June 17, 2024

Close-boiling Lava Earth May Still Have Day-Night Cycles

Extrasolar planet researchers obsess day and night about detecting habitable solar systems and planets. But the vast majority of planets in our galaxy are barely habitable and many are just plain weird.

Case in point is 55 Cancri e, a crazy, super-Earth-sized planet that orbits its red dwarf parent star in 17 hours. Located about 40 light-years away in the constellation of Cancer, the planet’s surface can get hot enough to melt iron and is known to have a global lava basin.

But until recently it was assumed that 55 Cancri e would be rotationally, tidally locked to its parent star, so that one side of the planet would remain in perpetual daylight.

But That may not be the case

New observations indicate that 55 Cancri e may have a day and night cycle.

Using NASA’s Webb Space Telescope observations as well as observations using ESA’s (European Space Agency) Characterization of Exoplanet Satellite (CHEOPS), Stockholm University astronomer Alexis Brandeker and colleagues found that 55 Cancri e temperature and orbital changes are greater than they ever expected.

Normally, you’d expect a planet orbiting so close to its parent star to be tidally locked to the star so that one side always faces the same way, Brandeker told me during a recent sit-down interview in his office.

But the team has seen temperature variations across the planet that could indicate it has a normal day-night cycle. That’s a possibility, Brandeker says, because 55 Cancri e may have a slightly eccentric orbit due to long-term gravitational perturbations from other members of the planetary system.

The other three known planets in this system orbit much further out and were discovered years earlier than 55 Cancri e.

It’s All In The Observations

Astronomers can learn a lot about a planet’s surface and predicted atmosphere by observing the planet during temporary in and out periods, as the planet slips behind its parent star and reappears from behind its parent star. And that is what the CHEOPS spacecraft has done many times since 2020.

We observed this planet at many different places and found it to be much more variable than we expected, says Brandeker. And frankly more than we can explain at the moment, he says. Our data is still under analysis, so we are not 100% sure that our conclusions are correct, he notes.

How did 55 Cancri end up this way?

It was certainly not an immediate location but probably came further out and migrated inwards. The details of that migration are currently unknown.

One hypothesis is that it was originally a gas giant planet that formed much further out and was somehow stripped of its outer gas envelope, probably by the solar wind of its parent star. Another hypothesis is that it is a rocky earth-type planet that happened to be 8 times more massive than our own planet.

Brandeker favors the latter hypothesis because as he notes, it is not so easy to lose a dense atmosphere.

It’s more likely to me that it’s just bare rock and that’s how he created it, he says.

A generation ago, astronomers were lucky enough to even indirectly detect any kind of planet in this kind of strange short orbit. Today, exoplanet scientists such as Brandeker take spectroscopy of such exoplanets close to dozens of stars.

Of Your 55 Cancri e?

The implication is that you would have a morning where the sun rises and the surface starts to melt and then evaporate to create an atmosphere of silicate minerals, Brandeker says. And then in the evening, when the planet cools down again, ​​the steamy atmosphere would rain out as lava, he says.

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