TESS detects first bound microlensing planet orbiting an orange dwarf in Gaia23bra

Star system: Gaia23bra | Distance from the Sun: 5057 light years

The Transiting Exoplanet Survey Satellite (TESS) has successfully identified its first gravitationally bound planet through a technique known as microlensing. Microlensing occurs when the gravity of a star and its orbiting planet acts like a magnifying glass, bending and brightening the light of a more distant background star as the system passes in front of it. The newly characterized planet, designated Gaia23bra b, orbits an orange dwarf star.

Initially identified as a simple single-lens event by Gaia, the system was monitored by TESS over two sectors. The data revealed caustic-crossing features, which are specific distortions in the brightness profile that indicate the presence of a second, smaller object—the planet—orbiting the primary star. This confirms the system as a binary-lens event.

Mathematical modeling of the combined Gaia and TESS data indicates that the host star is an orange dwarf with a mass approximately 0.79 times that of our Sun. The orbiting planet is a gas giant with a mass 1.63 times that of Jupiter. The planet maintains a projected distance of roughly 4.8 astronomical units from its host star, placing it at a distance comparable to the outer reaches of our own solar system.

This discovery highlights the effectiveness of using wide-field space telescopes to perform microlensing studies. By observing across the Galactic Plane, this mission demonstrates a capability to detect planetary systems in regions of the galaxy that were previously difficult to survey.

Key findings
- Gaia23bra b is the first gravitationally bound planet detected by TESS using microlensing.
- The host star is an orange dwarf with a mass of 0.79 solar masses.
- The planetary companion is a gas giant with a mass of 1.63 Jupiter masses.
- The planet orbits at a projected separation of approximately 4.8 astronomical units.
- The observation confirms the effectiveness of combining long-baseline monitoring with high-cadence photometry for planet detection.

Scientific study

TESS's First Bound Microlensing Planet: A Binary Microlensing Event Revealing a Planetary Companion toward the Galactic Plane (external link)