How the "hellish planet" got so hot

How the “hellish planet” got so hot

Newswise – New research sheds light on how the ‘Hellish Planet’ got so fiendishly hot and how other worlds could be getting too hot for life. This rocky world, 55 Cnc e (nicknamed “Janssen”), orbits so close to its star that a year only lasts 18 hours, its surface is a giant ocean of lava, and its interior may be filled with diamonds.

The new information comes from a new tool called EXPRES which captured ultra-precise measurements of bright starlight from Janssen’s Sun, known as Copernicus or 55 Cnc. The light measurements shifted slightly as Janssen moved between Earth and the star (an effect similar to our moon blocking out the sun during a solar eclipse).

Analyzing these measurements, astronomers found that Janssen orbits Copernicus along the star’s equator – unlike Copernicus’ other planets, which are on such different orbital paths that they never even cross between the star and the Earth, the researchers report on December 8 at natural astronomy.

The implication is that Janssen likely formed in a relatively cooler orbit farther out and slowly fell toward Copernicus over time. As Janssen got closer, Copernicus’ stronger gravitational pull altered the planet’s orbit.

“We learned how this multi-planet system – one of the systems with the most planets we have found – came to be in its current state,” says Lily Zhao, lead author of the study, a researcher at the Center for Research. from the Flatiron Institute. Computational Astrophysics (CCA) in New York.

Even in its original orbit, the planet “was probably so hot that nothing we know of could survive on the surface,” Zhao says. Still, the new findings could help scientists better understand how planets form and move over time. This information is essential to discovering how common terrestrial environments are in the universe and, therefore, how abundant extraterrestrial life can be.

Our solar system, after all, is the only place in the cosmos where we know life exists. It’s also flat as a pancake – all the planets orbit within a few degrees of each other, formed from the same disc of gas and dust. When exoplanet-hunting missions began to discover worlds around distant stars, they found many planets that did not orbit their host stars on a flat plane. This raised the question of whether our pancake-shaped solar system is really a rarity.

The Copernican planetary system, located 40 light-years from Earth, is particularly interesting given its complexity and degree of study: Five exoplanets orbit a main-sequence star (the category of stars the most common) in a binary pair with a red dwarf star. In fact, Janssen was the first “super-Earth” discovered around a main-sequence star. While Janssen is similar in density to Earth and likely rocky, it is about eight times as massive and twice as wide.

Upon its discovery and confirmation, Janssen became the first known example of an ultrashort-period planet. Janssen’s orbit has a minimum radius of about 2 million kilometers. (For comparison, Mercury’s is 46 million kilometers and Earth’s is about 147 million.) Janssen’s orbit is so tight around Copernicus that some astronomers at first doubted its existence.

Determining Janssen’s path around Copernicus could reveal a lot about the planet’s history, but making such measurements is incredibly difficult. Astronomers studied Janssen by measuring the drop in Copernicus’ luminosity each time the planet interposes between the star and Earth.

This method does not tell you which direction the planet is moving. To find out, astronomers take advantage of the same Doppler effect used in radar. When a light source is shining towards you, the wavelength of the light you see is shorter (and therefore bluer). As it moves away, the frequency is shifted wider and the light is redder.

As Copernicus rotates, half of the star rotates towards us and the other half moves away. This means that half of the star is a little more blue and the other half is slightly more red (and the space in the middle is not shifted). So astronomers can track Janssen’s orbit by measuring when it blocks light from the redder side, the bluer side, and the unchanged midsection.

The resulting difference in starlight, however, is almost immeasurably small. Teams had tried before but could not accurately determine the planet’s orbital path. The breakthrough in the new research came from the EXtreme PREcision Spectrometer (EXPRES) of the Lowell Discovery Telescope at the Lowell Observatory in Arizona. True to its name, the spectrometer offered the precision needed to notice tiny red and blue shifts in light.

EXPRES measurements revealed that Janssen’s orbit is roughly aligned with the Copernicus equator, a trajectory that makes Janssen unique among its siblings.

Previous research suggests that the close orbit of the red dwarf caused the planets to be misaligned with Copernicus. In the new study, the researchers propose that interactions between celestial bodies moved Janssen to his current hellish location. As Janssen approached Copernicus, the star’s gravity became more and more dominant. Because Copernic rotates, centrifugal force caused its midsection to bulge outward slightly and flatten its top and bottom. This asymmetry affected the gravity Janssen felt, aligning the planet with the star’s thicker equator.

With Janssen’s story illuminated, Zhao and his colleagues now plan to study other planetary systems. “We hope to find planetary systems similar to ours,” she says, “and better understand the systems we know.”

Zhao co-authored the new paper with Vedad Kunovac and Joe Llama of Lowell Observatory; John Brewer of San Francisco State University; Sarah Millholland of the Massachusetts Institute of Technology; Christina Hedges of the University of Maryland and NASA’s Goddard Space Flight Center; and Andrew Szymkowiak, Rachael Roettenbacher, Samuel Cabot, Sam Weiss, and Debra Fischer from Yale University.


The Flatiron Institute is the research division of the Simons Foundation. The mission of the institute is to advance scientific research through computational methods, including data analysis, theory, modeling and simulation. The institute’s Center for Computational Astrophysics creates new computational frameworks that enable scientists to analyze large astronomical datasets and understand complex multiscale physics in a cosmological context.

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