What a surprise to discover a planet that instantly evokes the Star Wars universe! Instead of a single sun, it orbits two twin stars, and at a distance never observed before. This configuration recalls the sky of Tatooine, where Luke Skywalker begins his adventure, but it is very real and located 446 light-years from Earth.
Named HD 143811 AB b, this exoplanet is six times closer to its parent stars than any other directly imaged planet in a binary system. However, its year lasts 300 times longer than on Earth. Astronomers identified this object through advanced observation techniques, opening a window onto uncommon planetary systems.
Artist's view of a planet orbiting two stars - image NASA
Planetary systems around binary stars are extremely rare. According to Jason Wang from Northwestern University, quoted in a statement, out of the 6000 known exoplanets, only a small fraction orbit binaries. The possibility of simultaneously observing the orbits of the star and the planet offers a unique study opportunity, allowing to trace their movements in the sky. Consequently, this rarity makes HD 143811 AB b particularly valuable for understanding the dynamics of multiple systems.
The identification of this planet comes from old data, collected almost ten years ago by the Gemini South telescope and its Gemini Planet Imager instrument. Researchers re-examined these archives before the instrument's upgrade, not expecting such a find. Nathalie Jones from CIERA cross-referenced this information with data from the W.M. Keck Observatory, revealing a faint object that followed the movement of a star.
With a size about six times that of Jupiter, this planet is massive. Its age is estimated at 13 million years, which is relatively young on a cosmic scale. It thus still retains some of the heat from its formation, as indicated by Jason Wang.
Despite its youth, it is already well-established in its stellar environment, offering clues about the early phases of planetary evolution. The twin stars themselves are very close, completing a mutual orbit in only 18 Earth days.
A time-lapse image of exoplanet HD 143811 AB b orbiting around its parent stars.
Credit: Jason Wang/Northwestern University
How HD 143811 AB b formed remains uncertain, as few similar planets are known. Nathalie Jones from CIERA plans to request more telescope time to track its orbit and that of the stars, to better understand their interactions. Scientists hope that future observations, especially with the GPI 2.0 instrument, will clarify this process and discover other objects in the archives.
This discovery, published in
The Astrophysical Journal Letters, motivates researchers to continue exploring archived data, where other objects might be hiding.
Direct imaging of exoplanets
Direct imaging of exoplanets is a technique that allows capturing images of planets outside our Solar System. Unlike indirect methods, it requires blocking the dazzling light of parent stars, often using a coronagraph. This instrument acts as an artificial eclipse, masking the central part of the star to reveal faint nearby objects.
To improve image quality, astronomers also use adaptive optics. This technology corrects in real-time atmospheric disturbances that blur the view, offering sharper images. The Gemini Planet Imager instrument, used to discover HD 143811 AB b, combines these two approaches, allowing to isolate planets.
This method is particularly useful for studying giant and young planets, which still emit residual heat. It allows directly measuring their size, brightness, and orbital motion. However, it remains difficult to implement due to the scarcity of targets and current technological limitations.
The development of instruments like GPI 2.0 promises to expand these capabilities. By improving sensitivity and resolution, scientists hope to image more exoplanets, including in binary systems with multiple interactions, to better understand the diversity of extrasolar worlds.
Planetary formation in binary systems
The formation of planets in binary star systems presents unique characteristics. In these configurations, two stars orbit each other, creating an unstable gravitational environment. The dust and gas disks, from which planets form, can be disturbed by tidal forces, making accretion more difficult.
Current theories propose that planets can form at a safe distance from the stars, where interactions are less intense. But they can later end up on another orbit after being displaced by mechanisms like planetary migration. The discovery of HD 143811 AB b, both young and very close to its twin stars, challenges these models and invites reconsidering the processes at play.
Observations of such systems allow studying how planet orbits evolve under the influence of two massive bodies. The collected data help test numerical simulations that reproduce the dynamics of binary systems, taking into account factors like stellar separation and the age of components.
Understanding these formations also sheds light on the frequency of habitable planets in the galaxy. Binary systems being common, their properties influence the probability of life elsewhere, making each discovery an important piece of the cosmic puzzle.