Pluto: Calls for rock to become a planet again mount after scientists suggest clouds have been spotted on its surface

The clouds wouldn’t allow it to satisfy the rule that got Pluto kicked out of the list of planets — but might show that list should be reformed, scientists say

NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. (NASA)

Pluto could be about to become a planet again, after scientists spotted what appears to be clouds on its surface.

As part of the New Horizons mission — which has already found far more complexity on Pluto than had been expected — scientists have spotted cloud-like parts of the images released from the mission. That could mean that the planet has an even richer atmosphere than had been thought, according to the New Scientist, which first reported the images.

Scientists aren’t yet sure that the images show clouds, and the discovery hasn’t been reported publicly. But emails seen by the magazine seem to indicate that the now dwarf planet might have clouds made up of the same things in its general atmosphere, which is mostly made up of nitrogen.

The discovery could lead to further calls for Pluto to be reinstated as a planet — a question that has already been asked more and more since New Horizons sent back detailed images of the dwarf planet’s rich surface.

Pluto still won’t satisfy the International Astronomical Union’s rules for what is and isn’t a planet. It was excluded on the basis of a criterion that it still doesn’t pass, whether or not the pictures show clouds: that a planet should have a clear neighbourhood of orbiting bodies.

But that IAU definition has proven controversial. Scientists including the head of the New Horizons team, Alan Stern, have argued that the definition is needlessly complicated and should be redefined around the ways that people actually use the words.