Recent observations have removed from NASA's asteroid impact hazard list the near-Earth object (NEO) known to pose the most significant risk of Earth impact over the next 100 years.
2007 VK184, an asteroid estimated to be roughly 430 feet (130 meters) in size, has been on NASA's Impact Risk Page maintained by the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory for several years, with an estimated 1-in-1,800 chance of impacting Earth in June 2048. This predicted risk translates to a rating of 1 on the 10-point Torino Impact Hazard Scale. In recent months, 2007 VK184 has been the only known NEO with a non-zero Torino Scale rating.
2007 VK184 was discovered in November 2007 by the NASA-funded Catalina Sky Survey (CSS) at the University of Arizona and tracked by the CSS and other stations for two months before moving beyond view of ground based telescopes in January 2008.
But in the early morning hours of March 26 and 27, 2014, David Tholen of the University of Hawaii sighted 2007 VK184 once again. Using the 3.6-meter-diameter Canada-France-Hawaii Telescope at the Mauna Kea Observatories in Hawaii, he was able to detect and track the asteroid. Because it had not been observed for almost six years, its predicted position was only approximate. Nonetheless, Tholen was able to find it within the predicted search region, which is called a "recovery." He measured the asteroid's position and movement relative to the background of stars, and forwarded his tracking data to the Minor Planet Center
(MPC) in Cambridge, Mass., the central node for the global NEO observer community.
Tholen said, "Although the asteroid will be closer to Earth and brighter in May, I made the recovery attempt in March because I didn't want the position uncertainty to grow so much that it would force a time-consuming search of much more of the sky. The trade-off was increased exposure time to detect such a faint, distant object. Greater atmospheric turbulence on March 26 blurred the images of the asteroid enough to make the detection questionable, but the March 27 images were much better and confirmed the recovery."
The "Sentry" asteroid monitoring system at JPL automatically retrieved the new observations of 2007 VK184 from the database run by the Minor Planet Center, updated the orbit for the object, and computed a new impact hazard assessment. This new work shows that 2007 VK184 will pass no closer than 1.2 million miles (1.9 million kilometers) from Earth in June 2048, with no closer encounters predicted for the foreseeable future. The NEO Program Office removed 2007 VK184 from the Impact Risk Page about three hours after receiving Tholen's observations from the MPC.
"While these new observations of 2007 VK184 were challenging for Dave Tholen to obtain, they were reported quickly, and the global, distributed NEO impact hazard monitoring system worked smoothly to provide the all-clear for this object," said Steven Chesley of the NEO Program Office at JPL.
NASA's NEO Program supports and monitors this process at every stage. The program funds and oversees the efforts of the Catalina Sky Survey, JPL's Near-Earth Object Program Office, the Minor Planet Center and Tholen.
JPL's Sentry is an automated monitoring system that continually scans the most current catalog of known asteroids and predicts potential hazards of impacts with Earth over the next 100 years. As additional observations become available, objects will be removed from Sentry's Impact Risk Page when sufficient data become available to eliminate any potential for impact in the projected future. According to the Torino Impact Hazard Scale, developed and used by NEO observers to assess potential impact risks, a rating of one indicates a predicted event that "merits careful monitoring," and a rating of zero indicates the predicted event has "no likely consequences."
Objects typically appear on the Sentry Impact Risk Page because a imited number of available observations may indicate a potential hazard of impact with Earth but do not provide astronomers enough information to precisely define their orbital movements. Whenever a newly discovered NEO is posted on the Sentry Impact Risk Page, the most likely outcome is that the object will eventually be removed as new observations become available, the object's orbit is more precisely known, and its future motion is more tightly constrained. NASA's NEO Program Office at JPL, which operates Sentry, receives asteroid observations and orbit predictions daily from the Minor Planet Center. Once an asteroid is classified as a near-Earth object, the Sentry system automatically calculates orbit updates for it as new data become available.
NASA's Near-Earth Object Observation (NEOO) Program, located in the Planetary Science Division of the Science Mission Directorate at NASA Headquarters in Washington, D.C., is responsible for finding, tracking and characterizing near-Earth objects (NEOs) - - asteroids and comets whose orbits periodically bring them close to Earth. The NEOO Program sponsors internal NASA and external research projects. The Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the NEO Program Office for the Headquarters' NEOO Program and conducts a number of NASA-sponsored NEO projects.
"Asteroid 2007 VK184 is another case study on how our system works," said Lindley Johnson, NASA's NEO Programs Executive at NASA Headquarters. "We find them, track them, learn as much as we can about those found to be of special interest -- an impact hazard or a space mission destination -- and we predict and monitor their movement in the inner solar system until we know they are of no more concern."
In conducting its work, the NEOO Program collaborates with other U.S. government agencies, other national and international agencies, and professional and amateur astronomers around the world. For example, NASA works closely with the Federal Emergency Management Administration and other federal government departments and agencies on NEO impact warning, mitigation and response planning. The program is responsible for facilitating communications between the astronomical community, the federal government and the public should any impact threat by an NEO be discovered.
Date: Apr 4, 2014