Two earlier stellar-lensing events yielded planetary mass estimates with markedly different precision in a single new preprint. Earth’s motion helped constrain a planet of roughly 41 Earth masses. For the other, Euclid images and a Galactic model yielded around 143 Earth masses with much broader uncertainty. These are model-based estimates rather than direct planetary images.
A new single preprint compares two planetary microlensing events observed in 2021 and 2023. In microlensing, gravity from a foreground star and planet temporarily magnifies a background star. The authors combine older brightness measurements with additional observations and lens models; the planets themselves were not photographed. The study’s new contribution is the mass analysis rather than the original brightening events.[1]
For the event observed in 2021, the source star’s finite size and the apparent shift associated with Earth’s annual motion helped constrain mass. The preferred model yields a planet around 41 Earth masses, with uncertainty of roughly five Earth masses, orbiting a star of approximately 0.92 solar masses. A competing model with a closer projected separation gives similar masses.[1]
The 2023 event lacks a reliable annual-parallax measurement. Images obtained by the Euclid space telescope in March 2025 separated the event’s light from a nearby neighbour. Combining the remaining light with a Galactic population model gives a planet near 143 Earth masses; its lower and upper uncertainties are about 63 and 103 Earth masses. The result depends on the interpretation of the remaining light and the population assumptions, with no measurement of atmospheric conditions or habitability.[1]
