How big can a planet be is a question being redefined after NASA’s JWST detected sulfur in the HR 8799 system, revealing that massive gas giants likely formed through core accretion at extreme distances from their star.
NASA’s JWST observed the HR 8799 star system, located 133 light-years away in the constellation Pegasus. These planets are five to ten times Jupiter’s mass, orbiting much farther than Neptune orbits our sun.
Researchers used spectroscopy to detect refractory sulfur in planetary atmospheres for the first time. This chemical signature proves these massive objects grew by pulling in solid rocky and icy pebbles during their formation.
Understanding How big can a planet be
Planets reach their upper mass limit when they transition into brown dwarfs, typically around 13 times Jupiter’s mass. Recent JWST evidence of core accretion in massive objects demonstrates how big can a planet be when orbiting at distances 15 to 70 times farther than Earth is from the sun.
Astronomers analyzed the HR 8799 system to observe how gas giants form at extreme distances. This research determines if massive objects originate from solid cores or rapid gas collapse within a disk.
Core Accretion in the HR 8799 System
Core accretion involves solid cores growing by attracting rocky and icy pebbles until they are massive enough to pull in surrounding hydrogen and helium. In the HR 8799 system, this process successfully created planets orbiting 15 to 70 times farther from their star than Earth orbits the sun.
| Mission/Instrument | Target System | Core Discovery | Lead Institution |
| JWST (NIRSpec IFU) | HR 8799 | Refractory Sulfur Detection | UC San Diego |
- Mass Range: Gas giants in this system range from 5 to 10 Jupiter masses.
- Star Age: HR 8799 is a young system, approximately 30 million years old.
- Chemical Tracers: Sulfur serves as a stable “refractory” tracer for solid core formation.
Spectroscopic Insights and Refractory Elements
JWST detected sulfur molecules like hydrogen sulfide, which serve as stable tracers of planetary origin. Unlike volatile carbon or oxygen, these refractory elements are only present in solids within the protoplanetary disk, confirming that the HR 8799 giants formed through planetary accretion pathways rather than rapid gravitational collapse.
Scientific importance and theories
These findings render older core accretion models outdated because they didn’t account for massive planets forming so far from their host stars. Newer theories now focus on how gas giants can build solid cores in the outer regions of a disk before the star blows away the gas.
Analyzing HR 8799 Mass and How big can a planet be
Scientists are now investigating the transition between massive exoplanets and brown dwarfs, which fail to fuse hydrogen. Detecting sulfur helps astronomers differentiate between objects that formed like stars and those that grew through the accumulation of rocky planetary material in a disk.
Extracting Data to Determine How big can a planet be
Because these planets are 10,000 times fainter than their star, researchers developed new data analysis techniques to extract spectral signals. These tools allow scientists to accurately assess these objects by refining the chemistry and physics within existing atmospheric models used to compare JWST spectra.
Implications and what comes next
Future studies will apply these high-resolution spectroscopic methods to other multi-planet systems. This work will eventually define the exact mass boundary where planetary formation ends and star formation begins.
Conclusion
JWST’s discovery of sulfur in massive gas giants confirms that planetary formation is more robust than once thought. By refining our models, we gain a clearer understanding of how big can a planet be in the vast universe. Explore more on our YouTube channel—join NSN Today.
