Astronomers working with NASA’s Goldstone Deep Space Network, NSF’s Green Bank Telescope and Arecibo Observatory’s 1,000-foot (305-m) antenna have released the first radar images of a big near-Earth asteroid called 2003 SD220. The asteroid flew past Earth on Saturday, December 22, 2018, at a distance of about 1.8 million miles (2.9 million km). This was the asteroid’s closest approach in more than 400 years and the closest until 2070, when the asteroid will safely approach Earth slightly closer.
These three radar images of near-Earth asteroid 2003 SD220 were obtained on December 15-17, 2018. Image credit: NASA / JPL-Caltech / GSSR / NSF / GBO.
Asteroid 2003 SD220 was discovered on September 29, 2003, by astronomers at the Lowell Observatory Near-Earth-Object Search (LONEOS).
The object is classified as being a ‘potentially hazardous’ asteroid because of its size and close approaches to Earth’s orbit.
The radar measurements refine the understanding of 2003 SD220’s orbit, confirming that it does not pose a future impact threat to Earth.
The radar images show that the asteroid is at least one mile (1.6 km) across and has a shape similar to that of the ‘exposed portion of a hippopotamus wading in a river.’
“The images achieve an unprecedented level of detail and are comparable to those obtained from a spacecraft flyby,” said Dr. Lance Benner, a researcher at NASA’s Jet Propulsion Laboratory.
“The most conspicuous surface feature is a prominent ridge that appears to wrap partway around the asteroid near one end. It extends about 330 feet (100 m) 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 show that 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.
“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 Dr. Patrick Taylor, senior scientist with Universities Space Research Association at the Lunar and Planetary Institute.
“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 Dr. Edgard Rivera-Valentín, also from Universities Space Research Association at the Lunar and Planetary Institute.
“Detailed shape reconstruction lets us better understand how these small bodies formed and evolved over time.”
