Sprawling across Pluto’s icy landscape is an unusual geological feature that resembles a giant spider.
“Oh, what a tangled web Pluto’s geology weaves,” said Oliver White, a member of the New Horizons geology team from NASA Ames Research Center, Moffett Field, California. “The pattern these fractures form is like nothing else we’ve seen in the outer solar system, and shows once again that anywhere we look on Pluto, we see something different.”
As shown in the enhanced colour image above — obtained by NASA’s New Horizons spacecraft on 14 July 2015 — this feature consists of at least six extensional fractures (indicated by white arrows) converging to a point near the centre. The longest fractures are aligned roughly north-south, and the longest of all, the informally named Sleipnir Fossa, is more than 360 miles (580 kilometres) long. The fracture aligned east-west is shorter and is less than 60 miles (100 kilometres) long. To the north and west, the fractures extend across the mottled, rolling plains of the high northern latitudes, and to the south, they intercept and cut through the bladed terrain informally named Tartarus Dorsa.
Curiously, the spider’s “legs” noticeably expose red deposits below Pluto’s surface.
New Horizons scientists think fractures seen elsewhere on Pluto — which tend to run parallel to one another in long belts — are caused by global-scale extension of Pluto’s water–ice crust. The curious radiating pattern of the fractures forming the “spider” may instead be caused by a focused source of stress in the crust under the point where the fractures converge — for example, due to material welling up from under the surface. The spider somewhat resembles radially fractured centres on Venus called novae, seen by NASA’s Magellan spacecraft, as well as the Pantheon Fossae formation, seen by NASA’s MESSENGER spacecraft on Mercury.
The image above was obtained by New Horizons’ Ralph/Multispectral Visible Imaging Camera (MVIC). The image resolution is approximately 2,230 feet (680 metres) per pixel. It was obtained at a range of approximately 21,100 miles (33,900 kilometres) from Pluto, about 45 minutes before New Horizons’ closest approach on 14 July 2015.