WEEKLY WHINE

Are we there yet?

Near Earth Asteroid Rendezvous is not there yet. But it is near.

Of course it is near. That's its name. Actually, its name is NEAR, not near. But nonetheless, it is now near asteroid 433 Eros. At 07:33 PST, it will reach orbit about the asteroid and begin telling us neat things about it.

Asteroid 433 Eros was discovered in 1898. At roughly 33 × 13 × 13 km, it is one of the most elliptical asteroids out there. Its surface gravity is .0006 g, which is very small. NEAR's initial orbiting burn comes at a distance of 333 km from the asteroid's center. From its initial orbit, we'll be able to figure out the asteroid's mass. Figuring out objects' masses in space is easy if they have moons. But if they don't, it's not easy. That's why one practical way to figure out objects' masses is to make your own moons.

It's even better when those moons have onboard science equipment, like a magnetometer, spectrometers, and a laser altimeter. Conveniently, NEAR is equipped with all of these. Results from the instruments will also show more about the rock's shape and gravity field. Knowing all this, mission managers will be able to maneuver NEAR nearer to 433 Eros, and more importantly, do so accurately.

Within the first two months of orbit, NEAR will pull within 50 km of 433 Eros, from whence the X ray/gamma ray spectrometer will kick in to determine some element abundances. After that, it will raise its orbit to 500 km to construct a detailled map of the surface. If all goes well, in DEC 2000 it will be ready to lower its orbit again, perhaps as low as 1 km above the surface.

It was launched almost four years ago, but NEAR was originally to enter orbit around 433 Eros in DEC 1998. But a hyperactive thruster caused the spacecraft to safe itself, so mission controllers watched 433 Eros pass by. Then, they performed a deep space maneuver that would bring NEAR back in FEB 2000. And here we are.

NEAR is a landmark, the first mission to orbit a minor body in the Solar System. [Asteroids and comets have been flown by previously.] Its goals are ambitious: if we find out what we want to find out about NEAR, we will have an understanding of the parent body from which it fragmented, a possible understanding of how that fragmentation came about, and a chance of understanding a little more about the early Solar System. It could also tell us more about that class of objects we call Near Earth Asteroids, of which 433 Eros is one. [Its aphelion is beyond Mars's orbit at 1.78 AU, but its perihelion is close to Earth's orbit at 1.13 AU. That makes it Near Earth.] Were they all formed from larger parents, or do they just happen to be near Earth?

In space, you can add as many answers as you like, but the questions always get added much more rapidly. That's what's so much fun.