New research suggests Pluto’s equator could be home to far more of its towering “bladed terrain” than previously thought, with methane ice spires possibly covering around 60% of the region, much of it on the dwarf planet’s far side.
These giant, ridge‑like structures were first spotted in 2015 by NASA’s New Horizons spacecraft during its fly‑by. Standing up to 300 metres high, about the height of the Eiffel Tower, and spaced roughly seven kilometres apart, they form parallel rows across high‑altitude terrain in the Tartarus Dorsa region, just east of Pluto’s heart‑shaped Tombaugh Region. The bladed terrain is thought to be a larger, more widely spaced version of penitentes on Earth, narrow spikes of ice found in high‑altitude regions like the Andes, which reach no more than three metres in height. Similar features have also been identified on Jupiter’s moon Europa and may exist on Mars.
On Pluto, however, these icy spires appear on a vastly greater scale. Until now, they had only been confirmed on the “encounter hemisphere”, the side imaged in high resolution during New Horizons’ fly-by. Infrared mapping suggested much of Pluto’s equatorial region, even on the unseen hemisphere, is methane‑rich, hinting that bladed terrain could exist there too.
Detecting Spires Without Seeing Them
Direct imaging of Pluto’s far side is still too low in resolution to pick out individual spikes. Instead, the research team, led by Ishan Mishra of NASA’s Jet Propulsion Laboratory, turned to surface photometry. Under the same lighting, rougher terrain scatters more light into shadow, making it appear darker overall.
Using reflectance data from multiple viewing angles, the team modelled how surface brightness changes with roughness. They compared confirmed bladed terrain with suspected methane‑rich zones on the far side, finding that the latter were, on average, twice as rough.
A Planet‑Wide Band of Blades
The results imply a belt of icy spires stretching around Pluto’s equator, between 30° north and 30° south latitude, covering roughly 60% of its circumference, about five times the width of the continental United States. Whether this belt is continuous or broken into patches remains unclear.
Formation is thought to depend on long‑term cycles of methane condensation and sublimation, driven by Pluto’s seasons and orbital variations. These conditions appear to be met in the equatorial band, making it the planet’s prime zone for the growth of such features.
Confirming the extent of Pluto’s bladed terrain will require another close‑range mission. For now, studies like this offer the best indirect evidence from the data we have, and suggest the dwarf planet’s equator may be far stranger than the already extraordinary images sent back by New Horizons.
The full study appears in the Journal of Geophysical Research: Planets
