Asteroid's shape and size determined for first time

Volunteer astronomers in the US have determined for the first time the shape and size of the double asteroid Patroclus-Menoetius that passed directly in front of a star Oct 20.

Led by Marc Buie, staff scientist in Southwest Research Institute (SwRI), the astronomers observed the event, known as an occultation, from multiple sites where each observer recorded the precise time the star was obscured.

Seven of those were analysed to estimate an outline, or an elliptical limb fit, of Patroclus of 125 km by 98 km.

Six of the observations were combined for Menoetius and yielded a size of 117 km by 93 km.

"Previous estimates of the shape of the asteroid pair had indicated essentially spherical objects," Buie said.

Our new observations indicate a significantly more non-spherical shape, and that shape is identical for the two bodies, Buie pointed out.

The observations point to mostly oblate shape, or one that appears flattened at the poles and slightly bulged at the equator.

"The very similar shapes of the pair suggest that they were both spinning much faster when they formed," Buie said.

"The current system is in a doubly synchronous state, much like Pluto and Charon, where they orbit each other in the same time it takes for them to rotate," Buie explained.