From: Ames Research Center
Posted: Friday, June 30, 2006
This edition of NEO News briefly discusses asteroid 2004 XP14, which on July 3 will be the best NEO radar target ever. However, most of the material below deals with the Congressional request to NASA to plan a new NEO program for the discovery, characterization, and defense against sub-km NEAs. There are two reports from the NASA NEO Workshop held this week in Colorado to study options for Discovery, Characterization, and Hazard Mitigation, down to NEAs with diameter 140 m. Also included is the text of the relevant Congressional request to NASA.
CLOSE PASS JULY 3 BY 2004 XP14
On July 3, 2006, our planet will receive a close visit by Near Earth Asteroid (NEA) 2004 XP14, which will pass by at 1.1 times the distance to the Moon (a little more than 400,000 km). This NEA was discovered in 2004 but was only recovered last week. There is no risk of its hitting either the Earth or the Moon, but it is unusually well placed for study, especially by radar. The asteroid will swing past us at a relative speed of 17 km/s.
While XP14 will not be visible to the unaided eye, its relatively large size (estimated at roughly half a kilometer) combined with its closeness makes it one of the best-placed targets for study in the history of planetary radar. Extensive observations are planned with the NASA 70-m radar at Goldstone, California, which is part of the NASA Deep Space communications network. It is anticipated that these radar studies will yield detailed images of the asteroid, as well as highly precise values for its orbit and spin state. Many NEAs have recently been found to have satellites, and the presence of a satellite will also be looked for with the radar.
This close pass by such a large asteroid has little historical precedent, but calculations show that a NEA this large comes this close about once per decade on the average. However, similar close passes in the past were not observed, since it is only in the past decade that the Spaceguard Survey has begun to inventory NEAs in this size range.
NASA NEO WORKSHOP
By David Morrison
On June 26-29, nearly one hundred scientists, engineers, astronauts, and managers from NASA, industry, and academia met in Colorado for an informal workshop to discuss how best to respond to NASA's new Congressional mandate to survey and characterize sub-km-diameter NEAs in order to understand and mitigate the threat of impacts by such objects. Following the model of the current Spaceguard Survey, which has a goal to discover 90 percent of NEAs larger than 1 km by the end of 2008, the new request from Congress is for NASA to develop a program to discover 90 percent of the NEAs larger than 140 m by 2020. The value of 140 m was derived in a 2003 NASA study that estimated that 90 percent of the risk of unpredicted impacts from sub-km NEAs could be eliminated (or retired) by extending the Spaceguard Survey down to 140 m diameter. (Full Congressional text is at end of this report).
Discussions at the NEO Workshop were grouped into three general topics: Discovery, Characterization, and Hazard Mitigation. In the areas of Discovery and Characterization, the presentations were about equally divided between techniques involving ground-based astronomy and those that required access to space. For example, both ground-based telescopes and space-based telescopes were described that suggested they could meet the 90 percent goal of 140 m and larger NEAs. In the area of characterization, suggestions were made for broadly-based surveys that could provide some additional information for a substantial fraction of the newly discovered NEAs, for surveys to characterize a small subset of these, and for approaches to be used for intense investigation of any NEA that might appear to be a real hazard. The techniques included ground-based telescopes, space-based telescopes, and missions to visit individual NEAs with spacecraft to orbit or land on the surface. Prominently discussed were recent results from the Japanese Hayabusa mission to asteroid Itokawa, the first sub-km NEA to be visited by spacecraft. (A series of technical papers describing Itokawa were just published in the June 6 issue of Science). Under Hazard Mitigation, almost all discussions assumed the requirement to actually deflect an asteroid on a collision course with Earth. Also receiving attention were issues of how much lead time we are likely to have, and under what circumstances different deflection techniques might be used. Prominent were the cases of Apophis, which has a low-probability of impacting in 2036, and 2004 VD17, with a low-probability impact in 2102 (see the NASA NEO Program webpage http://neo.jpl.nasa.gov for current information on these and the other 4000+ known NEAs)
The shift from emphasis on the NEAs larger than 1 km to the sub-km NEAs is a major one. The Spaceguard Survey has already discovered more than 75 percent of those larger than 1 km, and none is on a collision course. However, there are only about 1100 NEAs this large. In contrast, the number of NEAs larger than 140 m is approximately 100,000, and there may be as many as a million that are as large as the object that produced the Tunguska explosion in 1908. Discovery rates in the new surveys will have to be 100 times faster than the current Spaceguard System, and the orbit calculations and archiving of data will scale in the same way. As the survey progresses, many more potential targets for spacecraft missions will also be identified. However, these are at present just hopes and plans; a new survey has not yet been approved, nor any funds appropriated to support it. A formal report from NASA to the Congress will be made later this year.
CONGRESSIONAL TEXT ON NEW NEO PROGRAM
"The U.S. Congress has declared that the general welfare and security of the United States require that the unique competence of NASA be directed to detecting, tracking, cataloging, and characterizing near-Earth asteroids and comets in order to provide warning and mitigation of the potential hazard of such near-Earth objects to the Earth.
The NASA Administrator shall plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near-Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the survey program to achieve 90 percent completion of its Near-Earth Object catalogue (based on statistically predicted populations of near-Earth objects) within 15 years after the date of enactment of this Act.
The NASA Administrator shall transmit to Congress not later than 1 year after the date of enactment of this Act an initial report that provides the following:
(A) An analysis of possible alternatives that NASA may employ to carry out the Survey program, including ground-based and space-based alternatives with technical descriptions.
(B) A recommended option and proposed budget to carry out the Survey program pursuant to the recommended option.
(C) Analysis of possibly alternatives that NASA could employ to divert an object on a likely collision course with Earth."
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