NEAR Voyage 5-1: Waltzing w/Mathilde

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Waltzing with Mathilde: June 27, 1997
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The long, looping trajectory to Eros took NEAR close by another asteroid, 253 Mathilde. Using only a very small additional amount of fuel, NEAR was able to fly by Mathilde at a distance of only 1212 kilometers (750 miles) turning on its Multispectral Imager camera as it flew by. At a distance of 1.99 AU, the Sun did not provide enough power to enable the rest of NEAR’s instruments to be powered up and used. Mathilde was a valuable target of opportunity, because unlike Gaspra, Ida, and Eros, it is a carbon-rich "C-type" asteroid, a type never before visited by a spacecraft.

The orbit of Mathilde, NEAR's first encountered asteroid.

The biggest difficulty in flying so close by Mathilde was that the asteroid's position was poorly known. Very few observations of Mathilde had been made from telescopes, so NEAR itself took additional measurements to pinpoint the asteroid during the two days prior to the flyby.

Final navigation image prior to the Mathilde encounter, taken June 26, 1997.

The main objectives of the Mathilde flyby were to take a high-resolution picture of the surface, to take pictures of the whole illuminated part of the asteroid, to map Mathilde's color properties, and to search for satellites like the small moon of Ida. These objectives were met using a series of 10 image mosaics taken as NEAR approached from the night side of Mathilde and departed from the day side.

NEAR's investigation of Mathilde took place over only 25 minutes as the spacecraft raced by at 9.93 kilometers per second.

The first mosaic taken while approaching the night side, which was expected to show a small crescent, instead showed a bizzare form promptly christened "the pterodactyl," after the ancient winged dinosaur.

The first image mosaic of Mathilde, taken over the asteroid's night side.

The next mosaic, taken at the time of closest approach, was more shadow than asteroid: most of the surface was covered in enormous craters whose interiors were hidden in shadow!

Second image mosaic of Mathilde, taken at the time of closest approach to the
asteroid, from a range of 1212 kilometers (750 miles). From this viewpoint,
most of the surface lies shadowed in the interiors of enormous craters.

The subsequent mosaics revealed the origin of the surreal, contored form of Mathilde: at least five large craters, each comparable in size to Mathilde's radius, shape the asteroid's mountains and valleys. Even the asteroid's profile is shaped by the craters. But after detailed examination of all the mosaics, no moons were found.

Third image mosaic of Mathilde, taken from a range of 1800 kilometers (1120 miles).

Fourth image mosaic of Mathilde, taken from a range of 2400 kilometers (1500 miles).

This computer-generated model of Mathilde's shape is dominated by
the effects of largeimpact craters. It’s maximum diameter is 56 km.

When arranged into a time sequence, NEAR's images of Mathilde form a movie of what it would look like to fly by an asteroid.

MPEG Video 228K

Animation of NEAR's Mathilde flyby, using
actual images returned by the spacecraft.

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