Vulcanoid Asteroid - Physical Characteristics

Physical Characteristics

Any vulcanoids that exist must be relatively small. Previous searches, particularly from the SOHO spacecraft, rule out asteroids larger than 60 kilometres (37 mi) in diameter. The minimum size is about 100 metres (330 ft); particles smaller than 0.2 μm are strongly repulsed by radiation pressure, and objects smaller than 70 m would be drawn into the Sun by Poynting–Robertson drag. Between these upper and lower limits, a population of asteroids between 1 kilometre (0.62 mi) and 25 kilometres (16 mi) in diameter is thought to be possible. They would be almost hot enough to glow red hot.

It is believed that the vulcanoids would be very rich in elements with a high melting point, such as iron and nickel. They are unlikely to possess a regolith because such fragmented material heats and cools more rapidly, and is affected more strongly by the Yarkovsky effect, than solid rock. Vulcanoids are probably similar to Mercury in colour and albedo, and may contain material left over from the earliest stages of the Solar System's formation.

There is evidence that Mercury was struck by a large object relatively late in its development, a collision which stripped away much of Mercury's crust and mantle, and explaining the thinness of Mercury's mantle compared to the mantles of the other terrestrial planets. If such an impact occurred, much of the resulting debris might still be orbiting the Sun in the vulcanoid zone.