Astronomen entdecken ein nahe gelegenes Mehrplanetensystem mit zwei erdgroßen Planeten

Das nur 33 Lichtjahre von der Erde entfernte System scheint zwei erdgroße Gesteinsplaneten zu beherbergen.

Astronomen haben in unserer Nachbargalaxie ein neues Multiplanetensystem entdeckt[{“ 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.

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 NASA’s Transiting Exoplanet Survey Satellite (TESS), an MIT-led mission that is designed to observe the nearest and brightest stars, and detect periodic dips in light that could signal 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 detections through the mission’s science inspection pipeline, and the signals were soon classified as two TESS Objects of Interest, or TOIs — objects that are flagged as potential planets. The same signals were also found independently by the Science Processing Operations Center (SPOC), the official TESS planet search pipeline based at NASA Ames. Scientists typically plan to follow up with other telescopes to confirm that the objects are indeed planets.

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

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]. „

planetarische Anziehungskraft

Letztendlich bestätigte diese gemeinsame Anstrengung schnell die Anwesenheit von zwei Planeten um HD 260655 in etwa sechs Monaten.

Um zu bestätigen, dass die Signale von TESS tatsächlich von zwei umlaufenden Planeten stammten, betrachteten die Forscher Daten sowohl von HIRES als auch von CARMENES des Sterns. Beide Durchmusterungen messen die Gravitationsschwingung eines Sterns, auch bekannt als seine Radialgeschwindigkeit.

„Jeder Planet, der einen Stern umkreist, hat eine kleine Gravitationskraft auf seinen Stern“, erklärt Kunimoto. „Was wir suchen, ist jede leichte Bewegung dieses Sterns, die darauf hindeuten könnte, dass ein Objekt mit planetarer Masse ihn anzieht.“

Aus beiden Archivdatensätzen fanden die Forscher statistisch signifikante Anzeichen dafür, dass es sich bei den von TESS entdeckten Signalen tatsächlich um zwei umlaufende Planeten handelte.

„Da wussten wir, dass wir etwas sehr Spannendes vor uns haben“, sagt Sporer.

Das Team sah sich dann die TESS-Daten genau an, um Eigenschaften beider Planeten zu bestimmen, einschließlich ihrer Umlaufzeit und Größe. Sie stellten fest, dass der innere Planet mit dem Spitznamen HD 260655b den Stern alle 2,8 Tage umkreist und etwa 1,2-mal so groß wie die Erde ist. Der zweite Exoplanet, HD 260655c, rotiert alle 5,7 Tage und ist 1,5-mal so massereich wie die Erde.

Aus Radialgeschwindigkeitsdaten von HIRES und CARMENES konnten die Forscher die Masse der Planeten berechnen, die in direktem Zusammenhang mit der Amplitude steht, mit der jeder Planet an seinem Stern schleift. Sie fanden heraus, dass der innere Planet die doppelte Masse der Erde hat, während der äußere Planet eine Masse von etwa drei Erdmassen hat. Aus seiner Größe und Masse schätzte das Team die Dichte jedes Planeten. Der kleinere innere Planet ist etwas dichter als die Erde, während der größere äußere Planet etwas weniger dicht ist. Beide Planeten sind je nach ihrer Dichte wahrscheinlich terrestrisch oder felsig in ihrer Zusammensetzung.

Die Forscher schätzen auch, basierend auf ihren kurzen Umlaufbahnen, dass die innere Oberfläche des Planeten eine Röstung von 710 K (818 Grad) hat.[{“ 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.