“Bite mark” on Pluto’s surface likely caused by sublimation
An odd feature on Pluto’s western hemisphere eerily resembling a bite mark is missing the surface methane characteristic of surrounding terrain, according to compositional images created from those taken by New Horizons’ Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument.
The region in question is highlighted in the blown up inset image produced by the mission team, in which north is up.
Visible in the highly detailed photos, the ‘bite’ or indentation appears to have been caused by the sublimation of methane ice that once was present in the area but transitioned directly from ice into gas, revealing a layer of water ice below.
A region of cratered uplands known as Vega Terra, located on the left side of Pluto’s encounter hemisphere, is separated from adjacent young, craterless plains named Piri Planitia by a long, jagged line of cliffs known as a scarp.
Dubbed Piri Rupes, the scarp at some points breaks up into many mesas – flat-topped hills with steep sides.
A fault known as Innana Fossa, stretching 370 miles (600 km) to the east, cuts across Piri Planitia horizontally, running all the way to the western section of Sputnik Planum, the left side of Pluto’s “heart” – an area covered in nitrogen ice.
The inset at the left of the (above) photo covers a region measuring 280 miles (450 km) long by 255 miles (410 km) wide. It was taken about 45 minutes before the July 14, 2015, closest approach from a distance of about 21,000 miles (33,900 km).
The LEISA data used to create the false-color image on the right was taken from a distance of 29,000 miles (47,000 km) from Pluto, with the best resolution at 1.7 miles (2.7 km) per pixel.
Areas on the latter image depicted in purple are those rich in methane ice, whereas those shown in blue have abundant water ice.
Mission scientists think that the erosion of material on the plateau along the edge of the scarp cliffs is being caused by the sublimation of methane ice.
As was noted in a Discovery.com article, LEISA data shows the Piri Planitia region has far more water ice than the hilly areas, indicating the area has a bedrock of water ice. Methane ice that sat on top of the water ice has largely though not completely sublimated into the atmosphere, which is why some mottled areas in this region show up as methane-rich.
Water ice on Pluto behaves much like solid rock on Earth and is immobile, due to Pluto’s extremely cold temperatures.
“The methane ice-rich surface on Pluto may be sublimating away into the atmosphere, exposing a layer of water-ice underneath,” a NASA statement said.
An AOL.com post has noted how sublimation is triggered by even the lowest levels of heating, whether from the distant Sun or from an, as yet, undetermined internal heat source.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.