Operating a newly installed electronic camera pointed at the night sky from atop Maui's Haleakala volcano, NASA astronomers have discovered four new Earth-crossing asteroids and a fast-moving comet, just months after initiating a new near-Earth asteroid and comet discovery program.
The camera -- called NEAT, for Near-Earth Asteroid Tracking system -- enabled astronomers at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, to make their first discovery of a new long-period comet on March 15, the first night of the monthly observing program. The comet was officially designated 1996 E1, after confirmation was received from observers in Maui, Australia, Japan, the Czech Republic and Camarillo, CA.
"This relatively bright, magnitude 16 comet was discovered in the constellation of Cancer," said Dr. Eleanor Helin, principal investigator of the NEAT camera team at JPL. "Its closest approach to Earth, at about 30 million miles, occurred at the end of March."
Four unusual Earth-crossing asteroids also were discovered using NEAT, which is the world's first autonomous imaging system. These near-Earth asteroids have been designated 1996 EN, 1996 EO, 1996 FR3 and 1996 FQ3.
Two of the discoveries -- 1996 EN and 1996 FR3 -- are classified as "potentially hazardous asteroids," capable of coming exceedingly close to the Earth.
"All are noteworthy for different reasons," Helin said. "1996 EN is a large, 1.8 mile-diameter asteroid which moves in a very elliptical orbit and displays a high inclination of 39 degrees relative to the ecliptic plane. As a result of its brightness at magnitude 15.5, and its placement with respect to Earth, it will be accessible for observations through the end of the year."
Of the other Earth-crossers, 1996 EO has a diameter of a little more than 1/2 mile. It is not on a collision course with Earth, but asteroids of this size and larger have been identified by the scientific community as sufficient to cause severe damage over a large area of Earth should one impact the planet, Helin noted.
Significant because it moves in a long elliptical orbit extending well inside the orbit of Venus, 1996 FR3 is one of only a handful of asteroids that passes so close to the Sun. Astronomers speculate that this object may be an extinct comet, having passed close to the Sun enough times to have lost its gaseous atmosphere.
About 328 feet in diameter, 1996 FQ3 is a small near-Earth asteroid with an absolute magnitude of 21. Although small, Helin believes this asteroid may prove to be a possible candidate for a future spacecraft fly-by mission, given its very low inclination of one degree relative to the ecliptic plane.
"These discoveries certainly suggest that we could face a surprise encounter with a large, unseen object," Helin said. "If these newly discovered Earth-crossing asteroids have not been seen before, then there is strong evidence that many others are near the vicinity of Earth and the inner planets, which NEAT and other programs are designed to discover."
March was the first "good weather" month for NEAT astronomers since the new electronic camera came on-line in December 1995, said Dr. Steven Pravdo, manager of the project at JPL. The March observing run alone produced more than 1,000 asteroid sightings, including high-inclination inner-belt asteroids and a number of potential Mars-crossers. Total detections since NEAT went on-line in December 1995 have climbed to more than 2,400 objects, of which about 45 percent are known objects and more than 200 to date are new discoveries receiving new asteroid designations.
When the camera is upgraded later this month to use a very large 4,096 by 4,096-pixel charge-coupled device (CCD), astronomers expect to detect four times the number of comets and asteroids currently being observed.
Developed at the JPL, the NEAT system and its operation mark the beginning of a new era in observing programs focused on discovering and tracking asteroids and comets -- fleeting chunks of rock and ice -- as they enter the inner solar system from deep space. The autonomous imaging system contains a sophisticated computer controller and a highly sensitive CCD camera sensor "that will significantly improve our capabilities to detect near-Earth objects," Pravdo said.
The NEAT camera is installed on a 39-inch telescope operated at the summit of Mt. Haleakala by the U.S. Air Force. With its short exposure time and fast electronics, NEAT is able to achieve wide-sky coverage and detect objects much fainter than was possible using the photographic Schmidt telescope at Palomar Observatory in Southern California.
Systematic searches for asteroids and comets destined to cross Earth's orbit have been the topic of renewed interest in recent years, especially in the aftermath of Comet Shoemaker Levy-9 and the recent arrival of Comet Hyakutake. Today charge-coupled devices -- light detectors made of silicon -- are emerging as a favored approach to asteroid detection because CCD sensors can record light 100 times more efficiently than the most sensitive photographic film.
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