“We are now in a new era for imaging other worlds,” says Thayne Currie, lead author of the ground-breaking paper published in Science.

Direct imaging is a method that will someday reveal an Earth-like exoplanet around a nearby star. In the past 14 years, large ground-based telescopes equipped with adaptive optics (AO) to sharpen starlight have taken key steps towards this goal, revealing the first direct images of Jupiter-like gas giant exoplanets. These discoveries draw from so-called blind surveys: targets are selected based on system properties like age and distance but are otherwise unbiased. Unfortunately, the low yields of these blind surveys show that exoplanets we can image with current telescopes are rare. 

Direct imaging searches focused on stars showing dynamical evidence for a planet may greatly increase the rate of imaging discoveries. Precision astrometry — measuring the position and motion of stars on the sky — could identify which stars are being pulled by the gravitational influence of an unseen companion and thus may host planets we can image. 

An international research team led by Subaru Telescope, the University of Tokyo, the University of Texas-San Antonio, and the Astrobiology Center of Japan report the world’s first joint direct imaging and astrometric discovery of an exoplanet, using Subaru Telescope’s extreme adaptive optics system (SCExAO; Note 1) coupled with its near-infrared spectrograph (CHARIS) combined with astrometry from European Space Agency’s Gaia mission and its predecessor, Hipparcos. The planet was imaged around the nearby bright star HIP 99770, located in the constellation Cygnus.

“Once we knew which star to look at, Subaru’s extreme adaptive optics system was able to sharpen starlight so well that our infrared instruments could see the faint planet hinted at by Gaia and Hipparcos” notes Olivier Guyon, the Principal Investigator of SCExAO.

The planet – HIP 99770 b – is about 100,000 times fainter than the star it orbits. Its CHARIS spectrum, combined with follow-up imaging from the W.M. Keck Observatory, reveals an atmosphere shaped by water and carbon monoxide, with a temperature about 10 times hotter than Jupiter’s. Its atmosphere resembles an older and slightly less cloudy counterpart to the atmospheres of the first imaged planets, HR 8799 bcd.

By jointly analyzing data from the Subaru Telescope, Keck, Gaia and Hipparcos, the team was able to directly measure the planet’s mass and constrain its orbit. HIP 99770 b is about 14-16 times the mass of Jupiter in our own Solar System, and orbits a star that is nearly twice as massive as the Sun. The planet’s orbit is three times larger than Jupiter’s around the Sun or just over half of Neptune’s distance from the Sun. However, it receives nearly the same amount of light as Jupiter because it’s host star is far more luminous than the Sun. 

“Combining direct imaging from Subaru and Keck with precision astrometry tells us far more about planets like HIP 99770 b than was previously possible,” says Currie.

The discovery has broader implications for the field of extrasolar planets. HIP 99770 b was detected as a part of a SCExAO direct imaging program using Gaia data to identify stars being gravitationally pulled by unseen planets. While many results are currently unpublished, their detection rate so far appears much higher than from previous blind surveys.

“This approach is a better way to find planets that we can then image and study in detail. As our instruments are improving, more will be found,” says Guyon.

The combined approach will also allow us to find an Earth-like planet around a nearby star with upcoming ground-based observatories like the Thirty Meter Telescope or space-based ones like the Habitable Worlds Observatory. Such a planet will be much closer to its star than any planet imaged to date and so will spend a large amount of time either in front or behind that star, making it impossible to see. 

“The indirect detection method will point us to a star around which a rocky, terrestrial planet could be imaged. Once we know when to look, we hope to learn whether this planet has an atmosphere compatible with life as we know it on Earth,” says Motohide Tamura, Professor of the University of Tokyo.

The Subaru Telescope and the W. M. Keck observatory are located at the summit of Maunakea in Hawai`i, an inactive volcano known for its unsurpassed qualities as an astronomy site and its deep personal and cultural significance to many Native Hawaiians.

“Maunakea is the best place on the planet Earth to see other worlds. We are extremely grateful for the privilege of being able to study the heavens from this mountain,” says Currie.

These results appeared as Currie et al. “Direct Imaging and Astrometric Detection of a Gas Giant Planet Orbiting an Accelerating Star” in Science on April 13, 2023.

