June 8, 2001 Identifying what may be a galactic replay of how our own solar system was formed, UCLA astronomers have found evidence of a massive asteroid belt around a nearby star - findings that could indicate that planets are forming there or have already formed.
The observations, reported June 4 at the annual meeting of the American Astronomical Society by UCLA graduate student Christine Chen and her advisor, Michael Jura, reveal that a star identified as zeta Leporis (HR 1998) is enveloped by swirling dust in quantities and at temperatures that indicate a massive asteroid belt could surround the star.
"Because of the conditions we identified near zeta Leporis, we believe that the dust around this star may contain asteroids that appear to be colliding violently with each other," said Jura, a professor in UCLA's Department of Physics and Astronomy. "Zeta Leporis is a relatively young star - approximately the age of our sun when the Earth was forming. The system we observed around zeta Leporis is similar to what we think occurred in the early years of our own solar system when planets and asteroids were created."
Zeta Leporis is located in the constellation Lepus (the Hare) about 70 light years from our sun. About twice as massive as our sun, zeta Leporis is young in astronomical terms - about 100 million years old, compared to our sun, which is approximately 4.5 billion years old.
"Our current findings may be just the tip of the iceberg of what we may ultimately learn about the objects surrounding zeta Leporis," Chen said.
"In simplest terms, our planets formed when smaller objects smashed together," she said. "Dust that surrounds a star will eventually either fall into the star, or collide with itself and create bigger particles. The particles we can identify around zeta Leporis may be forming chunks of rock or larger objects; asteroids or even planets may be forming or have already formed around zeta Leporis."
Orbiting dust around hydrogen-burning stars such as Vega, beta Pictoris and zeta Leporis was first discovered in 1983 with the Infrared Astronomy satellite (IRAS). The orbiting dust absorbs optical light from the central star and is emitted as infrared. The presence of this dust around zeta Leporis indicates that material similar to that found in our own solar system surrounds this star.
In February Chen and Jura observed zeta Leporis with Long Wavelength Spectrometer, an infrared camera on the 10-meter telescope at the Keck Observatory on Mauna Kea, Hawaii. Chen and Jura found infrared-emitting dust confined to a region smaller than 12.2 astronomical units in diameter, a region similar in size - in astronomical scales - to the asteroid belt in our solar system, which is about 5.4 astronomical units in diameter.
By observing at two infrared wavelengths, Chen and Jura estimate that the average temperature of the dust around zeta Leporis is about 340 Kelvins (150 F), a relatively high temperature for such material. Given this high temperature, the grains may be as close as 2.5 astronomical units to the star.
"There must be objects larger than dust around zeta Leporis, which may resemble asteroids in our own solar system, that are creating the infrared-emitting dust by violently colliding with each other," Jura said.
The discovery that the dust around zeta Leporis is unusually warm was first published in 1991 by astronomers Hartmut Aumann and Ronald Probst.
Chen and Jura plan to confirm their findings with additional infrared observations of zeta Leporis.
"We hope to obtain infrared spectra of the emission from zeta Leporis," Chen said. "We want to know if the asteroids around this star are similar in composition to objects in our solar system, and we want to learn if the processes we now see unfolding on zeta Leporis can help us understand how the planets in our own solar system formed."
"The next step is to get an infrared spectrum of this area, which would give us an indication of their composition."
The research by Chen and Jura is supported by funding from NASA.
For an illustration of this research, go to: http://www.astro.ucla.edu/~cchen/hr1998_pr.html.)
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