Recently, we discovered an exoplanet about identical in size to Earth that
is orbiting a little star not too far from us.
Its parallels (and differences) to Earth may help us understand how
Earth-like planets arise and evolve differently, in systems extremely unlike
to our own. This planet is known as K2-415b.
According to a
global team of scientists
led by Teruyuki Hirano of the Astrobiology Center in Japan, "small planets
circling M dwarfs provide an ideal laboratory to examine the atmospheric
variety of rocky planets and the circumstances under which a livable
terrestrial world can exist."
"K2-415 will be an attractive target for future follow-up studies,
including extra radial velocity monitoring and transit spectroscopy," the
authors write. "It is one of the lowest mass stars known to host an
Earth-sized transiting planet."
The study is accessible on the preprint service
arXiv and has
been approved for publication in The Astronomical Journal.
Although the Milky Way galaxy is large and contains many fascinating
planets, it has thus far eluded attempts to answer one of the most important
questions that humanity has ever asked: why are we here? Not just why, but
also how, why this planet, and is there somewhere else in the universe where
life may exist?
A population of exoplanets that are comparable to Earth might assist
provide answers since Earth is the only location in the universe where we
can say with certainty that life has begun to exist. In terms of mass, size,
composition, temperature, and maybe even planetary system design, they are
comparable.
Tiny, Earth-sized planets circling relatively nearby, small stars in a way
that allows them to transit, or pass between us and the star, are the finest
exoplanet population from which to begin this investigation. This is due to
the fact that they are the most qualified to describe an environment.
A portion of the star's light will travel through the exoplanet's
atmosphere as it moves in front of it, with various wavelengths of the
spectrum being absorbed or enhanced by atmospheric constituents.
The habitable temperature zone is considerably closer to the star than it
is around a star like the Sun because smaller, dimmer, colder stars like red
dwarfs have these characteristics. This implies that the orbital period is
shorter, allowing for the recording and stacking of several transits to
magnify the spectrum data. Furthermore, nearby stars will definitely seem
brighter, making such observations simpler.
But finding small exoplanets is more challenging than finding big ones.
Only 14 exoplanets smaller than 1.25 Earth radii have been discovered
circling red dwarf stars within 100 light-years of the Solar System,
including all 7 planets in the TRAPPIST-1 system.
There are never too many data points, and Hirano and his colleagues appear
to have discovered a big one in this case. The exoplanet K2-415b, which
orbits one of the tiniest red dwarf stars discovered supporting an
Earth-sized planet, has a radius 1.015 times that of our planet. K2-415 is a
star with a mass that is just 16% that of the Sun.
The exoplanet was discovered for the first time in 2017 in data from the
planet-hunting Kepler telescope, which is no longer operational. It also
showed up in data from Kepler's successor, TESS.
The scientists next used
infrared measurements
to check whether they could see a very little 'wobble' in the star's
velocity, caused by the exoplanet's gravity tugging at it just a little
bit.
This plethora of information made it clear that there was a planet and
described some of its features. The exoplanet's radius may be determined by
measuring the amount of sunlight that is obstructed during transits. The
degree of wobbling determines the mass.
The density of the exoplanet may be determined by combining those two
variables. Additionally, the exoplanet's orbital period is obvious from the
transits' regularity.
Here, K2-415b starts to diverge significantly from Earth. The exoplanet is
around the size of Earth, but it has a mass that is three times greater.
Therefore, K2-415b must also be denser than Earth.
Furthermore, it is incredibly near to its star: It only has a four-day
orbital period. True, a red dwarf star's habitable zone can be considerably
closer than the Sun's, with orbits measurable in days rather than months,
but even for a red dwarf, that's a touch too near for comfort.
Only a bit, though. Near the edge of K2-habitable 415's zone is K2-415b.
That could imply that there is yet an atmosphere to explore. Venus'
atmosphere is a complex and fascinating horror show, and it is located just
inside the habitable region of the Solar System.
It's also likely that K2-415 is a multi-planet system, which increases the
likelihood that the star's habitable zone has an undiscovered
exoplanet.
It is therefore improbable that we will discover life on K2-415b. However,
the system is a prime candidate for exoplanet atmosphere characterisation
and follow-up searches for undiscovered worlds that could support
life.
