Pluto Volcano Must Be Young

A cryo-supervolcano on Pluto
cannot be as old as the planet. What
made it erupt relatively recently?

An Unusual Crater on Pluto Might be a Supervolcano (Universe Today, 23 Oct 2023). Meet Kiladze, a new supervolcano in the solar system. This one erupts ice, not hot lava. But erupting ice implies water was able to move within Pluto’s interior. How could that be, after the assumed 4.5 billion years it has been orbiting far from the sun in the solar system’s icebox region?

Reporter Carolyn Peterson brought attention to a study published in the arXiv preprint server last May. Dale Cruikshank and other planetary scientists zoomed in for a look on a region near the edge of Sputnik Planitia (the heart-shaped, crater free iconic landscape on Pluto) called Virgil Fosse. Part of this region contains what looks like a supervolcano that has erupted multiple times over the planet’s history, implying that enough heat has remained over its lifetime to move material from the interior to the surface. (A supervolcano is considered an eruptive vent that has spread material over at least 1,000 square kilometers.) The feature is named Kiladze.

Planetary scientist Dale Cruikshank and a group of colleagues have been studying a strange feature on Pluto called Kiladze Crater. Its existence raises a lot of questions about what’s happening inside Pluto to create this weird landscape. The researchers recently released a paper exploring this region and offering an explanation for its appearance.

How can a planet that should have frozen solid billions of years ago contain enough heat to drive a “young” volcano? They believe it has erupted episodically throughout Pluto’s history, and estimate its most recent deposits are as young as 2 or 3 million Darwin Years old. That would be less than .067% of Pluto’s assumed age. Does Cruikshank know the answer to this mystery?

According to Cruikshank, heating is the culprit. “For Pluto, internal heat is also expected to be the driver for volcanism seen in some places at the surface, but we don’t know if there is a subsurface global ocean of water plus various chemicals, or simply pockets of water plus chemicals left over from the time Pluto formed and had a hot interior,” he said. “This is a mystery for the next generation of planetary scientists to solve.”

Portion of Hyecho Palus SW of Sputnik Planitia on Pluto, showing Wright Mons (center). Credit: Schenk et al, Icarus, 2018. Wright Mons is one of two huge cryovolcanoes investigated in the 2018 paper.

Kiladze Caldera: A possible “supervolcano” on Pluto (Cornell arXiv Preprint Server, 22 May 2023). In the publication, the team does not deal with the problem of what heat source could last billions of years out there. They realize, though, that the fresh-looking deposits on this vent must be young. To evolutionary scientists, “young” can be millions of Darwin Years, but in this case they fall far short of the assumed age of the solar system.

In consideration of the discussion above, a logical conclusion is that the water ice at Kiladze is geologically young. If a surface accumulation of haze particles amounting to a layer of 10 mm is sufficient to mask the principal water ice absorption bands, such a layer will form in ~3 million years. If a thicker layer of aerosol particles would be needed to mask the ice spectral signature of the surface, the time-scale for accumulation would be correspondingly longer, but surely much less than 1 Gy.

One billion years (1Gy), the high side estimate, is still not enough time. That would be a little more than 1/5 the age of the solar system. If one pictures a rope 4.5 feet long as a timeline, and indicates 1 foot on the near end, that leaves most of the rope representing Pluto being active for most of its history, and other features on Pluto look younger than that (search on Pluto at this site).

Before the New Horizons spacecraft encountered Pluto in 2015, planetary scientists expected it to be an ice ball with craters. National Geographic on June 1, 2016 remarked about active processes “scientists didn’t exactly expect to see on a small, freezing world.” Science Daily concurred the same day, reporting that “Many people expected Pluto to be a cold, dead world.” When principal scientist Alan Stern saw all the youthful features on the surface, he exclaimed, “Finding that Pluto is geologically active after 4.5 billion years — there’s not big enough typeface to write that in.”