Astronomers Find a Multiplanet System Nearby

MIT astronomers have discovered a new multiplanet system that exists just 10 parsecs, or approximately 33 light-years, from Earth, making it one of the closest known multiplanet systems to our own. The star at the system’s heart likely hosts at least two terrestrial, Earth-sized planets. Credit: MIT News, with TESS Satellite figure courtesy of NASA.

Astronomers at MIT and elsewhere have discovered a new multiplanet system within our galactic neighborhood that exists simply 10 parsecs, or approximately 33 light-years, from Earth, making it one of the closest known multiplanet systems to our own.

A multiplanet system

At the heart of the system lies a little and cool M-dwarf star, called HD 260655, and astronomers have found that it hosts at least two terrestrial, Earth-sized planets. The rocky worlds are likely not habitable, as their orbits are relatively limited, exposing the planets to temperatures too high to maintain liquid surface water.

However, scientists are excited regarding this system due to the fact that 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 research due to 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 leads scientists. “Is there a volatile-rich atmosphere around these planets? Moreover, are there indicators of water or carbon-based types? These planets are fantastic test beds for those explorations.”

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

Data power

The new planetary system was at first identified by NASA’s Transiting Exoplanet Study Satellite (TESS), an MIT-led mission that is designed to observe the closest and brightest stars and spot periodic dips in light that could indicate a passing planet.

In October 2021, Kunimoto, a member of MIT’s TESS science team, was monitoring the satellite’s incoming data when she noticed a pair of periodic dips in starlight, or transits, from the star HD 260655.

She ran the discoveries through the mission’s science inspection pipeline and the signals were quickly categorized as 2 TESS Objects of Interest, or TOIs– objects that are flagged as potential planets. The same signals were likewise discovered independently by the Science Processing Operations Center (SPOC), the official TESS planet search pipeline based at NASA Ames. Scientists commonly plan to follow up with other telescopes to confirm that the objects are certainly planets.

The process of categorizing and subsequently confirming new planets can frequently take numerous years. For HD 260655, that process was shortened significantly with the help of archival data.

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 study of stars taken by the High-Resolution Echelle Spectrometer (HIRES), an instrument that runs as part of the Keck Observatory in Hawaii. HIRES had been monitoring the star, together 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 an additional independent survey by CARMENES, an instrument that operates as part of the Calar Alto Observatory in Spain. As these data were personal, the team connected to members of both HIRES and CARMENES with the objective of combining their data power.

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

Planetary pull

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

To confirm that the signals from TESS were certainly from two orbiting planets, the researchers checked out both HIRES and CARMENES data of the star. Both surveys measure a star’s gravitational wobble, likewise called its radial velocity.

“Every planet orbiting a star i going have a little gravitational pull on its star,” Kunimoto describes. “What e are looking for is any slight movement of that star that could indicate a planetary-mass object is tugging on it.

From both sets of historical data, the researchers discovered statistically substantial indicators that the signals detected by TESS were indeed two orbiting planets.

“Then we knew we had something fascinating,” Shporer states.

The team then looked more closely at TESS data to pin down properties of both planets, including their orbital period and size. They established that the inner planet, referred to as HD 260655b, orbits the star every 2.8 days and is about 1.2 times as huge as the Earth. The nd outer planet, HD 260655c, orbits every 5.7 days and is 1.5 times as huge as the Earth.

From the radial-velocity data from HIRES and CARMENES, the researchers were able to determine he planet’s mass, which is straight related to the amplitude by which each planet tugs on its star. They found the inner planet is about two times as massive as the Earth, while the outer planet is about three Earth masses.

From their size and mass, the team estimated each planet’s density. The nner, smaller planet is a little denser than the Earth, while the external, larger planet is a little bit less dense. ased onn their density, both planets are likely terrestrial or rocky in composition.

The researchers also approximate, based upon their short orbits, that the surface of the inner planet is a roasting 710 kelvins (818 degrees Fahrenheit), while the external 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 states.

“But there might be more planets in the system,” Shporer adds. “There are lots of multiplanet systems hosting five or six planets, especially around little stars like this one. Hopefully we will find more, and one might be in the habitable zone. That is positive thinking.

Read the original article on MIT News.

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