Kepler-1625 b/ Exomoon Kepler-1625 b I

Imaginary picture of Kepler-1625 and its exoplanet (Yui Nagato)

Imaginary picture of Kepler-1625 b

Kepler-1625 b is an exoplanet orbiting the star Kepler-1625, located 7,587.4 light-years (parsecs) from the Solar System, and was announced in 2016. The star Kepler-1625 has an apparent magnitude of 14.4 and an absolute magnitude of 2.5. This star has 1.0 times the mass of the Sun, a radius 1.8 times that of the Sun, a surface temperature of 5,586 K, and a spectral type of G5. In this star’s planetary system, Kepler-1625 b orbits Kepler-1625 with an orbital period of 287.4 days and a semi-major axis of 0.84 astronomical units (1,257,744,156 km).

Kepler-1625 b is one of the 2,662 exoplanets discovered by NASA’s Kepler Space Telescope; it is a Jupiter-sized gas giant orbiting Kepler-1625, located 8,000 light-years from Earth. Although it is a gas giant and therefore not a habitable planet, it lies near the habitable zone.

Credits: ExoKyoto(http://www.exoplanetkyoto.org/exohtml/Kepler-1625_bJP.html)

A detailed analysis of transit data from the Kepler Space Telescope revealed a faint transit signal immediately following the transit of Kepler-1625 b in 2018. Follow-up observations with the Hubble Space Telescope suggested that this signal might be a moon orbiting Kepler-1625 b, and it has been named Kepler-1625 b I as a candidate for an (exomoon) and has been named Kepler-1625 b I. However, because the transit signal from Kepler-1625 b I is faint, follow-up studies have pointed to the possibility that it could be experimental noise, and its existence has not yet been confirmed. It is hoped that detailed observations by the James Webb Space Telescope will lead to the confirmation of the first exomoon.

If Kepler-1625 b I exists, it is believed to be a Neptune-sized gas giant. Since it is a gas giant, a habitable environment is not expected on this moon; however, research using simulations on Kepler-1625 b and Kepler-1625 b I is ongoing, and it has been suggested that a moon the size of Earth may exist orbiting Kepler-1625 b I. That moon would be a rocky satellite and could be a habitable moon located near the habitable zone, raising hopes for the existence of extraterrestrial life.

Credits: NASA
(https://exoplanets.nasa.gov/news/1525/new-moon-astronomers-find-first-evidence-of-a-possible-moon-outside-our-solar-system/)

The status of Kepler-1625 b I as a potential exomoon remains unconfirmed, and the idea of it having a moon is still purely speculative. However, if we consider our own solar system, we see that all planets except Mercury and Venus have moons, so I believe it’s safe to say that moons are a common feature among planets. I look forward to further observations by the James Webb Space Telescope confirming the first exomoon.

Artist’s concept of Kepler-1625, its planets, moons, and stars orbiting the moons (Yui Nagato)

An artist’s concept of the planet Kepler-1625 b as seen from Earth, orbiting its moon (Yui Nagato)

（文責：小塚）

＜References＞

http://www.exoplanetkyoto.org/exohtml/Kepler-1625_bJP.html

https://exoplanets.nasa.gov/news/1525/new-moon-astronomers-find-first-evidence-of-a-possible-moon-outside-our-solar-system/

https://academic.oup.com/mnras/article-abstract/510/2/2583/6498286?redirectedFrom=fulltext

https://arxiv.org/pdf/1810.02712.pdf

Click here for detailed information on Kepler-1625 b

http://www.exoplanetkyoto.org/exohtml/Kepler-1625_bJP.html

HD 110067系

Imaginary Picture of Exoplanets of HD 110067 (Yuna Watanabe)

Imaginary Picture of HD 110067

This star is HD 110067. The star HD 110067 is located 105.1 light-years (32.2 parsecs) from the Solar System. The star HD 110067 has an apparent magnitude of 8.4 and an absolute magnitude of 5.9. It has 0.8 times the mass and 0.8 times the radius of the Sun. Its surface temperature is 5,266 Kelvin, and its spectral type is K0V.

HD110067 is an 8th-magnitude K-type main-sequence star with a mass and radius of just under 80% that of the Sun, located approximately 100 light-years from Earth in the direction of the constellation Coma Berenices. A K-type main-sequence star is a main-sequence star with a spectral class of K and a luminosity class of V, in which hydrogen fusion occurs in the core; such stars are also known as orange giants.

From Wikipedia

In 2023, observations using the transit method confirmed that six exoplanets orbit this star. The transit method is an observational technique for detecting planets by detecting periodic changes in the host star’s brightness caused by a planet periodically passing in front of it as it orbits. HD 11067 is the brightest known star to host at least four transiting planets. Although not confirmed, it is estimated to be approximately 8.1 billion years old, with a metallicity of 63% that of the Sun. Furthermore, while HD 11067 is its designation in the Henry Draper Catalog, this star has also been assigned the catalog number TOI-1835 as a TESS Object of Interest (TOI) because potential exoplanets orbiting it were detected by observations from TESS, the Transiting Exoplanet Survey Satellite.

