NASA’s TESS spacecraft discovers a weird system of exoplanets unlike anything seen before
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Illustration of a super-Earth exoplanet orbiting its star with very different siblings. | Credit: Robert Lea (created with Canva)
Using NASA’s Transiting Exoplanet Survey Satellite (TESS) exoplanet-hunting spacecraft and the Antarctic Search for Transiting ExoPlanets (ASTEP) on the Antarctic Plateau, astronomers have discovered a rare and particularly strange planetary system.
The extrasolar planets, or exoplanets, that orbit the star TOI-201 have orbits that change so quickly that astronomers can see the changes in real time. The behavior of the system, located about 370 light years from Earth, is something scientists have never seen before.
TOI-201 is 1.3 times the mass of the sun and also has a diameter 1.3 times the size of our home star. The exoplanets orbiting the star include a rocky super-Earth with a mass six times that of our planet and whose year lasts just 5.8 Earth days. Its planetary siblings are a gas giant with half the mass of Jupiter, completing an orbit every 53 days, designated TOI-201b, and another gas giant that has 16 times the mass of Jupiter that completes an orbit every 2,883 days (about 7.9 years).
“Most planetary systems appear like peas in a pod, meaning the planets have a similar range of parameters and share a similar orbital plane,” team member Amaury Triaud of the University of Birmingham in the United Kingdom said in a statement. “This is not the case in the TOI-201 system, which contains three objects in orbit that are very distinct from each other and interact gravitationally.”
The team’s results were published April 15 in the journal Science.
This planetary system is undergoing changes
Changes in planetary systems and shifts in orbits are not unique to TOI-201, but these transformations typically occur on timescales of millions or even billions of years.
TOI-201 is different because of the outer planet’s very flattened or elliptical and tilted orbit, which gravitationally pulls on the inner worlds. This causes changes in the orientation of the orbits of the inner planets and changes in the timing of their “transits,” the times when a planet passes directly across the face of its parent star. The situation is so extreme that in about 200 years, the planets will no longer line up in front of their star at all.
“In the solar system, almost all the planets are coplanar, but here, that is not the case and each planet is different,” explains Tristan Guillot, astronomer at the Observatoire de la Côte d’Azur. “This indicates active orbital reorganization within the system, giving us insight into what happens shortly after planets form.”
Guillot is one of the principal investigators of the ASTEP project, an observatory at Concordia Station in Antarctica, located atop a 3.2 kilometer deep glacier in one of the most isolated environments in the world and which takes advantage of the long polar nights to observe other planetary systems.
An illustration showing NASA’s exoplanet hunter, TESS | Credit: Robert Lea (created with Canva)
“The goal was to characterize the TOI-201 planetary system to understand not only which planets are there, but also how they interact with each other dynamically,” said research team leader Ismael Mireles, a doctoral student at the University of New Mexico. “This helps scientists understand how planetary systems like our own solar system form and evolve over time.”
TESS spotted a rare transit by the outer planet as telescopes around the world saw this object’s gravity pull on TOI-201. Astronomers then noticed delays in the transit of TOI-201b.
“Usually, planets are like metronomes, with each transit in front of the star occurring exactly one orbital period after the other. However, we were tracking TOI-201b and suddenly the planet started transiting about half an hour late,” Triaud said. “This sudden jump was very surprising and we reported our observations. Other astronomers around the world also noticed intriguing signals, and by working together the team was able to begin to understand this system.
“This discovery was made possible by the presence of a telescope in Antarctica. Although the logistics involved are difficult, its unique location and access to optimal astronomical conditions are essential for studying exoplanetary systems with long orbital periods such as TOI-201.”
