by Jessica Orwig
A newly discovered exoplanet has a lot of astronomers excited, and for good reason.
The exoplanet, dubbed GJ 1132b, is about the size of Earth and
lives in a solar system roughly 39 light-years from Earth, a team of
scientists reported in the November 12, 2015, issue of the journal
Nature.
Furthermore, the exoplanet is the closest rocky Earth-sized exoplanet ever discovered, by far.
The next closest is about three times farther away.
GJ 1132b's size and distance are what have astronomers like Drake
Deming at the University of Maryland — who was not part of the study —
saying that this planet is "arguably the most important planet ever
found outside the solar system," he told
The Guardian.
The reason is because GJ 1132b is close enough for astronomers to
point their telescopes at it and sniff out any traces of an atmosphere.
Atmospheric signatures of life
Studying the atmospheres of exoplanets for signs of life is the
next big step in the search for extraterrestrial life beyond our solar system.
But it's an extremely difficult
project because most Earth-sized planets — the exoplanets that
astrobiologists think are most likely to harbor life — are too distant
to study in any detail.
One of the ways astronomers
determine the chemical composition of gases on planets in our own solar
system is by studying the light passing through their atmospheric
layers, like Earth's shown in the photo below with our crescent moon in
the foreground:
Chemical
compounds and molecules interact differently with different energies of
light, and, as a result, each molecule leaves a unique fingerprint that
scientists can see when they map out the light over what is called a
spectrum.
But when an object is hundreds of light-years away, it's
nearly impossible to differentiate the light that's passing through an
exoplanet's atmosphere from the light that's emanating from the larger,
brighter host star.
A significant stepping stone
Now, GJ 1132b has changed that, offering astronomers a perfect
specimen to test their instruments and methods for detecting life.
"It's nearby, it's Earth-like, and its star won't interfere," Deming told
The Guardian.
This newly discovered exoplanet is, however, just a stepping stone.
The possibility of finding life on it is practically zero. GJ 1132b
might be only 16% larger than Earth, but it's surface temperature is a
balmy 450 degrees Fahrenheit.
"Our ultimate goal is to find a
twin Earth, but along the way we've found a twin Venus," David
Charbonneau, a co-author on the new paper and an astronomer at the
Harvard-Smithsonian Center for Astrophysics, said in
a press release. "We suspect it will have a Venus-like atmosphere, too, and if it does we can't wait to get a whiff."
The reason for these toasty
temperatures is because GJ 1132b sits just 1.4 million miles from its
host star — 26 times closer than Mercury is to our sun.
It takes just 1.6 days for GJ 1132b to complete a single orbit around its star, which is very different from our sun.
The most common star in the galaxy
The star is what is called a red dwarf, which astronomers suspect is
the most common star throughout our home galaxy, the Milky Way.
Red-dwarf stars are cooler,
smaller, and dimmer than our sun. The one that GJ 1132b is orbiting is
about one-fifth the size of our sun and only emits about 1/200th the
amount of light.
Here's a diagram comparing, to scale, the size of our sun with a red dwarf (second from the left) and Jupiter (far right):
Just
because they're different from our sun, however, doesn't mean life
couldn't spawn around them. It just means that the habitable zone — the
region in space where liquid water could exist on a planet's surface —
is closer to the star than it is for our sun.
Some astronomers estimate
that red-dwarf stars comprise 75% of all stars in the galaxy. This
means that most of the exoplanets in our galaxy are likely orbiting
red-dwarfs.
Whether any of those planets are
habitable, however, is a subject of intense debate, which is why the
discovery of GJ 1132b is so exciting. And while GJ 1132b is not likely
habitable, it's possible that it has some neighbors that are.
To first spot GJ 1132b as it
passed in front of the star, scientists used the MEarth-South array, a
group of telescopes at the Cerro-Tololo Inter-American Observatory in
Chile.
Now that they know it's there,
the researchers have requested time on the Hubble Space Telescope (which
observes the same type of light we see with our eyes) and the Spitzer
Space Telescope (which observes longer wavelengths than Hubble, in the
infrared range) to study GJ 1132b more fully.
With the viewing powers of
Hubble and Spitzer combined, the scientists could get a much broader
spectrum of light to study even more chemical compounds than they
otherwise would with just one of the telescopes.