Through a global collaborative observation campaign involving space-based and ground-based telescopes, six transiting planets have been discovered orbiting the star HD 110067, located approximately 100 light-years from the Solar System. Furthermore, these six planets exhibit a “lucid ratio” relationship, in which the orbital periods of all adjacent pairs of planets are expressed as simple integer ratios.

The planets orbiting inside HD 110067 are known as TOI-1835.03 (later HD 110067b) and TOI-1835.04 (later HD 110067c). In addition, ESA discovered HD 110067d, which orbits with a period of approximately 20.52 days, and subsequently found HD 110067e, which has an orbital period of approximately 30.79 days and is in a 2:3 orbital ratio with HD 110067d. Subsequently, the existence of HD 110067 f, with an orbital period of approximately 41.06 days, and HD 110067 g, with an orbital period of approximately 54.77 days, was confirmed. HD 110067 e and HD 110067 f, as well as HD 110067 f and HD 110067 g, all have orbital periods in a 3:4 ratio, and when considering the orbital period ratios of all six planets, they form a 9:12:16:24:36:54 ratio.

This planetary system is not only a valuable model for understanding how planets form, but it is also expected that observations of the atmospheres of each planet will lead to a better understanding of the processes by which planets acquire atmospheres, as well as the effects of starlight on atmospheric escape and chemical evolution.

A geometric pattern formed by lines connecting the positions of the six discovered planets at regular intervals
Credit: Thibaut Roger/NCCR PlanetS, CC BY-NC-SA 4.0

Full View of the Concept Art for the HD110067 Series (Yuna Watanabe)

【References】

The University of Tokyo, “Discovery of Six Resonant Planets—The HD 110067 Planetary System, Where All Adjacent Planets Share a Total Relation in Their Orbital Periods”:
https://www.u-tokyo.ac.jp/focus/ja/press/z0109_00101.html

Wikipedia「HD 110067」：https://ja.wikipedia.org/wiki/HD_110067

Sorae, 「「HD 110067」に共鳴し合う6つの惑星を発見　惑星科学における重要な “化石”」：
https://sorae.info/astronomy/20231210-hd110067.html

Yahoo News, 「6つの惑星が「軌道共鳴」状態にある恒星系、100光年先で新たに発見」：https://news.yahoo.co.jp/articles/60006f29da1de5f15dac66c2d4cf5956624aebf9

（文責：新原）

HD 110067系の詳細な情報はこちら

http://www.exoplanetkyoto.org/exohtml/HD_110067JP.html

TOI-174系

Imaginary Illustration of TOI-174 b

Imaginary Illustration of TOI-174

TOI-174 is a star located 127 light-years from Earth. This star, TOI-174, has five exoplanets, which are likely to be super-Earths and super-Mercuries.

The Transiting Exoplanet Survey Satellite (TESS) (a space telescope launched as part of NASA’s Explorer Program. Its mission is to search for exoplanets by observing an area 400 times larger than that of the Kepler Space Telescope using the transit method. (Launched in 2018) Observations using the transit method by TESS have indicated the possible existence of two exoplanet candidates, “TOI-174.01” and “TOI-174.02.”

Subsequently, in 2019, follow-up observations using Doppler spectroscopy were conducted with the High Accuracy Radial velocity Planet Searcher (HARPS) (an exoplanet observation instrument operated by the European Southern Observatory (ESO) since 2003), the existence of two planet candidates, TOI-174.01 and TOI-174.02, was confirmed through follow-up observations using Doppler spectroscopy, and they were named “TOI-174 b” and “TOI-174 c,” respectively.

Their orbital periods are approximately 17.7 days and 29.8 days, respectively, and the transit depths of these planets are 663 ± 48 ppm and 627 ± 61 ppm, respectively.

Following the confirmation of these planets, it was suggested in 2019 that “TOI-174.03,” “TOI-174.04,” and “TOI-174.05” might exist.

On September 27, 2022, follow-up observations using Doppler spectroscopy with ESPRESSO (the Echelle spectrograph mounted on the European Southern Observatory’s VLT) confirmed the existence of these three planets: “TOI-174.03,” “TOI-174.04,” and “TOI-174.05.” Starting with the planet having the shortest orbital period, TOI-174.04 was named “TOI-174 d,” TOI-174.05 was named “TOI-174 e,” and TOI-174.03 was named “TOI-174 f.”

Furthermore, research has indicated that b, c, and f are “super-Earths”—Earth-like planets with masses ranging from several to about ten times that of Earth. Additionally, it has been shown that d and e likely have compositions similar to Mercury in our solar system and are “super-Mercuries” with masses greater than that of Mercury.

