Astronomers have discovered a third planet orbiting the star Beta Pictoris. The newly found planet, Beta Pictoris d, is one of the least massive exoplanets ever to be directly observed from Earth. Remarkably, the planet turned out to be 'hidden' in archived observations that are more than a decade old.
Stars are so bright compared to the planets orbiting them that photographing those planets is often impossible. Most of the more than 6,000 exoplanets known today have been discovered when they pass in front of their host star and block a small fraction of its light. Scientists have succeeded in detecting light directly from planets on only a few dozen occasions. These are usually large, hot worlds.
'It is exciting to see that a planetary system we thought we knew so well can still surprise us'
Beta Pictoris d, the newly discovered planet, has a mass 2.4 times that of Jupiter, making it significantly less massive than its sibling planets Beta Pictoris b and Beta Pictoris c. Because it is smaller, this gas giant is cooler and around 100 times fainter than the previously discovered and imaged planets orbiting the star. The planet follows a wide orbit at a distance roughly 25 times greater than that between Earth and the Sun.
'It is exciting to see that a planetary system we thought we knew so well can still surprise us,' says co-author Matthew Kenworthy of Leiden Observatory. 'What is more, we found it thanks to ERIS, an instrument to which we contributed through NOVA in the Netherlands.'
The discovery was made using the Enhanced Resolution Imager and Spectrograph (ERIS) on the European Southern Observatory's (ESO) Very Large Telescope (VLT) in northern Chile. It was subsequently confirmed with the James Webb Space Telescope. Beta Pictoris is a well-studied star located about 63 light-years from Earth in the southern constellation Pictor. The star is surrounded by a young disc of dust and gas that provides astronomers with valuable clues about how planetary systems form and evolve.
Spotting a previously unknown planet
'This was a chance discovery,' says lead author Ben Sutlieff of the University of Edinburgh, UK. 'Our original aim was to study another planet, Beta Pictoris b, and see how it changes over time.' However, while examining the data, the researchers spotted signs of a previously unknown planet.
The planet was visible in archival images taken with both the ERIS and SPHERE instruments on the VLT. Some of those observations are now 11 years old. 'Beta Pictoris d seems to have been playing hide-and-seek with us all this time, and only now can we say that we have finally found it,' says co-author Jayne Birkby of the University of Oxford, UK.
Excellent laboratory for studying planet formation
Beta Pictoris has now become only the second planetary system, after HR 8799, in which more than two planets have been directly imaged. Such systems offer scientists a unique opportunity to study how different exoplanets appear when they form in the same environment.
'Beta Pictoris d seems to have been playing hide-and-seek with us all this time, and only now can we say that we have finally found it'
Future observations may allow researchers to determine the composition of the new planet's atmosphere. ESO's Extremely Large Telescope, currently under construction, could also reveal additional planets around Beta Pictoris. 'This planetary system is an excellent laboratory for studying planet formation,' says Sutlieff. 'It shows how different types of planets can emerge. Ultimately, that helps us better understand our own Solar System, where planets follow very different orbits and have a wide range of masses.'
The discovery of Beta Pictoris d also helps explain the unusual shape of the debris disc previously observed around the young star. The sharp outer edge of that disc could not be explained by the gravitational influence of the two planets discovered earlier, suggesting that a smaller planet in a more distant orbit was present. The new finding provides strong evidence for exactly such a world.
Scientific papers
'Direct Imaging Discovery of Giant Exoplanet β Pictoris d: A Decade-Long Game of Hide-and-Seek', B. Sutlieff et al., The Astrophysical Journal Letters, 15 juli 2026
'Discovery of an Exterior Third Planet Orbiting Pictoris', A. Gibbs et al., The Astrophysical Journal Letters, 15 juli 2026
This press release originally appeared on astronomie.nl
