PUiodically crosses Earth's orbit was recently discovered by JPL planetary scientist Eleanor Helin, who found the asteroid while photographing two components of rare split comet.

       The asteroid has been calculated to be the best candidate known for an asteroid-rendezvous mission under study at JPL.

       The newly discovered body, l982 DB, is member of group of Earth-crossing objects called Apollo asteroids. They are maverick asteroids in unique orbits outside the main asteroid belt between Mars and Jupiter.

       Asteroids, of which there are thousands, are called minor planets, or planetesimals. They may be the remains of planet that was torn apart by collision or they may represent some of the original debris from which the planets and satellites coalesced. It is possible asteroids are chunks of planet that never formed.

       While near-Earth asteroids are potential hazards to Earth, they are also located close enough to Earth to be utilized for resources in the future.

       l982 DB, one of 34 known Apollo asteroids, made its closest approach to Earth in January, when it passed as close as 4.6 million kilometers (2.9 million miles). (The Moon is 384,375 kilometers, or 238,840 miles from Earth.) The asteroid is also especially accessible from Earth since it is nearly in the plane of the ecliptic -- the approximate plane of the solar system in which the planets orbit the Sun.

       Helin, who with Dr. Eugene Shoemaker of the U.S. Geological Survey, has conducted systematic search for asteroids and comets at Palomar Observatory for l0 years, discovered the new asteroid while obtaining follow-up observation of Comet du Toit-Hartley, which was last observed 45 years ago as single body. Observations were being made of the comet, which had split since its earlier apparition. Both components of the comet were recorded about one degree apart, on single photographic plate using the l.2 meter (4-foot) Schmidt telescope at Palomar. In between the two cometary bodies Helin found the characteristic streak of the new asteroid -- l982 DB.

       "To obtain an observation of split comet _a_n_d this object in that position in the sky is quite extraordinary," Helin said of the discovery.

       When the asteroid was found it displayed retrograde motion in relation to the Earth.

       Observations from the Kitt Peak Observatory in Arizona and the Mauna Kea Observatory in Hawaii are underway to determine the composition and size of the asteroid, in addition to its rotation rate. Its size could range from less than mile to several miles in diameter, Helin said.

       The asteroid was determined to be the most accessible target for an asteroid rendezvous mission, replacing the asteroid Anteros as prime candidate for possible future mission to explore and sample an asteroid. Asteroids may contain geologic record of the early solar system, and could provide clues to the formation of planets and satellites.

       According to mission designers at JPL, l982 DB could be reached by spacecraft with relatively little energy. The Mariner Mark 2 spacecraft, under study at JPL for low-cost space exploration missions, could be used for an asteroid rendezvous mission.

       Helin initiated systematic search for Apollo-type asteroids in the early l970s, in collaboration with Shoemaker.

       The search, conducted with the Schmidt telescopes at Mt. Palomar, has yielded many discoveries, including the Apollo asteroid Aten, the first asteroid found to have an orbit smaller than Earth's and period of revolution about the Sun of less than year. Other discoveries include unusual asteroids that cross Venus' Earth's and Mars' orbits, and numerous main-belt asteroids. She discovered Comet Helin in the spring of l977.

       Helin's observational work is sponsored by NASA, Caltech, and private donations.

4/20/82 MBM