Pluto's blue sky.

Astronomers have proposed a new explanation for the mysterious blue veil that surrounds Pluto. Credit: NASA/JHUAPL/SWRI/SPL

Planetary science

Ice bathes Pluto in a blue haze

Dwarf planet on the Solar System’s outer fringes might have particles of frozen organic matter in its atmosphere.

An analysis suggests that Pluto’s atmosphere is rich in particles of frozen organic compounds, which might account for the distinctive blueish haze enveloping the dwarf planet.

Both Pluto and Saturn’s moon Titan have hazy atmospheres and similar atmospheric compositions. As a result, planetary scientists have thought that Pluto’s haze, like Titan’s, is formed by light-driven chemical reactions that yield complex organic compounds.

Panayotis Lavvas at the University of Reims Champagne-Ardenne in France and his colleagues analysed data from the New Horizons spacecraft and other sources to reveal a chillier explanation for Pluto’s haze. The team found that organic compounds condense more readily in Pluto’s skies than in Titan’s, because the dwarf planet’s atmosphere is colder than that of the large moon. The resulting organic ice particles are probably a major contributor to Pluto’s haze.

The researchers folded organic ice particles into models of Pluto’s atmosphere, which improved the models’ prediction of the amount of light scattered by the dwarf planet’s haze. The authors propose that the hazy skies of Triton, Neptune’s largest moon, might also be caused by organic ice.