New Earth-size planet is only 6 light-years from us, might harbor life

An
illustration of the exoplanet candidate Barnard’s star b, also
known as GJ 699 b.
IEEC/Science-Wave/Guillem Ramisa;
Shutterstock

• Astronomers think they’ve found a “cold super-Earth” exoplanet orbiting
  Barnard’s star.
• Barnard’s star less than 6 light-years away from us and
  the closest single-star system to our sun.
• The new world is called Barnard’s star b (or GJ 699 b)
  and is at least 3.2 times as massive as Earth.
• It orbits in the “snow line” of its parent
  star: 
  a region at the edge of a star’s
  habitable zone where
  scientists suspect most rocky planets form.
• This Earth-size exoplanet may be the first to be
  photographed by a new generation of powerful
  telescopes.

Astronomers have suspected for decades that a
nearby red
dwarf star, called Barnard’s star, might be hiding an
Earth-size planet.

On Wednesday, researchers revealed that they’ve discovered
the first such exoplanet with about 99.2% certainty.

A team of dozens of scientists published that work in the journal
Nature, and said there are
even hints that a second world may lurk nearby.

Barnard’s star is just 5.87 light-years away from Earth, making
it the closest one-star system to us. Only
Proxima Centauri, a three-star system, is closer.

What’s more, the newly discovered world is close enough to Earth
— yet far enough from its blindingly bright star — to be
photographed by an upcoming generation of
giant telescopes.

“This is probably the first Earth-sized planet we will directly
image by future missions,” Abel Méndez, an astrobiologist at the University
of Puerto Rico at Arecibo who wasn’t involved in the study, told
Business Insider.

The new world is currently known as Barnard’s star b or, in other
circles, GJ 699 b. The team who found it leaned on more than 20
years of telescope observations, and that data suggests the
planet is at least 3.2 times more massive than Earth and has a
233-day-long year.

The world appears to orbit in the “snow line” of Barnard’s star —
a region just on the edge of the
habitable zone, where liquid water can exist on the surface
of a planet.

For that reason, scientists consider the possible planet to be a
“cold super-Earth,” and some are wondering if
alien life might exist there.

What it might be like on Barnard’s star b

ESO/M.
Kornmesser

Barnard’s star is not like the sun — it’s an M-dwarf, which means
it’s smaller, cooler, less massive, and older than our own star.

“M dwarfs are prime targets for planetary searches because they
favor the detection of small companions,” Rodrigo F. Díaz, an
astrophysicist at University of Buenos Aires who wasn’t part of
the research team, wrote in a Nature “News and Views” piece.

The newly discovered planet is about as far from its star as
Mercury is from the sun. That’s fairly close. However, next to a
smaller and lower-temperature star, this puts Barnard’s star b at
the edge of its habitable zone in the snow line region.

An
illustration showing the sun in relation to Barnard’s star and
the Alpha Centauri triple-star system.
IEEC/Science-Wave/Guillem Ramisa

Practically, this means the surface temperature of Barnard’s star
b is likely -150 degrees Celsius. This is cold enough to freeze
carbon dioxide solid into dry ice.

But bone-chilling temperatures doesn’t mean the exoplanet is a
dead world.

Can a cold super-Earth be habitable?

Half
of Jupiter’s icy moon Europa as seen via images taken by NASA’s
Galileo spacecraft in the late 1990s.

NASA/JPL-Caltech/SETI
Institute

The surface of Europa — an icy moon that orbits Jupiter — is 10
degrees colder than the newly discovered world. And Ganymede — a
smaller icy moon around Saturn — is about 20 degrees colder than
that.

Yet both have expansive
oceans of salt water
hiding below their crusts, and there’s growing
evidence that
organic molecules are mixed into that liquid.

Plus, the researchers’ estimate of the temperature of planet
Barnard’s star b assumes there’s no atmosphere hugging the world.
But there very well could be.

“Since the planet is more massive than Earth, it may retain a
hydrogen atmosphere,” Sara Seager, the deputy
science director for NASA’s
TESS mission and an astrophysicist at MIT, told Business
Insider.

It’s not a far-fetched idea. Seager said all planets — even Earth
— are born with a hydrogen atmosphere. This is because hydrogen
is the dominant material in nebulas, the clouds of gas and dust
out of which stars (and their planets) form.

“Hydrogen is a potent greenhouse gas and could conceivably keep
the surface temperature warm enough for life, if the atmosphere
pressure is high enough,” Seager said.

Future ground observatories like the Extremely Large Telescope,
or perhaps even the Giant Magellan Telescope, might be able to
capture a small image of Barnard’s star b. Some of the light that
passes through or bounces off its atmosphere might even be
sampled for indirect signs of life.

If Barnard’s star b turns out to be a bust, future observations
may discover it isn’t alone.

“I don’t discard the possibility of smaller Earth-sized planets
in the habitable zone of Barnard’s Star, now we know that Barnard
has planets and there is plenty of space between the star and
this new planet for a few small ones,” Méndez said.