29
November
2023
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10:58 AM
America/New_York

USRA Scientist Unlocks Crucial Data, Validating Rare Discovery of a Synchronized Six-Planet System

Washington, D.C.—November 29, 2023. An international team of researchers led by Rafael Luque of the University of Chicago discovered a system with six planets that orbit their central star in a rhythmic beat, a rare case of “in-sync” gravitational lockstep that could offer deep insight into planet formation. Universities Space Research Association’s Senior Scientist David Rapetti was a coauthor on the paper and findings were published in the journal Nature on November 29, 2023.

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A rare family of six exoplanets has been unlocked with the help of ESA’s Cheops mission. The planets in family revolve around their star HD110067 in a very precise waltz. When the closest planet to the star makes three full revolutions around it, the second one makes exactly two during the same time. This is called a 3:2 resonance. The six planets form a resonant chain in pairs of 3:2, 3:2, 3:2, 4:3, and 4:3, resulting in the closest planet completing six orbits while the outer-most planet does one. Cheops confirmed the orbital period of the third planet in the system, which was the key to unlocking the rhythm of the entire system. Credit: ESA, CC BY-SA 3.0 IGO

Orbit Geometry  Illustration. Image Credit: Thibaut-Roger NCCR-PlanetS

Tracing a link between two neighbour planets at regular time interval along their orbits, creates a pattern unique to each couple. The six planets of the HD110067 system create together a mesmerising geometric pattern due to their resonance-chain. Image Credit: Thibaut Roger/NCCR PlanetS, CC BY-NC-SA 4.0

The researchers found that a star smaller and cooler than our Sun hosts a truly rare family of planets: six “sub-Neptunes” moving in two, three, or four-step rhythm. The planets in the HD 110067 system revolve around the star in a precise orbital pattern. When the closest planet to the star makes 3 full revolutions, the second one makes exactly 2 during the same period. This is called a 3/2 resonance. Among the over 5500 exoplanets discovered so far, it is not uncommon to discover several planets orbiting a star. However, it is very rare to find solar systems with exoplanets in which the resonances span a long chain of six planets, as is in this case with 3/2 resonances for the four innermost planets and 4/3 resonances for the two outermost planets.

Originally, the scientists were on a quest to find out if all six planets were in resonance. They first determined that the orbits of the three inner planets displayed 3/2 resonances, and then found the same for the fourth. Two more transits (small dips in the apparent brightness of the star due to planets passing in front of it) were seen, one for each of the two outer planets, but their orbits remained unmeasured because these were single observations.

The scientists ran through the list of possible orbits and wanted to know if the two additional outer planets would fit the expected chain of resonances across the whole system. But a significant part of the observations from NASA’s Transiting Exoplanet Survey Satellite (TESS) that had the chance of confirming the predicted orbits of the two outer planets had to be removed because of excessive light scattered from the Earth and Moon.

The team reached out to Universities Space Research Association’s Senior Scientist David Rapetti at NASA’s Ames Research Center who had been developing a  relevant code  as a member of the TESS Science Processing Operations Center. The code would enable the use of other methods of removing scattered light in an attempt to find the hidden transits in the discarded data.  Rapetti’s code was the game changer in enabling the research team to complete this discovery, confirming a six -planet resonance chain.

Spiral Plot illustration. Image Credit: Hugh Osborn, University of Bern

Orbital motion for all six planets relative to a single year of planet c. Due to the precise resonant orbits of all six planets, the orbits of each planet are closely linked. For every 360 degree rotation around HD110067 from planet c, planet b moves 540deg, planet d 240, planet e 160deg, planet f 120deg and planet g 90 degrees. Image Credit: Hugh Osborn, University of Bern

The code applies and optimizes alternative techniques to correct for instrumental and environmental effects, such as scattered light, that contaminate the valuable TESS data. When Rapetti applied his new code to the TESS data, one additional transit for the innermost planet, and crucially two more transits, one for each of the two outer planets, were found exactly where the team led by Luque had predicted them. “It is exciting to have been able to uncover the remaining expected transits needed to complete the resonance chain – it’s like finding the missing pieces of a puzzle” noted Rapetti.

The significance of this discovery lies in the extremely rare finding of a pristine system that has largely preserved six planets orbiting in resonance since essentially its formation more than a billion years ago, without being perturbed by for example a close encounter with a passing star or a giant impact event. This makes this system critically important for the study of planet formation and evolution. In addition, the brightness of the star and the likely presence of extended atmospheres in sub-Neptune-size planets make these six planets ideal candidates for observing the composition of their atmospheres using the James Webb Space Telescope.

Additional Resources:

DOI: 10.1038/s41586-023-06692-3.

URL for Paper : Once the paper has been  published, it will be available at the following URL: https://www.nature.com/articles/s41586-023-06692-3 

Annotated orbital visualisation video:  
https://youtu.be/U8jQEnpQfBM

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Additional Resources:

DOI: 10.1038/s41586-023-06692-3.

URL for Paper : Once the paper has been  published, it will be available at the following URL: https://www.nature.com/articles/s41586-023-06692-3   

 

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