Comets Could Masquerade as Planets |
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Written by spacetravel.org
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Monday, 06 June 2005 13:48 |
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Space missions looking for planets could be fooled into thinking that a comet is a planet. Most astronomers have assumed that comets, which range from 1 to 20 kilometers across, would be impossible to see around stars. Mike Jura of the University of California at Los Angeles says this is not true. As a comet nears the sun, its tail can stretch to as long as 50 kilometers. The tail will reflect sunlight and appear as a fan-shaped glow in the night sky. Jura says that while the tail would not be seen as a streak because of its great distance from Earth, it could still be seen from Earth as a point of light. Jura has calculated that a large comet like Hale-Bopp, which was seen from Earth in 1997, would appear twice as bright as an Earth-sized world orbiting the same star. Its possible that extra-solar comets could appear even brighter, since we dont know if the Solar Systems comets are typical of comets elsewhere.
Malcolm Fridlund, study scientist on the European Space Agencys proposed planet-finding mission, Darwin, believes that analyses of reflected light from potential planets at different wavelengths could reveal whether they are planets or comets, because planetary atmospheres absorb certain wavelengths that comets do not absorb. However, identifying planets without atmospheres will require longer observation times. Fridlund says that Darwin plans to look at each system three times during its five-year mission. Confusion between stars and planets should be avoided, because in that time, comets will change in brightness and move in highly elliptical orbits, while planets will not.
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