Holiday Asteroid Imaged with NASA Radar
The asteroid will fly safely past Earth on Saturday, Dec. 22, at a distance of about 1.8 million miles (2.9 million kilometers).
The
December 2018 close approach by the large, near-Earth asteroid 2003 SD220 has provided
astronomers an outstanding opportunity to obtain detailed radar images of the surface
and shape of the object and to improve the understanding of its orbit.The
asteroid will fly safely past Earth on Saturday, Dec. 22, at a distance of about
1.8 million miles (2.9 million kilometers).
This will be the
asteroid's closest approach in more than 400 years and the closest until 2070, when
the asteroid will safely approach Earth slightly closer.The
radar images reveal
an asteroid with a length of at least one mile (1.6 kilometers) and a shape similar
to that of the exposed portion of a hippopotamus wading in a river. They were obtained
Dec. 15-17 by coordinating the observations with NASA's 230-foot (70-meter) antenna
at the Goldstone Deep Space Communications Complex in California, the National Science Foundation's
330-foot (100-meter) Green Bank Telescope in West Virginia and the Arecibo Observatory's
1,000-foot (305-meter) antenna in Puerto Rico.The Green Bank Telescope was the receiver for the powerful microwave signals transmitted by either Goldstone
or the NASA-funded Arecibo planetary radar in what is known as a "bistatic
radar configuration." Using one telescope to transmit and another to receive
can yield considerably more detail than would one telescope, and it is an invaluable
technique to obtain radar images of closely approaching, slowly rotating asteroids
like this one."The
radar images achieve an unprecedented level of detail and are comparable to those
obtained from a spacecraft flyby," said Lance Benner of the Jet Propulsion
Laboratory in Pasadena, California, and the scientist leading the observations
from Goldstone. "The most conspicuous surface feature is a prominent ridge
that appears to wrap partway around the asteroid near one end. The ridge extends
about 330 feet [100 meters] above the surrounding terrain. Numerous small bright
spots are visible in the data and may be reflections from boulders. The images also
show a cluster of dark, circular features near the right edge that may be craters."The
images confirm what was seen in earlier "light curve" measurements of
sunlight reflected from the asteroid and from earlier radar images by Arecibo: 2003
SD220 has an extremely slow rotation period of roughly 12 days. It also has what
seems to be a complex rotation somewhat analogous to a poorly thrown football. Known
as "non-principal axis" rotation, it is uncommon among near-Earth asteroids,
most of which spin about their shortest axis.With
resolutions as fine as 12 feet (3.7 meters) per pixel, the detail of these images is
20 times finer than that obtained during the asteroid's previous close approach
to Earth three years ago, which was at a greater distance. The new radar data will
provide important constraints on the density distribution of the asteroid's interior
- information that is available on very few near-Earth asteroids."This
year, with our knowledge about 2003 SD220's slow rotation, we were able to plan
out a great sequence of radar images using the largest single-dish radio telescopes
in the nation," said Patrick Taylor, senior scientist with Universities Space
Research Association (USRA) at the Lunar and Planetary Institute (LPI) in
Houston."The
new details we've uncovered, all the way down to 2003 SD220's geology, will let
us reconstruct its shape and rotation state, as was done with Bennu, target of the
OSIRIS-REx mission," said Edgard Rivera-Valentín, USRA scientist at LPI. "Detailed
shape reconstruction lets us better understand how these small bodies formed and
evolved over time."Patrick
Taylor led the bistatic radar observations with Green Bank Observatory, home of
the Green Bank Telescope, the world's largest fully steerable radio telescope. Rivera-Valentín will be leading the shape
reconstruction of 2003 SD220 and led the Arecibo Observatory observations.Asteroid
2003 SD220 was discovered on Sept. 29, 2003, by astronomers at the Lowell Observatory Near-Earth-Object Search (LONEOS) in
Flagstaff, Arizona - an early Near-Earth Object (NEO) survey project supported
by NASA that is no longer in operation. It is classified
as being a "potentially hazardous asteroid" because of its size and close
approaches to Earth's orbit. However, these radar measurements further refine the
understanding of 2003 SD220's orbit, confirming that it does
not pose a future impact threat to Earth.The Arecibo, Goldstone and
USRA planetary radar projects are funded through NASA's Near-Earth Object Observations
Program within thePlanetary Defense Coordination
Office(PDCO), which manages the Agency's
Planetary Defense Program. The Arecibo Observatory is a facility of the National
Science Foundation operated under cooperative agreement by the University of Central
Florida, Yang Enterprises and Universidad Metropolitana. GBO is a facility of the
National Science Foundation, operated under a cooperative agreement by Associated
Universities, Inc.JPL hosts the Center for Near-Earth
Object Studies (CNEOS) for NASA's Near-Earth Object Observations Program.More information about CNEOS,
asteroids and near-Earth objects can be found at:https://cneos.jpl.nasa.govhttps://www.jpl.nasa.gov/asteroidwatchFor more information about
NASA's Planetary Defense Coordination Office, visit:https://www.nasa.gov/planetarydefenseMore information about the National Science Foundation's
Arecibo Observatory can be found at:http://www.naic.edu/ao/For asteroid and comet news
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