Want to stay on top of all the space news? Follow @universetoday on TwitterA near Earth object is an asteroid, comet, or meteroid whose orbit takes it within a close proximity to Earth. Many of this type of object have impacted the Earth in the past. Some as recent as last year. Most of them would burn up in the atmosphere and create a wonderful light show, but pose not real danger to humans. Still, others are large enough to cause the devastation of entire countries or continents. While it is commonly acknowledged that these past collisions helped to form the world as we know it, no one would like to see another large scale impact. To avoid this in the future, several countries have combined their efforts to track near Earth objects.
By definition near Earth objects have orbits that lie between .983 and 1.3 astronomical units(AU) away from the Sun. Every NEO is submitted to the Harvard Minor Planet Center for cataloging immediately after it is discovered. A few of these NEOs have orbits that bring them dangerously close to Earth. Several have the potential for impact. The largest of these is the asteroid Apophis. It will come recklessly close to Earth in April of 2029. It is possible that it will hit a gravitational keyhole during that pass that will alter its course enough to cause an impact on its next near approach in 2036. Study has shown that it is unlikely, but possible.
The United States, the European Union, and other nations are currently scanning for neat Earth objects in an effort called Spaceguard. NASA has orders from Congress to catalog all NEOs 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. The Shoemaker space mission will study the near Earth object 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 at least 10 different scientific missions that are studying, searching for, and cataloging near Earth objects. If they were not such a threat to our planet we would not have to devote so many resources to them. Luckily, science and government have recognized the importance of solidarity in studying these demons from above.
You can find the names and links to all of the Spaceguard member facilities here. We also have some interesting articles about NEOs and Earth impacts here on Universe Today. Astronomy Cast offers several good episodes on the topic, too.