Astrônomos descobrem um sistema multiplanetário próximo com dois planetas do tamanho da Terra

Os astrônomos do MIT descobriram um novo sistema multiplanetário que fica a apenas 10 parsecs, ou cerca de 33 anos-luz, da Terra, tornando-o um dos sistemas multiplanetários conhecidos mais próximos do nosso. A estrela no coração do sistema provavelmente hospeda pelo menos dois planetas terrestres do tamanho da Terra. Crédito: MIT News, com figura do satélite TESS cortesia da NASA

Localizado a apenas 33 anos-luz da Terra, o sistema parece hospedar dois planetas rochosos do tamanho da Terra.

Um novo sistema multiplanetário dentro de nossa vizinhança galáctica foi descoberto por astrônomos em[{” 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].”

Tração planetária

No final, este esforço colaborativo rapidamente confirmou a presença de dois planetas em torno de HD 260655 em cerca de seis meses.

Para confirmar que os sinais do TESS eram de fato de dois planetas em órbita, os pesquisadores analisaram os dados HIRES e CARMENES da estrela. Ambas as pesquisas medem a oscilação gravitacional de uma estrela, também conhecida como sua velocidade radial.

“Todo planeta orbitando uma estrela terá uma pequena atração gravitacional em sua estrela”, explica Kunimoto. “O que estamos procurando é qualquer movimento leve dessa estrela que possa indicar que um objeto de massa planetária está puxando-a.”

De ambos os conjuntos de dados de arquivo, os pesquisadores encontraram sinais estatisticamente significativos de que os sinais detectados pelo TESS eram de fato dois planetas em órbita.

“Então sabíamos que tínhamos algo muito emocionante”, diz Shporer.

A equipe então olhou mais de perto os dados do TESS para identificar as propriedades de ambos os planetas, incluindo seu período orbital e tamanho. Eles determinaram que o planeta interior, apelidado de HD 260655b, orbita a estrela a cada 2,8 dias e é cerca de 1,2 vezes maior que a Terra. O segundo planeta externo, HD 260655c, orbita a cada 5,7 dias e é 1,5 vezes maior que a Terra.

A partir dos dados de velocidade radial de HIRES e CARMENES, os pesquisadores conseguiram calcular a massa dos planetas, que está diretamente relacionada à amplitude com que cada planeta puxa sua estrela. Eles descobriram que o planeta interno tem cerca de duas vezes a massa da Terra, enquanto o planeta externo tem cerca de três massas terrestres. A partir de seu tamanho e massa, a equipe estimou a densidade de cada planeta. O planeta interno menor é um pouco mais denso que a Terra, enquanto o planeta externo maior é um pouco menos denso. Ambos os planetas, com base em sua densidade, são provavelmente terrestres ou rochosos em composição.

Os pesquisadores também estimam, com base em suas órbitas curtas, que a superfície do planeta interior é uma torrefação de 710 kelvins (818 graus[{” 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.