The approach of the large asteroid 2003 SD220 is a great opportunity to obtain detailed radar images of its shape and surface and to improve understanding of its orbit.
The asteroid reached a maximum approach of 2.9 million kilometers on Dec. 22, closest in more than 400 years and by 2070, when something else is approaching, but without risk to our planet.
Radar images reveal an asteroid with a length of at least 1.6 kilometers and a shape similar to that of the exposed hippo that occupies the river.
They were received from December 15 to 17, coordinating observations with NASA's 70-meter antenna at Goldstone, the 100-meter Green Bank telescope. The National Science Foundation and the 305-meter-wide antenna at the Arecibo Observatory in Puerto Rico.
The Green Bank telescope was a receiver of powerful microwave signals transmitted from Goldstone or NASA-funded NASA-based planetary Radar radar in what is known as "biatronic radar configuration". The use of a telescope for transmission and another for receiving can produce substantially more detail than the telescope, and this is an important technique for getting radar images of asteroids that are approaching and rotating slowly like this one.
"Radar images have reached unprecedented levels of detail and are comparable to those obtained by spacecraft," said Lance Benner, a reactive nozzle laboratory in Pasadena, California, in charge of Goldstone observation.
"The characteristic of the most visible surface is a known ridge that seems to circle around the asteroid near an edge. The reef extends about 100 meters above the surrounding terrain. Many small light spots are visible in the data and can be reflections from the rocks, the same so, they show a group of dark, circular features near the right edge that can be craters. "
The images confirm what was noted in previous measurements of sunlight reflecting the asteroid and previous radar images of Arecibo: 2003 SD220 has an extremely slow period of rotation of about 12 days. It also appears to be a complex rotation somewhat similar to a weakly launched football. Known as the "non-main axis" rotation, it is rare in asteroids near the Earth, most of which revolve around the shortest axis.
With resolutions as much as 3.7 meters per pixel, the details of these images are 20 times finer than those obtained during the asteroid approach to Earth three years ago, which was at a greater distance. New radar data will provide important constraints on the density distribution of the asteroid's interior, information available in very few asteroids near Earth.
"The new details we have discovered, up to the geology of the 2003 SD220, will allow us to reconstruct the shape and rotational state, as Bennu did, the goal of the OSIRIS-REx mission," said Edgar Rivera-Valentine, a USRA scientist in LPI. "Detailed form refinement allows us to better understand how these small bodies were formed and evolved over time."
2003 SD220 The asteroid was discovered on September 29, 2003 by astronomers at the Lowell Observatory. It is classified as a "potentially dangerous asteroid" due to its size and approaches to orbit on Earth. However, these radar measurements further improve the understanding of the orbit of the 2003 SD220, confirming that this does not pose a threat to future impact on the Earth.