It is a baby picture like no other: A maelstrom of gas and dust swirling around what is likely a newborn giant planet. This stunning portrait is a composite that could be the first direct evidence of the hellacious site of a planet’s birth, according to a study published on Wednesday in Astronomy & Astrophysics.
AB Aurigae, a star located some 520 light years from Earth, has fascinated scientists for years because it is encircled by a thick disk of gas and dust, creating the perfect conditions for birthing new planets, like a cosmic placenta. Past observations even spotted spiral structures within the disk, close to the star, that hinted at the presence of a developing planet—an extremely rare sight to capture.
A team led by Anthony Boccaletti, an astronomer at the Observatoire de Paris, PSL University, wanted to take a closer look at this nascent world, which has produced some of “the most spectacular spirals imaged so far,” according to the new study.
“We went to that star because we already knew it was interesting if we wanted to investigate planet formation,” Boccaletti said in a call. “We knew the star was surrounded by gas and dust. In addition to that, we knew the disk had specific structural spirals in a cavity.”
Scientists think that this spiraling effect is the signature of interactions between budding planets and the gassy dusty material that both surrounds and nourishes them. The mass of these young worlds produces wave-like ripples in the gas disk, which are then distorted into spirals as the planet orbits its star. At the same time as it sculpts these disk spirals, the baby planet also incorporates gas into its growing body.
“In this way, the planet accretes and accumulates the gas and it forms a huge envelope we see in the giant planets in our solar system,” such as Jupiter or Saturn, Boccaletti said. “To build these atmospheres of gas, you really need something to bring the gas from somewhere and put it on the planet. This is the process we believe is working for these kinds of planets.”
Boccaletti and his colleagues set out to image this tantalizing feature in more detail with the help of a specialized instrument called Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), which is located at the Very Large Telescope in Chile. SPHERE is designed to look for exoplanets—planets that orbit stars other than the Sun—and it is equipped with a coronagraph that can blot out the distracting light from the host stars of these planets.
The team imaged the AB Aurigae system using SPHERE in January 2020 and removed the blinding starlight, resulting in these mesmerizing images of the environment surrounding a planet-in-progress. While the planet itself does not appear in these images, the team was able to “resolve a feature in the form of a twist” that can be “perfectly reproduced” in models of planet formation, according to the study.
In the new image, the twist is located slightly below the star AB Aurigae, which occupies the central part of the swirling disk (the twist is circled in white in the below image, while the blue circle represents where Neptune would be if this were the solar system).
In other words, the team captured an unprecedented look at the probable spot where this planet is coalescing. “Here, in this particular case, we don’t see the planet,” Boccaletti said. “We see the structure that the planet produces on the spiral—this is what we call a twist.”
Future observations of AB Aurigae may reveal new details about this baby planet, such as its mass or its orbit. Boccaletti and his colleagues plan to continue examining the system to see if they can peg its path around its star, or figure out whether it is a fully formed world or is still in the process of condensing into a planet.
Within the next decade, observations of the system using massive ground observatories, such as the Extremely Large Telescope (ELT) currently in construction in Chile, will also help scientists constrain models of gas accretion in emerging giant planets.
“We would need a much bigger telescope to go even closer to the star; to see even closer to the spiral,” Boccaletti said. “If we were able to resolve the gas around the planet, then we can know the dynamic of the gas and how it falls on the planet.”
Such intricate details about the origins and evolution of planets could help untangle broader mysteries about these worlds and the systems that bear them. Also, if the new images from AB Aurigae are any indication, this line of research will produce a whole lot of spectacular views of the next generation of planets.