Every exoplanet has its own unique qualities, but a recently found exoplanet 186 light-years distant is a particularly delectable treat. It is a very tiny planet that is around the same size as Earth and orbits its star in only 3.14 days.
That comes very near to the value of the mathematical constant (Pi), which expresses the relationship between a circle's circumference and diameter. The exoplanet's scientific name is K2-315b, but its discoverers have given it the moniker "Earth."
The star's discovery has been in the making for a while. The earliest indications of its existence originally surfaced in 2017, during the second extended mission of the Kepler Space Telescope (RIP).
Kepler discovered 20 tiny dips at regular intervals in the light of a tiny, faint red dwarf star, just 20% the size of the Sun. This is the primary method we use to look for exoplanets; such dips often indicate that a planet is transiting—that is, passing in front of—the star in question. Those transits are detected as very minute variations in brightness.
However, a single collection of dips is insufficient to definitively rule out the presence of an exoplanet. With the Kepler data at hand, astronomer Prajwal Niraula and his team set out early this year to investigate the star using SPECULOOS.
This is a group of telescopes cooperating to look exclusively for exoplanets the size of Earth orbiting faint dwarf stars.
The researchers pointed the SPECULOOS telescopes toward the star K2-315 during three observational runs in February, March, and May. With the help of the HIRES instrument at the W. M. Keck Observatory, they discovered three further dips and derived a spectrum of the star.
The dips were exactly in line with the 3.14-day timeframe that Kepler noted three years before. The star's spectra also proved that the dips were really caused by a transiting exoplanet.
Stellar transits provide a wealth of information. We can determine the size of an exoplanet simply by measuring how much light the star dims. Niraula and his colleagues came to the conclusion that K2-315b is around 95% the size of Earth based on this.
The planet is most likely rocky, like Earth, Venus, Mercury, and Mars, at that size, while alternative compositions can't be completely ruled out.
We need Doppler spectroscopy for it. As a star and a tiny planet orbit each other around a common centre of gravity, these motions cause extremely slight shifts in the wavelengths of the star's light, which are compressed as the star travels closer to the observer and extended as it goes further away.
The mass of the exoplanet may depend on how much the star moves. Since fluffy gas giants have low densities, it is obvious that a huge planet with a low mass is composed of gas. Rocky planets have a larger mass-to-size ratio because they are denser.
However, even if K2-315b is rocky, there is little likelihood that it could support life as we know it.
Even at its blazing orbital speed of 81 km/s (50 miles/second), which is far faster than Earth's orbital speed of 29.78 km/s (18.5 miles/second), it has a short orbit of only 3.14 days, making its surface unbearably hot. It might become as hot as 450 Kelvin (177 degrees Celsius, or 350 degrees Fahrenheit).
However, the planet may provide an excellent subject for further investigation. Small, faint stars provide a greater chance to examine for atmospheres when the exoplanet transits since they don't flash as brightly as their bigger siblings.
As various components absorb or emit certain wavelengths, the light of the star should fluctuate somewhat as it travels through the atmosphere of an exoplanet.
The team predicts that the forthcoming James Webb Space Telescope will need only 40 transits to have enough data to make an identification. Even the atmosphere of an inhospitable exoplanet would be an interesting thing to investigate.
But that's science for the future. The team intends to keep utilising SPECULOOS to look for more targets in the meantime.
According to Niraula, "there will be more intriguing planets in the future, just in time for JWST, a telescope built to examine the atmosphere of these extraterrestrial worlds." "Hopefully one day, with improved algorithms, we can search for smaller planets, even ones as tiny as Mars."
The Astronomical Journal has published the study.
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