Discovery Alert

The finding: Six planets orbit their central star in a steady beat, a unique instance of gravitational lockstep that is "in sync" and may provide important new information on the origin and development of planets.

Important details: Six "sub-Neptunes," which may be smaller copies of our own Neptune, orbit a star that is smaller and colder than our Sun in a really bizarre family of planets that move in a cyclic pattern. This orbital waltz is easily adapted to music since it repeats itself so accurately.

Although multi-planet systems are widespread in our galaxy, astronomers seldom discover those in a tight gravitational configuration known as "resonance." This is an example of a 3/2 resonance, in which the planet nearest to the star completes three orbits for every two orbits of the planet beyond it. This pattern is repeated among the four nearest planets.

A 4/3 resonance, or pattern of four orbits for every three of the planet beyond, occurs twice among the outermost planets. These resonance orbits are also extremely stable: This is probably the same rhythmic dance that the planets have been doing since the formation of the solar system billions of years ago. Because of its dependable stability, this system has avoided the shocks and shakeups that scientists would normally anticipate during the early stages of planet formation, such as collisions and smashups, mergers, and breakups as planets compete for place. And that could thus reveal something significant about the formation of this system. The 3/2 and 4/3 resonances of the planets are nearly precisely as they were at the moment of creation, indicating that their rigorous stability was locked in early. More accurate calculations of these planets'More masses and orbits will be required to refine the picture of the system's formation.

Fun facts: This system's discovery is reminiscent of a detective narrative. The initial indications came from NASA's TESS (Transiting Exoplanet Survey Satellite), which monitors the brief eclipses - or "transits" - that planets create when they cross the faces of their stars. Combining the TESS results from two years apart showed a variety of transits for the host star, known as HD 110067. However, it was impossible to tell how many planets they represented or to pinpoint their orbits.

Astronomers eventually identified the two innermost planets, with orbital periods - "years" - of 9 days for the nearest planet and 14 days for the next one out. A third planet with a year of roughly 20 days was discovered using data from CHEOPS, The European Space Agency's CHaracterising ExOPlanets Satellite.

The scientists then observed something unusual. The orbits of the three planets matched what would be predicted if they were locked in a 3/2 resonance. The next phases were all about mathematics and gravity. The research team, coordinated by Rafael Luque of the University of Chicago, went through a well-known list of resonances that may potentially be discovered in such systems, attempting to match them to the remaining transits seen by TESS. The single resonance chain that matched suggested a fourth planet in the system with a 31-day orbit. Two further transits had been observed, but their orbits remained unknown because they were single observations (more than one transit observation is required to pinpoint a planet's orbit).The scientists went over the list of probable orbits once more if there were two more outer planets that fit the predicted chain of resonances across the entire system. They discovered the best fit: a fifth planet with a 41-day orbit and a sixth just shy of 55.

The science team was nearly at a standstill at this time. During processing, a portion of the TESS data that had a potential of validating the projected orbits of the two outer planets was thrown aside. Excessive light dispersed by Earth and the Moon appeared to render the observing field useless. But not so quickly. The dispersed light problem was noticed by scientist Joseph Twicken of the SETI Institute and NASA Ames Research Center. He was aware that Ames scientist David Rapetti, a member of the Universities Space Research Association, was working on a novel computer code to retrieve transit data assumed to be lost due to dispersed light. Rapetti ran his new code on the TESS data at Twicken's recommendation. He discovered two transits of the outer planets, which were anticipated by the research team lead by Luque.