GJ 367b is Another Dead World Orbiting a Red Dwarf

This artist's concept illustrates a young, red dwarf star surrounded by three planets. There's growing evidence that red dwarfs place serious limits on exoplanet habitability. Image Credit: By NASA/JPL-Caltech - NASA Image of the Day, Public Domain, https://commons.wikimedia.org/w/index.php?curid=17104843

Red dwarf exoplanet habitability is a hot topic in space science. These small dim stars host lots of exoplanets, including small rocky ones the size of Earth. But the little stars emit extremely powerful flares that can damage and strip away atmospheres.

If we’re ever going to understand red dwarf habitability, we need to understand the atmospheres of the exoplanets that orbit them.

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Hubble Succeeds Where TESS Couldn’t: It Measured the Nearest Transiting Earth-Sized Planet

This is an artist’s concept of the nearby exoplanet, LTT 1445Ac, which is a nearby Earth-size world. The planet orbits a red dwarf star. The star is in a triple system, with two closely orbiting red dwarfs seen at upper right. The black dot in front of the foreground star is planet LTT 1445Ab, transiting the face of the star. Image Credit: NASA, ESA, L. Hustak (STScI)

Twenty-two light-years away, a rocky world orbits a red dwarf. It’s called LTT 1445Ac, and NASA’s Transiting Exoplanet Survey Satellite (TESS) found it in 2022. However, TESS was unable to gauge the small planet’s size.

That’s okay. The venerable Hubble took care of it.

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Do Red Dwarfs or Sunlike Stars Have More Earth-Sized Worlds?

This artist's concept illustrates a young, red dwarf star surrounded by three planets. There's growing evidence that red dwarfs place serious limits on exoplanet habitability. Image Credit: By NASA/JPL-Caltech - NASA Image of the Day, Public Domain, https://commons.wikimedia.org/w/index.php?curid=17104843

Earth is our only example of a habitable planet, so it makes sense to search for Earth-size worlds when we’re hunting for potentially-habitable exoplanets. When astronomers found seven of them orbiting a red dwarf star in the TRAPPIST-1 system, people wondered if Earth-size planets are more common around red dwarfs than Sun-like stars.

But are they? Maybe not.

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Astronomers are Watching a Planet Get its Atmosphere Blasted Away into Space

This artist's illustration shows a planet (dark silhouette) passing in front of the red dwarf star AU Microscopii. The planet is so close to the eruptive star a ferocious blast of stellar wind and blistering ultraviolet radiation is heating the planet's hydrogen atmosphere, causing it to escape into space. The illustration is based on measurements made by the Hubble Space Telescope. Credits: NASA, ESA, and Joseph Olmsted (STScI)

What do you get when a hot young world orbits a wildly unstable young red dwarf? For AU Microsopii b, the answer is: flares from the star tearing away the atmosphere. That catastrophic loss happens in fits and starts, “hiccuping” out its atmosphere at one point and then losing practically none the next.

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Are Planets Tidally Locked to Red Dwarfs Habitable? It’s Complicated

habitable exoplanet interstellar message
Artist's impression of a habitable exoplanet orbiting a red dwarf star. The habitability of the planets of red dwarf stars is conjectural (Credit ESO/M. Kornmesser public domain)

Astronomers are keenly interested in red dwarfs and the planets that orbit them. Up to 85% of the stars in the Milky Way could be red dwarfs, and 40% of them might host Earth-like exoplanets in their habitable zones, according to some research.

But there are some problems with their potential habitability. One of those problems is tidal locking.

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Two New Rocky Planets Discovered Close to the Solar System

An artist's illustration of two newly-discovered super-Earths. They're only 33 light years away and they orbit a red dwarf named HD 260655. Image Credit: NASA/JPL-Caltech

TESS has struck paydirt again. NASA’s planet-hunting spacecraft has found two new super-Earths orbiting a star only 33 light-years away. These are two of the closest rocky planets ever found.

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It Turns out, We Have a Very Well-Behaved Star

Our Sun is a Population II star about 5 billion years old. It contains elements heavier than hydrogen and helium, including oxygen, carbon, neon, and iron, though only in tiny percentags. Image: NASA/Solar Dynamics Observatory.
Our Sun is a Population II star about 5 billion years old. It contains elements heavier than hydrogen and helium, including oxygen, carbon, neon, and iron, though only in tiny percentags. Image: NASA/Solar Dynamics Observatory.

Should we thank our well-behaved Sun for our comfy home on Earth?

Some stars behave poorly. They’re unruly and emit powerful stellar flares that can devastate life on any planets within range of those flares. New research into stellar flares on other stars makes our Sun seem downright quiescent.

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Stellar Flares May Not Condemn a Planet’s Habitability

An artistic rendering of a series of powerful stellar flares. New research says that flaring activity may not prevent life on exoplanets. CREDIT NASA's Goddard Space Flight Center/S. Wiessinger

Red dwarf stars are the most common kind of star in our neighbourhood, and probably in the Milky Way. Because of that, many of the Earth-like and potentially life-supporting exoplanets we’ve detected are in orbit around red dwarfs. The problem is that red dwarfs can exhibit intense flaring behaviour, much more energetic than our relatively placid Sun.

So what does that mean for the potential of those exoplanets to actually support life?

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Just How Bad are Superflares to a Planet’s Habitability?

superflare
An artist's conception of a superflare event, on a dwarf star. Image credit: Mark Garlick/University of Warwick

Star’s can be full of surprises; some of them nasty. While our own Sun appears pretty placid, science has shown us that’s not the case. Coronal mass ejections and solar flares are the Sun’s angry side.

And the Sun has only a mild case of the flares, compared to some other stars.

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Astronomers Have Found the Star/Exoplanet Combo That’s the Best Twin to the Sun/Earth

An artist's illustration of TOI 700d, an Earth-size exoplanet that TESS found in its star's habitable zone. Image Credit: NASA

At times, it seems like there’s an indundation of announcements featuring discoveries of “Earth-like” planets. And while those announcements are exciting, and scientifically noteworthy, there’s always a little question picking away at them: exactly how Earth-like are they, really?

After all, Earth is defined by its relationship with the Sun.

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