Radar Studies of Asteroids

This is 253 Mathilde, a heavily cratered main-belt asteroid viewed in June 1997 by the Near Earth Asteroid Rendezvous spacecraft.  Mathilde is made of dark, carbon-rich material which is relatively unchanged from 4.6 billion years ago.  Other asteroids have undergone thermal metamorphism, and a few are largely metallic.  We are now beginning a two-year radar survey of main-belt asteroids, focusing on carbonaceous objects like Mathilde.

Chris Magri has spent the past five years carrying out radar studies of asteroids, concentrating on the main belt between Mars and Jupiter.  Powerful transmitters and large telescopes enable us to detect faint radio echoes from these small, rocky objects.  Analysis of the echoes helps to determine the target's size, shape, smoothness, rotation state, and surface composition -- in turn giving clues to the history of the solar system.  In 1999 Dr. Magri and his collaborators at NASA's Jet Propulsion Laboratory statistically analyzed the 37 main-belt asteroids detected by radar up to that point and published their findings in the planetary science journal Icarus.  Since then, new observations carried out at the world's largest single-dish telescope, the Arecibo Observatory in Puerto Rico, have more than doubled the number of detections and have provided detailed information on an exotic "dog bone" asteroid.

Here is a portion of the radar Doppler spectrum of the newly detected main-belt asteroid 198 Ampella, covering the frequency range -600 Hz to +600 Hz.  Ampella's echo is mostly in the opposite circular (OC) polarization to that transmitted, indicating a smooth surface and uniform subsurface layers at scales from centimeters to meters.

Here's a full view of the spectrum.

We conducted radar imaging of 216 Kleopatra in November 1999, learning that it is a metallic dumbbell the size of New Jersey.  The paper describing our results made the cover of the journal Science on May 5, 2000.  Similar observations of other main-belt asteroids are in progress, using the recently upgraded Arecibo telescope.

Here's more on Kleopatra.

For more information, contact Dr. Chris Magri

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