No Caverns Found Inside Rosetta's Comet

What lies beneath the surface of comet 67P is a question that intrigued scientists for a long time. A new study came to give the answer. Contrary to some expectations, the interior of the comet does not contain caverns but is rather made mostly of dust and water ice.

The study was published this week in the journal Nature. The new research has solved the mystery of the most well-studied space rocks in our solar system, comet 67P.

Until now, only eight comets have been visited by human technology, of 5,507 comets streaming through space. With the Rosetta spacecraft mission on comet 67P organized by the European Space Agency, scientists have been able for the first time to provide precise measurements and analysis.

Comets are usually a mixture of rock and water ice and they date from the formation of the solar system. We would expect them to be denser than water if they are fully compact, but this isn't the case. Many comets, including Rosetta's comet, have very low densities. This fact made some scientists to expect that the comets' interior might contain caves and caverns.

According to The Christian Science Monitor, researchers found that the comet 67P is filled with very light, powdery dust grains but solid all the way through. Astronomers have came to that conclusion by studying the effect of the gravity field of the comet on radio signals on the ground.

The comet's gravitational pull on Rosetta would cause a change in acceleration because it would be stronger during some parts of the spacecraft's orbit, if the comet's interior was pitted. That change in acceleration would produce in turn a Doppler shift in Rosetta's radio signals frequency.

Scientists concluded that 67P is homogenous, since no large acceleration changes were detected. According to researchers' estimations, the interior comet is about 25 percent water ice and 75 percent dust grains.