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Potentially Habitable Earth-Sized World Discovered Just 40 Light-Years Away SPACE
24 May 2024
ByMICHELLE STARR
An artist's impression of Gliese-12b orbiting the red dwarf star
Gliese-12. (NASA/JPL-Caltech/R. Hurt, Caltech-IPAC)
A world that bears more than a passing similarity to Earth has just been discovered orbiting a star just 40 light-years from the Solar System.
This exoplanet has a very similar radius to our home planet, suggesting
a similar rocky composition. Tantalizingly, Gliese-12b, as the exoplanet
is named, is at a distance from its host star that could be habitable to
life as we know it.
"In my opinion, this planet will give us the clearest answer yet for any potentially habitable planet as to whether it could support habitable conditions," astrophysicist Shishir Dholakia of the University of
Southern Queensland in Australia tells ScienceAlert.
"Its host star is inactive, it's extremely nearby and therefore very characterizable."
What we don't yet know is whether Gliese-12b has an atmosphere. That's
the factor that could make a huge difference to whether the world is
hospitable to life like Earth, or a scorching hell planet like Venus.
"Gliese-12b represents one of the best targets to study whether
Earth-size planets orbiting cool stars can retain their atmospheres, a
crucial step to advance our understanding of habitability on planets
across our galaxy," Dholakia explains.
Over 5,600 planets outside the Solar System, or exoplanets, have been discovered to date, but we're yet to find an Earth 2.0. Most of the
worlds we find are larger.
That's not to say that we've not found those with similar sizes and
masses to Earth. We've found quite a few, but finding Earth-sized
exoplanets that meet the conditions for habitability is a little more difficult.
One of those conditions is that the exoplanet needs to be within a
specific distance range from the star, known as the habitable or
Goldilocks zone. This is defined by the temperature inflicted on the
exoplanet by the star. The exoplanet needs to be close enough for any
water on the surface to be liquid, not frozen; but not so close that any
water would evaporate clean away.
An artist's impression of the Gliese-12 system, with the exoplanet
retaining a thin atmosphere. (NASA/JPL-Caltech/R. Hurt, Caltech-IPAC)
In the Solar System, Earth sits smack-bang in the middle of the
Goldilocks zone. Venus is a bit too close to the Sun. Mars is right at
the outer limits, and proof that just sitting in the habitable zone
doesn't guarantee habitable conditions – but it's a starting point for identifying worlds that we should examine more closely for other signs
of habitability.
This is what we have with Gliese-12b. It was found in data from the TESS exoplanet-hunting telescope, and Dholakia, his co-lead author Larissa Palethorpe of the University of Edinburgh and University College London,
and their team followed up with a number of different telescopes to
confirm that the TESS detecting was legit.
They found that the exoplanet has a radius almost exactly the same as
Earth's, and orbits its host star once every 12.76 days. Here in the
Solar System, that would be way too close for comfort – but the star Gliese-12 is a red dwarf, much cooler and dimmer than the Sun; the
radiation the exoplanet receives is about 1.6 times the radiation Earth
gets from the Sun.
The estimated surface temperature of the exoplanet is 42 °C (107 °F).
Earth, by comparison, has an average surface temperature of 15 °C (59 °F).
Whether or not the exoplanet has an atmosphere could play a huge role in
what the surface conditions are like, though.
"We are quoting the planet's 'equilibrium temperature', which is the temperature the planet would be if it had no atmosphere," Dholakia says.
"Much of the scientific value of this planet is to understand what kind
of atmosphere it could have. Since Gliese-12b gets in between the amount
of light as Earth and Venus get from the Sun, it will be valuable for
bridging the gap between these two planets in our Solar System."
An illustration with different interpretations of Gliese-12b compared to
Earth, from a bare rock, to a thick, Venus-like atmosphere. (NASA/JPL-Caltech/R. Hurt, Caltech-IPAC)
Gliese-12b gets about 85 percent of the radiation received by Venus –
but Venus is covered in a thick, choking atmosphere that generates a
greenhouse effect, resulting in an average surface temperature of 464 °C
(867 °F).
"It is thought that Earth's and Venus's first atmospheres were stripped
away and then replenished by volcanic outgassing and bombardments from
residual material in the solar system," Palethorpe says.
"Earth is habitable, but Venus is not due to its complete loss of water. Because Gliese-12b is between Earth and Venus in temperature, its
atmosphere could teach us a lot about the habitability pathways planets
take as they develop."
Due to its proximity to Earth, radius, position at the edge of the
habitable zone of its host star, and low flare activity of that star, Gliese-12b represents possibly the best candidate yet for studying the emergence and evolution of habitability.
The researchers hope that they'll be able to recruit JWST for a closer
look, to see if it has an atmosphere, and what that atmosphere is made of.
"JWST will probably be able to give us a clear picture of what its
atmosphere looks like. Right now, the atmosphere of a planet is probably
the greatest significant unknown that makes or breaks any claims of habitability," Dholakia tells ScienceAlert.
"In other words, the hypothesis that this planet is habitable is very
exciting, but it's particularly exciting that we can actually test this hypothesis clearly. We can also extend these findings to other
potentially habitable planets around red dwarfs – the most common kind
of star in our galaxy."
The research has been published in the Monthly Notices of the Royal Astronomical Society.
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