{"id":10003,"date":"2025-12-04T19:51:17","date_gmt":"2025-12-04T10:51:17","guid":{"rendered":"https:\/\/www.abc-nins.jp\/en\/?p=10003"},"modified":"2025-12-04T19:51:44","modified_gmt":"2025-12-04T10:51:44","slug":"first-results-from-the-subaru-telescopes-oasis-survey-direct-imaging-of-new-worlds-around-unexplored-stars","status":"publish","type":"post","link":"https:\/\/www.abc-nins.jp\/en\/2025\/12\/04\/10003\/","title":{"rendered":"First Results from the Subaru Telescope\u2019s OASIS Survey: Direct Imaging of New Worlds Around\u00a0Unexplored\u00a0Stars"},"content":{"rendered":"\n
\"\"
Figure1: Time lapse movie of the Subaru Telescope images which led to the discovery of HIP 54515 b (indicated by the arrow). The planet\u2019s host star has been blocked in this image. The star\u2019s position is indicated by the star mark. The dotted line shows the outline of the mask used to block the star. (Credit: T. Currie\/Subaru Telescope, UTSA)<\/figcaption><\/figure>\n\n\n\n

The discovery of two remarkable substellar companions orbiting\u00a0distant\u00a0stars\u00a0has been announced by\u00a0an international team of astronomersusing the Subaru Telescope\u2019s sharp adaptive-optics imaging together with precision stellar measurements from space-based astrometry.\u00a0This discovery is\u00a0the first results\u00a0from\u00a0OASIS (Observing Accelerators with SCExAO Imaging Survey) program, which aims to find and characterize massive planets and brown dwarfs.<\/p>\n\n\n\n

Only about 1% of stars host\u00a0massive planets and brown dwarfs that can be photographed directly with current telescopes. Even in young planetary systems where these objects are still glowing hot with the energy of having just been formed, making them brighter and easier to detect,\u00a0they are\u00a0still much fainter than their host stars and\u00a0are easily\u00a0lost in the stellar glare. The key question for astronomers has been: where to look\u00a0for these objects?<\/p>\n\n\n\n

That\u00a0is\u00a0where OASIS comes in. The program uses measurements from two European Space Agency missions\u2014Hipparcos and Gaia\u2014to identify stars being tugged by the gravity of unseen companions. OASIS then targets these promising candidates with\u00a0the\u00a0Subaru Coronagraphic Extreme Adaptive Optics (SCExAO)\u00a0system, which provides the exceptional precision and advanced technology needed to actually photograph these hidden companions.<\/p>\n\n\n\n

“With OASIS, we are able to find, weigh, and track the orbits of massive planets and brown dwarfs around stars we never thought of looking at before,” says\u00a0OASIS Principal Investigator\u00a0(PI), Thayne Currie\u00a0at The University of Texas at San Antonio (UTSA).<\/p>\n\n\n\n

The first discovery, HIP 54515 b, is a gas giant planet with a mass just under 18 times that of Jupiter, orbiting a star twice the mass of the Sun.\u00a0\u00a0HIP 54515 b orbits its star at approximately 25 astronomical units (au).\u00a0This is\u00a0roughly the\u00a0same\u00a0distance\u00a0as between\u00a0Neptune\u00a0and theSun.\u00a0\u00a0Because the planetary system is so distant\u2014about 275 light-years from Earth\u2014HIP 54515\u00a0b appears extremely close to its star in the sky, pushing the limits of current direct imaging technology.<\/p>\n\n\n\n

“HIP 54515\u00a0b was imaged about 0.15 arc-seconds from its star. That\u2019s roughly how small a baseball would appear from 100 km away, so we needed extremely sharp images enabled by Maunakea and SCExAO\u2019s advanced technology,”\u00a0says Currie.<\/p>\n\n\n\n

