Pluto's famous heart may drive winds that darken its icy surface

Pluto's famous heart may drive winds that darken its icy surface
A mosaic of Pluto taken by NASA's New Horizons spacecraft in 2015
A mosaic of Pluto taken by NASA's New Horizons spacecraft in 2015
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A mosaic of Pluto taken by NASA's New Horizons spacecraft in 2015
A mosaic of Pluto taken by NASA's New Horizons spacecraft in 2015

New research has shed light on how Pluto’s famous heart-shaped plane of frozen nitrogen creates winds in the dwarf planet’s thin atmosphere, that lead to vast discolorations on its bright surface. The study used information collected by NASA’s New Horizons spacecraft during its close pass with Pluto in 2015, during which the probe captured a stunning treasure trove of imagery and data on the distant alien world.

The Tombaugh Regio formation – which lies at the center of the new study – captured the public's attention during New Horizon’s speedy approach to Pluto back in 2015. From a distance, the structure resembled an oversized cartoon heart. Upon closer inspection, the vast basin that formed the left "lobe" of the heart revealed itself to be nothing short of a geological marvel. That basin is known as Sputnik Planitia.

The icy plane seemed to be divided up into cells, and was relatively devoid of craters. An analysis of New Horizons’ data revealed that Sputnik Planitia was constantly refreshing its surface through a process called convection, wherein warmer liquid nitrogen rises from beneath the surface and solidifies in the middle of the cells, while colder nitrogen ice slips back beneath the surface at the edges.

New research relying on advanced computer modelling has now granted further insight into how this unusual landscape interacts with its surroundings.

According to the team behind the new study, a thin layer of surface nitrogen evaporates from Sputnik Planitia each day, and is then born aloft into the tenuous atmosphere. When the temperature drops during the night, the nitrogen descends, and settles once more as ice.

This periodic evaporation and resettling of material has been likened to the beating of a heart, and with each beat, the resulting atmospheric disturbance pumps nitrogen winds across the surface of the planet.

The team took data on Pluto’s topography and ice distribution gathered by New Horizons, and ran computer simulations on potential weather cycles in order to figure out how the circulating gas may affect surface features.

The scientists discovered that nitrogen gas which has evaporated from ice sheets to the north travels southward and settles, and that this triggers a western wind. Surprisingly, the atmospheric current prevailing 4 km (2.4 miles) above the surface travels counter to the eastward spin of the dwarf planet for the majority of Plutonian year. This is a rare atmospheric process known as retro-rotation.

Another relatively strong wind current was also found in the simulation travelling near the surface across the western edge of Sputnik Planitia. According to the authors, this current mirrors a similar wind that blows across the eastern edge of Asia back on Earth.

The researchers found that the atmospheric currents described in the simulations could account for the differences in color and composition of ice located to the west of Sputnik Planitia. As the wind travels west, it may transport heat from the atmosphere that would then come into contact with the ice, causing it to sublimate faster and become less reflective. Alternatively the wind could carry with it dark materials that are subsequently deposited in streaks across the surface.

"Sputnik Planitia may be as important for Pluto’s climate as the ocean is for Earth’s climate," comments lead author of the study Tanguy Bertrand, and astrophysicist and planetary scientist at NASA’s Ames Research Center, California. "If you remove Sputnik Planitia – if you remove the heart of Pluto – you won’t have the same circulation."

A paper on the study has been published in the Journal of Geophysical Research.

Source: American Geophysical Union

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