Cosmic Rhythms: Strange Discovery of a Six-Planet System in Perfect Harmony

Study led by University of Chicago astronomer Rafael Luque may tell us about how planets form.

Scientists have discovered a rare sight in a nearby star system: Six planets orbiting their central star in a rhythmic beat. The planets move in an orbital waltz that repeats itself so precisely it can be readily set to music.

A rare case of an “in sync” gravitational lockstep, the system could offer deep insight into planet formation and evolution.

The analysis, led by UChicago scientist Rafael Luque, was published on November 29 in the scientific journal Nature.

“This discovery is going to become a benchmark system to study how sub-Neptunes, the most common type of planets outside of the solar system, form, evolve, what are they made of, and if they possess the right conditions to support the existence of liquid water in their surfaces,” said Luque.

A Cosmic Ballet in Coma Berenices

The six planets orbit a star known as HD110067, which lies around 100 light-years away in the northern constellation of Coma Berenices.

In 2020, NASA’s Transiting Exoplanet Survey Satellite (TESS) detected dips in the star’s brightness that indicated planets were passing in front of the star’s surface. Combining data from both TESS and the European Space Agency’s CHaracterising ExOPlanet Satellite (Cheops), a team of researchers analyzed the data and discovered a first of its kind configuration.

While multi-planet systems are common in our galaxy, those in a tight gravitational formation known as “resonance” are observed by astronomers far less often.

In this case, the planet closest to the star makes three orbits for every two of the next planet out – called a 3/2 resonance – a pattern that is repeated among the four closest planets. Among the outermost planets, a pattern of four orbits for every three of the next planet out (a 4/3 resonance) is repeated twice.

“It shows us the pristine configuration of a planetary system that has survived untouched.”

Rafael Luque

And these resonant orbits are rock-solid: The planets likely have been performing this same rhythmic dance since the system formed billions of years ago, the scientists said.

This animation shows six “sub-Neptune” exoplanets in rhythmic orbits around their star – with a musical tone as each planet passes a line drawn through the system. The line is where the planets cross in front of (“transit”) their star from Earth’s perspective. In these rhythms, known as “resonance,” the innermost planet makes three orbits for every two of the next planet out. Among the outermost planets, a pattern of four orbits for every three of the next planet out is repeated twice. Credit: Dr. Hugh Osborn, University of Bern

A Rarity in the Galaxy

Orbitally resonant systems are extremely important to find because they tell astronomers about the formation and subsequent evolution of the planetary system. Planets around stars tend to form in resonance but can be easily perturbed. For example, a very massive planet, a close encounter with a passing star, or a giant impact event can all disrupt the careful balance. As a result, many of the multi-planet system known to astronomers are not in resonance but look close enough that they could have been resonant once. However, multi-planet systems preserving their resonance are rare.

“We think only about one percent of all systems stay in resonance, and even fewer show a chain of planets in such configuration,” said Luque. That is why HD110067 is special and invites further study: “It shows us the pristine configuration of a planetary system that has survived untouched.”

More precise measurements of these planets’ masses and orbits will be needed to further sharpen the picture of how the system formed.

For more on this discovery, see Unraveling the 6-Planet Resonance Mystery.

Reference: “A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067” by R. Luque, H. P. Osborn, A. Leleu, E. Pallé, A. Bonfanti, O. Barragán, T. G. Wilson, C. Broeg, A. Collier Cameron, M. Lendl, P. F. L. Maxted, Y. Alibert, D. Gandolfi, J.-B. Delisle, M. J. Hooton, J. A. Egger, G. Nowak, M. Lafarga, D. Rapetti, J. D. Twicken, J. C. Morales, I. Carleo, J. Orell-Miquel, V. Adibekyan, R. Alonso, A. Alqasim, P. J. Amado, D. R. Anderson, G. Anglada-Escudé, T. Bandy, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, D. Bayliss, J. L. Bean, M. Beck, T. Beck, W. Benz, N. Billot, X. Bonfils, L. Borsato, A. W. Boyle, A. Brandeker, E. M. Bryant, J. Cabrera, S. Carrazco-Gaxiola, D. Charbonneau, S. Charnoz, D. R. Ciardi, W. D. Cochran, K. A. Collins, I. J. M. Crossfield, Sz. Csizmadia, P. E. Cubillos, F. Dai, M. B. Davies, H. J. Deeg, M. Deleuil, A. Deline, L. Delrez, O. D. S. Demangeon, B.-O. Demory, D. Ehrenreich, A. Erikson, E. Esparza-Borges, B. Falk, A. Fortier, L. Fossati, M. Fridlund, A. Fukui, J. Garcia-Mejia, S. Gill, M. Gillon, E. Goffo, Y. Gómez Maqueo Chew, M. Güdel, E. W. Guenther, M. N. Günther, A. P. Hatzes, Ch. Helling, K. M. Hesse, S. B. Howell, S. Hoyer, K. Ikuta, K. G. Isaak, J. M. Jenkins, T. Kagetani, L. L. Kiss, T. Kodama, J. Korth, K. W. F. Lam, J. Laskar, D. W. Latham, A. Lecavelier des Etangs, J. P. D. Leon, J. H. Livingston, D. Magrin, R. A. Matson, E. C. Matthews, C. Mordasini, M. Mori, M. Moyano, M. Munari, F. Murgas, N. Narita, V. Nascimbeni, G. Olofsson, H. L. M. Osborne, R. Ottensamer, I. Pagano, H. Parviainen, G. Peter, G. Piotto, D. Pollacco, D. Queloz, S. N. Quinn, A. Quirrenbach, R. Ragazzoni, N. Rando, F. Ratti, H. Rauer, S. Redfield, I. Ribas, G. R. Ricker, A. Rudat, L. Sabin, S. Salmon, N. C. Santos, G. Scandariato, N. Schanche, J. E. Schlieder, S. Seager, D. Ségransan, A. Shporer, A. E. Simon, A. M. S. Smith, S. G. Sousa, M. Stalport, Gy. M. Szabó, N. Thomas, A. Tuson, S. Udry, A. M. Vanderburg, V. Van Eylen, V. Van Grootel, J. Venturini, I. Walter, N. A. Walton, N. Watanabe, J. N. Winn and T. Zingales, 29 November 2023, Nature.
DOI: 10.1038/s41586-023-06692-3

UChicago Prof. Jacob Bean was also a co-author on the paper.

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