(Note 1) With ground-based telescopes, the images of celestial objects appear out of focus and shaky, as if looking out from underwater, due to the effects of the Earth’s atmosphere. Extreme adaptive optics corrects the turbulence caused by the Earth’s atmosphere in real time with exceptional precision, making the Subaru Telescope produce extremely sharp images.

(Related Links)

NAOJ April 14, 2023 Press Release 

Subaru Telescope April 13, 2023 Press Release

The University of Tokyo April 14, 2023 Press Release 

The University of Texas-San Antonio April 13, 2023 Press Release

The post Subaru Images, Weighs, and Tracks Massive Benchmark Exoplanet first appeared on Astrobiology Center, NINS.

While there are eight planets in our solar system, about 5,000 distant planets beyond our solar system (exoplanets) have been discovered since their first discovery in 1995. How are exoplanets born, how do they evolve, and how can some of them become life-supporting planets like Earth?　To solve this mystery, it is essential to capture planets in the act of formation at the very site where they are being born. However, due to observational difficulties, observations of young planets with ages of about 1 million years have been extremely limited.

Since the 1980s, it has been known that planets are born in protoplanetary disks, which are disk-like structures found around young stars (main stars), and observations with the Subaru Telescope in the 2010s and the ALMA Telescope in recent years have revealed many gaps and spiral arms in protoplanetary disks, These structures are considered to be indirect evidence of planet formation in the disk. However, only one example of a newborn planet in a disk has been captured in images so far. The young planet, PDS70, is a young star with an age of about 4 million years. However, the “young planet” PDS70b is located “in the gap” of the protoplanetary disk, which limits the amount of material, if any, falling from around it. In other words, PDS70b is considered an advanced planet in the final stages of formation (Note 1).

An international research team led by Subaru Telescope, NASA, the University of Tokyo, and the Astrobiology Center of Japan has successfully discovered a protoplanet buried in the protoplanetary disk of AB Aur in the constellation Auriga (Figure 1), using super-compensation optics (Note 2) on the Subaru Telescope. (Figure 1). The existence of this object was also confirmed by follow-up observations using the infrared camera on the Hubble Space Telescope.

The Subaru Telescope’s super-compensating optics allowed us to clearly distinguish between the protoplanet and the disk,” says Dr. Olivier Guyon, the instrument’s principal investigator.

In general, it is difficult to distinguish between a planet embedded in a disk and a small structure in the disk. However, since light from a disk is polarized by reflection, polarimetric observations can distinguish between a disk that reflects light from its host star and a planet that emits light by itself. Polarization observations with the Subaru Telescope’s super-compensating optics confirmed that the discovered object was not a fine structure in the disk. The visible light instrument mounted on the same super-compensating optics also showed that a large amount of hydrogen gas has fallen into this planet.

Because the main star is so young (about 2 million years old) and a large amount of material is still visible around the planet, this planet, AB Aur b, may be the first example of a so-called “protoplanet,” a planet that is just now being born. At the same time, this is the first evidence that the gaps, spiral arms, and other structures in the protoplanetary disk surrounding AB Aur discovered by the Subaru and ALMA telescopes are caused by the effects of a planet on the disk (Note 3).

AB Aur b has about four times the mass of Jupiter (Note 4) and orbits 93 times farther from its host star than the Earth-Sun distance. This provides evidence that AB Aur b is a model for the formation of a planetary system distinct from the Jupiter-like planets in our solar system,” said Dr. Thane Curie, lead author of the study.

The formation of the planets in our solar system can be well explained by the so-called standard planetary system formation model. In this model, microplanets grow in a protoplanetary disk around a young star, which then collects more material and forms giant planets such as Jupiter and Saturn. It has been suggested that after formation, these planets may move closer to or farther away from their host star, or scatter. However, this discovery indicates that giant protoplanets formed far from their host stars during a period shortly before planetary migration occurred. The formation of such distant giant protoplanets cannot be explained by the Standard Model or the planetary migration and scattering model. Rather, it is a clear example of “formation of a planetary system by gravitational instability,” in which a giant planet is formed by self-gravity in a disk.

