A new planetary system has been found. Two Earth-sized exoplanets are around a star just 33 light-years away. It's the fourth closest multi-planet system. There could be more planets we haven't seen yet.
HD 260655 is a red dwarf, which is a small, cool star. It is not as bright as the dimmest star you can see, but it is close. There are red dwarfs in the universe.
The planets were discovered by the TESS in November of 2021. When a planet passes in front of a star, it causes a mini-eclipse, which is a small dip in the star's light. The size of the planet is determined by the amount of light blocked.
HD 260655 had a number of transits that appeared to be two cycles on top of each other. Both caused a small dip in the star's light, but enough to alert the astronomer.
HD 260655 b is the inner planet and HD 260655 c is the outer planet.
The planets' mass was also found. By looking at how they affect the star, they were able to make small circles around its center of gravity. The star can't be seen directly, but it can be seen as it travels around the barycenter.
As part of a survey of bright stars, the HIRES camera on the 10-meter Keck I telescope was used to make observations of HD 260655. The astronomer found that the mass of planet b is 2.1 times that of the Earth.
The mass and size of each planet gives us a clue into their composition. The densities of planet b and planet c are 6.1 and 4.7 g/cc. Earth has a density of 5.5 grams percc, so these planets probably have the same composition as us.
Are they like Earth in other ways? Planet b can be seen at a distance of just over four million km from the star, and planet c can be seen at a distance of over seven million km. That is not far away. Both planets have temperatures that are hotter than an oven despite the star being dim.
Is the atmosphere of these planets? It can be difficult for a planet to hold onto air when it is hot. Its surface temperature is much hotter than ours and it's atmosphere is much thicker. The surface gravity of the exoplanets is 40% stronger than Earth's, so they could hold onto a lot of gas.
There is a way to say something. The starlight travels through the planet's atmosphere on its way to us. If you take a spectrum of the star that absorption can potentially be detected, you can see the different atoms and Molecules in the air. This has been done for many planets and their atmospheres.
HD 260655 b and c are ranked very highly by the astronomer as potential targets. We don't know a lot about the atmosphere of rocky exoplanets. It would be helpful if there was an observation at this point.
One thing that makes this observation interesting is that red dwarf stars are overambitious when it comes to having small, rocky planets. Despite being only 40 light-years away, TRAPPIST-1 has seven Earth-sized planets circling it, making it the most famous example. Three of them are close to the star and could have liquid water on their surfaces as well.
There are two planets that we have seen. It could have several more undetected, either too small, too far away from the star, or with an angle to be seen through transit at this time. Astronomers will likely point their telescopes at this star to see if there are any more secrets to be found.
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