Late-Blooming Rocky World, JWST Chemistry Recast Planet Formation

Overview

• A Science study of the M-dwarf LHS 1903 reports four planets arranged as rocky, gas-rich, gas-rich, and an outer rocky Super-Earth about 1.7 times Earth’s radius.
• Authors say simulations rule out giant impacts and large migrations, proposing sequential formation in which the distant rocky planet emerged after the protoplanetary gas thinned.
• The LHS 1903 system was first flagged by TESS and characterized with ESA’s CHEOPS and ground-based observatories using NASA and ESA resources.
• Separate JWST NIRSpec spectroscopy of HR 8799’s giants detected H2O, CH4, CO2, and a robust H2S signal, alongside metal enrichment up to nine times the host star.
• Researchers interpret the HR 8799 chemistry as evidence that the giants built up heavy elements—on the order of hundreds of Earth masses—supporting the core-accretion model, while calling for further JWST follow-up on LHS 1903’s outer world.