Summer lets orbiter see asteroid Eros in new light

larger   A mosaic of NEAR images, showing the asteroid's entire north polar region from a distance of about 200 km (124 miles)

June 27, 2000
Web posted at: 3:00 p.m. EDT (1900 GMT)

From staff reports

(CNN) -- The sun rose over the south pole of Eros this week, illuminating terrain hidden in darkness since a NASA spacecraft went into orbit around the asteroid four months ago.

The arrival of summer in the southern half of the asteroid excited mission scientists, since three instruments aboard the robot ship depend on reflected sunlight to gather data.

"We're looking forward to seeing the south polar regions of Eros," NEAR (Near Earth Asteroid Rendezvous) project scientist Andrew Cheng said.

The Manhattan-sized space rock was in the middle of northern summer when the NEAR-Shoemaker arrived on February 14. Since then the asteroid orbiter has focused its observations on the sunny north.

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Stargazing

Like Earth, Eros experiences two equinoxes and two solstices during its annual trip around the sun, which lasts 1.76 terrestrial years.

The seasonal similarities end there. The asteroid has an axis tilt of 89 degrees, leading to brutal temperature changes in the polar regions between summer and winter, perhaps as great as those between liquid nitrogen and boiling water.

This view of Eros' terminator, the line dividing the asteroid's day side and night side, shows the relief of its heavily cratered surface in the low sunlight

Eros also has a highly elliptical orbit, creating long autumns and short springs in the north and the opposite conditions in the south.

Because of the unusual orbit, which ranges in distance from the sun between 1.13 to 1.8 Astronomical Units (AUs), an observer on Eros would see the relative size of the sun nearly double between autumn and spring, NASA said.

An AU is about 93 million miles (150 million km), the distance between the sun and Earth.

The first spacecraft ever to orbit an asteroid, NEAR-Shoemaker currently circles the center of Eros from a distance of 31 miles (50 km). The automobile-sized robot ship will descend to just 22 miles (35 km) on July 7, mission scientists said.

The Johns Hopkins University Applied Physics Lab in Laurel, Maryland, manages the yearlong NASA mission.

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Near Earth Asteroid Rendezvous Mission
Johns Hopkins University Applied Physics Laboratory
NASA

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