A system with a red dwarf and two rocky planets
At the center of this system, which consists of two rocky planets, is an M-type red dwarf star called HD260655. A red dwarf, also known as a red main sequence star, is a star of spectral type M. It’s a small, cool star. Its mass is usually between 0.075 and 0.4 solar mass. And its surface temperature is not more than 4000 Kelvin. The red dwarfs are the common stars of the universe. In the Milky Way alone, they represent 80 to 85% of all known space objects.
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HD260655 is home to two rocky Earth-sized planets. However, due to their very narrow orbits, these planets are certainly not habitable. The temperature in these exoplanets must be very high in order to retain liquid water on the surface.
Since their star is so bright, astronomers and astrophysicists have benefited from the ideal conditions for studying their atmosphere. They asked themselves the following questions. Do these planets benefit from volatile atmospheres? Is it possible to find signs of the presence of water there? And carbonaceous matter?
The discovery of these stars and these two rocky planets was made possible by NASA’s Transiting Exoplanet Survey Satellite (TESS). It is a small 350 kg space telescope that was launched into high Earth orbit in April 2018. This satellite was created to observe the closest and brightest stars It is also used to detect periodic declines in illumination, characterizing the passage of a planet in front of a star.
Two periodic dips in the red dwarf light
The presence of the two rocky planets was first reported in October 2021 when an astronomer from the TESS team for MIT was working on data analysis sent by a satellite. At one point he noticed the alternating appearance of two dips in the light of the red dwarf star. After evaluation, these signals quickly become interesting and are classified as potential planets.
These signals from the TESS satellite were independently detected and studied by the SPOC (Science Processing Operations Center), NASA’s official TESS data analysis pipeline.
In general, the process of classification and confirmation of the presence of new planets takes a long time. For HD260655 systems, this delay is greatly reduced due to the fairly large amount of data collected and archived data.
For example, the Red Dwarf HD260655 has been known and even observed since 1998 by the High Resolution Scale Spectrometer (HIRES), an astronomical observatory at the Cake Observatory on the island of Hawaii. Other information on the HD260655 is provided by observations made by CARMENES, a device based in Spain and consisting of two high-resolution scale spectrographs, visible for one and infrared for the other.
Combining all this data, thanks to the cooperation of all the teams, has made it possible to shorten the process of confirming the presence of these two rocky planets orbiting around HD260655.
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A measure of gravitational oscillation
To confirm that these are really rocky planets orbiting HD260655, astronomers have analyzed data from HIRES and CARMENES. They were able to get information about gravitational oscillations or radial velocities.
“Every planet orbiting a star is going to exert a small gravitational pull on its star,” said Mrs Kunimoto, a TESS scientist at MIT. “What we are looking for is very little movement of this star. This may indicate the presence of a planet-shaped object. The device’s archival data and data from TESS confirmed that the detected signals came from both planets.
Astronomers have determined the properties of these two planets. The innermost planet in the HD260655b system orbits the red dwarf in 2.8 days. It is 1.2 times larger than Earth. The other, outermost planet is named HD260655c. It orbits the star in 5.7 days and is 1.5 times larger than Earth.
Scientists estimate that HD260655b is a terrestrial planet twice the size of Earth. Where the mass of HD260655c is 3 times that of Earth. In terms of density, the inner planet is a little denser than Earth. For its part, the outer planet is a little less dense.
From the analysis of their orbits, they were able to determine the surface temperature of the inner planet. It was 710 Kelvin. And the outer planet was 560 Kelvin.
Researchers are hoping to identify other rocky planets in the HD260655 system in hopes of finding one that could be habitable.
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Jennifer Chu, “Astronomers Discover Nearby Multiplanet System,” MIT News Office, June 15, 2022, https://news.mit.edu/2022/multiplanet-system-nearby-0615