The boiling new world is one of the lightest exoplanets discovered to date, zipping around its star at ultra-close range.
NASA/ESA/G.
Bacon (STScI) |
Ultra-short-period
planets are small, compact worlds that orbit their stars in close proximity,
completing an orbit — and a single, scorching year — in less than 24 hours. One
of the unsolved mysteries of exoplanetary science is how these planets came to
be in such extreme forms.
According
to MIT News, astronomers have identified an ultra-short-period planet (USP)
that is also super light. GJ 367 b is the name of the planet, and it orbits its
star in under eight hours. The planet is about the same size as Mars and half
the mass of Earth, making it one of the lightest planets ever discovered.
GJ 367 b,
which orbits a neighbouring star 31 light years from our sun, is close enough
that astronomers were able to determine features of the planet that were not
achievable with previously discovered USPs. GJ 376 b, for example, was
discovered to be a rocky planet with a solid core of iron and nickel,
comparable to Mercury's interior.
GJ 376 b
is blasted with 500 times more radiation than the Earth receives from the sun,
according to astronomers, due to its extraordinary proximity to its star. As a
result, the dayside of the planet can reach 1,500 degrees Celsius. Any major
atmosphere would have melted long ago, along with any evidence of life, at
least as we know it, at such severe temperatures.
However,
there is a possibility that the planet has habitable companions. Its star is a
red dwarf, also known as a M dwarf, which is a type of star that can support
several planets. The discovery of GJ 367 b around such a star suggests that
there could be additional planets in this system, which could help astronomers
figure out where GJ 376 b and other ultra-short-period planets came from.
"The
habitable zone for this sort of star would be somewhere around a month-long
orbit," explains team member George Ricker, a senior research scientist at
MIT's Kavli Institute for Astrophysics and Space Research. "We have a
decent possibility of seeing other planets in this system because this star is
so close by and so brilliant." It's almost as if there's a sign that says,
'Look here for extra planets!'"
The team's
findings were published in the journal Science. Researchers at the German
Aerospace Center's Institute of Planetary Research spearheaded the study, which
included MIT co-authors Ricker, Roland Vanderspek, and Sara Seager, as well as
an international group of researchers.
Transit tests
Ricker is the principal investigator of NASA's Transiting Exoplanet Survey Satellite (TESS), an MIT-led project that identified the new planet. TESS keeps an eye on the sky for variations in the brightness of nearby stars. TESS data is analysed for transits, or periodic dips in brightness that signal a planet is passing in front of a star and briefly blocking its light.
TESS
captured an area of the southern sky that contained the star GJ 376 for nearly
a month in 2019. Scientists from MIT and other institutions evaluated the data
and discovered a transiting object with an eight-hour orbit. They did many
tests to make sure the signal wasn't coming from a "false positive"
source like an eclipsing binary star in the foreground or background.
They used
the High Accuracy Radial Velocity Planet Searcher (HARPS), an instrument built
on the European Southern Observatory's telescope in Chile, to investigate the
planet's star more closely after establishing the object was definitely an
ultra-short-period planet.
They
calculated that the planet had a radius of 72 percent and a mass of 55 percent
that of Earth, making it one of the lightest planets ever discovered. The
planet's proportions imply that it has an iron-rich core.
The
researchers then narrowed down several scenarios for the planet's interior
composition until they discovered the one that best suited the data, which
revealed that an iron core likely makes up 86 percent of the planet's interior,
comparable to Mercury's composition.
"We're
looking for a Mars-sized planet with Mercury's composition," adds
Vanderspek, an MIT principal research scientist. "It's one of the tiniest
planets ever discovered, spinning in an extremely tight orbit around a M
dwarf."
Scientists
expect to detect signals from other planets in the system as they continue to
investigate GJ 367 b and its star. The features of these planets, such as their
orbital direction and separation, could reveal how GJ 367 b and other
ultra-short-period planets formed.
"Understanding how these planets got so near to their host stars is a bit of a mystery," explains Natalia Guerrero, a member of the TESS team. "What is the reason for this planet's lack of an outer atmosphere?" How did it get so close? Was this a calm or a violent process? Hopefully, this method will provide us with some additional information."
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