Astronomers spot ‘twist’ evidence of a baby planet in a young star system

A spiral marks the spot where a baby planet is forming around a star in a young system 520 light-years from Earth in the Auriga constellation. The planet birth is visible in new images and observations made by astronomers using the European Southern Observatory’s Very Large Telescope in Chile.

A study was also published Wednesday in the journal Astronomy & Astrophysics.

AB Aurigae is a young star in the constellation symbolizing the celestial charioteer. It’s surrounded by a thick disk made of cold gas and dust. When these come together in clumps, they’re the right ingredients to make a planet. Within that disk is a spiral feature that suggests a baby planet is indeed forming in the disk.

And astronomers believe it may be the first direct evidence of planet birth.

“Thousands of exoplanets have been identified so far, but little is known about how they form,” said Anthony Boccaletti, lead study author and astronomer at the Observatoire de Paris, Université Paris Sciences et Lettres in France, in a statement. “We need to observe very young systems to really capture the moment when planets form.”

Peering into young star systems surrounded by gas and dust is difficult, as is capturing sharp and detailed images of them.

Capturing the “twist” in the disk was key for astronomers during this observation. The spiral is essentially the baby planet kicking the gas in the disk and causing “disturbances in the [disk] in the form of a wave, somewhat like the wake of a boat on a lake,” said Emmanuel Di Folco, study coauthor and astrophysicist at the Astrophysics Laboratory of Bordeaux in France.

The spiral arm forms as the planet moves around the star, bending and shaping the wave. In the image, this spiral is bright yellow and appears close to the center. In reality, the baby planet symbolized by the spiral is quite far from the star, about the distance from Neptune to the sun. That average distance equals 2.7817 billion miles.

Previous observations of this young star system were also made using the Atacama Large Millimeter/submillimeter Array of telescopes, called ALMA, in Chile a few years ago. Those observations suggested that planet formation was occurring around the star, with two spiral gas arms appearing close to the star in the inner region of the disk.

Boccaletti and an international team of astronomers followed up on this by aiming the SPHERE instrument on the Very Large Telescope in Chile at the star, creating the deepest images of the young star system yet.

The SPHERE instrument, which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch, can image exoplanets, or planets outside of our solar system, in optical and near-infrared light.

Thanks to SPHERE’s capabilities, the researchers were able to see light from the inner disk illuminating small dust grains. The observations revealed the spiral arms detected by ALMA as well as the signature twist detailed in the new study signifying a baby planet.

“The twist is expected from some theoretical models of planet formation,” said Anne Dutrey, study coauthor and researcher at the Astrophysics Laboratory of Bordeaux in France. “It corresponds to the connection of two spirals — one winding inwards of the planet’s orbit, the other expanding outwards — which join at the planet location. They allow gas and dust from the [disk] to accrete onto the forming planet and make it grow.”

More detailed observations of exoplanets will be possible in the future when the European Southern Observatory’s Extremely Large Telescope in Chile is completed and comes online in 2025.

“We should be able to see directly and more precisely how the dynamics of the gas contributes to the formation of planets,” Boccaletti said.