In the inner Solar System, the biggest volcano we know of is Olympus Mons on Mars, 624 kilometers (374 miles) across and 25 kilometers (16 miles) high. But what about in the outer Solar System?

Well, that record might now belong to Pluto. If a feature known as Wright Mons on this dwarf planet is confirmed as a volcano, it will take the title of the biggest such feature beyond Mars.

Named in honor of the Wright brothers, this massive ice structure can be seen circled by the red ring in the new image above. It is 150 kilometers (90 miles) wide and 4 kilometers (2.5 miles) high and appears to have volcano-like features, including a central depression that resembles a volcanic crater.

This image was returned by the New Horizons spaceraft, part of the ongoing data that is being returned after the flyby on July 14, 2015. Taken by the Long Range Reconnaissance Imager (LORRI) from a distance of 48,000 kilometers (30,000 miles), it shows features as small as 450 meters (1,500 feet) across.

Color data was provided by the Ralph/Multispectral Visible Imaging Camera (MVIC), obtained from a distance of 34,000 kilometers (21,000 miles).

^{Wright Mons is located near to a large smooth region called Sputnik Planum. NASA/JHUAPL/SwRI}

One intriguing unanswered question is why there is only a smattering of red material – known as tholins – in the region. In addition, a lack of impact craters suggests that this surface is relatively young, meaning it has changed in the last few million years, possibly due to Wright Mons being active in Pluto’s late history. Wright Mons also has similarities to another theorized cryovolcano (ice volcano) on Pluto, Piccard Mons, which is slightly higher at 6 kilometers (3.5 miles). 

“We’re not yet ready to announce we have found volcanic constructs at Pluto, but these sure look suspicious, and we’re looking at them very closely,” said Jeff Moore, a planetary scientist at NASA’s Ames Research Center in Moffett Field, California, who heads the New Horizons geology team, when the structures were first studied last year.

If they are confirmed to be volcanoes that were active relatively recently, it would mean that Pluto likely has some sort of internal heat source. The cause of this is not known, but it could be the radioactive decay of elements that remain from Pluto’s birth.