James Webb Space Telescope sees hints of exomoons forming in a child star system

By | April 4, 2024

Three is certainly not a mass for planets around a distant young star.

Astronomers had already discovered two planets forming in the disk of gas and dust, or protoplanetary disk, around the young star PDS 70. Now, using the James Webb Space Telescope (JWST) with the MIRI mid-infrared Disk Survey, astronomers can (MINDS) project have seen hints of a third world taking shape around the young star located about 400 light-years from Earth.

In addition, using JWST’s Near Infrared Camera (NIRCam), the MINDS crew also spotted a large spiral stream of material fueling the growth of one of the previously discovered planets, PDS 70C. This giant planet is already surrounded by its own disk of material, which is also fed by this flow and is expected to produce moons.

Related: The youngest exoplanet found by the Hubble telescope is the size of Jupiter (and still growing)

“We have found new evidence for the presence of a third planet in the system, which was proposed based on VLT observations,” Valentin Christiaens, MINDS team member and postdoctoral researcher in astrophysics at KU Leuven and the University of Liège, said. to Space.com. (The VLT is the Very Large Telescope, operated by the European Southern Observatory in Chile.)

“In addition, the new infrared measurements we obtained for the two known protoplanets suggest the presence of heated material around them – which could be the building blocks for the formation of moons around them,” Christiaens added.

The PDS 70 system has already been extensively studied by a large number of telescopes, including the ground-based Atacama Large Millimeter/submillimeter Array (ALMA) and the VLT.

It remains a fascinating system for astronomers because the protostar and its protoplanetary disk are estimated to be no older than 5.5 million years – a cosmic infant compared to our 4.5 billion-year-old solar system.

“PDS 70 is special because it is the only protoplanetary disk so far where all astronomers agree that we have found planets caught red-handed,” Christiaens said. “Detailed study of this system has thus allowed us to learn a lot about planet formation.”

The researcher said that little is known so far about the properties of the potential third planet around PDS 70. The planet – which if confirmed would be named PDS 70D – appears to be shrouded in a huge amount of dust and orbiting its young star is about 13 times the distance between Earth and the Sun.

‘What’s interesting is that this separation places an average motion resonance of 1:2:4 with the planets PDS 70B and PDS 70C. This means that its orbit would be almost exactly twice as short as B and four times shorter than planet C, respectively,” said Christiaens. “This is a situation we know in the solar system with Jupiter’s three inner Galilean moons: Io, Europa and Ganymede.”

hazy orange, concentric rings surround a central star in deep space.

hazy orange, concentric rings surround a central star in deep space.

Spiral accretion flows like those observed by the team have previously been theoretically predicted in the protoplanetary disks around young stars. Signals of these currents have even been observed in other young systems. Yet this new discovery still stands out, team members said.

“It’s the first time we can directly connect this feature to a forming planet,” Christiaens said. ‘This could indicate that some of the spirals observed in other protoplanetary disks could also be linked to planet formation. These findings have thus led to increased suspicion that spirals observed in other disks may well also be directly connected to planets embedded within them. disk.”

Related: Planets can form much faster than thought, new ALMA telescope photos show

The detection of PDS 70D is not fixed; Christiaens said more observations of this system will be needed before full confirmation is given. That’s not bad, considering the researcher wasn’t convinced the planet was there to begin with!

“The most surprising aspect for me was certainly that this signal was consistent with a third planet, as I was initially very suspicious of the original claim from the first work – I thought the signal might be following the tip of the inner disk,” he said.

When the researchers applied their best image processing algorithms, they noticed an additional signal in their images that did not appear to match the disk or the other known planets. This signal also happens to be where they would expect the previously proposed candidate to be now, if that signal is indeed tracking a planet moving in its orbit.

“The third planet was first detected during ground-based observations. We did not expect to detect it again,” Christiaens said. “It wasn’t the original purpose of this observation to confirm it at all!”

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And the team has more JWST observations from the PDS 70 system to analyze.

In the medium term, it will be a very interesting system to follow up, in particular the Extremely Large Telescope (ELT), to confirm and possibly characterize the candidate third planet,” Christiaens concludes. “This could help us better understand the composition of the forming planets and the properties of the material around the planets, the building blocks for potential moons.”

The MINDS team’s research was recently posted on the online paper repository arXiv.

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