Space exploration finds 'diamond planet' in Milky Way galaxy
By Amanda Jermyn

Have you ever wanted a diamond, a really big one, perhaps? Well, a mere forty light-years from Earth, in our very own Milky Way galaxy, a “diamond planet” has been found orbiting a star called 55 Cancri. The star itself may be observed with the unaided eye in the constellation Cancer. According to Yale University’s Dr. Nikku Madhusudhan, lead researcher in the discovery, “This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth. The surface of this planet is likely covered in graphite and diamond rather than water and granite.”

The planet, officially known as 55 Cancri e, was first observed transiting its star in 2011. It is the first diamond planet identified orbiting a Sun-like star and is one of five planets orbiting the star. This highly dense planet, with a radius twice that of Earth and a mass eight times greater, is considered a “super-Earth,” a term used to describe extra-solar planets with masses between one and ten times that of Earth. The planet orbits extraordinarily fast. Its year lasts only 18 hours, as compared to Earth’s 365 days. Because it is so close to its star, about 26 times closer than Mercury is to our Sun, it is scorchingly hot, with a temperature of 3,900 degrees Fahrenheit, making it inhospitable to life.

While astronomers had previously assumed the planet would have a similar makeup to Earth, Madhusudhan and his colleagues, Kanani Lee of Yale and Olivier Mousis of The Research Institute in Astrophysics and Planetology in Toulouse, France, discovered something entirely different – a planet with no water, composed primarily of carbon, in the form of graphite and diamond. In contrast, Earth’s interior, while oxygen-rich, has very little carbon, less than one part per thousand. The surface of the planet appears to be mostly graphite (used to make pencils) surrounding a thick layer of diamond, below which is a layer of silicon-based minerals, with a molten iron core at the center. The study, published in 2012 in “Astrophysical Journal Letters,” estimates that at least a third of the planet’s mass, equivalent to three times the mass of Earth, could be diamond.

With the discovery of a carbon-rich super-Earth, Madhusudhan notes that rocky exoplanets can no longer be assumed to have chemical constituents, atmospheres or biologies similar to those of Earth. The very different properties of carbon-rich minerals compared to Earth-based minerals imply entirely new geological, atmospheric and biological processes on carbon planets, and require a revision of our understanding of planet formation. With recent studies indicating an abundance of rocky planets orbiting stars beyond our solar system, who knows what exotic discoveries still await us?

Join the Springfield Stars Club on Tuesday, May 28th at 7:30pm at the Springfield Science Museum for a talk by astrophysicist Dr. Nikku Madhusudhan on “Super-Earths and Diamond Planets.” Dr. Madhusudhan has a PhD in physics from MIT and is currently a postdoctoral researcher at the Yale Center for Astronomy and Astrophysics at Yale University. His talk will present astronomers’ latest understanding of the interiors, atmospheres and geophysical conditions on super-Earths. These alien worlds have interiors spanning a wide range of chemical compositions, from water worlds with thick, gaseous envelopes to super-Mercuries, lava planets and diamond planets. The recent discovery of the “diamond planet,” 55 Cancri e, will be discussed in detail. Refreshments will be served, and the public is welcome free of charge.