Astronomers discover a nearby multi-planet system with two planets the size of Earth

New multiplanet system near Earth

MIT astronomers have discovered a new multiplanet system located just 10 parsecs, or about 33 light-years, from Earth, making it one of the closest known multiplanet systems to our own. The star at the heart of the system is likely to host at least two Earth-sized planets. Credit: MIT News, with TESS satellite figure courtesy of NASA

Located just 33 light-years from Earth, it appears that the system hosts two rocky planets the size of Earth.

A new multiplanet system in our galactic neighborhood has been discovered by astronomers at[{” attribute=””>MIT and elsewhere. It lies just 10 parsecs, or about 33 light-years, from Earth, making it one of the closest known multiplanet systems to our own.

At the heart of the system lies a small and cool M-dwarf star, named HD 260655, and astronomers have found that it hosts at least two terrestrial, Earth-sized planets. The rocky worlds have relatively tight orbits, exposing the planets to temperatures that are too high to sustain liquid surface water. Therefore, they are unlikely to be habitable.

Nevertheless, scientists are excited about this system because the proximity and brightness of its star will give them a closer look at the properties of the planets and signs of any atmosphere they might hold.

“Both planets in this system are each considered among the best targets for atmospheric study because of the brightness of their star,” says Michelle Kunimoto, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research and one of the discovery’s lead scientists. “Is there a volatile-rich atmosphere around these planets? And are there signs of water or carbon-based species? These planets are fantastic test beds for those explorations.”

The team will present its discovery on June 15, 2022, at the meeting of the American Astronomical Society in Pasadena, California. Team members at MIT include Katharine Hesse, George Ricker, Sara Seager, Avi Shporer, Roland Vanderspek, and Joel Villaseñor, along with collaborators from institutions around the world.

NASA TESS in Space

Illustration of NASA’s Transiting Exoplanet Survey Satellite (TESS) at work. Credit: NASA’s Goddard Space Flight Center

Data power

The new planetary system was initially identified by Keck Observatory Domes

The Keck observatory domes atop Mauna Kea. Credit: T. Wynne / JPL

Soon after Kunimoto identified the two potential planets around HD 260655, Shporer looked to see whether the star was observed previously by other telescopes. As luck would have it, HD 260655 was listed in a survey of stars taken by the High Resolution Echelle Spectrometer (HIRES), an instrument that operates as part of the Keck Observatory in Hawaii. HIRES had been monitoring the star, along with a host of other stars, since 1998, and the researchers were able to access the survey’s publicly available data.

HD 260655 was also listed as part of another independent survey by CARMENES, an instrument that operates as part of the Calar Alto Observatory in Spain. As these data were private, the team reached out to members of both HIRES and CARMENES with the goal of combining their data power.

“These negotiations are sometimes quite delicate,” Shporer notes. “Luckily, the teams agreed to work together. This human interaction is almost as important in getting the data [as the actual observations]. “

Planetary move

Finally, this collaboration quickly confirmed the presence of two planets around HD 260655 in about six months.

To confirm that the signals from TESS actually came from two planets in orbit, the researchers looked through both HIRES and CARMENES data from the star. Both studies measure a star’s gravitational oscillations, also known as its radial velocity.

“Every planet orbiting a star will have a small gravitational force on the star,” Kunimoto explains. “What we are looking for is any small movement of the star that may indicate that an object with planetary mass is pulling at it.”

From both sets of archival data, the researchers found statistically significant evidence that the signals detected by TESS were actually two planets in orbit.

“Then we knew we had something very exciting,” says Shporer.

The team looked more closely at TESS data to determine the properties of both planets, including their orbital period and size. They determined that the inner planet, called HD 260655b, orbits the star every 2.8 days and is about 1.2 times the size of Earth. The other outer planet, HD 260655c, orbits every 5.7 days and is 1.5 times the size of Earth.

From the radial velocity data from HIRES and CARMENES, scientists were able to calculate the mass of the planets, which is directly related to the amplitude that each planet draws in its star. They found that the inner planet is about twice as massive as the earth, while the outer planet is about three masses of earth. Based on their size and mass, the team estimated the density of each planet. The inner, smaller planet is slightly denser than Earth, while the outer, larger planet is slightly less dense. Both planets, based on their density, are likely to be terrestrial or rocky in composition.

Scientists also estimate, based on their short orbits, that the surface of the inner planet is scorching 710 kelvin (818 degrees).[{” attribute=””>Fahrenheit), while the outer planet is around 560 °K (548 °F).

“We consider that range outside the habitable zone, too hot for liquid water to exist on the surface,” Kunimoto says.

“But there might be more planets in the system,” Shporer adds. “There are many multiplanet systems hosting five or six planets, especially around small stars like this one. Hopefully, we will find more, and one might be in the habitable zone. That’s optimistic thinking.”

This research was supported, in part, by NASA, the Max-Planck-Gesellschaft, the Consejo Superior de Investigaciones Científicas, the Ministerio de Economía y Competitividad, and the European Regional Development Fund.