Eight Years of Wobble Point to a Planet Around a Dim Star
An ultracool dwarf barely shines, but its motion gave it away: an eight-year telescope campaign has flagged a possible giant planet nearby.
The Discovery
A star can betray an unseen companion without anyone photographing the companion. In an October 8 study in Astronomy & Astrophysics, astronomers report an exoplanet candidate around the nearby early-L dwarf DENIS-P J1253108-570924. They named the candidate PALTA-1 b.
Using the FORS2 instrument at the Very Large Telescope, the team tracked small departures from the dwarf's expected motion for more than eight years. The host sits about 17 parsecs away. A gravitational tug, rather than a bright planet image, is the signal under investigation.
What Makes It Strange
Ultracool dwarfs are faint and low-mass, making giant companions a particularly interesting test of how planets form around small hosts. The inferred companion falls around 0.54–0.77 Jupiter masses, depending on the host's uncertain mass. The authors estimate a separation of 1.6–3.4 astronomical units and a system mass ratio near 0.010.
- Measured: the dwarf's astrometric motion over years.
- Inferred: a sub-Jupiter-mass companion from that motion.
- Not yet established: independent confirmation of a planet.
The Implications
This result completes the team's astrometric search of 20 nearby ultracool dwarfs. If PALTA-1 b is confirmed, the researchers say it would join a very small group of known giant planets around nearby ultracool dwarfs. The mass range is model-dependent: pinning down the host's mass and checking the orbital interpretation remain essential.
The dimmest stars can leave the longest trails of clues.