Subaru Telescope reveals a hidden giant planet
Astronomers working with the Subaru Telescope in Hawaiʻi have identified two remarkable objects circling distant stars: a giant planet
Astronomers working with the Subaru Telescope in Hawaiʻi have identified two remarkable objects circling distant stars: a giant planet and a brown dwarf. These findings mark the first successes of OASIS (Observing Accelerators with SCExAO Imaging Survey), a project that pairs precise space-based data with Subaru’s powerful imaging systems to uncover worlds that are otherwise extremely difficult to see. The discoveries also provide an important stepping stone for NASA’s upcoming Roman Space Telescope, which will test new tools designed to image Earth-like planets.
Only about 1 percent of stars are known to host massive planets or brown dwarfs that can be directly photographed with today’s telescopes. Even when these objects are young and still glowing from the heat of their formation, they remain vastly dimmer than the stars they orbit. As a result, their faint light is often overwhelmed by the intense brightness of their host stars. For astronomers, the long-standing challenge has not just been how to see these objects, but knowing where to search in the first place.
How OASIS Pinpoints Hidden Companions
OASIS [Principal Investigator (PI): Thayne Currie / Deputy-PI: Masayuki Kuzuhara] addresses this challenge by narrowing down the most promising targets. The survey analyzes measurements from two European Space Agency missions — Hipparcos and Gaia — which track tiny motions in stars caused by the gravitational pull of unseen companions. Once a star shows signs of being tugged by an invisible object, OASIS turns the Subaru Telescope toward it. Using the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, astronomers can then capture extremely sharp images that make it possible to directly photograph these hidden worlds.
A Giant Planet Revealed in Leo
One of the new discoveries is a planet known as HIP 54515 b, which orbits a star located 271 light-years away in the constellation Leo. This planet has nearly 18 times the mass of Jupiter and travels around its star at a distance similar to that of Neptune in our own solar system. From Earth, however, the planet and its star appear incredibly close together. The separation is comparable to spotting a baseball from 100 km away. Thanks to the precision of the SCExAO system, astronomers were able to resolve the planet clearly despite this challenge.
A Rare Brown Dwarf With Special Potential
The second object, HIP 71618 B, is a brown dwarf with a mass about 60 times that of Jupiter. It lies 169 light-years away in the constellation Bootes. Brown dwarfs are often referred to as “failed stars” — because they form in a similar way to stars but never grow massive enough to ignite nuclear fusion in their cores.
A Perfect Test Target for NASA’s Roman Telescope
HIP 71618 B stands out because it is exceptionally well suited for study by NASA’s Roman Space Telescope. Roman is scheduled to conduct a technology demonstration that will test advanced coronagraph systems. These instruments are essential for future missions that aim to directly image Earth-like planets around other stars, objects that can be ten billion times fainter than the stars they orbit. Until now, astronomers had not identified a single confirmed target that met all the strict criteria for this test. HIP 71618 B fills that gap. Its host star is bright, the brown dwarf sits at an ideal position, and at the Roman Coronagraph’s operating wavelengths it will appear faint enough relative to its star to properly evaluate the new technology.
A New Era of Teamwork in Planet Hunting
Together, these discoveries highlight the power of combining precise measurements from space with advanced imaging from the ground. This coordinated approach allows astronomers to find planets and brown dwarfs that would otherwise remain hidden in starlight. The success of OASIS demonstrates that the Subaru Telescope will continue to play a leading role in astronomical discovery, even as a new generation of powerful telescopes comes online.
