A new image transmitted by NASA's New Horizons spacecraft has led mission scientists to theorize that sections of Pluto's heart-shaped plain behave much like a lava lamp – with blobs rising to the surface when warmed by the dwarf planet's internal heat, and sinking when they cool.
The image was captured by the spacecraft's Long Range Reconnaissance Imager (LORRI) at a distance of roughly 10,000 miles (17,000 km) on July 14, 2015. The shot covers an area 50 miles (80 km) wide and more than 400 miles (700 km) in length.
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The unusual cell-like appearance of the region surprised scientists across the world when they were first transmitted by the distant probe, and theories have been formulated ever since to address the unusual features. It is now believed that the strange pits that permeate the landscape are the result of a process known as sublimation.
On a larger scale, the cells observed from orbit, which measure 10-25 miles (16-40 km) across are believed to result from a mechanism by which the surface periodically renews itself. The cell-like structure of the plains owes its formation to a thermal convection process. Solid nitrogen would be warmed by Pluto's weak interior heat, becoming buoyant and rising to the surface in a great blob from a reservoir which could, in places, be miles deep.
Parts of the raised edges of the cells are occasionally left behind, as the nitrogen-rich ice that makes up the bulk of each cell cools and falls beneath the surface. According to the team, such an event may have been responsible for creating the distinctive x-like artefact observed in the image at the top of this page, which may once have been the meeting point of four separate cells.
According to mission scientists, the sporadic dark areas visible in the mosaic may represent the presence of a contaminated block of water ice.
This process would effectively allow a cycle of periodic rebirth of large sections of Sputnik Planum, and would explain the relative scarcity of impact craters which would ordinarily mark the terrain.
A second composite image has been released by NASA, capturing a densely-cratered region of Pluto informally designated Viking Terra. The observations were made by New Horizons' LORRI instrument from a range of 31,000 miles (49,000 km), supplemented by data captured by the spacecraft's Ralph/Multispectral Visible Imaging Camera (MVIC).
The terrain captured in the composite is roughly 160 miles (250 km) in width, displaying bright methane ice lining numerous crater rims. The ordinarily bright landscape is blemished by dark red particles known as tholins.
Large quantities of the darker particles appear to have flowed into a number of channels and crater basins, leading mission scientists to theorize that the tholins are being manipulated by ice flows, or possibly even being blown by Pluto's winds.
Source: NASAView gallery - 3 images