AB Auriga has a long history with the Subaru Telescope. Subaru discovered the spiral disk surrounding this star in 2004, and in 2011, Subaru also discovered the disk’s structure of gaps and rings. However, no planets were detected in either case. This time, we finally succeeded in discovering a protoplanet buried in the disk, which had long been a dream of ours,” recalls co-researcher Prof. Motohide Tamura (University of Tokyo).

Subaru Telescope is located at the summit of Mauna Kea in Hawaii, which is not only the best place for astronomy, but also an important place for Native Hawaiians.

Mauna Kea is the best place on Earth to see the world beyond our solar system. Mauna Kea is the best place on Earth to see the world beyond our solar system, and we are deeply grateful for the opportunity to study the universe in such a place,” said Dr. Curie.


This research result was published in the British scientific journal “Nature Astronomy” on April 4, 2022 (Currie et al. “Images of embedded Jovian planet formation at a wide separation around AB Aurigae“).

(Note 1) The existence of another planet candidate PDS70c has also been noted in this planetary system, but it is only visible in hydrogen emission lines and no direct light from the planet itself is thought to be visible. There are other young planet candidates in other planetary systems, but it is difficult to distinguish between a planet and a part of a disk, and no one has yet found one that can be considered a planet with certainty.

(Note 2) Ground-based telescopes produce out-of-focus and shaky images of celestial objects, as if looking out from underwater, due to the effects of the Earth’s atmosphere. The super-compensating optics corrects the turbulence caused by the Earth’s atmosphere in real time at the limit, and realizes beautiful images of celestial objects as if the Subaru Telescope were placed in space. The CHARIS imaging spectrograph and the VAMPIRES visible light polarizer were used as detectors.

(Note 3) For detailed observations of the protoplanetary disk with a complex structure surrounding AB Aur by the Subaru Telescope, please see the Subaru Telescope Press Release on February 17, 2011.

(Note 4) Taking into account errors, the mass of AB Aur b is about 4 to 9 times that of Jupiter.

About Subaru Telescope 
Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan (NAOJ) and supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) under the Large-Scale Scientific Frontier Initiative. Mauna Kea, where Subaru Telescope is located, is a precious natural environment and an important place in Hawaiian culture and history, and we are deeply grateful for the opportunity to explore the universe from Mauna Kea.

■関連リンク

• NAOJ April 5, 2022 Press Release
• Subaru Telescope April 5, 2022 Press Release
• The University of Tokyo April 5, 2022 Press Release
• The World’s Most Clear Image of a Planet-Birth Site: A Giant Planet’s Disk Pattern (Subaru Telescope, Hawaii, February 17, 2011)
• Subaru Telescope’s image of the birthplace of a planet in the shape of a spiral (Subaru Telescope observation on April 18, 2004)

The post Subaru Telescope Images Planet Just Starting to Form first appeared on Astrobiology Center, NINS.

Most extrasolar planets (exoplanets) are found by the indirect method, in which the presence of a planet is detected indirectly from observations of its host star (star). This is because planets are so faint that it is difficult to separate their light from that of the nearby bright main star and observe them directly. The planet’s host star, 2M0437, is a newly born star in the star-forming region of Taurus, about 420 light years away from Earth, and the accompanying planet is considered to be of the same age. Generally, young planets glow brighter in the near-infrared because of the heat from their formation. Using Subaru Telescope’s near-infrared spectroscopic imager IRCS and adaptive optics instrument AO188 in 2018, the research team discovered 2M0437b at 0.9 arcseconds away from 2M0437 by direct imaging (Figure 1).

The follow-up observations to confirm that 2M0437b is indeed a planet orbiting 2M0437 and not a background star were made with the Subaru Telescope and the Keck Telescope, also on Mauna Kea. After three years of observations and precise tracking, the two objects were confirmed to be a planetary system bound by each other’s gravity.

Based on the brightness observed by IRCS and other instruments, the mass of 2M0437b is estimated to be three to five times the mass of Jupiter. This is one of the lightest exoplanets found by direct imaging observations, and is a testament to the power of the Subaru Telescope and adaptive optics. The age of this planetary system is estimated to be 2-5 million years, making this the youngest planet ever discovered among the 10 Jupiter masses or less that can be reliably called a planet (Note 1).