HIP 54515 b adds to a growing trend of superjovian planets whose orbits are slightly less circular than those\u00a0of\u00a0lower-mass Jupiter-like planets. This may suggest that these planets have slightly different formation histories than the gas giants in our\u00a0Solar\u00a0System.<\/p>\n\n\n\n

The second discovery, HIP 71618 B, also orbits a two-solar-mass star but is a brown dwarf, a type of\u00a0object that forms\u00a0like\u00a0a\u00a0star\u00a0but lackssufficient mass\u00a0to be\u00a0a\u00a0true star. HIP 71618 B is about 60 times as massive as Jupiter, orbits its star at an average distance slightly larger than Saturn\u2019s orbit around the Sun, and follows a highly elongated, elliptical orbit. In addition to astrometry and SCExAO imaging,\u00a0W. M.\u00a0Keck Observatory imaging data were crucial to its discovery.\u00a0\u00a0<\/p>\n\n\n\n

\"\"
Figure 2: Image of HIP 71618 B (indicated by the arrow) taken by the Subaru Telescope. The planet\u2019s host star has been blocked in this image. The star\u2019s position is indicated by the star mark. (Credit: T. Currie\/Subaru Telescope, UTSA)<\/figcaption><\/figure>\n\n\n\n

While not a planet itself, HIP 71618 B may play an important role in future searches for Earth-like planets around other stars. This is because it meets the requirements for the Roman Space Telescope\u2019s Coronagraph Instrument technology demonstration, planned for 2027.This experiment will be the first to test advanced planet imaging technologies in a space telescope to suppress the glare of Sun-like stars to see rocky, Earth-like planets ten billion times fainter.\u00a0The Roman Coronagraph Technology Demonstration has strict requirements for its target stars, and until the discovery of HIP 71618\u00a0B, no system was known in the peer-reviewed literature to meet these criteria.<\/p>\n\n\n\n

The discoveries\u00a0of\u00a0HIP 54515 b\u00a0and HIP 71618\u00a0B\u00a0showcase\u00a0how combining space-based precision star-tracking and ground-based direct imaging can reveal planets and brown dwarfs that would otherwise remain hidden. The OASIS program continues to survey dozens of additional candidate systems, with more discoveries expected in the coming years which will\u00a0deepen our understanding of how planets and brown dwarfs form and how their atmospheres evolve. The discoveries will also contribute to the development of technologies needed to detect habitable, Earth-like worlds in the future.\u00a0\u00a0<\/p>\n\n\n\n

“Thanks to innovative instruments like SCExAO and Maunakea\u2019s world-leading astronomical observing conditions, Subaru Telescope will continue to be a preeminent observatory even as other telescopes come online, making breakthrough discoveries far into the future,” says\u00a0Dr. Masayuki Kuzuhara (Astrobiology Center), who co-leads OASIS with\u00a0Currie.<\/p>\n\n\n\n

These results appeared in\u00a0Currie & Li et al.\u00a0“SCExAO\/CHARIS and Gaia Direct Imaging and Astrometric Discovery of a Superjovian Planet\u00a03\u20134 \u03bb\/D from the Accelerating Star HIP 54515<\/a>”\u00a0in the\u00a0Astronomical\u00a0Journal\u00a0on December 3, 2025 and El Morsy et al. “OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration<\/a>” in the\u00a0Astrophysical Journal\u00a0Letters on December 3, 2025.<\/p>\n\n\n\n

OASIS is an international collaboration involving astronomers from institutions across the United States, Japan, Canada, Chile, and Europe, and is supported by the National Science Foundation for its scientific merit and NASA as Key Strategic Mission Support for the Roman Space Telescope.\u00a0This research was supported by JSPS KAKENHI (Grant Numbers: 24K07108).<\/p>\n\n\n\n

<\/div>\n\n\n\n
About the Subaru Telescope<\/strong>
The Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences with the support of the MEXT Project to Promote Large Scientific Frontiers. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawai`i.
<\/pre>\n\n\n\n
<\/div>\n\n\n\n
Related links:<\/p>\n\n\n\n