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| Asteroids |
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MORE ASTEROIDS
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Rocks from space hit Earth every day. The larger the rock, though, the less often Earth is struck. Larger bits appear initially as a bright meteor. Baseball-sized rocks and ice-balls streak through our atmosphere daily, most evaporating quickly to nothing.
Significant threats do exist for rocks near 100 meters in diameter, which strike the Earth roughly every 1000 years. An object this size could cause significant tsunamis were it to strike an ocean, potentially devastating even distant shores. A collision with a Massive asteroid, over 1 km across, is more rare, occurring typically millions of years apart, but could have truly global consequences.
Many asteroids remain undiscovered. In fact, one was discovered in 1998 as the long blue streak in the above archival image taken by the Hubble Space Telescope. In 2002 June, the small 100-meter asteroid 2002 MN was discovered only after it whizzed by the Earth, passing well within the orbit of the Moon. 2002 MN passed closer than any asteroid since 1994 XM1, but not as close as 2004 MN4 will pass in 2029.
A collision with a large asteroid would not affect Earth's orbit so much as raise dust that would affect Earth's climate. One likely result is a global extinction of many species of life, possibly dwarfing the ongoing extinction occurring now.
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GASPRA
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Asteroid 951 Gaspra is a huge rock tumbling in space. Gaspra became one of the best-studied asteroids in 1991 when the spacecraft Galileo flew by. In the above photograph, subtle color variations have been exaggerated to highlight changes in reflectivity, surface structure and composition. Gaspra is about 20 kilometers long and orbits the Sun in the main asteroid belt between Mars and Jupiter.
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SYLVIA - REMUS - ROMULUS
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Discovered in 1866, main belt asteroid 87 Sylvia lies 3.5 AU from the Sun, between the orbits of Mars and Jupiter. Also shown in recent years to be one in a growing list of double asteroids, new observations during August and October 2004 made at the Paranal Observatory convincingly demonstrate that 87 Sylvia in fact has two moonlets - the first known triple asteroid system.
At the center of this composite of the image data, potato-shaped 87 Sylvia itself is about 380 kilometers wide. The data show inner moon, Remus, orbiting Sylvia at a distance of about 710 kilometers once every 33 hours, while outer moon Romulus orbits at 1360 kilometers in 87.6 hours. Tiny Remus and Romulus are 7 and 18 kilometers across respectively. Because 87 Sylvia was named after Rhea Silvia, the mythical mother of the founders of Rome, the discoverers proposed Romulus and Remus as fitting names for the two moonlets.
The triple system is thought to be the not uncommon result of collisions producing low density, rubble pile asteroids that are loose aggregations of debris. |
ASTEROID 2004 FH |
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Last week, a small asteroid approached unusually close to the Earth. Asteroid 2004 FH posed no danger, but became bright enough to see with binoculars. Passing only 7 Earth radii away, this asteroid pass was the closest yet that was previously predicted, although it was discovered only two days before.
Pictured above, the 30-meter sized 2004 FH was imaged from Switzerland crossing the sky on March 18, near its closest approach. The asteroid, centered in the above time-lapse movie covering about 30 minutes, changing in brightness as it tumbles by.
An asteroid this size passes this close to Earth about every two years. Were 2004 FH to have struck the Earth, it would have likely burned up in the atmosphere. Large impact features on the Earth are testaments, however, to larger asteroids and comets that actually impacted the Earth in the distant past.
Astronomers continue to discover, track, and study potentially hazardous asteroids with a goal of making planet Earth a safer place.
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