Jan 26, 2021 - Science

Understanding the rhythm and music of 5 alien planets

Artist's illustration of the planets orbiting TOI-178.
Artist's illustration of the planets orbiting TOI-178. Image: ESO/L. Calçada/spaceengine.org

Five planets orbiting a star 200 light-years from Earth are locked in a strange dance that could help scientists learn more about how far-off worlds form.

The big picture: In recent years, researchers have found that nearly every star has at least one planet orbiting it. Now, astronomers are starting to learn more about those worlds, helping them piece together why the universe looks the way it does.

Details: The five outer planets of the star TOI-178 orbit in resonance with one another, meaning patterns emerge in their orbits, with some of the planets occasionally aligning. The closest planet to the star isn't in resonance with the others.

  • Perhaps the best way to visualize this complicated planetary rhythm is via this video from the European Southern Observatory. (Be sure to have your sound on.)
  • "The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth," Yann Alibert, an author of a new study on the star system said in a statement.
  • If the system had been disrupted by large impacts early in its history, the natural alignments of these planets would have been thrown off.

Yes, but: Instead of an arrangement of planets like our own — with the rocky, dense planets closer to the Sun and the gaseous ones farther out — the planets orbiting TOI-178 seem to be in a more haphazard arrangement.

  • "It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune," Nathan Hara, one of the study's authors, said in the statement.
  • That strange assortment of densities could force astronomers to re-examine current theory that holds more dense planets tend to form closer to their stars.
Go deeper