Astronomers are discovering a multi-planetary system nearby

Newswise – Astronomers at MIT and elsewhere have discovered a new multiplanetary system in our galactic quarter just 10 parsecs, or about 33 light-years, from Earth, making it one of the closest multiplanetary systems. to ours.

At the heart of the system is a small, cool dwarf star M, called HD 260655, and astronomers have discovered that it is home to at least two Earth-sized planets. Rocky worlds are unlikely to be habitable, as their orbits are relatively narrow, exposing planets to temperatures too high to keep surface water liquid.

However, 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 the signs of any atmosphere they may contain.

“The two planets in this system are considered among the best targets for atmospheric study because of the brightness of their star,” said Michelle Kunimoto, a postdoc at the Kavli Institute for Astrophysics and Space Research at MIT. one of the leading scientists of the discovery. “Is there a volatile atmosphere around these planets? And are there any evidence of water-based or carbon-based species? These planets are great test benches for these explorations.”

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

Data power

The new planetary system was initially identified by NASA’s TESS (Transiting Exoplanet Survey Satellite), an MIT-led mission designed to observe the nearest bright stars and detect periodic light drops that could indicate a planet. what’s going on.

In October 2021, Kunimoto, a member of MIT’s TESS scientific team, was monitoring incoming satellite data when he noticed a couple of periodic drops in starlight, or traffic, from the HD star. 260655.

He ran the detections through the mission’s scientific inspection channel, and the signals were soon classified as two objects of interest TESS, or TOI, objects that are marked as potential planets. The same signals were also found independently by the Scientific Processing Operations Center (SPOC), the official TESS planetary research channel based at NASA Ames. Scientists often track other telescopes to confirm that the objects are actually planets.

The process of classifying and later confirming new planets can often take several years. For HD 260655, this process was significantly shortened with the help of archive data.

Shortly after Kunimoto identified the two potential planets around HD 260655, Shporer looked to see if the star had been previously observed by other telescopes. Luckily, HD 260655 was included in a star survey conducted 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 number of other stars, since 1998, and researchers were able to access publicly available data from the survey.

HD 260655 was also included as part of another independent survey of CARMENES, an instrument that operates as part of the Calar Alto Observatory in Spain. As this data was private, the team contacted both HIRES and CARMENES members with the aim of combining their data power.

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

Planetary attraction

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

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

“Each planet orbiting a star will have some gravitational pull on its star,” says Kunimoto. “What we’re looking for is any slight movement of this star that could indicate that an object of planetary mass is pulling it.”

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

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

The team then looked more closely at TESS data to determine the properties of the two 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 approximately 1.2 times larger than Earth. The second outer planet, HD 260655c, orbits every 5.7 days and is 1.5 times larger than Earth.

From the radial velocity data of 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 pulls its star. They found that the inner planet is about twice the size of Earth, while the outer planet has about three Earth masses. Based on its size and mass, the team estimated the density of each planet. The inner planet, smaller, is slightly denser than Earth, while the outer planet, larger, is slightly less dense. Both planets, depending on their density, are probably terrestrial or rocky in composition.

Researchers also estimate, based on their short orbits, that the surface of the inner planet is 710 kelvins (818 degrees Fahrenheit), while the outer planet is around 560 K (548 F).

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

“But there could be more planets in the system,” Shporer added. “There are a lot of multi-planet systems that house five or six planets, especially around small stars like this. Hopefully we’ll find more, and one could be in the habitable zone. That’s optimistic thinking.”

This research is supported, in part, by NASA, Max-Planck-Gesellschaft, the Higher Council for Scientific Research, the Ministry of Economy and Competitiveness, and the European Regional Development Fund.


Written by Jennifer Chu, MIT News Office

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