A new study offers insights into how the “hell planet” became so hot and how other planets may become too hot for life. 55 Cnc e, often known as “Janssen,” is a rocky planet that circles its star so tightly that a year only lasts 18 hours. Its surface is covered in a vast ocean of lava, and its innards may be full of diamonds.

The latest findings are the result of a new method called EXPRES, which took ultra-precise measurements of the starlight emitted by Janssen’s sun, known as Copernicus or 55 Cnc. As Janssen passed between Earth and the star, the light readings slightly changed (an effect akin to our moon blocking the sun during a solar eclipse).

By examining these observations, astronomers determined that Janssen circles Copernicus around the star’s equator, in contrast to Copernicus’ other planets, whose orbital routes are so dissimilar that they never pass between the star and Earth, the researchers write in Nature Astronomy today.

This suggests that Janssen originally originated in a more distant, colder orbit and gradually migrated inward toward Copernicus. As Janssen approached Copernicus, the increased gravitational force shifted the orbit of the planet.

“We’ve learned about how this multi-planet system — one of the systems with the most planets that we’ve found — got into its current state,” adds study lead author Lily Zhao.

Even in its initial orbit, the planet was likely so hot that nothing known to us could have survived on its surface, according to Zhao. Still, the new information could help scientists learn more about how planets are made and how they move over time. Such knowledge is crucial for determining the frequency of Earth-like settings throughout the cosmos and, therefore, the potential abundance of alien life.

After all, the only region of the universe where we are aware of life is our solar system. It’s also as flat as a pancake; all the planets, which originated from a single disk of gas and dust, circle within a few degrees of one another. When missions to find planets around faraway stars began to find them, they found many planets that didn’t orbit their stars in a flat plane. This raises the issue of whether our solar system’s pancake-like structure is genuinely unique.

Copernicus’ system of planets, which is 40 light-years from Earth, is especially interesting because it has been studied a lot and is so complicated: In a binary system with a red dwarf star, five exoplanets circle a main-sequence star, the most common kind of star. Janssen was the first planet found around a main-sequence star. Even though Janssen has the same mass as Earth and is probably made of rocks, it is about eight times bigger and twice as wide.

Janssen was the first ultra-short-period planet to be discovered and confirmed. The minimum size of Janssen’s orbit is about 2 million kilometers. Mercury’s orbit is about 46 million kilometers, while Earth’s is about 147 million.  Janssen’s orbit is so close to Copernicus that some astronomers at first didn’t believe it was real.

Janssen’s path around Copernicus could tell us a lot about the history of the planet, but it is very hard to measure it. Astronomers have studied Janssen by keeping track of how much the brightness of Copernicus drops every time the planet moves between Earth and the star.

With that method, you can’t tell which way the planet is moving. To determine this, astronomers use the same Doppler effect utilized by speed cameras. When a light source is approaching you, its wavelength is shorter (and therefore bluer). As it moves away, the frequency shifts and the light becomes redder.

When Copernicus spins, half of the star moves toward us while the other half moves away. This indicates that one part of the star is somewhat bluer and the other is slightly redder (and the space in the middle is unshifted). So, astronomers can figure out Janssen’s orbit by measuring when it blocks light from the side that is redder, the side that is bluer, and the middle part that hasn’t changed.

The difference in starlight, though, is almost impossible to measure. Previous attempts failed to precisely predict the planet’s orbital path. The EXtreme PREcision Spectrometer (EXPRES) at the Lowell Observatory’s Lowell Discovery Telescope in Arizona provided the scientific breakthrough in the current study. The spectrometer, as its name suggests, provided the accuracy required to detect the light’s minute red and blue alterations.

The EXPRES measurements showed that Janssen’s orbit is roughly in line with Copernicus’ equator. This makes Janssen’s path different from those of its other siblings.

Previous study indicates that the misalignment of the planets relative to Copernicus was caused by the neighboring orbit of the red dwarf. In the new study, the researchers say that Janssen’s current location in hell is due to interactions between the heavenly bodies. The gravitational pull of Copernicus increased as Janssen drew near. Because Copernicus is spinning, centrifugal force has caused its middle to bulge out slightly and its top and bottom to flatten. Janssen experienced a change in gravity that caused the planet to move into alignment with the star’s thicker equator.

Now that Zhao and her colleagues know more about Janssen’s past, they want to learn about other planetary systems. 

“We’re hoping to find planetary systems similar to ours,” she adds, “and to better understand the systems that we do know about.”

Source: 10.1038/s41550-022-01837-2

Image Credit: ESA/Hubble, M. Kornmesser


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