Astronomers discover what shapes young star systems

(CN) — Astronomers using the James Webb Space Telescope have spotted a small gas giant inside the dusty ring of a young star. This supports what scientists have long suspected — that planets help shape the disks around newborn stars.

These gas and dust rings, called disks, are where planets form. As they grow, planets can carve gaps and shape the disk’s structure.

The planet, TWA 7b, was spotted in the three-ringed system of TWA 7, a 6.4-million-year-old star. The planet is about one-third the mass of Jupiter and orbits 52 astronomical units away, farther than Pluto is from our sun.

The findings were published Wednesday in the journal Nature.

“We were looking for planets that cause gaps in disks,” said Anne-Marie Lagrange, an astronomer at the Observatoire de Paris and senior author of the study, in an email.

Planets are thought to form within swirling disks of gas and dust that surround newborn stars. These protoplanetary disks often show mysterious gaps or ring-like structures.

Astronomers have long suspected that hidden planets might be responsible for clearing these paths, but direct observations of such planets have been rare, especially for smaller ones like TWA 7b.

This discovery shows, for the first time, that smaller planets can be directly observed shaping their star systems.

The research team used JWST’s MIRI instrument to study disks face-on, which reduces interference from dust and gas and makes faint planets easier to detect.

“Thanks to such geometry, the signal of potential planets is less contaminated by the signal of the disk,” Lagrange said.

Lagrange said TWA 7b appears to sit right in the disk’s gap, and has just the right mass to account for the structure seen around the star.

“We are very confident [that TWA 7b is responsible for the gap in the disk] because the planet sits exactly and has the right mass to produce the observed structures in the disk,” she said.

Sub-Jupiter planets like this are thought to be common around low-mass stars like TWA 7, but have been notoriously hard to find. Earlier instruments, such as SPHERE or GPI, could only detect planets larger than approximately three Jupiter masses. TWA 7b, by contrast, appears to be just 0.3 times the mass of Jupiter.

That kind of sensitivity leap is part of what makes JWST so powerful, especially when paired with smart target selection, say researchers.

Lagrange’s team chose stars with ringed disks oriented nearly face-on and then calculated the kind of planets that would be needed to explain the disk gaps.

“We kept those disks for which, given expected JWST/MIRI performances, [a planet] has good chances to be detected,” Lagrange said.

Researchers say the discovery supports current models of planet formation and demonstrates that smaller planets can still significantly shape their environments. It also suggests astronomers may be able to detect more of these hidden planets in the near future.

Next, the team plans to study TWA 7b’s atmosphere with spectroscopy to learn more about its composition and origins.

“We’d also like to find additional planets in the disk, like we did, for instance, on Beta Pictoris and HD 206893,” she said.