Asteroid 253 Mathilde Asteroid 253 Mathilde was discovered on Nov. 12, 1885, by Johann Palisa in Vienna, Austria. The name was suggested by V.A. Lebeuf, a staff member of the Paris Observatory who first computed an orbit for the new asteroid. The name is thought to honor the wife of astronomer Moritz Loewy, then the vice director of the Paris Observatory. Although Mathilde's existence has been known for more than a century, it wasn't until 1995 that observations with ground-based telescopes first identified the asteroid as a C-type. The 1995 observations also revealed an unusually long rotation period: 418 hours, or approximately 17 days. Orbital period is 4.30 years. Perihelion is 1.94 AU (180 million miles/290 million kilometers). Mathilde's inclination is 6.7 degrees. Geometric albedo is 0.036. Data obtained by the Infrared Astronomy Satellite has established Mathilde's diameter at approximately 38 miles (61 kilometers). This is substantially larger than the diameters of either Gaspra (10 miles/16 kilometers) or Ida (20 miles/33 kilometers), which would make Mathilde the largest asteroid to be visited by a spacecraft. The proposed NEAR encounter with 253 Mathilde would produce the first close-up images of a C-class asteroid. Preliminary plans call for a closest approach distance of 750 miles (1,200 kilometers) on June 27, 1997. Mathilde Facts -------------- Diameter: 61 km Approximate mass: 200. x 10^15 kg Rotation Period: 418. hrs Orbital Period: 4.31 yrs Spectral Class: C Semimajor Axis: 2.645 AU Perihelion Distance: 1.94 AU Aphelion Distance: 3.35 AU Orbital Eccentricity: 0.2663 Orbital Inclination: 6.7 deg Geometric Albedo: 0.036