Astronomers have discovered in a binary system the brightest star, by far, known to host a transiting planet in the habitable zone where liquid water can exist.
Planet hunters spotted the Neptune-like planet as it crossed in front of its host star, temporarily dimming the star’s light in a manner similar to a solar eclipse on Earth. This “transit method” typically identifies planets with narrow orbits, since they are more likely to follow paths that put them between Earth and their host star, and when they follow those paths, they more often move toward positions that block light. That’s why this newly discovered planet is considered unusually distant: it takes 272 days to circle its star.
Follow-up observations of the system revealed even more peculiarities. The star is also orbited by a second, as yet unconfirmed planet with a 34-day orbit and, perhaps most interestingly, another star. This unique system provides valuable data for scientists trying to understand how planets form and remain in stable orbits in multistellar systems. The researchers present their discoveries in The Astrophysical Journal.
“Finding planets in multistellar systems is crucial to our understanding of how different planets can be created from the same material,” says the study’s lead author, Nora Eisner, a researcher at the Center for Computational Astrophysics at the Flatiron Institute in New York, in a statement. .
Star and planet systems form when clouds of gas and dust begin to clump together. When a star forms next to another star, the pair can form a binary star system. Because planets are estimated to be half as likely to form in a binary star system compared to single-star systems, Eisner says “it’s very exciting that we found this one.”
The newly discovered planet, formally named TOI 4633 c but nicknamed Percival (after a character in the “Harry Potter” book series) by scientists, was first identified by citizen scientists who examined data collected by the satellite. NASA’s Transiting Exoplanet Study System (TESS). The Planet Hunters TESS program allows anyone with an Internet-connected computer to search for undiscovered planets in the TESS data.
Citizen scientists help astronomers sort through the huge data sets, which are too large for researchers to analyze alone. To date, the project has enabled more than 43,000 volunteers from 90 countries to help catalog some 25 million objects. Citizen scientists are particularly valuable in finding exoplanets on long orbits because these objects are difficult for computers to identify.
“The human brain has a really incredible ability to recognize patterns and filter out noise,” says Eisner, principal investigator of Planet Hunters TESS. “While our algorithms struggle to identify these longer period planets, citizen scientists do not.”
After 15 citizen scientists pointed out the possible planet, Eisner and his team decided to take a closer look. The star’s radial velocity tracking study, which looked for small oscillations in the star’s motion that revealed the gravitational pull of its nearby companions, showed a potential second planet near the star.
Other images and archival data revealed that what scientists initially thought was a single star is actually two. The two currently co-orbiting stars are too close together to distinguish them individually from our point of view on Earth. However, archival observations of the star collected over the past 119 years showed that the system is actually a pair of binary stars.
The new exoplanet has the second longest orbit of all the planets discovered with TESS data and is one of five with orbits longer than 100 days. “This planet is extraordinary in many ways,” Eisner says. “It’s extraordinary in its orbit, it’s extraordinary for being in the habitable zone, and it’s extraordinary for orbiting a bright star.”
While scientists believe the planet is in the habitable zone, they wouldn’t recommend it as a destination for your next interstellar vacation. TOI 4633 c has no solid surface and the atmosphere is probably filled with water vapor, hydrogen and methane. However, previous studies have shown that long-period planets are more likely to have satellites or moons, which can provide solid surfaces for life to establish.
“If this planet had a moon, that moon would probably have a solid surface, which could be a great place to find water,” Eisner says.
