Near Earth Asteroids

A near Earth asteroid is any asteroid whose orbit takes it within close proximity to Earth. Several of these asteroids have impacted the Earth over its history. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the planet. In order to avoid future impact events, several countries have combined their efforts to track near Earth asteroids.

Near Earth asteroids have orbits that lie partly between 0.983 and 1.3 astronomical units away from the Sun. When an NEA is detected it is submitted to the Harvard Minor Planet Center for cataloging. A few of the NEA’s have orbits that intersect that of the Earth and pose a potential threat. The United States, the European Union, and other nations are currently scanning for NEOs in an effort called Spaceguard. NASA has orders from Congress to catalog all NEAs that are larger than 1 km. These need tracking because they would cause significant damage to the planet and life as we know it. As of today, there have been nearly 1,000 of these objects found. There is still 30% of the sky to be studied for more objects. Scientists predict that asteroids larger than 1 km in diameter collide with the Earth every 500,000 years. Collisions with asteroids that are 5 km happen about every 10 million years. Asteroids with diameters of 5-10 m impact on a yearly basis, but they burn up in the atmosphere leaving a nice light show, but no damage in their wake.

NASA thinks that the chance of a near Earth asteroid collisions is real enough that is has set up the SENTRY and NEAT programs to study near Earth asteroids. In the next 28 years there are supposed to be at least two close calls. Neither asteroid should actually collide with the Earth, but they will be close enough that Earth’s gravity could pull them off their orbit enough to cause a strike the next time they come our way. Hopefully, we will be able to avoid such a gravitational keyhole event and the asteroids will go on following their original orbit.

The Shoemaker space mission will study the near Earth asteroid Eros. Hopefully it will give a better understanding of the differences between space objects and their relationship to Earth and the other planets.

There are several articles on Universe Today that are related to this topic plus quite a bit of information on the internet and on NASA’s web page.

References:
NASA: Near Earth Objects
NASA: Will an asteroid hit the Earth?

Tagged as: NEA, near earth asteroids, near earth objects, NEAs