The bizarre, hourglass-shaped Kuiper belt object 2001QG298 spins round like a propeller as it orbits the Sun, according to an astronomer from Queens University Belfast. The discovery that the spinning object is tilted at nearly 90 degrees to the ecliptic plane was surprising, and suggests that this type of object could be very common in the Kuiper belt.
The Kuiper belt objects (KBOs
) orbit the sun beyond Neptune and are the best preserved leftovers of the formation of the planets. 2001QG298 is a remarkable KBO made up from two components that orbit each other very closely, possibly touching. “Imagine that you glue two eggs together tip to tip – that’s approximately the shape of 2001QG298. It looks a bit like an hourglass,” said Dr Pedro Lacerda at the Joint Meeting of the European Planetary Science Congress and the Division for Planetary Sciences
in Nantes, France.*
The strange shape of 2001QG298 was uncovered by Dr Scott Sheppard and Prof David Jewitt in 2004. They noticed that 2001QG298’s apparent brightness periodically tripled every 7 hours or so.
"The object is so distant that we cannot resolve its shape. But this brightness oscillation, called a lightcurve, reveals the strange shape of 2001QG298 as it spins round. The object appears faint at times because one lobe is hidden behind the other, so less area is reflecting sunlight. As the hidden component rotates back into view, we can see the full hour-glass shape. The reflecting area increases and the whole thing looks brighter," explains Lacerda.
However, Lacerda’s study shows that 2001QG298’s rotation is almost perpendicular to the plane of its orbit around the sun. Lacerda re-measured the object’s lightcurve in late 2010 and noticed that it had changed from Sheppard and Jewitt’s observations. The lightcurve variation has become visibly shallower.