How ‘Hell Planet’ Got Too Hot: New Measurements Reveal The Orbital Trajectory Of Planet 55 Cnc e

An artist’s impression of the planet Jansen, which orbits its star so closely that its entire surface is an ocean of lava with a temperature of about 2,000 degrees Celsius. Credit: ESA/Hubble, M. Kornmesser

New research sheds light on how Hell got too hot and how other worlds might become too warm for life. This rocky world, 55 Cnc e (nicknamed “Janssen”), orbits its star so closely that a year lasts only 18 hours, its surface is an ocean of giant lava, and its interior may be full of diamonds.

The new insights come thanks to a new instrument called EXPRES that has taken ultra-precise measurements of bright starlight from Janssen’s sun, known as Copernicus, or 55 Cnc. The light measurements changed slightly as Jansen moved between the Earth and the star (an effect similar to our Moon blocking the Sun during a solar eclipse).

By analyzing these measurements, astronomers have discovered that Jansen orbits Copernicus along the star’s equator — unlike Copernicus’ other planets, which lie on orbital paths so different that they never cross between the star and Earth, researchers report Dec. 8. . natural astronomy.

The implication is that Janssen likely formed in a relatively cooler orbit and slowly fell toward Copernicus over time. As Jansen approaches, the stronger gravitational pull from Copernicus shifts the planet’s orbit.

Animation of Janssen orbiting his star. Credit: Lucy Reading-Ikkanda/Simons Foundation

“We’ve learned how this multi-planetary system — one of the systems with the most planets we’ve found — got into its current state,” says lead study author Lily Zhao, a research fellow at the Flatiron Institute’s Center for Computational Astrophysics (CCA) in New York City. .

Even in its original orbit, “the planet would likely have been too hot for anything we know of to survive on the surface,” Zhao says. However, the new findings could help scientists better understand how planets form and move over time. This information is needed to find out how common Earth-like environments are in the universe and, therefore, how abundant extraterrestrial life is.

Our solar system is, after all, the only place in the universe where we know life exists. It’s also flat as a pancake – all the planets orbit within a few degrees of each other, having formed from the same disk of gas and dust. As exoplanet search 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-like solar system is really rare.

How he became

An artist’s impression of the planet Jansen (orange circle), which orbits its star so closely that its entire surface is an ocean of lava with a temperature of about 2,000 degrees Celsius. Credit: Lucy Reading-Ikkanda/Simons Foundation

The Copernican planetary system, located 40 light-years from Earth, is of particular interest given how well-studied and complex it is: five exoplanets orbit a main-sequence star (the most common class of stars) in a binary pair with a. red dwarf star. In fact, Janssen was the first “super-Earth” to be discovered around a main sequence star. While Janssen has a similar density to Earth and is likely rocky, it is eight times larger and twice as wide.

Upon its discovery and confirmation, Janssen became the first known example of an extremely short planet. The minimum radius of Jansen’s orbit is about 2 million km. (For comparison, Mercury is 46 million km away, and Earth is about 147 million.) Jansen’s orbit is so warm around Copernicus that some astronomers initially doubted its existence.

Determining the Jansen trajectory around Copernicus could reveal a lot about the planet’s history, but making such measurements is very difficult. Astronomers studied Jansen by measuring the dip in Copernicus’ brightness each time a planet came between the star and Earth.

This method does not tell you which direction the planet is moving. To find out, astronomers make use of the same Doppler effect used in speed cameras. As the light source moves toward you, the wavelength of light you see is shorter (and therefore bluer). As it moves further away, the frequency travels wider and the light becomes redder.

How the 'hell planet' got so hotnatural astronomy 2022″/>

Diagram of the star Copernicus (large circle) from a new study looking at how exoplanet 55 Cnc e (nicknamed “Janssen” and represented by a black dot) orbits its star. The research revealed that the planet’s orbit (the inclined horizontal line) is very much in line with the star’s equator. This new information was obtained from precise measurements of the host star’s light. As Jansen moves between the star and Earth, the measured starlight decreases. The resulting change in the star’s observed color depends on which half of the star crosses Janssen. Due to the Doppler effect, the hemisphere that rotates toward Earth is slightly bluer, the opposite hemisphere that rotates away is somewhat redder, and the center is unchanged. Credit: L. Zhao et al./natural astronomy 2022

As Copernicus rotates, half of the star rotates toward us, and the other half moves away. This means that half of the star is slightly bluer, and the other half is redder (and the distance in the middle is unchanged). So astronomers can track Jansen’s orbit by measuring the time it blocks out light from the red side, the blue side, and the unchanging medium.

However, the resulting difference in starlight is almost incommensurably small. Teams have tried before but could not accurately determine the planet’s orbital path. The breakthrough in the new research came from the Extreme Perience Spectrometer (EXPRES) in the Lowell Discovery Telescope at Lowell Observatory in Arizona. True to its name, the spectrophotometer provided the resolution needed to notice small red and blue shifts.

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

Previous research indicates that the close orbit of the red dwarf led to planetary imbalances for Copernicus. In the new study, the researchers suggest that interactions between the celestial bodies may have shifted Jansen toward her current hellish location. As Jansen approached Copernicus, the gravitational pull of the star became increasingly dominant. As Copernicus rotated, centrifugal force caused the middle part of it to bulge outward slightly and the top and bottom to flatten. This asymmetry affected the gravity that Jansen felt, pulling the planet into alignment with the star’s thick equator.

With Jansen’s history shedding light, Zhao and her colleagues now plan to study other planetary systems. “We hope to find planetary systems similar to ours, and to better understand the systems we already know about,” she says.

more information:
Lily Zhao et al, Measured orbital rotation alignment of the very short-period super-Earth 55 Cancri e, natural astronomy (2022). DOI: 10.1038/s41550-022-01837-2.

Provided by the Simons Foundation

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