Two new worlds of probable rocky mineral goodness have just been discovered orbiting a star close to our own cosmic neighborhood.
The two newly discovered exoplanets are so-called super-Earths – larger than Earth, but smaller than an ice giant – orbiting a cool red dwarf star called HD 260655, located just 33 light years.
Although the worlds are unlikely to be habitable, given our current understanding of life, the star and its exoplanets are among the closest multi-world systems to Earth.
This makes it an excellent target for follow-up surveys aimed at understanding what exoplanets are made of and assessing their atmospheres – an endeavor that will aid our search for extraterrestrial life, even if both worlds prove unable to host them. themselves.
“The two planets in this system are each considered among the best targets for atmospheric study because of their star’s brightness,” says astronomer Michelle Kunimoto of MIT’s Kavli Institute for Astrophysics and Space Research.
“Is there a volatile-rich atmosphere around these planets? And are there signs of water-based or carbon-based species? These planets are fantastic testbeds for these explorations. .”
To date, more than 5,000 exoplanets have been confirmed in the Milky Way, and astrobiologists are deeply interested in finding terrestrial or rocky worlds like Earth, Venus, and Mars.
We have a sample of exactly one world known to host life – our own – so finding planets similar to Earth in size and composition is one of the main criteria in the search for life elsewhere in the galaxy.
Rocky exoplanets, however, are relatively small in size and mass, making them harder to detect; most of the exoplanets we’ve been able to measure to date tend to fall into the giant category. Rocky worlds – and even better, neighboring rocky worlds – are highly sought after.
The two worlds orbiting HD 260655 – named HD 260655 b and HD 260655 c – were discovered because they pass between us and their star during their orbit. The faint dips in starlight due to these exoplanetary transits have been recorded by NASA’s TESS exoplanet-hunting telescope, designed to detect exactly such phenomena.
When Kunimoto spotted these transit dips in the TESS data, the next step was to look to see if the star had appeared in previous surveys – and it did.
The high-resolution Echelle spectrometer at the Keck Telescope (now known as ANDES) had publicly available data dating back to 1998. Another spectrometer, CARMENES at the Calar Alto Observatory in Spain, had also recorded the star .
This makes a huge difference to exoplanet science: spectrographic data can reveal whether or not a star is moving in place.
“Every planet orbiting a star is going to have a little gravitational pull on its star,” Kunimoto said. “What we’re looking for is any slight movement of this star that might indicate a planetary-mass object is pulling on it.”
Between the TESS data and data from HIRES and CARMENES, the team was able to confirm that two exoplanets were orbiting HD 260655. Additionally, with both datasets, the team was able to compile a full profile of both exoplanets.
The transit data provides a physical size, based on the amount of light blocked by the star; and the spectral data reveals the exoplanet’s mass, as a function of the star’s rate of motion. Both sets of data can be used to calculate the orbit of the exoplanet.
The inner exoplanet, HD 260655 b, is about 1.2 times the size of Earth and twice the mass of Earth, and orbits the star every 2.8 days. The outer world, HD 260655 c, is 1.5 times the size and three times the mass of Earth, and has a 5.7 day orbit.
At these sizes and masses, their densities suggest that both exoplanets are likely to be rocky worlds.
Unfortunately, even though the star is cooler and dimmer than the Sun, the planets’ proximity to HD 260655 means the worlds would be far 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 284 degrees Celsius (543 degrees Fahrenheit).
“We consider this range outside the habitable zone to be too warm for liquid water to exist on the surface,” Kunimoto says.
Both exoplanets may still have atmospheres, however, which should be ripe for probing by the newly deployed James Webb Space Telescope, which includes observing exoplanet atmospheres among its mission objectives.
Plus, there might even be other exoplanets orbiting the star that we haven’t discovered yet.
“There are many multiplanetary systems that host 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 find some more, and maybe there will be one in the habitable zone. That’s an optimistic thought.”
The team presented their findings at the 240th meeting of the American Astronomical Society.