The behaviour of Pluto’s unpredictable moons

This illustration depicts Pluto and its five moons from a perspective looking away from the sun. The outermost moon is Hydra, seen in the bottom left corner. The other moons are roughly scaled to the sizes they would appear from this perspective, although they are all enlarged relative to the planet.
NASA/JPL/M. Showalter, SETI Institute

A new study published in Nature today reveals the most detailed explanation so far of the unpredictable orbital and rotational patterns of Pluto and its five known moons, based on Hubble telescope data.

It describes a system dominated by Pluto and its largest moon, Charon, which together form a “binary planet”.

Four smaller moons orbit this pair.

“Like good children, our moon and most others keep one face focused attentively on their parent planet,” said Douglas Hamilton, professor of astronomy at the University of Maryland and a co-author of the study. “What we’ve learned is that Pluto’s moons are more like ornery teenagers who refuse to follow the rules.”

The authors say the shifting gravitational field created by Pluto and Charon is to blame, as it sends the smaller moons tumbling in unpredictable ways. The effect is amplified by the fact that the moons are roughly football shaped, rather than spheres.

All this, of course, whets our appetites for the arrival later this year of NASA’s New Horizons spacecraft.

The study also revealed that Kerberos is as dark as charcoal, while the other moons are as bright as white sand. ‘This is a very provocative result,’ said lead author Mark Showalter, a senior research scientist at the SETI Institute. Astronomers had predicted that dust created by meteorite impacts should coat all the moons evenly, giving their surfaces a uniform look.

Pluto’s moons in a composite image from NASA’s New Horizons spacecraft.
NASA/Johns Hopkins Univ. App. Physics Lab./Southwest Research Inst.

It will pass by Pluto and its five known moons, providing the most detailed look at this planetary system to date – as we preview in Knocking on Pluto’s door.

Please login to favourite this article.