The Forbidden Planet

If there’s a short list for extrasolar planets to visit, 55 Cancri e is definitely not going to be on it. It’s hot, hellish, and weird…really weird.

As our instruments become more sophisticated, we’re beginning to learn much more about distant alien planets than merely their size and mass. And the exoplanet catalogue is turning out to be an aquarium full of oddballs, indeed.

The most recent discovery involves 55 Cancri e, a “super Earth” in a system located some 40 light years away. The planet, also known as “Janssen,” is about twice the size of the Earth and eight times its mass; it completes an orbit every 18 hours, and—like the Moon—is tidally locked, always presenting the same face to its parent star (just as the Moon always presents the same side to Earth).

Now, using NASA’s infrared Spitzer Space Telescope, astronomers have managed to cobble together a thermal “map” of surface conditions on the planet. It’s a milestone achievement, because now we can put together a detailed census of what’s really out there.

Graphic of 55 Cancri e's light curve as detected by the Spitzer Space Telescope.  Credit: NASA/JPL-Caltech/B. Demory (Cavendish Laboratory)

The Two Faces of Janssen

The planet turns out to have two faces—one “hot” and one “cold.” But these are relative terms, you understand. Because the nightside is 1100° C (2012° F), hotter than the melting point of many familiar metals; and the dayside is a whopping 2500° C (4532° F), which is…well, it’s just really hot.

Venus, the hottest planet in our solar system, and with a surface temperature of just 462° C (864° F), seems positively arctic in comparison.

Astronomers think the dayside is an immense, molten ocean of magma; the nightside, in contrast, seems to be composed of cooled, solid lava. It’s a strange dichotomy, and even stranger because the dayside heat is not communicated to the nightside. The atmosphere, it seems, is being boiled off on the sunward hemisphere, but some remnant of it must cling to the nightside.

That’s consistent with a recent analysis of the planet’s atmosphere, which suggests it does have one, and that it’s mostly hydrogen and helium, infused with hydrogen cyanide (and other weird carbon species).

The bottom line is—55 Cancri e is one hell of a place, and it’s showing us just how bizarre these “super Earths” (which seem to be quite common) really are. Which makes you appreciate our plain, homely old “regular Earth” that much more.

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