spaceSpace and Physics

Infrared Maps Of Pluto Reveal Water-Ice And Its Scattered Atmosphere


Jonathan O'Callaghan

Senior Staff Writer

1004 Infrared Maps Of Pluto Reveal Water-Ice And Its Scattered Atmosphere
Left is just water-ice, right is all ices on the surface. NASA/JHUIAPL/SwRI

The first infrared Pluto data from New Horizons has been returned, and it reveals two interesting findings. The first is that water-ice is more widespread across the surface than thought, and the second shows sunlight scattering in the dwarf planet’s atmosphere.

The data was gathered by the Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument on board New Horizons, used during the closest approach on July 14, 2015. The water-ice data was collected by two LEISA scans of Pluto, taken from a distance of about 108,000 kilometers (67,000 miles).


An initial map, shown above on the left, shows purely detections of water-ice on the surface, by analysing the spectra. It shows only a smattering of water-ice because the spectra is masked by methane ice, so only extremely dense areas show up.

On the right, all types of ice on the surface are mapped together. While this only shows ice types that LEISA could model for, it does show a greater spread of water-ice than had been thought from initial findings in October 2015.

Notably, regions such as Sputnik Planum (the large “heart” to the right) remain absent of water-ice. This could be because it is covered by large amounts of other ices – methane, nitrogen and carbon dioxide – and thus not detectable by LEISA in this dataset.

The same instrument was also used to create a fascinating new view of Pluto’s atmosphere, observed by New Horizons as it looked back on the dwarf planet as it flew past.


Future data from LEISA will include the lower portion of the atmosphere, which is missing from this image. NASA/JHUAPL/SwRI

Taken from 180,000 kilometers (112,000 miles) away, the image shows a blue ring around Pluto, caused by sunlight scattering as it hits haze particles in the atmosphere. The white patches are where sunlight has bounced off the surface. The brightest patch, at roughly the 2 O’Clock position, is a region called Cthulhu Regio.

Haze on Pluto is thought to be caused by sunlight hitting methane and other molecules, producing a photochemical smog that includes hydrocarbons such as acetylene and ethylene. Although these hydrocarbons are small, a fraction of a micrometer wide, they are plentiful enough to scatter sunlight in the atmosphere.

Data from New Horizons will continue returning to Earth throughout this year, and we can expect more interesting findings like these along the way.


spaceSpace and Physics
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  • water ice