Since the Near Earth Asteroid Rendezvous (NEAR) spacecraft set out in February 1996 for a January 1999 date with an asteroid called 433 Eros, its circuitous path has taken it far beyond the orbit of Mars, where it flirted briefly with another chunk of space rock named Mathilde. But on January 23, NEAR swooped by Earth for one last look at home. To mark the occasion, it snapped a few photographs and shot some home video as well.
NEAR was neither lost nor suffering from cold feet over its impending engagement--the Earth flyby was all part of the plan. The first half of NEAR's journey was an elliptical orbit that would bring it back past Earth, where gravitational forces would cause it to accelerate and fling it out of the orbital plane of the major planets onto a new course toward Eros. NEAR was both punctual and precisely on course.
When the returning spacecraft was first sighted at about 1:30 p.m. EST on January 22 by an astronomer in Caussols, France, it was 580,000 miles from Earth and within a half-mile of its expected location. At the closest point in its two-hour encounter on January 23, NEAR swept within 336 miles of southwest Iran, precisely as predicted. It was "right on schedule and right on target," said a jubilant Thomas Coughlin, Space Programs Manager at the Johns Hopkins University Applied Physics Laboratory, which manages the NEAR mission.
As NEAR approached Earth, its instruments were turned on so they could be calibrated on this familiar sight. A spectacular series of images resulted, revealing Asia, Africa and Antarctica as they looked when NEAR sped back into space. An instrument called the multispectral imager created the pictures, using blue, green and infrared filters to differentiate between rock, water and vegetation.
The four images in the animation (top) show Antarctica and the surrounding southern sea, which is covered by sea ice and storm clouds; the South Pole is at the approximate center of each frame. The pictures were taken at 80-minute intervals, as NEAR's distance from Earth increased from 92,000 miles (148,000 kilometers) to 160,000 miles (257,000 kilometers). In the closest frame, the smallest feature visible is approximately eight miles (13 kilometers) in size. When viewed in sequence, the images clearly show the Earth's clockwise rotation. Scientists are now stringing together a full sequence of views--taken over 36 hours by the receding spacecraft; they will post the resulting movie to the in early February. NEAR also captured a first-time-ever view of the Earth and moon from space (below).
NEAR's flawless performance so far is a feather in the cap of NASA's Discovery Program. It was the first such low-cost, small-scale planetary mission. But even had it not come this far, NEAR's mission still would have been a success, based on the images it made last June of Mathilde, which are still the closest observations ever made of an asteroid.
For now, NEAR, like a bolt from Cupid's bow, is aiming for Eros. Mission controllers will shut down the spacecraft's instruments on February 6 for the duration of its journey. If it continues to function as it has until now, the spacecraft will begin its approach to Eros in late 1998 and enter its orbit on January 10, 1999. After conducting the first long-term study of a near-earth asteroid from orbit, NEAR is scheduled for one last maneuver in February 2000: a "soft" crash landing on Eros itself. If its instruments survive, it may well continue to provide data as it sails off with Eros on a lonely journey through the outer solar system.