Exploring Asteroids is NEAR

     I tend to feel sorry for NASA. Much publicity is made over a botched mission, but far less publicity is granted the successful missions, and NASA has far more successes than failures. One of their most interesting successes this year is the NEAR spacecraft and it's visit to an asteroid.

     NEAR stands for Near Earth Asteroid Rendezvous. The spacecraft is part of a program designed to further explore our solar system. Specifically, NEAR is  exploring asteroids whose orbits bring them close to Earth. In February, NEAR visited asteroid 433 Eros and sent back stunning images and quite a few surprises.

     Asteroids are the debris of the solar system, stuff left over from the making of planets. They, along with comets, are the oldest bodies in the solar system. Anything we learn from them will give us clues to the early solar system. Near Earth Asteroids are those bodies which come within 121 million miles of the Sun. Eros is one of the largest Near Earth Asteroids. It is about 21 miles long, eight miles wide and eight miles thick, giving it a sort of potato shape!

     NEAR slipped into orbit around 433 Eros February 14th of this year. It immediately began returning images. Eros' elongated shape causes the asteroid to slowly "tumble" about its orbit rather than sedately move along like a round planet would. This shape also made calculating orbits for the spacecraft a lot more complicated because the gravity field around such a body is also not spherical. NEAR has been lowering its orbit, getting even closer to 433 Eros and making orbital corrections as it goes. So far, all has worked as planned.

     On April 30th, NEAR entered into a 31 mile high circular orbit over Eros' north and south poles. For the next two months, the spacecraft will stay in this orbit and provide the closest ever images of this slowly tumbling ancient world.

     The first images of 433 Eros showed a world with grooves, craters, ridges, layering and a 170 foot wide boulder at the bottom of a large crater! While most of the surface is heavily cratered, there is an area on one side which was dubbed the "saddle."

     The saddle area has few craters which indicates that some geological event has wiped the area clean of craters. That is not an odd event on planets and moons, but is very odd for an asteroid. Even more puzzling is a series of layered grooves running down one side of the saddle and up the opposite wall. There are indications that the layering runs along Eros' length which could mean that the asteroid was once part of a larger body. More observations will be needed to determine if this is likely.

     Another odd features of Eros is that while most of Eros appears dark (reflecting little light) there are a few areas which reflect about 25 percent  more light and appear quite bright.  No one has even made a guess as to what this could be!

     Then there is the large crater with the boulder at the bottom. The house-sized boulder appears to have rolled down the side of the crater. That, along with slumping along the crater's walls, indicate geologic activity caused by gravity. Eros' gravitational field is only one-thousandth as strong as Earth's but even such a weak field has modified the little body's surface!

     The data returned from NEAR has caused surprises and generated even more questions about this strange, ancient world. The next two months should prove very interesting. You can take a look at the images of Eros on my website at http://starryskies.com/eros.html