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Astrophysics

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

Mallory Harris, Diana Dragomir, Etienne Bachelet, Michael Fausnaugh, Samson Johnson

Featured July 14, 2026

Original Paper

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Simply

By combining TESS's quick, detailed brightness measurements with Gaia's long-term observations, scientists found the first planet using gravitational microlensing with TESS, showing it can spot planets far from its usual hunting grounds.

In depth
The paper reports the discovery of Gaia23bra b, the first planet found by TESS using gravitational microlensing. This was achieved by combining TESS's rapid, detailed observations of flux changes during a caustic crossing with Gaia's long-term, precise baseline measurements. This joint analysis allowed for the robust characterization of the binary-lens system, revealing a Jovian planet orbiting a K dwarf, demonstrating TESS's potential for exoplanet detection beyond its primary transit mission.

Key Takeaways

  • 1
    TESS, primarily a transit mission, can detect microlensing planets when its high-cadence data is combined with long-baseline observations from other facilities like Gaia.
  • 2
    The joint modeling of TESS's detailed caustic-crossing features and Gaia's extended baseline is crucial for robustly characterizing binary-lens events and overcoming TESS's limitations (e.g., short observing windows, large pixel scale).
  • 3
    This discovery of Gaia23bra b, a super-Jupiter in the Galactic Plane, highlights TESS's capacity to probe planetary populations in regions beyond the Galactic Bulge, expanding the scope of microlensing surveys.

Conceptual Flow

HIGH LEVEL
1
Methodology: Combining Telescope Views

Scientists combined quick, detailed brightness changes from one telescope with long-term, steady brightness from another to precisely measure a planet's effect on a distant star's light.

Quick Brightness Changes
Long-Term Brightness
Combine & Analyze
Planet Properties
2
Results: Finding New Planets

This new way of combining telescope data successfully found a large planet orbiting a star far away, proving that this method can discover planets in new parts of space.

Old Way: Limited Planets
New Way: Combine Data
More Planets Found