Parents know the joy of the first ultrasound scan of their babies. Astronomers have now achieved the planetary equivalent, imaging a pair of twin planets as they form in the womb of gas and dust around their parent star.
The imaging of these forming exoplanets (or extrasolar planets, worlds outside of our solar system), comes courtesy of the 66 radio antennas that comprise the Atacama Large Millimeter/ submillimeter Array (ALMA). It brings astronomers closer than ever before to understanding the processes behind planet formation.
The ALMA image focuses on the system around the binary stars WISPIT 2, located around 437 light-years away. WISPIT 2 has an estimated age of around 5.4 million years. If that makes this star sound anything but an infant, consider that our middle-aged star, the sun, is 4.6 billion years old. Surrounding the young star is a disk of gas and dust known as a protoplanetary disk that serves as a prenatal envelope in which two planets, WISPIT 2b and WISPIT 2c, are forming.
The image shows clear evidence of how forming planets interact with their prenatal cocoon. Visible is a channel created in the protoplanetary disk by WISPIT 2b, a gas giant that already has a mass five times that of Jupiter, as it orbits its parent star, collecting material to facilitate its further growth.
WISPIT 2c is a little behind its sibling in terms of development, but it is still making its mark in its protoplanetary disk home.
"We clearly see both planets shaping their environment. WISPIT 2c has carved a cavity, and WISPIT 2b a gap," team member Myriam Benisty of the Planet Formation and Exoplanets (PFE) department at the Max Planck Institute in Germany, said in a statement. "Around WISPIT 2b, we find swirls of gas that had been predicted by simulations of disk-planet interactions, but never actually seen before. Now there is an image of them!"
What makes WISPIT 2 so special?
With this new ALMA data, WISPIT 2b has become the only protoplanet for which astronomers can see three important elements of planet formation: the protoplanetary disk, the planet itself, and evidence that the planet is still gathering, or accreting, matter, and, as the final piece of the puzzle, the gas interacting directly with the planet. That adds up to observing planet formation in action.
Many of these elements have been seen around infant stars before, notably in the system PDS 70, but not in unison.
"Hopefully, observations like this will teach astronomers to distinguish between disk features that indicate the presence of a protoplanet and features that don't," team leader Stefano Facchini of the University of Milan said.
The results are also remarkable because of how far WISPIT 2b is located from its parent star. The planet is accreting matter at a distance of 57 times the distance between Earth and the sun, or almost twice the distance between Neptune and our star. That is an orbit wider than that of almost any other currently known exoplanet.
Additionally, the techniques the team used to obtain these observations could be crucial when the next generation of telescopes starts to look at budding extrasolar planetary systems.
That includes upgrades to ALMA itself and the Extremely Large Telescope (ELT) currently under construction in the Atacama Desert region of northern Chile, both of which could deliver an even more detailed picture of the WISPIT 2 system and how it is being shaped by its formation planets.
The ALMA results are available in two papers on the repository site arXiv.
