity well of any planet or moon.