7.8 grams per cubic centimetre makes GJ 523b about 40% denser than Earth despite its 2.55-Earth-radius size, marking it as a gas-poor outlier among sub-Neptunes if the preprint result holds.
30 NEID radial-velocity measurements and TESS transit data produced the 23.5-Earth-mass estimate; the planet crosses its star every 17.74574 days, dimming it by 0.11%, while activity filtering was needed to separate stellar noise from the signal.
169 million years of age deepens the puzzle because photoevaporation alone appears too weak to strip a massive primordial atmosphere so quickly, leaving standard core-accretion models struggling to explain such a compact world.
71 degrees of minimum orbital misalignment hints at a violent or warped history, with the study weighing giant impacts, migration after scattering, or delayed gas accretion as possible explanations.
13 planets meet the paper's proposed 'mega-Earth' definition, but GJ 523b remains provisional until peer review and follow-up observations refine its mass, orbital tilt and any residual atmosphere.