We don't know much about the Main Belt asteroid 253 Mathilde, but it has a few outstanding characteristics that bear presenting up front.
Mathilde is large . It is about 60 km in diameter and the most massive asteroid yet to be visited by a spacecraft.
Mathilde's shape is poorly characterized. Within one rotational period its brightness varies by a factor of 1.5 or almost 0.5 magnitudes indicating an oblong or irregular shape.
Rotational Lightcurve
Mathilde hardly spins. It's rotation period is 17.406 days!
Mottola et al. 1996
253 Mathilde is a C-type asteroid, an asteroid with a low albedo, reflecting
only 4% of the incident sunlight and a reflectance spectrum consisting of
a charge-transfer absorption band in the ultraviolet only. To the extent
that the spectrum has been measured (between 0.38 -3.3 microns), its spectrum
contains no absorption features which can tell us of its specific mineralogy.
There is no evidence of a water or water of hydration absorption band in the
3.0 micron region. There is probably a charge transfer absorption in the UV
indicating the presence of unspecified Mg-Fe-bearing silicates.
Mathilde is a Main Belt Asteroid with semi-major axis = 2.46 AU.
It is presently near its perihelion point, q=1.94 AU providing this
flyby opportunity to the NEAR spacecraft.
Where in the Solar System is 253 Mathilde?
Mathilde Flyby
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