Astronomers discover two super-Earths orbiting nearby stars

Astronomers discover two super-Earths orbiting nearby stars

Translated by Julio Batista
Original by Michelle Starr for ScienceAlert

The two newly discovered exoplanets are called super-Earths — larger than Earth but smaller than ice giants — orbiting a cool red dwarf star called HD 260655, which is only 33 light-years away. While these worlds are unlikely to be habitable, given our current understanding of life, this star and its exoplanet are one of the closest multi-planet systems to Earth.

That makes it a good target for follow-up research trying to understand the makeup of exoplanets and analyze their atmospheres — an effort that will help us in our search for alien life, even if neither world can hold it. “Both planets in this system are considered to be among the best targets for atmospheric research due to the brightness of the stars,” said astronomer Michelle Couniben of MIT’s Kavli Institute for Astrophysics and Space Research. .”

“Are there volatile-rich atmospheres around these planets? Are there signs of water or carbon-based species? These planets are great testbeds for these kinds of explorations.”

To date, more than 5,000 exoplanets have been confirmed in the Milky Way, and astrobiologists are very interested in finding terrestrial or rocky worlds such as Earth, Venus and Mars. We only have a sample size of one world known to harbor life—ours—so finding planets similar in size and composition to Earth is one of the main criteria for finding life elsewhere in the galaxy.

However, rocky exoplanets are relatively small in size and mass, which makes them harder to find; most exoplanets we’ve been able to measure to date are giant planets. Rock worlds – and better yet, nearby rock worlds – are in high demand.

The two worlds orbiting HD 260655 — called HD 260655 b and HD 260655 c — were discovered as they orbited between us and their star. The faint dips in starlight caused by the transits of these exoplanets have been recorded by NASA’s TESS exoplanet-hunting telescope, which is designed to accurately detect these phenomena.

When Kunimoto detected these dips in light due to the transits in the TESS data, the next step was to verify whether the star had appeared in previous surveys — and it did. The High-Resolution Echelon Spectrometer on the Keck Telescope (now called the Andes) has publicly available data since 1998. Another spectrometer, CARMENES, at the Caral Alto Observatory in Spain, also recorded the star.

This has huge implications for exoplanet science: Spectral data can reveal whether a star is moving there.

“Each planet orbiting a star exerts a very small gravitational force on its star,” Kunimoto said. “What we’re looking for is any slight movement of the star that could indicate a planetary-mass object is pulling it.”

Between the TESS data and the HIRES and CARMENES data, the team was able to confirm that two exoplanets orbit HD 260655. Furthermore, using the two datasets, the team was able to compile a comprehensive profile of the two exoplanets.

Transit data provides a physical dimension based on how much light the star blocks; and spectral data reveals the mass of the exoplanet, based on how much the star has moved. Both sets of data can be used to calculate the orbits of exoplanets.

The inner exoplanet HD 260655 b is about 1.2 times the size of Earth and twice as massive, orbiting its star every 2.8 days. The outer world HD 260655 c is 1.5 times Earth’s mass, 3 times Earth’s mass, and has an orbit of 5.7 days.

At these sizes and masses, their densities suggest that the two exoplanets are likely rocky worlds.

Unfortunately, even though the star is cooler and dimmer than the sun, the planet’s proximity to HD 260655 means Earth is too hot for life as we know it. The HD 260655 b averaged 435 degrees Celsius, while in the HD 260655 c it was slightly milder, but still scorching hot, at 284 degrees Celsius.

“We think this belt is outside the habitable zone, too hot for liquid water to exist at the surface,” Kunimoto said.

However, both exoplanets may still have atmospheres and should be ready for detection by the newly deployed James Webb Space Telescope, which includes observing exoplanet atmospheres among its mission objectives.

Plus, there may even be more exoplanets orbiting stars we haven’t yet discovered.

“There are many multiplanetary systems with five or six planets, especially around small stars like this,” said astrophysicist Avi Shporer of MIT’s Kavli Institute for Astrophysics and Space Research.

“We’re hoping to find more, and one of them might be in the liveable zone. That’s an optimistic view.”

The team presented their findings at the 240th meeting of the American Astronomical Society.

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