Astronomy Picture of the Day Index - Solar System: Asteroids

APOD: 2003 December 31 - A Year of Assessing Astronomical Hazards
Explanation: Could an asteroid destroy civilization on Earth? Mountain-sized space rocks could potentially impact the Earth causing global effects, and perhaps even be mistaken for a nuclear blast of terrestrial origin. Such large impacts are rare but have happened before. Modern telescopes have therefore begun to scan the skies for signs of approaching celestial hazards. Over the past year, projects such as Spacewatch and Spaceguard have continually discovered previously unknown asteroids that indeed pass near the Earth. Such projects are still rather modest, however. In June, 100-metre asteroid 2002 MN was discovered only after it whizzed by the Earth, crossing even within the orbit of the Moon. This year brought much discussion in the astronomical community of expanding technology to discover most large Near Earth Objects and extend the time between discovery and impact for all potential astronomical hazards. Pictured above is an illustration of a busy planetary system, showing the view of a planet ringed with space debris from a recently formed crater of an orbiting moon.

APOD: 2004 June 19 - Ida and Dactyl: Asteroid and Moon
Explanation: This asteroid has a moon! The robot spacecraft Galileo destined to explore the Jovian system, encountered and photographed two asteroids during its long interplanetary voyage to Jupiter. The second asteroid it photographed, Ida, was discovered to have a moon which appears as a small dot to the right of Ida in this image from 1993. The tiny moon, named Dactyl, is about one mile across, while the potato shaped Ida measures about 36 miles long and 14 miles wide. Dactyl is the first moon of an asteroid ever discovered. The names Ida and Dactyl are from Greek mythology. Many other asteroids are now known to have moons.

APOD: 2005 April 17 - Asteroids in the Distance
Explanation: Rocks from space hit Earth every day. The larger the rock, though, the less often Earth is struck. Many kilograms of space dust pitter to Earth daily. 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 metres 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-metre 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.