Dancing with the Stars: Scientists spot 6 planets with dance-like orbit

Scientists have discovered a nearby six-planet system with an orbit around its star with a rhythmic beat, moving at such synchronicity that it can be compared to dancing and set to music, a study found.

The findings of this study were published on Wednesday in the peer-reviewed academic journal Nature.

What makes this planetary discovery so fascinating is that this type of gravitational formation, known as resonance, are rather rare, with the planets in question having likely been engaged in this long-term cosmic waltz since they were first formed billions of years ago.

But this finding could also offer clues about the formation of these rare system configurations, as well as the mysteries of the type of exoplanet known as sub-Neptunes.

A space samba: When planets dance to their own gravity and rhythm

The six exoplanets in question were found to orbit the star HD110067, a star similar in type to that of the Sun, which is located around 100 light years away in the Coma Berenices constellation - a relatively close distance, as far as space goes.

While the star itself was known for some time, the exoplanets orbiting it were a more recent discovery, having been detected as a result of data from NASA's Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency's (ESA) CHaracterising ExOPlanet Satellite (CHEOPS). 

At first, TESS had detected several dips in the star's brightness during 2020 and 2022. Using this information, as well as further data gained from CHEOPS, researchers were able to realize that the dips in brightness were caused by six different planets passing in front of the star. 

Each of these exoplanets were characterized as sub-Neptunes, meaning their radii was between that of the Earth's and Neptune's.

This classification is significant since planets that are like Neptune, or larger, are much rarer, due to needing much more gas during the planetary formation process.

The fact these exoplanets were sub-Neptunes wasn't surprising - after all, more than half of all Sun-like stars have been found to have these planets orbiting them. But despite being so common, scientists know very little about these planets, such as what they are made of, how they are formed, and how they evolve over time. 

But the discovery of this star system salsa may change that. 

When planetary systems form, the new worlds tend to form in resonance with each other. This means that most star systems tend to have synchronized orbits at first. But just takes two to tango, this dance requires all parties involved to stay in balance. 

Doing this is actually quite easy - any number of things can disrupt this synchronicity between planets. Whether it be a passing star's orbit or an asteroid impact, the number of things that can disrupt this careful balance is extensive. 

According to lead researcher Rafael Luque of the University of Chicago, around only 1% of all planetary systems stay in resonance, locked in this endless dance - and even then, not all the planets might stay that way.

But the six planets dancing around HD110067 have managed to do exactly that, staying in sync with each other billions of years later. 

The innermost exoplanet makes three orbits for every two orbits made by the next-closest world, a pattern known as a 3/2 resonance. This pattern holds true for the four innermost planets in the system. For the two outer planets, the resonance changes slightly to a 4/3 resonance, meaning the inner planet orbits four times for every three of the last planet.

The innermost planet in the system, dubbed HD110067b, has an orbit of just over nine Earth-days. Based on this calculations, the outermost planet, HD110067g, has an orbit of almost 55 Earth-days (to be more exact, it's that when rounding up, with a more precise estimation clocking in at around 54.76992 days).

This is caused by the planets exerting regular gravitational pulls on each other, helping keep the entire orbital dance moving along for over four billion years.

To put that orbit into visual perspective, a metaphorical bird's eye view of these planets' orbits would resemble the start of a seemingly perfect spiral, with the outermost planets dipping down before curving up, curling as it gets closer to the star.

But what does this discovery tell us about the exoplanets themselves? The composition of sub-Neptunes is a major source of scientific interest, especially since many of them could be rocky worlds like the Earth, which could possibly be able to have liquid water on their surfaces.

The level of information available has allowed the researchers to make some calculations for their masses, which in turn could help lead to an understanding of what these planets are made of in the first place. 

Using the data at hand, the researchers were able to determine that they were all relatively low-density planets, something that could be explained by large atmospheres rich in hydrogen. 

Now, this isn't a perfect explanation by any means. In particular, one of the exoplanets, dubbed HD110067e, is believed to not have any atmosphere at all. But this is paving the way for future research to figure that puzzle out.

“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,” Luque noted in a statement.

More information is needed, but tools such as NASA's James Webb Space Telescope are equipped with the necessary instruments to better study atmospheric gas and composition.

But that's something for future studies to work on.