NEAs Near Earth Asteroids are large rocks in space that cross the orbit of Earth. Sometimes they are called NEOs (O = objects). Many have been discovered, many have not. When they are discovered, the Minor Planet Center at Harvard calculates their orbit, and determines if they are a potential threat to Earth.

When describing orbits of objects, we can quantify “perihelion” (q), when the object is closest to the Sun, and “aphelion” (Q), when the object is farthest from the Sun. Q q

Apophis (2004 MN4) is a NEA, about ¼ mile across, weighing about 44,000,000,000 lbs. It caused some concern when it was discovered in Dec. 2004, because it appeared to have a large probability of hitting the Earth on Friday, April 13, 2029. More observations have indicated it will just miss us on that date. When it does go by, Earth’s gravity will change its orbit. Depending on how the orbit is changed, it could possibly impact on April 13, 2036 (NASA reduced the odds of hitting Earth in January 2013 to one in a million). It would impact with the force of 44000 Hiroshima nuclear bombs.