Asteroids can change orbits as they interact with the gravitational fields of planets, although most — including the largest — have settled safely into stable paths between the orbits of Mars and Jupiter, but unknown thousands wander in yet undetermined orbits.
Trojan Asteroids Occupy Lagrange Stability Points in a Planet’s Orbit
In 1772 Italian-French mathematician and astronomer Joseph Louis Lagrange developed the idea of gravitational stability points where a smaller object could be trapped by the gravity of two larger objects in a location where gravity was in balance. A new asteroid — 2011 TK7 — has been found in such a point ahead of Earth in its orbit.
The concept is now known to account for the location of special classes of asteroids known as Trojan asteroids in the orbits of Jupiter and other planets. Lagrange points are found in five locations relative to planets, but vary in stability. 2011 TK7 is orbiting near one of the Lagrange stability points — specifically the L4 point — ahead of Earth.
Earth Trojans Are Not Easily Seen
Because of the location of Earth Trojans, they are almost impossible to see with visible light due to their apparent proximity to the sun. This means that when 2011 TK7 is located in a spot high in the Earth’s sky, it is daytime on Earth. The Wide-field Infrared Survey Explorer satellite — WISE — located the object using infrared photography.
If additional Earth Trojans are found, they will likely be discovered in a similar fashion ahead or behind the Earth. Luckily, 2011 TK7 has an orbit that carries it above the plane of the Earth’s orbit. This places it temporarily in a position favorable for discovery.
The Newly Discovered Asteroid Is No Threat to Earth like Apophis
The orbits of the trapped Trojans are somewhat complex compared to planetary orbits. They wander within a confined space that is defined by the physics of the particular Lagrange point. Thus a number of asteroids may drift in a closed group out of harms way.
The L4 and L5 Lagrange points are very stable, consequently 2011 TK7 is expected to stay put for at least 10,000 years. Other asteroids — Apophis, for example — will pass uncomfortably close to Earth in 2029 and possibly again in 2036. In November, 2011 YU55 will miss Earth by about 200,000 miles.
Newly discovered asteroid 2011 TK7 is the first Trojan class asteroid to be discovered in Earth’s orbit. It is locked into Lagrange point L4 — sixty degrees ahead of Earth. The discovery was made by the WISE Explorer satellite using infrared imagery. The asteroid is of no danger to Earth because it is in a stable position.
Sources:
- "Trojan Asteroid Shares Orbit with Earth," Nasa,com. "Accessed July 29,2011"
- "What are Lagrange Points," Esa.int.com. "Accessed July 29,2011"
Harvey Craft - I am a retired educator with diverse experience. I read anything science, education, and history. I write to share what I learn.
