What Is Pluto Made Of?
QUICK ANSWER
Pluto is made of about 70 percent rock and 30 percent water ice, with a thin atmosphere of nitrogen, methane, and carbon monoxide. The surface contains frozen nitrogen, methane, and carbon monoxide ices over a layer of water ice. Pluto may have a subsurface liquid water ocean beneath its icy outer shell.
Pluto is mostly rock and ice, with the ratio favoring rock. The surface is coated in frozen versions of gases that exist as gases everywhere else: nitrogen, methane, and carbon monoxide. Beneath the visible surface, Pluto may even have a layer of liquid water, kept warm by leftover heat from the planet's formation.
What is Pluto's composition?
Mostly rock and water ice. According to NASA, Pluto is composed of about 70 percent rock and 30 percent water ice by mass. The interior is differentiated, meaning the heavier rock has settled toward the center while lighter ices remain on the outside. Pluto has a dense rocky core, a thick mantle of water ice, and an outer crust of various frozen gases. This three-layer structure was confirmed by New Horizons measurements during the 2015 flyby.
What's on Pluto's surface?
A surprising variety of frozen materials. The surface contains frozen nitrogen, methane, and carbon monoxide, all of which would be gases at Earth temperatures. These ices are tinted by tholins, dark organic compounds formed when sunlight breaks apart methane. The famous heart-shaped Tombaugh Regio is a vast plain of nitrogen ice that flows and convects like a very slow glacier. The surface also contains water-ice mountains, some up to two miles tall, that stick up through the softer nitrogen and methane ices.
Does Pluto have an atmosphere?
Yes, a thin one. Pluto's atmosphere is composed of nitrogen, methane, and carbon monoxide, with a surface pressure about 1/100,000th of Earth's. The atmosphere is dynamic: as Pluto moves closer to the Sun (during the closer half of its orbit), the surface ices vaporize and thicken the atmosphere. As Pluto moves farther away, the atmosphere refreezes back onto the surface. New Horizons captured high-altitude haze layers and other atmospheric features during the 2015 flyby, showing Pluto's atmosphere is more complex than expected.
Could Pluto have a subsurface ocean?
Possibly, and the evidence is suggestive. New Horizons found features on Pluto's surface that suggest geological activity, including possible cryovolcanoes (volcanoes that erupt water and ammonia instead of magma) and signs that the ice shell may have shifted recently. Some researchers think Pluto has a subsurface ocean of liquid water mixed with ammonia, kept liquid by leftover heat from formation and radioactive decay in the rocky core. If true, Pluto would join the list of solar system bodies that may host subsurface oceans, including Europa, Enceladus, and Titan.
Pluto is mostly rock and water ice in roughly a 70-30 split, with a thin nitrogen-methane atmosphere and a surface coated in frozen gases. The structure is more like a small moon than a typical planet, but Pluto is geologically active in ways that surprised everyone when New Horizons arrived in 2015. The possibility of a subsurface ocean of liquid water makes Pluto a candidate for further exploration, if any spacecraft is ever sent back.
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