Remember 55 Cancri e? Sure you do — and if you don't, you should. After all, it may be the first diamond planet ever discovered that orbits a Sun-like star. At least we think it is; if there's one thing 55 Cancri e is good at, it's fooling astronomers into thinking it's something that it's not.
55 Cancri e is an exoplanet, one of the billions of worlds in the Milky Way Galaxy that exist outside our solar system. NASA's Kepler telescope has identified thousands of exoplanets since it was launched in 2009, but 55 Cancri e, in particular, is worth remembering — partly because it's weird, but also because it's something of an OG when it comes to Earth-like planetary discoveries.
55 Cancri e was first spotted all the way back in 2004, so it actually pre-dates Kepler. It's old school. With a radius twice that of our own planet's, and a mass close to eight times greater, it was the very first super-Earth to be discovered orbiting what's known as a main sequence star. As such, it's been subject to its fair share of analysis over the years; and — by extension — its fair share of identity crises.
Astronomers originally thought 55 Cancri e was a torrid wasteland, its surface scorched and parched due to its proximity to its parent star. Later studies would conclude that the exoplanet had a mass-to-volume ratio comparable to solid lead.
This would have made 55 Cancri e the densest known planet in the galaxy, had another research group not come along and demonstrated its density to be much lower than previously estimated. This same group claimed that 55 Cancri e was not singed dry by its sun, but in fact home to water vapor, steaming gasses and a molten surface.
A few months later, in January of this year, the same researchers released findings that suggested 55 Cancri e may actually "ooze" with what are known as supercritical fluids — compounds which, under extreme pressures, behave like a hybrid of liquid/gas hybrid. "55 Cancri e may be wetter and weirder than anyone imagined," said NASA's Tony Phillips when news of planet's "oozing" status first broke.
But today, a team of researchers led by planetary scientists at Yale University is saying that 55 Cancri e is so geochemically different from Earth that it doesn't ooze at all.
"This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth," said lead researcher Nikku Madhusudhan in a statement. "The surface of this planet is likely covered in graphite and diamond rather than water and granite."
"By contrast, Earth's interior is rich in oxygen, but extremely poor in carbon," explained study co-author Kanani Lee, "less than a part in thousand by mass."
If Madhusudhan, Lee and their colleagues are right, 55 Cancri e would be the first diamond planet to be identified around a Sun-like star (though it's worth pointing out that other diamond planets have been discovered in the past, and they might actually be somewhat common in our galaxy).
The researchers intend to perform followup studies, both on 55 Cancri e's atmosphere and its neighboring planets, in hopes of corroborating their current "diamond-planet" conclusions. We think that's a good idea. After all, astronomers have been burned by 55 Cancri e before.
The paper reporting the researchers' findings has been accepted for publication in the journal Astrophysical Journal Letters.