Pluto May Be a Giant Comet, According to New Research

Over a decade ago, Pluto was downgraded from a planet to a dwarf planet. Now, scientists have a new theory about the celestial body: that it is a huge comet.

Scientists previously thought that Pluto was formed like a planet 4.6 billion years ago, after gas and ice bound together with a rocky core to create an enormous sphere in the Sun's protoplanetary disc.

But a team at Southwest Research Institute have come up with a new theory about how Pluto formed at the edge of our solar system, called the cosmochemical model of Pluto formation.

The researchers used data collected from NASA's New Horizons space interplanetary space probe to Pluto and the European Space Agency's Rosetta mission to the comet 67P/Churyumov–Gerasimenko. The preliminary paper outlining the theory was published in the journal Icarus.

NASA's New Horizons spacecraft captured this image of Sputnik Planitia — a glacial expanse rich in nitrogen, carbon monoxide and methane ices — that forms the left lobe of a heart-shaped feature on Pluto’s surface. SwRI scientists studied the dwarf planet’s nitrogen and carbon monoxide composition to develop a new theory for its formation. Image Courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

This idea centers around the nitrogen-packed ice of a large glacier named Sputnik Planitia, which makes up the left lobe of the Pluto's heart shaped Tombaugh Regio area.

Dr. Christopher Glein of Southwest Research Institute (SWRI) Space Science and Engineering Division and lead author of the study, said in a statement: "We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta."

But data on Pluto's very cold ices also enabled the team to float the idea that Pluto has a similar chemical composition to the Sun. So the origins of Pluto remain unanswered.

To arrive at the comet and sun models, the scientists considered the amount of nitrogen present on Pluto, and also estimated how much of the element could have escaped out of its atmosphere over the eons. This was considered alongside the levels of carbon monoxide believed to be at Pluto.

"Our research suggests that Pluto's initial chemical makeup, inherited from cometary building blocks, was chemically modified by liquid water, perhaps even in a subsurface ocean," Dr. Glein said.

He added: "Using chemistry as a detective's tool, we are able to trace certain features we see on Pluto today to formation processes from long ago. This leads to a new appreciation of the richness of Pluto's 'life story,' which we are only starting to grasp."