2010 JL33: How to see an asteroid from quite a long way away
Posted by Emily Lakdawalla
2011/01/13 11:42 CST
A terrific set of Goldstone radar images of a good-sized near-Earth asteroids named 2010 JL33 was posted to the JPL website yesterday. They also posted a movie version but something about these pixelated radar image series absolutely begs for them to be displayed as an old-school animated GIF, so I made one. I am amazed by how much detail of the shape of this 1.8-kilometer-across asteroid you can see with "images" that are constructed from radio signals that were broadcast from Earth, through 8.5 million kilometers of space, bounced off a small dark rock, and traveled all the way back, a trip that took 56 seconds.
The animation consists of 34 radar images of near-Earth asteroid 2010 JL33 taken by the Goldstone radio telescope on December 11 and 12, 2011. According to the JPL website, the radar observations reveal that "2010 JL33 is an irregular, elongated object roughly 1.8 kilometers wide that rotates once every nine hours." The image advisory went on to explain something that I hadn't previously known about radar imaging of asteroids -- namely, that while the larger Arecibo telescope is more sensitive (it can detect smaller or more distant asteroids), the smaller Goldstone telescope can get sharper images of the same object:
The 70-meter (230-foot) Goldstone antenna in California's Mojave Desert, part of NASA's Deep Space network, is one of only two facilities capable of imaging asteroids with radar. The other is the National Science Foundation's 1,000-foot-diameter (305 meters) Arecibo Observatory in Puerto Rico. The capabilities of the two instruments are complementary. The Arecibo radar is about 20 times more sensitive, can see about one-third of the sky, and can detect asteroids about twice as far away. Goldstone is fully steerable, can see about 80 percent of the sky, can track objects several times longer per day, and can image asteroids at finer spatial resolution. To date, Goldstone and Arecibo have observed 272 near-Earth asteroids and 14 comets with radar.
You can see lots more radar images of asteroids at echo.jpl.nasa.gov, a site that's now maintained by Lance Benner.
A note on my processing of this animation: radar images of asteroids have a "snowy" or "noisy" quality to them. I find it easier to pick out the large-scale details in these animations when I apply a Gaussian blur to the individual frames. The blurring does reduce the overall quality of the data. But the human eye wants to track bright spots as though they move coherently from one frame to the next, even there's no systematic motion in that background noise; I find that blurring the images reduces the visual distraction. JPL's version of the animation has no such blurring, if you want to see its original appearance.