A super-hot, super-dense super-Earth

A simulation of a transit by 55 Cancri e as its orbit takes it in front of the star 55 Cancri A. The Sun, Earth, and Jupiter are shown for comparison.

How would you like to visit a “super-Earth” with three times the gravity of Earth, a surface temperature that’s 100 times hotter, and a year that’s only 18 hours long?

Welcome to exo-planet 55 Cancri e. Located 40 light-years from our solar system, this super-Earth is 60 percent larger in diameter than Earth and eight times as massive, making it about as dense as lead. 55 Cancri e orbits its own sun, a star called 55 Cancri A, in such a tight orbit that the star appears 60 times bigger in the sky than the Sun appears to Earth observers.

Astronomers discovered 55 Cancri e using the Doppler “wobble” method, where slight variations in the wavelength of light coming from the star are used to infer the presence of unseen planets exerting tiny gravitational tugs on the star. (Any potential observers on 55 Cancri e could infer the presence of Earth the same way: our own Sun wobbles slightly as it spins due to the gravitational influence of the planets in our solar system.) The orbital period, or year, for 55 Cancri e was measured by the transit method. This method requires very sensitive instruments, as it measures the tiny decrease in light coming from the star as the planet periodically passes in front of it (see above illustration).

If you have a clear view of the sky at night you can see 55 Cancri A for yourself. It’s a sixth magnitude yellow dwarf star that’s just visible to the naked eye. Look for it in the constellation Cancer, but don’t strain yourself looking for any of its planets — they’re too small to be seen even with the best telescopes.

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