Conventional theories of planet formation suggest that it is difficult for a small-mass star like an M dwarf to form a giant planet like 2M0437b at some distance from its host star (about 100 AU in this case) in a few million years. 2M0437b is an extremely valuable discovery for understanding where and how giant planets are formed. It will be an extremely valuable observation target for elucidating how and where giant planets form, and will provide important insights into the study of planet formation.

Assistant Professor Teruyuki Hirano (Astrobiology Center, National Institutes of Natural Sciences/National Astronomical Observatory of Japan), who is one of the leaders of the research, said, “There have not been many cases where exoplanets have been discovered by directly observing light from planets, and only a few planets with ages younger than 10 million years have been found. The newly discovered planet is one of the youngest, and is a very unique planetary system. In addition to the Subaru Telescope, we hope to study the atmospheres and other properties of newly born planets through further observations with the James Webb Space Telescope (an infrared telescope scheduled for launch at the end of 2021) and other telescopes,” he said.

This research was published in the Monthly Notices of the Royal Astronomical Society on October 26th (Gaidos et al. “Zodiacal Exoplanets in Time (ZEIT) XII: A Directly-Imaged Planetary-Mass Companion to a Young Taurus M Dwarf Star“)。

(Note 1) If we include objects in the boundary region between “planets” and “brown dwarfs” that are larger than 10 Jupiter masses, objects as old as or slightly younger than 2M0437b have been reported.。

About Subaru Telescope：
Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan (NAOJ) and supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) under the Large-Scale Scientific Frontier Initiative. Mauna Kea, where Subaru Telescope is located, is a precious natural environment and an important place in Hawaiian culture and history, and we are deeply grateful for the opportunity to explore the universe from Mauna Kea.

■Related Links

Subaru Telescope, National Astronomical Observatory of Japan, October 23, 2021 (JST) Press Release
University of Hawaii (English) Oct. 22, 2021 (HST) Press Release

The post Subaru Telescope Discovers a newborn extrasolar planet first appeared on Astrobiology Center, NINS.

The combination of the new exoplanet imaging instrument on Subaru Telescope with innovative ideas for direct explorations of exoplanets has enabled the discovery of new objects orbiting stars more efficiently than ever before. Then they discovered the first ultra-low-mass object HD 33632 Ab by this method. This object is important even when compared to known exoplanets.

The SCExAO and CHARIS on Subaru Telescope represent the state-of-the-art instruments for observing exoplanets and circumstellar disks. SCExAO employs extreme adaptive optics, creating sharp point spread functions as if Subaru Telescope were launched into space free from the atmospheric turbulence of the Earth. CHARIS has a function of integral field spectroscopy enabling the acquisition of spectra from each tiny area of the sky simultaneously. By combining these instruments, it becomes possible to image objects with an unprecedented contrast level while observing their spectra at the same time.
This system has undergone approximately two years of engineering at Subaru Telescope and has already yielded achievements in observations of several objects (Note 1). This time, an international research team including researchers from National Astronomical Observatory of Japan and the Astrobiology Center discovered the ultra-low-mass object (brown dwarf: Note 2) HD 33632 Ab (see Figure 1) with this new system. HD 33632 Ab orbits a star that, except for being slightly younger at 1.5 billion years than the Sun, shares many characteristics with our Sun. It is located in the direction of Auriga, at a distance of 86 light-years from Earth.

Observations with SCExAO and CHARIS were made in October 2018, followed a month later by observations with the Keck telescope. As a result, HD 33632 Ab was found at a distance of only 20 AU from the star (the central star). Further observations were made on August 31 and September 1, 2020, with more time to follow up on the observations, despite the influence of COVID-19. This proved that HD 33632 Ab is not just a background star, but a new object gravitationally bound to its host star The spectrum of HD 33632 Ab obtained by CHARIS has a shape consisting of several peaks and troughs (Figure 2 left). This is due to the presence of water and carbon monoxide gases in the atmosphere of HD 33632 Ab.

Thanks to the extremely sharp images obtained with the new instrument, we have not only found HD 33632 Ab, but we have also obtained its exact position on the celestial sphere and a spectrum that will help us understand the nature of the object’s atmosphere,” said lead author of the study Dr. Thane Curie, who is affiliated with NASA’s Ames Research Center and concurrently holds a post at Subaru Telescope. Dr. Sein Curie, lead author of the study, who works at NASA’s Ames Research Center and also serves at Subaru Telescope.

