Two new worlds of probable rocky mineral goodness have just been found orbiting a star near our own cosmic neighborhood.
The two newly discovered exoplanets are what are known as super-Earths, larger than Earth but smaller than an ice giant, orbiting a cool red dwarf star called HD 260655, which is only 33 light-years away. away.
Although the worlds are unlikely to be habitable, given our current understanding of life, the star and its exoplanets are among the closest multimont systems to Earth.
This makes it an excellent target for follow-up surveys to try to understand what exoplanets are made of and to evaluate their atmospheres, an effort that will help our search for extraterrestrial life, even if the two worlds they are unable to do so. hosting it themselves.
“The two planets in this system are considered among the best targets for atmospheric study because of the brightness of their star,” says astronomer Michelle Kunimoto of MIT’s Kavli Institute for Astrophysics and Space Research. .
“Is there a volatile atmosphere around these planets? And are there any evidence of water or carbon-based species? These planets are great test benches for these explorations.”
To date, more than 5,000 exoplanets have been confirmed in the Milky Way, and astrobiologists are keen to find terrestrial or rocky worlds such as Earth, Venus, and Mars.
We have a sample size exactly of a world known to host life, ours, so finding Earth-like planets in size and composition is one of the main criteria for finding life elsewhere in the galaxy.
Rocky exoplanets, however, are relatively small in both size and mass, making them more difficult to detect; most exoplanets we have been able to measure so far tend to fall into the category of giants. Rocky worlds, and even better, nearby rocky worlds, are in high demand.
The two worlds orbiting HD 260655, called HD 260655 b and HD 260655 c, were discovered to pass between us and its star during its orbit. The slightest drop in starlight due to these exoplanetary transits was recorded by NASA’s TESS exoplanet hunting telescope, which is designed to detect exactly these phenomena.
When Kunimoto detected these traffic drops in TESS data, the next step was to see if the star had appeared in previous surveys, and so it was.
The Keck telescope’s high-resolution Echelle spectrometer (now known as ANDES) had been publicly available since 1998. Another spectrometer, CARMENES from the Calar Alto Observatory in Spain, had also recorded the star.
This makes a big difference to the science of exoplanets: spectrographic data can reveal whether or not a star moves in place.
“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.”
Between TESS data and HIRES and CARMENES data, the team was able to confirm that two exoplanets were orbiting HD 260655. In addition, with both data sets, the team was able to compile a complete profile of the two exoplanets.
Traffic data provides a physical size, based on the amount of blocked light from the star; and spectral data reveal the mass of the exoplanet, depending on how far the star moves. Both data sets can be used to calculate the orbit of the exoplanet.
The inner exoplanet, HD 260655 b, is about 1.2 times the size of the Earth and twice the mass of the Earth, orbiting the star every 2.8 days. The outer world, HD 260655 c, is 1.5 times the size and triple of the mass of the Earth, and has an orbit of 5.7 days.
At these sizes and masses, their densities suggest that the two exoplanets are likely to be rocky worlds.
Unfortunately, even though the star is cooler and fainter than the Sun, the proximity of the planets to HD 260655 means that the worlds would be too hot for life as we know it. HD 260655 b has an average temperature of 435 degrees Celsius (816 degrees Fahrenheit) and HD 260655 c is a milder but still scorching temperature of 284 degrees Celsius (543 degrees Fahrenheit).
“We consider this range outside the habitable zone, too hot for liquid water to surface,” Kunimoto says.
However, both exoplanets could still have atmospheres, which should be mature enough to be investigated by the newly deployed James Webb Space Telescope, which includes looking at the exoplanets’ atmospheres among their mission objectives.
In addition, there may even be additional exoplanets orbiting the star that we have not yet discovered.
“There are many multi-planet systems that house five or six planets, especially around small stars like this,” says astrophysicist Avi Shporer of MIT’s Kavli Institute for Astrophysics and Space Research.
“Hopefully we’ll find more, and one could be in the living area. That’s optimistic thinking.”
The team presented its findings at the 240th meeting of the American Astronomical Society.