Evidence found for ‘giant comet’ theory of Pluto’s origin

A huge nitrogen-ice glacier fills the Sputnik Planitia region of Pluto – the left lobe of the now-familiar heart-shaped feature first seen by the New Horizons spacecraft. Image: NASA

Whether you believe Pluto is a planet or not, its origin and history in the cold outer reaches of the solar system is a mystery that likely holds profound insights into the evolution of the Sun and its retinue of planets, comets and asteroids.

Scientists at the Southwest Research Institute have come up with a possible explanation based on data from NASA’s New Horizons Pluto flyby mission and the European Space Agency’s Rosetta spacecraft, which spent two years orbiting Comet 67P/Churyumov-Gerasimenko.

They call their theory the “giant comet” cosmochemical model of Pluto formation.

Studying nitrogen-rich ice in Sputnik Planitia, a huge glacier forming the left side of the heart-shaped region known as Tombaugh Regio, “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,” said Christopher Glein of SwRI’s Space Science and Engineering Division

The researchers also assessed a “solar model” in which Pluto formed from cold ices with a chemical composition similar to that of the Sun. But the “giant comet” model appears to better explain current levels of nitrogen and carbon monoxide.

The 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,” Glein said.

“This research builds upon the fantastic successes of the New Horizons and Rosetta missions to expand our understanding of the origin and evolution of Pluto,” he said. “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.”

A paper describing the research was published 23 May in the journal Icarus.