Shine On, You Crazy Diamond Planet

There’s a gigantic diamond in outer space, according to new research from a team led by Yale University scientists. About as twice as big as Earth and with eight times more mass, the rocky planet is a “Super Earth” and orbits a star 40 light years away in the constellation Cancer.

First detected in 2004,  the planet—dubbed “55 Cancri e”—moves fast and gets hot. It takes just 18 Earth-hours to orbit its star. It’s temperature is estimated to be around 3900 degrees Fahrenheit (2149 degrees Celsius). The planet has a very close relationship with its star—it orbits about 25 times closer to it than Mercury does to our sun). In May 2012, NASA’s Spitzer Space Telescope detected light emanating from the planet, which led some to believe 55 Canri e was a water world, but the latest findings indicate otherwise.

Lead researcher Nikku Madhusudhan, a Yale postdoctoral fellow in physics and astronomy, described the surface of the giant “gem” as “likely covered in graphite and diamond rather than water and granite. This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth.” The team’s findings, which have been accepted for publication in the journal Astrophysical Journal Letters,  represents the first time that astronomers have identified a likely diamond planet around a sun-like star and specified its chemical make-up.

Astronomers have been interested in the possibility of diamond planets for years. In 2005, scientists theorized that carbon-rich planets might exist (Related: “Diamond Planets” Hint at Dazzling Promise of Other Worlds). Then in 2010, a team led by Madhusudhan announced the discovery of the first carbon-rich world, a distant gas giant named Wasp 12-b. This tantalizing find led scientists to believe that carbon-rich rocky planets might be out there too.

Last year, Madhusudhan’s team was first able to record 55 Cancri e transitioning its host star. This observation allowed to measure the planet’s radius for the first time. This important data when combined with an estimate of the planet’s mass allowed the team to infer its distinctive chemical composition. Instead of a resembling Earth’s chemical make-up, this rocky planet was something completely different—a planet composed primarily of carbon (as graphite and diamond), iron, silicon carbide, and possibly, some silicates. They speculate that about one third of the planet’s mass is pure diamond.

The identification of a carbon-rich super-Earth means that distant rocky planets can no longer be assumed to have chemical constituents, interiors, atmospheres, or biologies similar to those of Earth, Madhusudhan said. It also has implications for a planet’s thermal evolution and plate tectonics.

“Stars are simple—given a star’s mass and age, you know its basic structure and history,” said David Spergel, professor of astronomy and chair of astrophysical sciences at Princeton University, who is not a co-author of the study. “Planets are much more complex. This ‘diamond-rich super-Earth’ is likely just one example of the rich sets of discoveries that await us as we begin to explore planets around nearby stars.”

Changing Planet

Meet the Author
Focusing on content that entertains, astounds, and informs, Amy Briggs is freelance writer and former senior editor with National Geographic Books . The author of National Geographic Angry Birds Space, Briggs worked closely with National Geographic NewsWatch's David Braun on National Geographic Tales of the Weird. Excited by all things trivial, odd, and just unusual, she lives in Virginia with her family.