Thibaut Roger/NCCR PlanetS
The orbits of the six planets orbiting a star called HD110067 create a geometric pattern due to their resonance.
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Astronomers have used two different exoplanet detection satellites to solve a cosmic mystery and reveal a rare family of six planets located about 100 light-years from Earth. This discovery may help scientists uncover the secrets of planetary formation.
The six outer planets revolve around a bright, sun-like star named HD110067, located in the constellation Coma Berenice in the northern sky. Larger than Earth but smaller than Neptune, the planets fall into a little-understood category called sub-Neptunian planets that are usually found orbiting Sun-like stars in the Milky Way. The planets, labeled b to g, orbit the star in a celestial dance known as orbital resonance.
There are discernible patterns when planets complete their orbits and exert gravitational forces on each other, according to a study published Wednesday in the journal Nature magazine. For every six orbits completed by planet b, the planet closest to the star, the farthest planet g completes one orbit.
Since planet c makes three orbits around the star, planet d makes two, and when planet e completes four orbits, planet f makes three.
This harmonic rhythm creates a resonant chain, where the six planets are aligned every few orbits.
What makes this planetary family an unusual discovery is that little has changed since the system formed more than a billion years ago, and this discovery could shed light on the evolution of planets and the origin of the dominant subplanets. In our home galaxy.
Researchers first noticed the star system in 2020 when NASA’s Transiting Exoplanet Survey Satellite, or TESS, detected dips in the brightness of HD110067. A dip in starlight often indicates a planet passing between its host star and an observing satellite as the planet moves along its orbital path. Detecting these dips in brightness, known as the transit method, is one of the main strategies scientists use to identify exoplanets via ground-based and space telescopes.
Astronomers determined the orbital periods of two planets around the star from that 2020 data. Two years later, TESS observed the star again, and evidence suggested different orbital periods for those planets.
When the data sets weren’t collected, astronomer and lead study author Raphael Luc and some colleagues decided to take another look at the star using a different satellite – a satellite. European Space Agency exoplanet satellite characterizationOr Khufu. While TESS is used to observe parts of the night sky for short observing purposes, Khufu is used to observe one star at a time.
This artist’s illustration shows Khufu in orbit around Earth while searching for exoplanets.
“We went looking for signals between all the possible time periods that these planets could go through,” said Luckey, a postdoctoral researcher in the Department of Astronomy and Astrophysics at the University of Chicago.
He said the data collected by Khufu helped the team solve the “detective story” initiated by TESS. Khufu was able to determine the presence of a third planet in the system, which was decisive in confirming the orbital periods of the other two planets, as well as their rhythmic resonance.
As the team matched the rest of the unexplained TESS data with Cheops’ observations, they discovered the other three planets orbiting the star. Follow-up operations using ground-based telescopes confirmed the existence of the planets.
Khufu’s allotted time observing the star helped astronomers weed out mixed signals from the TESS data to determine how many planets were transiting in front of the star and the echoes of their orbits.
“Khufu gave us this resonant formation that allowed us to predict all other periods. Had it not been for this revelation from Khufu, it would have been impossible,” Loki said.
The closest planet takes just over nine Earth days to complete its orbit around the star, and the farthest planet takes about 55 days. All planets have faster orbits around their star than Mercury, which takes 88 days to complete one orbit around the Sun.
Given how close they are to HD110067, the planets likely have average extreme temperatures similar to Mercury and Venus, ranging between 332°F and 980°F (167°C and 527°C).
The formation of planetary systems, like our solar system, can be a violent process. While astronomers believe that planets tend to initially form in resonance around stars, the gravitational influence of massive planets, their collision with a passing star or collision with another celestial body can upset the harmonic balance.
Most planetary systems are not in resonance, and those containing multiple planets that have maintained their initial rhythmic orbits are rare, Luckey said, which is why astronomers want to study HD110067 and its planets as a “rare fossil” in detail.
“We believe that only about one percent of all systems remain in resonance,” Luckey said in a statement. “It shows us the original formation of an untouched planetary system.”
This discovery is the second time that Khufu has helped detect a planetary system with orbital resonance. The first, known as TOI-178 announced in 2021.
“In the words of our science team: Khufu makes remarkable discoveries seem ordinary,” Maximilian Günther, ESA’s Khufu project scientist, said in a statement: “Of the three known six-planet resonance systems, this is now the second one found.” Khufu, and in only three years of operations.”
The system could also be used to study how sub-Neptunian planets form, the study authors said.
While sub-Neptunian planets are common in the Milky Way, they are not found in our solar system. There is little agreement among astronomers about how these planets formed and what they are made of, so an entire system made up of sub-Neptunian planets could help scientists determine more about their origin, Luckey said.
Many exoplanets have been found orbiting dwarf stars that are much cooler and smaller than our Sun, like our planet The famous TRAPPIST-1 system and its seven planetsIt was announced in 2017. While the TRAPPIST-1 system also contains a resonance string, the weakness of the host star makes observations difficult.
But HD110067, which has a mass of 80% that of our Sun, is the brightest star known and has more than four planets in its orbit, so observing the system is much easier.
Initial planetary mass detections suggest that some of them have puffy, hydrogen-rich atmospheres, making them ideal study targets for the James Webb Space Telescope. As starlight passes through planetary atmospheres, Webb can be used to determine the composition of each world.
“The sub-Neptunian planets in the HD110067 system appear to have low masses, indicating that they may be rich in gas or water. Future observations, on For example, using the James Webb Space Telescope, these planetary atmospheres can determine whether planets have rocky or water-rich interiors.
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