First ring-forming embedded planet discovered around a young sun-like star
Astronomers led by Leiden PhD candidate Richelle van Capelleveen have, for the first time, discovered an exoplanet that has carved a bright gap in the protoplanetary disc around its star. This rare observation provides new insights into how young planets shape their surroundings.
Over the past decade, advances in observational astronomy have revolutionised the study of regions around young stars where planets are born. Hundreds of high-resolution images of planet-forming discs have been captured, many showing structures such as rings and spiral arms – features thought to signal planet formation.
Since the discovery of the PDS 70 planetary system in 2018, however, no other embedded planets had been confirmed. Astronomers have been searching for a similar system for the past seven years. The team has now found such a planet through a research programme called ‘WIde Separation Planets In Time’ (WISPIT), using the SPHERE instrument on ESO’s Very Large Telescope in Chile. The newly discovered system has been named WISPIT 2, and the planet WISPIT 2b.
‘We were incredibly lucky’
Lead author Richelle van Capelleveen says: ‘Discovering this planet was an amazing experience – we were incredibly lucky. WISPIT 2, a young version of our Sun, sits in a little-studied group of young stars, and we didn’t expect to find such a spectacular system. I’m very grateful to our international partners for all their work, especially the group of students from the University of Galway in Ireland who really helped us share this discovery with the community in record time.’
First clear detection of an embedded planet
Van Capelleveen’s supervisor and third author Matthew Kenworthy (Leiden University) explains: ‘What we present here is the first clear detection of an embedded planet since PDS 70 seven years ago. It’s also the first detection of such a planet in a cleared gap.’
Second author Christian Ginski (University of Galway, Ireland) adds: ‘This is strong direct evidence that the gas giants we’ve found on wide orbits around slightly older stars could indeed have formed far from their parent star – exactly where we see them now.’
The team expects this system to have a major impact on the planet-formation community and to serve as a benchmark for models of planet formation and disc–planet interactions for years to come.
Understanding how planets form
Understanding how planets form is a key question in astronomy. We know that planets form in a disc around a young star. According to the leading theory, a planet first builds a core and then clears a path in the disc by pulling in gas and dust under its own gravity. To date, astronomers have confirmed nearly 6,000 planets and hundreds of discs, but only one system had shown planets still embedded in their disc: PDS 70, which contains two planets inside a large inner gap.
Searching for embedded planets
Two coronagraphic H-band ‘snapshot’ observations with VLT/SPHERE (each lasting less than five minutes and taken a year apart) revealed a disc around this star. The team suspected there might be a planet within the inner gap and carried out follow-up observations with SPHERE in both polarised and unpolarised light, to study the disc and any embedded planets.
They also contacted a team in Arizona to observe the system in H-alpha light – a specific optical wavelength used to detect hydrogen gas falling onto a planet. Detecting a planet in this narrow band indicates it is actively accreting gas and dust. These follow-up observations provided strong evidence for WISPIT 2b’s existence. A reanalysis of the original snapshots also revealed the planet, allowing the team to track part of its orbit.
A spectacular system with striking images
A parallel paper, led by Laird Close (University of Arizona, USA), describes the detection of gas accretion on the exoplanet in detail. Close says: ‘It was incredibly exciting to study this newly discovered disc with the 6.5-metre Magellan telescope and our MagAO-X adaptive optics system. MagAO-X is specially designed to look for hydrogen gas falling onto young planets. As soon as we took an image in H-alpha (visible deep red light), we found a beautiful accreting planet. Our strong H-alpha detection proves that this is a very rare example of a growing protoplanet.’
Van Capelleveen says the team is thrilled with the discovery: ‘It’s an extraordinary system, with the striking image of a planet embedded in the gap of a multi-ringed disc. This is the first ring-forming embedded planet ever observed, giving the planet-formation community a unique chance to learn more about the physics of planet-forming discs – especially how viscous they are, a key factor in how they spread over time and transport material and angular momentum. This system will likely remain a benchmark for many years.’
Scientific publications
WIde Separation Planets In Time (WISPIT): A gap-clearing planet in a multi-ringed disk around the young solar-type star WISPIT 2; Richelle van Capelleveen et al. Read the article here.
WIde Separation Planets In Time (WISPIT): Discovery of a Gap H-alpha Protoplanet WISPIT 2b with MagAO-X; Laird Close et al. Read the article here.
This press release originally appeared on astronomie.nl.