Scintillating Diamond Planet Meets Bumpy Potato Asteroid

55 Cancri e orbits 55 Cancri in just 18 hours. It has a graphite surface surrounding a thick mantle of diamond, below which is a layer of silicon-based minerals and a molten iron core at center. Credit: Haven Giguere / NASA

Every day we wake up to another surprise from the sky. A U.S.-French team of astronomers, using data from NASA’s Spitzer Space Telescope, have discovered that the extrasolar planet 55 Cancri e is composed largely of carbon, much of it in the form of diamonds. 55 Cancri e is one of five planets orbiting the star 55 Cancri located 40 light years away in the constellation Cancer.

Earth and 55 Cancri e compared. Credit: NASA

The pricey planet orbits so close to its host star its surface reaches a scorching 3,900 degrees, hot enough to instantly melt stainless steel.

55 Cancri e takes only 18 hours to make one spin around the star compared to Earth’s 365 days. If you could somehow live there (not likely), after the equivalent of 80 Earth years, you’d be 38,933 “years” old.

55 Cancri e, with a mass about 8 times that of Earth and twice as big, belongs to a class of planets nicknamed “super Earths” that have masses and sizes between that of Earth and the mid-size giant planets Uranus and Neptune.

What’s really unusual about 55 Cancri e is its composition. Instead of rocks rich in oxygen and silica like those that dominate Earth’s crust and mantle, this planet’s loaded with carbon in the form of graphite and diamonds. Talk about exotic:

55 Cancri is a 6th magnitude star in northern Cancer easily visible with binoculars in the morning sky. Created with Stellarium

“The surface of this planet is likely covered in graphite and diamond rather than water and granite,” said Nikku Madhusudhan, Yale researcher and lead author of the paper on the findings.

It’s believed that a thick layer of very pure diamonds more than twice the mass of planet Earth lies between the surface and 55 Cancri e’s core. Deeper yet, Madhusudhan speculates that the diamonds could exist in liquid form. The folks at De Beers must chomping at the bit.

Rough diamond

Diamond is a hard, pure, crystalline form of carbon. Most diamonds on Earth were made under great pressure and heat at depths between 90-120 miles; volcanic eruptions bring them to the surface. To create this coveted material you need two things – extreme pressure and extreme heat, both of which are found in abundance on this hot, dense “super Earth” of a planet.

55 Cancri may represent an entirely new class of carbon-rich worlds. There’s no particular reason why our solar system should be the standard model of planet composition. Every time a paradigm is challenged by new evidence, we sweep away a few more cobwebs and discover the universe is more surprising than we’d imagined.

Last night my cobwebs got blown away watching Earth-approaching asteroid 2012 TC4. To find it, I hand-plotted its location at five-minute intervals on a detailed star chart, pointed the telescope at the right spot and waited. Darn thing was right on time. I stayed with the 60-foot-long boulder for about 40 minutes, long enough to see one of the most amazing astronomical sights in my life – the change in the asteroid’s brightness as it rotated on its axis.

A model using an actual potato of asteroid 2012 TC4. During a full 12-minute rotation, the brightness of the potato changes in a regular, repeated manner depending on what side we see. The photo is for illustration only; the real asteroid has a more irregular shape and might be tumbling in another direction. Illustration: Bob King

When brightest, it was easy to see (13.6 magnitude), but when faintest at around 14.7 I nearly lost it a few times. For fun, I used my watch to time the asteroid’s brightness variations. At 8:11 p.m. (CDT), 2012 TC4 was brightest but then nearly faded away just 3 minutes later. After another three to four minutes passed, it returned to full brightness. This happened 7 times during my watch.

The reason for the light variation? Little asteroids have irregular shapes. If we can assume 2012 TC4 looked something like a potato, the observations make perfect sense. At brightest, we saw the broadside of the potato (lots of area to reflect sunlight), 3 minutes later the potato rotated so only its end faced us (less area to reflect sunlight, so faintest), and 3 minutes after that we faced the other broadside (bright again). That’s equal to half a rotation or about 6 minutes. Add in the potato’s opposite pointy end and a return to the first broadside we saw and that comes to about 12 minutes, in neat agreement with the data gleaned from light-measuring devices called photometers. If you saw 2012 TC4 and had a similar experience we’d love to hear your story.

7 Responses

  1. Lorena Marsh

    Hi Bob, great info. Regarding —55 Cancri e – This marvelous planet deserves a better name, I’ll suggest Nasa name it “Marylin Monroe” hahaha. Amazing your findings on TC4, evidently it’s a high roller spining his way throughout. Thank for sharing. As per 2012 AD14 I will just have to wait and see as it as it get closer even if I have to travel to a better spot. Also I’m preparing for Comet ISON, I hope to get all info for these events, will be awesome! Keep us posted and thanks!

    1. astrobob

      Yes indeed Lorena, some like it hot. Great name suggestion for the planet! I’ll be writing more about ISON and 2012 DA14 as they brighten.

  2. MBZ

    It’s a darn shame you don’t live in my neck of the woods. I could peer over your shoulder and get my cobwebs swiffered away too. What an outstanding experience. All while I’m creating aches and pains making me feel roughly equivalent to my 55 Cancri e age… What, 26-27,000 years old? Too lazy to do the math 😉 Home renovations, oh the joy.
    Please do NOT eat that sorry looking spud.

    1. astrobob

      Your commentary always gives me a chuckle. You have a good eye – that potato was on its last legs (eyes?). Kinda soft around the middle. I figured I’d give it one last shot at fame in the twilight of its career.

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