Three new, roughly Earth-sized exoplanets have been found orbiting a nearby star. Named L 98-59b, c and d, the small worlds were spotted by NASA's Transiting Exoplanet Survey Satellite (TESS), as part of a larger haul of data that finally brings the total tally past the milestone of 4,000 exoplanets discovered to date.

The majority of exoplanets discovered so far are gas and ice giants, like Jupiter and Neptune, for the simple reason that they're huge and easier to spot. Smaller, Earth-sized worlds are not only intriguing because they're rare, but because they're better suited to potential extraterrestrial life.

The three new planets are excitingly close to Earth-sized. The innermost world, L 98-59b, is about 80 percent the size of our home planet, putting it in between Earth and Mars and making it the smallest exoplanet discovered by TESS to date. L 98-59c is around 1.4 Earths in size, while the third planet, L 98-59c, is slightly bigger again at 1.6 times the size of Earth.

As small as L 98-59b is, it isn't the smallest exoplanet ever found. That honor belongs to Kepler-37b, which is smaller than Mercury and only a little bigger than our Moon.

These new worlds were discovered orbiting a star called L 98-59, an M dwarf about 35 light-years away in the constellation Volans. This type of star is smaller and cooler than our Sun, and makes up about three quarters of the stars in the Milky Way galaxy. Because they're so common, astronomers are curious about closely studying them and the planets they host, to see how friendly they are for any possible life. Other promising M dwarfs include TRAPPIST-1, home to seven Earth-sized worlds, and Proxima Centauri, our closest neighbor.

Unfortunately, none of these three new exoplanets are within the habitable zone, the region around a star where temperatures are just right for liquid water to form on the surface. They're all a little too close to the star for comfort: L 98-59b orbits the star in just 2.25 days, meaning it cops 22 times more radiation than Earth does from the Sun; L 98-59c orbits every 3.7 days and takes 11 times Earth's radiation; while L 98-59d has a 7.5-day orbit and receives four times the radiation.

Astronomers say that this close proximity means that all three planets are probably more Venus-like than Earth-like, with runaway greenhouse effects making them stifling. The furthermost world, though, could instead resemble a mini-Neptune, with a thick atmosphere wrapped around a small rocky core.

The team says these three new planets are prime targets for further investigation into whether they have atmospheres and, if so, what gases make them up.

The research was published in The Astronomical Journal. The team describes the discovery in the video below.

Source: NASA