The discovery of HD 33632 Ab utilized a new approach to overcome the low detection rates that have been a problem for direct exoplanet searches. The positional astronomical satellite Gaia, launched in 2013, has made it possible to measure the motion of central stars as changes in their positions in the celestial plane. The detection of HD 33632 Ab is proof that this approach is effective.

HD 33632 Ab is the first brown dwarf we have discovered by looking for stellar wobbles in the celestial plane. In the past, looking for brown dwarfs has been like trying our luck, but now we have a much better chance of finding one,” said Dr. Timothy Brandt, an assistant professor at the University of California, Santa Barbara, and a co-investigator familiar with Gaia data.

Based on the motion of the central star observed by Gaia and other instruments and the change in position of HD 33632 Ab observed by the Subaru/Keck telescope, the orbit of HD 33632 Ab was analyzed (Figure 2 right), and the mechanical mass of HD 33632 Ab was estimated to be about 46 times that of Jupiter based on Kepler’s Law. In distinguishing between planets and brown dwarfs, we usually refer to a planet if its mass is less than 13-14 times that of Jupiter; HD 33632 Ab’s mass is larger than this boundary value and in the brown dwarf range, but its orbital eccentricity is low and similar to planets discovered by direct imaging so far.

HD 33632 Ab will be an important object for understanding the exoplanet of HR 8799, a planetary system first imaged in 2008-2010 and most closely studied by direct imaging. Compared to HR 8799, which is 40 million years old, HD 33632 is much older. However, because of its large mass and surface gravity, HD 33632 Ab’s surface temperature will be about the same as that of HR 8799’s planet (Note 3). On the other hand, the mass of HD 33632 Ab is well determined by dynamics, and the mass of the planet of HR 8799 is also limited by various techniques. In other words, the planets in HD 33632 Ab and HR 8799 are the best objects for understanding the differences in atmospheres of very low-mass stars (planets and brown dwarfs) with different temperatures due to their different ages and gravities.

The atmospheres of exoplanets like the HR 8799 system are notoriously difficult to model and are thought to have peculiar properties like thick clouds. This new object is important for understanding the atmospheres of these complex exoplanets,” said Curie.

Detection rates of planets and brown dwarfs in previous direct imaging surveys have been very low, around a few percent (Note 4). The research team is using a new method of exploration and observation that utilizes data from positional astronomical satellites. Although this search has just begun, the team has already found several new promising candidates and expects to find planets and brown dwarfs more frequently than in the past.

With the combination of SCExAO and CHARIS, Subaru Telescope will remain at the forefront of direct observations of exoplanets and brown dwarfs,” said co-investigators Professor Motohide Tamura (Center for Astrobiology, University of Tokyo) and Assistant Professor Masayuki Kuzuhara (Center for Astrobiology, University of Tokyo) expressed their expectations for SCExAO/CHARIS.

This research achievement was published in the Astrophysical Journal Letters (November 30, 2020)(Currie et al., “SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-Mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star“).

Note 1: The research achievements using SCExAO and CHARIS include observations of protoplanetary disks “Subaru Telescope Images Hidden Young Planetary Systems” and other studies.

Note 2:  A brown dwarf is a type of celestial object that fell short in becoming a main-sequence star due to its insufficient mass.

(Note 3) In the case of giant planets like Jupiter, we generally expect younger planets to have higher temperatures, and brown dwarfs that are more massive than planets are expected to have higher temperatures. Since HR 8799 is a young planet, its temperature is expected to be similar to that of HD 33632Ab, a more massive brown dwarf.

(Note 4) Previous direct imaging surveys include the SEEDS project with the Subaru Telescope and the GPI (GPI) and SPHERE (SPHERE) surveys with the VLT (VLT) telescope at the Gemini Telescope in Chile, both of which have detected only a few percent of the planet and its brown dwarf companion. The detection rate of planets and brown dwarf companions by these surveys was only a few percent.

Related Links

Subaru Telescope　Press Release

The post The First Achievement of Discovery with the New Exoplanet Imaging Instrument on Subaru Telescope first appeared on Astrobiology Center, NINS.