Washington: Astronomers from the University of Maryland have mapped the composition of Pluto’s surface and confirmed the shapes, sizes and unique rotations of two of Pluto’s moons.

The findings will help scientists understand the origins and subsequent history of Pluto and its moons.

“Water ice is a new element that we must consider as we try to piece together Pluto’s complex surface composition,” said astronomer Silvia Protopapa.

To explore whether Pluto’s colour diversity is due to its composition, Protopapa and her colleagues analysed data from New Horizons probe.

The red colour on the surface indicates the presence of organic compounds called tholins, which are the result of energetic irradiation of methane, nitrogen and carbon monoxide mixtures.

However, Protopapa and her colleagues do not yet understand the relationship between water ice and tholins on Pluto’s surface.

“Why water ice appears where it does and not elsewhere and which types of tholins are present on Pluto’s surface are questions we hope to answer,” the authors noted.

The team also plans to compare the New Horizons mission data with ground-based measurements taken at different seasons during Pluto’s orbit to obtain a more complete picture of the complex mechanisms that shape Pluto’s surface.

“We knew Pluto’s surface was heterogeneous based on ground-based data. However, I was astonished to see such spectacular surface colour and geological diversity,” Protopapa explained.

Pluto is not alone in having water ice on its surface. The data indicates that Nix and Hydra – two of Pluto’s five moons – are also covered with water ice.

The rotational patterns of Pluto’s moons also puzzle astronomers as the two moons do not always have the same face locked toward Pluto.

According to them, the strange rotation patterns of these two moons could be due to the system’s domination by Pluto and its largest moon, Charon, which together form a “binary planet.”

“It’s possible that Nix and Hydra can’t focus on locking one face toward Pluto because Charon keeps sweeping past and stirring things up,” said study co-author Douglas Hamilton in a paper which appeared in the journal Science.