The double star system HD 135344 AB is located approximately 440 light-years away in the constellation Lupus. It consists of two young stars, A and B, that orbit each other at great distances.
Tomas Stolker of Leiden University in the Netherlands studied star B during his doctoral research from 2013 to 2017 because of its interesting planet-forming disk. "Star A had never been investigated because it does not contain a disk. My colleagues and I were curious if it had already formed a planet," says Stolker. "And so, after four years of careful measurements and some luck, the answer is yes."
The newly discovered exoplanet HD 135344 Ab is a young gas giant, no more than 12 million years old. It has a mass about 10 times that of Jupiter. The planet's distance from its star is comparable to Uranus' orbit around the Sun.
The researchers point out that star A has already finished forming planets, while star B still has a protoplanetary disk. This demonstrates that planet formation around binary stars can occur on different timelines.
Four years of tracking
The researchers used the SPHERE instrument on European Southern Observatory's Very Large Telescope (ESO's VLT) to capture the faint light of the potential planet. They found the planet quickly, but for a long time, it was unclear whether it was a planet or a background star. To rule out the possibility of a background star, the researchers tracked the planet also with the GRAVITY instrument. This instrument combines light from the VLT's four large telescopes, enabling it to map the planet's location with great precision. Over four years, the researchers observed the star and planet seven times and saw them move together. In other words, there is no background star.
"We've been lucky, though," says Stolker. "The angle between the planet and the star is now so small that SPHERE can barely detect the planet."
New population?
In the future, researchers will continue to monitor the planet using the GRAVITY instrument. They also hope to point the ELT, which is currently under construction, to the planet. This will allow them to determine the composition of the atmosphere and learn more about the planet's evolution. Additionally, they plan to search for gas giants near other young stars at distances similar to the orbit of the newly discovered exoplanet. The researchers think that HD 135344 Ab might be part of a population of exoplanets that have so far been difficult to detect.
Scientific paper
Direct imaging discovery of a young giant planet orbiting on solar system scales. By: T. Stolker, et al. In: Astronomy & Astrophysics, 9 July 2025. [original (open access, available after 9 July) | preprint (pdf)]
The newly discovered exoplanet HD 135344 Ab can be seen as a yellow dot on the right side of the image. It was measured in 2019 (2x), 2021, and 2022. The empty purple circle with the star in the middle indicates the location of the corresponding star. This star was filtered out, first by a coronograph and further by digital post-processing. The dashed line represents the planet's orbit. (c) Stolker et al. [high resolution]