Recent views of Eros. Click each image for a larger version and caption

Asteroid orbiter marks halfway point in historic flight

Color composite image of Eros

In this story: A haunting world Deflecting an asteroid RELATED STORIES, SITES

By Richard Stenger
CNN.com Writer

(CNN) -- Groundbreaking science. Suspenseful movies. Dramatic photos. What more could be expected from the first spacecraft to circle an asteroid, now halfway through its primary mission? Plenty, say scientists managing NEAR-Shoemaker, including the first asteroid landing.

Since it began orbiting the asteroid Eros on February 14, NASA's NEAR-Shoemaker has beamed back a steady stream of data, videos and photos that have shaken up solar system science. The data could someday be used to help save the Earth from a cataclysmic asteroid impact.

	GALLERY
View more from Eros
	MESSAGE BOARD
Stargazing
	ALSO
NASA unveils quartet of asteroid movies April 28, 2000

Among the mission's scientific discoveries, two in particular stand out, said NEAR scientist Andy Cheng.

"The first is that the surface shows evidence of continuing geologic activity, not just cratering. The second is that Eros is a primitive body and not a differentiated one."

In other words, heavy metals and lighter rock materials are distributed evenly in the interior and exterior of Eros. In contrast, planets of the inner solar system, Earth included, are differentiated bodies: Heavier substances like iron and nickel migrated to the center, while lighter ones, the silicates or rocks, moved closer to the surface.

"This question was the subject of a noisy debate over the years leading to NEAR, with strong proponents on both sides. With the NEAR result, the question is settled," Cheng said.

The finding could have implications for future space exploration. If other asteroids have similar compositions, with valuable metals distributed near the surface, they could prove economical to mine, Cheng said.

Artist's concept of NEAR-Shoemaker

The automobile-sized robot ship has trained a variety of instruments on Eros, studying its mass, geology, gravity and possible magnetic field.

At least for non-scientists, the most dramatic information has returned to Earth has been visual: a marathon of "movies" and scores of stark images that reveal an eerie world of boulders, craters, ridges and folds.

But the most vital data could originate deep inside the asteroid. By revealing asteroid Eros' inner secrets, the $224 million mission could help ensure that, if the time comes, humankind will know how to push a killer asteroid out of harm's way, rather than spinning it or breaking it up.

"If we decide to deflect an asteroid we will need to know just where the center is, and we need to know something about its mechanical (compositional) strength," Cheng said.

NEAR-Shoemaker traveled a circuitous route of 1.9 billion miles (3 billion km) to reach Eros, which is roughly twice the size of Manhattan. It will travel another 419 million miles (674 million km) during its yearlong orbit of Eros.

The craft's most impressive travel milestone could be measured in inches instead of millions of miles. It flew to within 22 miles (35 km) of Eros during the first half of its mission. During the second half, in October, plans call for it inch to within 4 miles (6 km) of the asteroid's dusty surface.

Project scientists at NASA and Johns Hopkins Applied Physics Laboratory will also consider having the craft briefly touch down in February.

Currently, NEAR-Shoemaker is about 73.5 million miles (118 million km) from Earth, circling Eros at just over 6 miles (10 km) per hour.

NASA orbiter backs off asteroid Eros
July 27, 2000
Spacecraft gets closest look yet at asteroid
July 18, 2000
Summer lets orbiter see asteroid Eros in new light
June 27, 2000
Instrument fails on asteroid orbiter
June 8, 2000
Asteroid Eros resembles 'building blocks' of Earth
May 31, 2000

NASA
Near Earth Asteroid Rendezvous Mission

Note: Pages will open in a new browser window

External sites are not endorsed by CNN Interactive.