NEAR Flyby of Asteroid 253 Mathilde

Images of Mathilde

Captions courtesy of the NEAR Project:

This first image of asteroid 253 Mathilde, returned by the NEAR spacecraft just before 10:00 AM EDT on June 27, 1997, was taken from a distance of 1120 miles (1800 kilometers). Sunlight is coming from the upper right. The part of the asteroid shown is about 36 miles across (59 kilometers), and the scale is approximately 780 feet (230 meters) per pixel. The surface is heavily cratered, and the large shadowed area on the left may be a single impact gouge well over 12 miles (19 kilometers) deep. The angular form of the edge of the shadowed area suggests that large impacts may haved spalled large pieces off the asteroid. This asteroid is very dark, reflecting only about 4% of the light falling on it, but was imaged easily by the sensitive NEAR multispectral camera. The spacecraft will return over 500 images of Mathilde over the next two days, including higher resolution views as well as color images. These data represent the first science return from NASA's Discovery Program of small missions designed to yield top-quality science for a low cost.

This image mosaic of asteroid 253 Mathilde is constructed from four images acquired by the NEAR spacecraft on June 27, 1997. The images were taken from a distance of 1,500 miles (2,400 kilometers). Sunlight is coming from the upper right. The part of the asteroid shown is about 36 by 29 miles (59 by 47 kilometers) across. Details as small as 1,250 feet (380 meters) can be discerned. The surface exhibits many large craters, including the deeply shadowed one at the center, which is estimated to be more than 6 miles (10 kilometers) deep. The shadowed, wedge-shaped feature at the lower right is another large crater viewed obliquely. The angular shape of the upper left limb of the asteroid results from the rim of a third large crater viewed edge-on. The bright mountainous feature at the far left may be the rim of a fourth large crater emerging from the shadow. Mathilde's angular shape is believed to result from a violent history of impacts. NEAR acquired over 500 images of Mathilde during the encounter, including high-resolution views and color images. NEAR data from Mathilde represent the first science return from NASA's Discovery Program of small missions designed to yield top-quality science at low cost.

These are views of the three asteroids that have been imaged at close range by spacecraft. The image of Mathilde (left) was taken by the NEAR spacecraft on June 27, 1997. Images of the asteroids Gaspra (middle) and Ida (right) were taken by the Galileo spacecraft in 1991 and 1993, respectively. All three objects are presented at the same scale. The visible part of Mathilde is 37 miles (59 kilometers) wide and 29 miles (47 kilometers) high. Mathilde has more large craters than the other two asteroids. The relative brightness has been made similar for easy viewing; Mathilde is actually much darker than either Ida or Gaspra.

This view of 253 Mathilde, taken from a distance of about 748 miles (1,200 kilometers), was acquired shortly after the NEAR spacecraft's closest approach to the asteroid on June 27, 1997. In this image, the asteroid has been rotated so that the illumination appears to come from the upper left. This portion of Mathilde shows numerous impact craters, ranging from over 18 miles (30 kilometers) to less than 0.3 miles (0.5 kilometers) in diameter. Raised crater rims suggest that some of the material ejected from these craters traveled only short distances before falling back to the surface; straight sections of some crater rims indicate the influence of large faults or fractures on crater formation. The number of craters as a function of size, and the number of each size within the visible area, are similar to values seen on asteroid 243 Ida, viewed by the Galileo spacecraft in 1993. A major difference between Ida and Mathilde appears to be the abundance of very large craters: Mathilde has at least 5 craters larger than 20 kilometers in diameter on the roughly 60% of the body viewed during the encounter.

Two different views of asteroid 253 Mathilde were obtained by the NEAR spacecraft on June 27, 1997. The image at left was obtained as the spacecraft approached Mathilde with its camera pointed near the direction of the Sun; only a few of the prominent ridges on Mathilde are illuminated. The visible area at left is 18 miles (29 kilometers) high, and the phase angle (the angle from Sun-Mathilde-spacecraft) is 136 degrees. As the spacecraft receded from Mathilde, it observed the asteroid (about 38 miles or 60 kilometers across) almost fully lit by the Sun at a phase angle of 43 degrees (right image). Mathilde's irregular shape results from a long history of severe collisions with smaller asteroids. The largest visible crater is 19 miles (30 kilometers) in diameter.

The Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 1200 km of the asteroid Mathilde on Friday, 27 June 1997 at 12:56 UTC (8:56 AM EDT). Due to power limitations, only the multispectral imaging instrument was turned on for this encounter. The multispectral imager has 7 color filters and one clear. A total of approximately 534 images should be returned during the close encounter phase of the flyby. There will be no communication with NEAR until 13:40 UTC (9:40 AM EDT) when communications will be re-established and telemetry and images will begin to be returned. Two unprocessed pictures should be available on-line Friday sometime after noon EDT at the NEAR web-site, we will post them on this page when they become available. NASA Select TV may broadcast the first images Friday, they will broadcast the press conference on Monday, 30 June, at 1:00 PM EDT, when the first hard-copy images are made available.

The first pre-encounter optical navigation images were taken Wednesday, and the last were taken approximately 12 hours before closest approach, about 01:00 UTC, 27 June (9:00 PM EDT, 26 June). The flyby took place at 9.93 km/sec. The asteroid is lit primarily from the back as seen by the approaching spacecraft, so the best images were taken during and immediately after closest approach. The highest resolution images will be about 180 meters/pixel. The seven color global images will be at 400-500 meters/pixel. Because of Mathilde's slow rotation rate, it was only be possible to image half the asteroid.

The images will be only the third close-up view of an asteroid's surface features, after Galileo's images of Gaspra and Ida. They will also be used to determine the size and shape of Mathilde and the surface colors. Finally, later images will be searched for signs of any small natural satellites orbiting Mathilde. Shape and size determinations of the one side facing NEAR will be supplemented by Earth-based Arecibo radar measurements in October and November of 1997. Detailed tracking of the spacecraft's motion as it passes Mathilde will be used to estimate the gravitational effect and hence the mass of the asteroid.

253 Mathilde is a main-belt asteroid, in an eccentric orbit with a perihelion at 1.94 AU and aphelion at 3.35 AU. It is a C-type asteroid, the most common spectral class. It is approximately 50 x 50 x 70 km in size. Reflecting only 3.6% of the light incident on it, Mathilde is one of the darkest objects in the solar system. The asteroid rotates very slowly, once every 418 hours (about 17.5 days).

More information on asteroid 253 Mathilde
Asteroid Fact Sheet
NSSDCA Asteroid Home Page

Information on the Multispectral Imager
Information on the NEAR Mission Profile and Trajectory

NEAR Mathilde Images - Applied Physics Lab, JHU
NEAR Mathilde encounter - Applied Physics Lab, JHU

NSSDCA NEAR Home Page
Detailed information on NEAR from the NSSDCA Master Catalog
NSSDCA Planetary Home Page

NASA Official: Dave Williams, david.r.williams@nasa.gov
Last Updated: 18 December 2001, DRW