Exoplanet with eccentric orbit discovered in the habitable zone of a red dwarf

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Astronomers have found a planet in the habitable zone of a red dwarf star, but its orbit is so long that it would have wildly variable temperatures and could not possibly support life.

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The planet, named TOI-2257 b, was first observed using data from NASA’s planet-hunting telescope TESS (Transiting Exoplanet Survey Satellite) and then in greater detail using the Las Cumbres Observatory Global Telescope and SAINT-EX Telescope in Mexico was seen from Using SAINT-EX observations, the researchers were able to confirm that a planet was orbiting the red dwarf star every 35 days.

Sainte-Ex Telescope.
Sainte-Ex Telescope Astronomy Institute, UNAM / E. Caden

Since red dwarf stars are smaller and cooler than our Sun, the habitable zone around them, or the region in which liquid water can exist on the surface of an orbiting planet, is also different. Planets orbiting red dwarf stars may contain liquid water, even though they are much closer to the orbit of the Sun than Earth. And the closer the planet is to the star, the easier it is to detect it.


However, even though TOI-2257 b is in the habitable zone, don’t make any plans to go there. The first issue with habitability is that the planet has a radius of 2.2 times that of Earth, meaning it is large and potentially gaseous with a high atmospheric pressure. The second and most interesting fact about this planet is that it has a highly eccentric orbit, meaning that its orbit traces an elliptical or oval shape rather than a circle. Sometimes the planet is closer to its star, and sometimes it is further away from it.

In fact, it is the most eccentric orbit of a planet around a cool star ever discovered. And it has a big effect on the surface temperature there.

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“We found that TOI-2257 b does not have a circular, concentric orbit,” explained lead researcher Nicole Shanch in a Statement, “In terms of potential habitability, this is bad news. While the planet’s average temperature is comfortable, it varies from -80 °C to about 100 °C, depending on where the planet is in its orbit, Far from or close to the star.

Researchers are curious as to why the planet’s orbit is so eccentric, which could be due to a giant planet in the same system influencing this planet’s orbit. To learn more, the researchers hope the planet can be studied further using the James Webb Space Telescope.

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