|
The discovery was made by the Lowell Observatory Near-Earth Object Search (LONEOS), Arizona, USA, on the evening of 10 May by observer Brian Skiff. "I immediately noticed the unusual motion," said Skiff, "so it was certain that it was of more than ordinary interest." He quickly reported it to the Minor Planet Center (MPC) in Massachusetts, USA, which acts as an international clearinghouse for asteroid and comet discoveries.
The MPC then posted it on their Web page for verification by astronomers across the world. Initially dozens of amateur and professional astronomers trained their telescopes to the skies to measure the position of the object. However, it was a few days later that an orbit was accurately calculated and an announcement could be made. The official discovery announcement and preliminary orbit were published by the MPC on 13 May. They showed that the object was located between Earth and Venus.
In addition, 2004 JG6’s orbit takes it around the Sun in just six months, making it the shortest known orbital period. Ordinary asteroids are located between the orbits of Mars and Jupiter, roughly two to four times farther from the Sun than Earth, taking several years to go around the Sun. Instead, 2004 JG6 orbits entirely inside the Earth's orbit, only the second object so far found to do so. "What makes this asteroid unique is that, on average, it is the second closest Solar System object orbiting the Sun," said Edward Bowell, LONEOS Director. Only planet Mercury orbits closer to the Sun.
As shown in the Lowell Observatory orbital diagram, 2004 JG6 crosses the orbits of Venus and Mercury, passing less than 48 million kilometres from the Sun, travelling at approximate 30 kilometres per second. Depending on their locations, the asteroid may pass as close as 5.6 million kilometres from Earth and about 3.2 million kilometres from the planet Mercury.
From present estimates, 2004 JG6 is probably between 500 meters and one kilometre in diameter. Despite its proximity, the object poses no danger of colliding with Earth. Asteroids with orbits entirely within the Earth's orbit have been informally called "Apoheles," from the Hawaiian word for orbit. Apohele also has a Greek heritage, "apo" for outside, and "heli" for Sun.
Objects orbiting entirely within Earth's orbit are thought to comprise just two percent of the total near-Earth object population, making them rare as well as difficult to discover. This is because they stay in the daylight sky almost all of the time. There may exist about 50 Apoheles of comparable size to or larger than 2004 JG6, but many of them are certain to be unobservable from the ground.
The first asteroid found entirely inside the Earth's orbit was 2003 CP20, found just over a year ago by the NASA-funded Lincoln Laboratory Near-Earth Asteroid Research project, which observes near Socorro, New Mexico. Although larger than 2004 JG6, 2003 CP20 is a little more distant from the Sun.
LONEOS is one of five programs funded by NASA to search for asteroids and comets that may approach our planet. The NASA program's current goal is to discover 90 percent of near-Earth asteroids larger than one kilometre in diameter by 2008. There are thought to be about 1 100 such asteroids.
More info: Lowell Observatory
Related News
Hazardous Asteroid Found
NASA Releases Near-Earth Object Search Report
Closest asteroid yet flies past the Earth
Asteroids change colour as they age
|
