Astronomers discover a multi-planet system nearby | MIT news

Astronomers at MIT and elsewhere have discovered a new multiplanet system within our neighboring galaxy located 10 parsecs, or about 33 light-years, from Earth, making it one of the closest known multiplanet systems to our system.

At the heart of the system is a small, cool dwarf star, called HD 260655, which astronomers have found hosts at least two Earth-sized terrestrial planets. Rocky worlds are likely uninhabitable, because their orbits are relatively narrow, exposing planets to temperatures too high to tolerate liquid surface water.

However, scientists are excited about the system because its star’s proximity and brightness will give them a closer look at planetary properties and signs of any atmospheres they might have.

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

The team will present its discovery today at the American Astronomical Society meeting in Pasadena, California. Team members at MIT include Katherine Hess, George Reeker, Sarah Seeger, Avi Shborer, Roland Vandersbeek and Joel Villasenor, along with collaborators from institutions around the world.

data power

The new planetary system was initially identified by NASA’s Transiting Exoplanet Survey Satellite (TESS), a mission led by the Massachusetts Institute of Technology designed to observe the nearest and brightest stars, and to detect periodic dips in light that could indicate a passing planet.

In October 2021, Kunimoto, a member of the TESS science team at MIT, was monitoring incoming satellite data when she noticed a periodic starlight dip, or transit, from the star HD 260655.

The discoveries ran through the mission’s science inspection pipeline, and the signals were soon classified as TESS Objects of Interest, or TOIs—objects that have been flagged as possible planets. The same signals were found independently by the Scientific Processing Operations Center (SPOC), the official TESS planet research pipeline headquartered at NASA Ames. Scientists usually plan to follow up with other telescopes to confirm that the objects are indeed planets.

The process of classifying and confirming new planets often takes several years. For HD 260655, this process is significantly shortened with the help of archival data.

Soon after Kunimoto identified potential planets around HD 260655, Schpurer looked to see if the star had previously been observed by other telescopes. Fortunately, HD 260655 was included in a survey of stars conducted by the High Resolution Echelon Spectrograph (HIRES), an instrument operating as part of the Keck Observatory in Hawaii. HIRES has been observing the star, along with a host of other stars, since 1998, and researchers have had access to publicly available survey data.

HD 260655 is also included as part of another independent survey by CARMENES, an instrument operating as part of the Calar Alto Observatory in Spain. Because this data was private, the team reached out to members of both HIRES and CARMENES with the goal of combining the power of their data.

“These negotiations are sometimes very sensitive,” notes Sporer. “Fortunately, the teams agreed to work together. This human interaction is almost as important in getting the data.” [as the actual observations]. “

pull planets

Ultimately, this collaborative effort quickly confirmed the presence of two planets around HD 260655 in about six months.

To confirm that the signals from TESS were indeed from two orbiting planets, the researchers looked at data from both the HIRES and CARMENES of the star. Both surveys measure a star’s gravitational oscillation, also known as its radial velocity.

“Every planet orbiting a star will have a small gravitational force on its star,” Kunimoto explains. “What we’re looking for is any slight movement of this star that could indicate a planetary-mass object pulling it in.”

From both sets of archival data, the researchers found statistically significant signals that the signals detected by TESS were indeed two orbiting planets.

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

The team then looked closely at the TESS data to determine characteristics of both planets, including their orbital period and size. They determined that the inner planet, nicknamed HD 260655b, orbits the star every 2.8 days and is about 1.2 times the size of Earth. The second exoplanet, HD 260655c, rotates every 5.7 days and is 1.5 times as massive as Earth.

From radial velocity data from HIRES and CARMENES, the researchers were able to calculate the mass of the planets, which is directly related to the amplitude with which each planet drags on its star. They found that the inner planet has a mass twice the mass of Earth, while the outer planet has a mass of about three Earth masses. From its size and mass, the team estimated the density of each planet. The smaller inner planet is slightly more dense than Earth, while the larger outer planet is slightly less dense. Both planets, depending on their densities, are likely terrestrial or rocky in composition.

The researchers also estimate, based on their short orbits, that the inner planet’s surface is a roasting of 710 K (818 degrees Fahrenheit), while the outer planet is about 560 K (548 F).

“We consider this range to be outside the habitable zone, too hot to allow liquid water to be present at the surface,” Kunimoto says.

“But there may be more planets in the system,” Sppurer adds. “There are many multiple planet systems that host five or six planets, especially around small stars like this. Hopefully we can find more, and one of them might be in the habitable zone. That’s optimistic thinking.”

This research was supported in part by NASA, Max-Planck-Gesellschaft, Consejo Superior de Investigaciones Científicas, the Ministry of Economy and Competition and the European Regional Development Fund.

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