(253) Mathilde

Asteroid· orbits the Sun

(253) Mathilde is a dark, carbon-rich (C-type) asteroid about 53 km across in the main belt. NASA's NEAR flew 1,212 km from it on 27 June 1997 — the first close look at a C-type asteroid — and the pull it felt from Mathilde gave its mass.

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Key facts

Radius

26.4 km

Distance from Sun

2.65 AU

Orbital period

4.31 years

Eccentricity

0.2643

Rotation

17.4 days

Science

Physical

Mean radius: 26.4 km
Mass: 1.03 × 10¹⁷ kg · 0.00000141 Moon masses
Density: 1,340 kg/m³ · 1.3× water; Computed from mass and radius
Rotation period: 17.4 days

Orbital

Semi-major axis: 2.65 AU; From catalogued orbital elements (MPC)
Eccentricity: 0.2643; From catalogued orbital elements (MPC)
Inclination: 6.74 °; From catalogued orbital elements (MPC)
Orbital period: 4.31 years; From catalogued orbital elements (MPC)
Perihelion: 1.95 AU; Computed from the orbital elements
Aphelion: 3.35 AU; Computed from the orbital elements
Mean orbital velocity: 18.3 km/s; Computed from the orbital elements

Discovery

Discovered: November 12, 1885
Discoverer: Johann Palisa (Vienna)

Composition

Make-up: Carbon-rich rock with a uniform surface — no colour or brightness differences were found (Clark et al. 1999). Its density, from its measured mass and volume, is about half that of the carbon-rich meteorites it resembles, so it is probably very porous inside, perhaps a rubble pile (Yeomans et al. 1997; Veverka et al. 1999). At least four craters are about as wide as Mathilde's radius; the largest two, Karoo and Ishikari, are 33.4 and 29.3 km across. It turns once every 17.4 days, one of the slowest spins known (Mottola et al. 1995).

Radiation & temperature

Insolation: 0.143 S⊕ · 14% of the sunlight Earth receives; Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
Geometric albedo: 0.05; Geometric albedo 0.047 ± 0.005 (Clark et al. 1999) — one of the darkest surfaces a spacecraft has seen.
Equilibrium temperature: 169 K (-104 °C); Computed from albedo + distance from the Sun (airless black body); uses the geometric albedo as an estimate

Discovery & history

Discovered: November 12, 1885
By: Johann Palisa (Vienna)
Name: Named probably in honour of Mathilde Loewy, the wife of Moritz Loewy, vice-director of the Paris Observatory; V. A. Lebeuf, who computed its orbit, named it.

Johann Palisa found it at Vienna on 12 November 1885. On 27 June 1997 NEAR passed it at 9.93 km/s, 1,212 km away, and took over 300 pictures covering about 60% of its surface — the first close look at a C-type asteroid. The slight bend the asteroid's gravity gave NEAR's path measured its mass.