Radial velocity study puts upper limits on massive moons around Beta Pictoris b

Star system: Beta Pictoris | Distance from the Sun: 64 light years

Beta Pictoris b is a massive gas giant planet directly imaged in orbit around a star, and its orbit is aligned in a way that makes it a prime target for studying potential large moons, known as exomoons. By monitoring the radial velocity — the speed at which the planet moves toward or away from us along our line of sight — of this distant world, researchers aimed to detect the gravitational tug caused by an orbiting moon.

The observations were conducted between October 2024 and March 2025 using the cross-correlation of a template spectrum with the planet's atmospheric absorption lines. This technique provided a mean precision of 160 meters per second. The resulting radial velocity measurements were analyzed using a periodogram to search for signs of a massive exomoon.

While no exomoon signal was detected, the study established significant upper limits for moon mass. For a moon with an orbital period of one day, the limit is 80 Earth masses, while for a period of 200 days, the limit is 1 Jupiter mass. These findings are comparable to other searches for moons around substellar companions. Future observations with CRIRES+ are expected to improve sensitivity, potentially allowing the detection of a planet-to-moon mass ratio of about one-fourth of Earth's mass for short-period orbits.

Key findings
- No exomoon signals were detected around the gas giant Beta Pictoris b.
- Radial velocity monitoring achieved a mean precision of 160 meters per second.
- Detection limits for a potential moon range from 80 Earth masses at 1-day periods to 1 Jupiter mass at 200-day periods.
- Future observations with the CRIRES+ instrument will enhance the capability to detect even smaller moons in close-in orbits.

Scientific study

Upper limits on exosatellites around Pictoris b (external link)