London, June 11 : An astronomer has suggested that Nix and Hydra, two of Pluto's moons, are spray-painting the planet and Charon with their dust.
According to a report in New Scientist, Alan Stern at the Lunar and Planetary Institute in Houston, Texas, US, has come up with this theory. luto's dazzling red stands in sharp contrast to the greys of its three moons Hydra, Nix and Charon.
The moons' similarity was thought to be because the trio was created at the same time from the same material in a massive smash in the early solar system.
Now, Stern has determined that the similarity is due to Nix and Hydra throwing up some dust at Charon, as well as Pluto.
Stern reckons that debris from the surrounding Kuiper belt - left over from the solar system's formation - is colliding with Pluto and its moons and throwing up loose material.
Because Charon and Pluto are bigger, their gravity prevents that material from escaping, but it spews out from Nix and Hydra, coating the surfaces of Charon and Pluto with a layer of material a few centimeters thick.
"The reason we can't see the dust on Pluto is that its thin nitrogen atmosphere regularly forms a fresh frost, covering up the debris and maintaining its red sheen," said Stern.
The debris should eventually make Charon look more like the other two moons - a slightly brighter, subtly different grey - a change which could be observed when NASA's New Horizons spacecraft flies by in 2015.