Scientists working with NASA's 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, California, have released the first radar images of asteroid 2004 BL86. The images show the asteroid, which made its closest approach on Jan. 26, 2015 at 8:19 a.m. PST (11:19 a.m. EST) at a distance of about 745,000 miles (1.2 million kilometers, or 3.1 times the distance from Earth to the moon), has its own small moon.
The 20 individual images used in the movie were generated from data collected at Goldstone on Jan. 26, 2015. They show the primary body is approximately 1,100 feet (325 meters) across and has a small moon approximately 230 feet (70 meters) across. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are a binary (the primary asteroid with a smaller asteroid moon orbiting it) or even triple systems (two moons). The resolution on the radar images is 13 feet (4 meters) per pixel.
The trajectory of asteroid 2004 BL86 is well understood. Monday's flyby was the closest approach the asteroid will make to Earth for at least the next two centuries. It is also the closest a known asteroid this size will come to Earth until asteroid 1999 AN10 flies past our planet in 2027.
Asteroid 2004 BL86 was discovered on Jan. 30, 2004, by the Lincoln Near-Earth Asteroid Research (LINEAR) survey in White Sands, New Mexico.
Radar is a powerful technique for studying an asteroid's size, shape, rotation state, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than if radar observations weren't available.
NASA places a high priority on tracking asteroids and protecting our home planet from them. In fact, the U.S. has the most robust and productive survey and detection program for discovering near-Earth objects (NEOs). To date, U.S. assets have discovered over 98 percent of the known NEOs.
In addition to the resources NASA puts into understanding asteroids, it also partners with other U.S. government agencies, university-based astronomers, and space science institutes across the country, often with grants, interagency transfers and other contracts from NASA, and also with international space agencies and institutions that are working to track and better understand these objects.
NASA's Near-Earth Object Program at NASA Headquarters, Washington, manages and funds the search, study and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.
January 27, 2015 Update:
The Goldstone scientists observing 2004 BL86 are part of a team of astronomers from around the world who have been characterizing the asteroid. Spectroscopic observations of 2004 BL86 made by Vishnu Reddy, a research scientist at the Planetary Science Institute in Tucson, using the NASA Infrared Telescope Facility on Mauna Kea, Hawaii, indicate the asteroid's spectral signature is similar to that of massive asteroid Vesta. Located in the heart of the solar system's main asteroid belt, asteroid Vesta was the recent destination of NASA's Dawn mission, which is now on its way to the icy world Ceres.
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More information about asteroid radar research is at: http://echo.jpl.nasa.gov/
More information about the Deep Space Network is at: http://deepspace.jpl.nasa.gov/dsn
Media Contact: DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
Article Source: JPL Press Release 2015-033
Donald K. Yeomans, in his book "Near-Earth Objects, Finding them before they find us (2012)," suggests that 15% of all Near-Earth Asteroids are binaries: 232 asteroid satellites have been found in 209 systems, there are at least three triples, and one sextuple; I guess those figures need to be updated, but with the discovery rate of Near-Earth Objects, this will always be the case.
Another interesting way to discover binary asteroids is via the occultation method.
"An astronomical occultation (pronounced “occ-kull-tay-shun”) occurs when the Moon, an asteroid or another planetary body eclipses a star, momentarily blocking its light. Occultations are fun to observe, but more importantly they provide important scientific data on the occulting body, the occulted star or sometimes both! It is exciting to watch a star vanish and return from behind a lunar mountain, or to see the star disappear for several seconds as an asteroid passes in front of it. Anyone with a small telescope, tape recorder or camcorder and shortwave radio can make valuable scientific observations to help determine the size and shape of asteroids and to aid in new discoveries about these mysterious objects, including some of the elusive small moons that orbit them." ~Astronomical League