Two 'Earth-like' Planets Discovered in 'Habitable Zone' Around Star in Our Cosmic Backyard

Astronomers have discovered two "Earth-like" planets orbiting a star just 12.5 light-years away in our cosmic backyard, according to a study published in the journal Astronomy & Astrophysics.

The finds represent the tenth and eleventh planets to be identified by an international collaboration that has searched for worlds around nearby stars since 2016.

Scientists have used a number facilities around the world including the CARMENES instrument at the Calar Alto Observatory in Spain, the Muscat2 instrument on the Carlos Sánchez Telescope at the Teide Observatory—also in Spain—and the Las Cumbres Observatory in California.

Researchers from the University of Göttingen, Germany, the Instituto de Astrofísica de Canarias (IAC,) Spain, and other institutions, found the planets orbiting the Teegarden star in the constellation Aries.

Discovered in 2003, Teegarden is a red dwarf—a small and relatively cool class of stars—with a mass less than a tenth that of our sun and a surface temperature of nearly 4,900 degrees Fahrenheit. Despite its proximity to Earth in cosmic terms—it is the 24th nearest stellar system—it was difficult to spot initially due to its dimness.

To identify the new planets, the scientists monitored the star for three years in search of evidence that a planet or planets could be orbiting it.

"We measured the velocity of the star and found that [it] oscillates periodically,"
Mathias Zechmeister, first author of the study from the University of Göttingen, told Newsweek. "We are convinced that these perturbations are due to the gravitational pull of the planets."

"The velocity is measured via the Doppler effect," he said. "People realize the Doppler-effect when a fast car or ambulance passes them. The sound—i.e.
the acoustical frequencies—changes."

The data that the scientists collected indicated the presence of two planets, slightly bigger than the Earth, orbiting Teegarden in the "habitable zone"—usually defined as the region around a host star within which liquid water, a key component for life as we know it, could exist on the surface. Furthermore, the researchers suggest that that the two planets, known as B and C, could be part of a larger system.

"Around the sun [the planets] would be very hot," Zechmeister said. "But Teegarden's Star is so small and cool—its energy emission is lower than 0.1 percent compared to the Sun—that planet B receives almost the same
energy as Earth and planet C around 40 percent, more similar to Mars. So, in this mini-solar system both planets are in the habitable zone."

In terms of their suitability for life, Zechmeister says that the most important parameters—distance from the star and mass—are in an excellent range. However, we don't know the planets' radii.

"From the radius, one could conclude about the present of an atmosphere
and maybe their chemical composition," he said. "But this requires the next generation of telescopes."

The researchers were not able to use the the most popular technique for identifying new worlds—what's known as the "transit method." This involves looking for small dips in brightness around a host star, indicating that a planet has passed in front of it when observed from our viewpoint, thus temporarily blocking some of the light being emitted.

However, because the planets orbiting Teegarden are not aligned in the right way relative to the Earth, using this technique was not possible. Nevertheless, the scientists were able to discount other explanations for the variations in the star's velocity that they observed.

"These studies demonstrate that the signals of the two planets cannot be due to the activity of the star, even though we could not detect the transits of the two new planets," Victor Sánchez Béjar, another author of the paper from the IAC, said in the statement.

This article was updated to include additional comments from Mathias Zechmeister.

Teegarden star, exoplanets
Artist's illustration of the newly identified planets around the Teegarden star. Instituto de Astrofísica de Canarias

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