Astronomers Weigh 0.22-Jupiter Free-Floating Object Using 0.842-Day Microlensing Event
Updated
Updated · spacedaily.com · Aug 24
Astronomers Weigh 0.22-Jupiter Free-Floating Object Using 0.842-Day Microlensing Event
1 articles · Updated · spacedaily.com · Aug 24
Summary
A microlensing event seen from Earth and Gaia yielded a direct mass of 0.219 Jupiter masses—about 70 Earth masses—for an object with no detected host star, placing it in the planetary range near Saturn.
Gaia’s six scans over 16 hours caught the event peaking 1.9 hours later than ground observations, and that offset provided a roughly seven-sigma parallax signal needed to break the usual mass-distance degeneracy.
The team also used a finite-source effect—where the lens crossed the background star’s apparent disc—to derive an angular Einstein radius of 18.6 microarcseconds and infer a distance of about 3.05 kiloparsecs.
No extra lensing signature revealed a host star, but the data cannot exclude one on an extremely wide orbit, so the Science paper describes the object as either unbound or very widely separated from any star.
The result secures one short isolated event as truly planetary-mass, but it does not settle claims that such worlds outnumber stars by about 20 to 1; that broader census remains disputed and awaits larger Roman telescope samples.