A Planet Almost Exactly Earth's Size Has Been Found 72 Light-Years Away

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.