How to use Near-infrared imaging device and slitless spectrometer Using the NIRISS instrument on the NASA/ESA/CSA James Webb Space Telescope, astronomers have discovered six new free-floating planet-mass members of NGC 1333, with estimated masses ranging from 5 to 15 times that of Jupiter. One of these objects is five times the mass of Jupiter (about 1,600 times that of Earth), making it likely the lowest-mass object with a dusty planetary orbiting disk.

NGC 1333 is a star-forming cluster located about 1,000 light-years away in the northern constellation Perseus.

Also known as Ced 16 and LBN 741, the star cluster was first discovered in 1855 by German astronomer Eduard Schoenfeld.

NGC 1333 is only 1 to 3 million years old and harbors brown dwarfs equivalent to about half the number of stars, a higher proportion than previously observed.

“We're exploring the limits of the star formation process,” said astrophysicist Adam Langeveld of Johns Hopkins University.

“If we had a young Jupiter-like object, could it become a star under the right conditions? This is important context for understanding the formation of stars and planets.”

Dr. Langeveld and his colleagues used Webb's NIRISS instrument to carry out an extremely deep spectroscopic survey of NGC 1333.

Observations have discovered 19 known brown dwarfs and six free-floating planetary-mass objects with masses between 5 and 10 times that of Jupiter.

This means they are among the most lightweight objects yet discovered that were formed from processes that normally produce stars or brown dwarfs (objects that straddle the boundary between stars and planets, do not undergo hydrogen fusion reactions, and disappear over time).

“We used the Webb Telescope's unprecedented sensitivity at infrared wavelengths to search for the faintest members of young star clusters and answer a fundamental question in astronomy: how can objects form star-like shapes with light?” said Ray Jayawardene, an astrophysicist at Johns Hopkins University.

“The smallest stray objects forming like stars turn out to be comparable in mass to giant exoplanets orbiting nearby stars.”

Webb's observations, despite being sensitive enough to detect such objects, did not find any objects with a mass less than five times that of Jupiter.

This strongly suggests that stars less massive than this threshold are likely to form in the same way as planets.

“Our observations confirm that nature produces planetary-mass objects in at least two different ways: from the collapse of clouds of gas and dust as stars form, and from disks of gas and dust around young stars, such as Jupiter in our own solar system,” Dr Jayawardene said.

The most interesting of the planetary-mass objects is NIRISS-NGC1333-5, which is the lightest, with an estimated mass of five Jupiters.

“The presence of a dust disk means that the object almost certainly formed like a star, because cosmic dust typically revolves around a central object during the early stages of star formation,” Dr Langeveld said.

“Disks are also a prerequisite for planet formation, so our observations could also have important implications for potential small planets.”

“These small objects with masses comparable to the giant planets could potentially form planets themselves,” said Dr Alex Scholz, an astrophysicist at the University of St Andrews.

“This could be a nursery for small planetary systems, much smaller in scale than our solar system.”

Astronomers also discovered a new brown dwarf with a planetary-mass companion, a rare find that calls into question theories about how binary star systems form.

“Such pairs likely formed from a contracting, fragmenting cloud, much like a binary star system,” Dr Jayawardene said.

“The diversity of systems created by nature is astonishing and inspires us to refine our models of star and planet formation.”

of Survey results will be published in Astronomical Journal.

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Adam B. Langefeld others2024. JWST/NIRISS Deep Light Survey of Young Brown Dwarfs and Free-Floating Planets. AJin press; doi: 10.3847/1538-3881/ad6f0c