Year of Discovery of the TOI-174 Series and Summary of the Project

Basic Information on the TOI-174 Series

References:

NASA, EXOPLANET CATALOG HD 23472b from https://exoplanets.nasa.gov/exoplanet-catalog/7338/hd-23472-b/

IAC, Astronomers discover a planetary system with three super-Earths and two super-Mercuries, from https://www.iac.es/en/outreach/news/astronomers-discover-planetary-system-three-super-earths-and-two-super-mercuries

Ia, Two rare super-mercuries discovered around the same star from https://divulgacao.iastro.pt/en/2022/09/27/hd23472-eng/

Weblio, TOI-174, from https://www.weblio.jp/wkpja/content/TOI-174_TOI-174%E3%81%AE%E6%A6%82%E8%A6%81

（文責：新原）

For detailed information on the TOI-174 system, click here (You can also access the detailed pages for each planet from the star’s detailed page.)

http://www.exoplanetkyoto.org/exohtml/TOI-174JP.html

K2-141 b

K2-141 b is an exoplanet orbiting the star K2-141, located 202.2 light-years (parsecs) from the Solar System, and was announced in 2018. The star K2-141 has an apparent magnitude of 11.5 and an absolute magnitude of 7.5. This star has 0.7 times the mass of the Sun, a radius of 0.7 times that of the Sun, a surface temperature of 4,599 K, and a spectral type of K4. In this star’s planetary system, K2-141 b orbits the star K2-141 with an orbital period of 0.3 days and a semi-major axis of 0.01 astronomical units (1,117,678.6 km).

K2-141 b is a Super Earth-sized exoplanet with a diameter approximately 1.5 times that of Earth and a mass approximately five times that of Earth. Its host star, K2-141, has a radius and mass both approximately 0.7 times that of the Sun and is located about 202 light-years from Earth. It has an orbital period of approximately 0.28 days and orbits at a semi-major axis of about 0.01 astronomical units. The inner boundary of the habitable zone around the host star K2-141 (the orbital radius where the planet receives Venus-like radiation) is 0.312 astronomical units, meaning that K2-141 b orbits well within the habitable zone.

According to a research group led by McGill University, K2-141 b is believed to be in a state of tidal locking, with its rotation and orbital periods synchronized. As a result, the temperature on the day side—which is constantly illuminated by the host star—is estimated to reach 3,000 degrees Celsius, while the temperature on the opposite night side is estimated to drop to minus 200 degrees Celsius; it is further estimated that a magma ocean approximately 100 kilometers deep covers the planet’s surface.

On the day side of this planet, temperatures are high enough to vaporize rock, so it is believed that substances that make up the rock—such as sodium, silicon monoxide, and silicon dioxide—vaporize and form the atmosphere. Simulations conducted by the research team predict that these substances are carried by the wind to the night side, where they cool and condense, falling as a “rock rain” into the magma ocean on the surface, thereby driving the rock cycle. However, the rate of this rock cycle is extremely slow, and as the planet’s composition changes over time, it may eventually develop a completely different atmosphere and surface. These simulation results are expected to be confirmed by the James Webb Space Telescope and may provide significant clues for understanding the temporal changes in rock composition on hot planets.

（文責：可児）

Click here for detailed information about K2-141 b

http://www.exoplanetkyoto.org/exohtml/K2-141_bJP.html

LP 791-18 d

LP 791-18 d is an exoplanet orbiting the star LP 791-18, located 86.4 light-years (parsecs) from the Solar System, and was announced in 2023. The star LP 791-18 has an apparent magnitude of 16.9 and an absolute magnitude of 14.8. This star has 0.1 times the mass of the Sun, 0.2 times the Sun’s radius, a surface temperature of 2,960 K, and a spectral type of M6V.

A planet roughly the same size as Earth. And there’s even a possibility of volcanic activity and an atmosphere!?

The Earth-sized exoplanet LP 791-18 d is a planet orbiting the red dwarf star LP 791-18, located approximately 90 light-years from the Solar System in the direction of the constellation Copernicus. Planets b and c have previously been discovered in this star system. The newly discovered planet d is located in an orbit between planets b and c, orbiting the star with an orbital period of 2.75 days. Its radius is estimated to be approximately 1.03 times that of Earth, making it very similar in size. Additionally, Planet d’s mass is comparable to that of Earth. Planet b has a radius about 1.2 times that of Earth and an orbital period of approximately 0.94 days, while Planet c has a radius about 2.5 times that of Earth, a mass about nine times that of Earth, and an orbital period of approximately 4.99 days.

Planet d is located near the inner boundary of the habitable zone and is attracting attention as a planet of interest for research into the origins of life, as it has the potential to retain an atmosphere. The planet’s orbit is slightly elliptical due to gravitational pull from the large, massive Planet c, which orbits in the adjacent outer orbit. As it orbits along this elliptical path, Planet D is subjected to tidal forces from the star, causing it to deform slightly. This deformation may generate internal friction within the planet, heating it and triggering active volcanic activity on its surface—a mechanism similar to that which heats Io, Jupiter’s moon, which exhibits the most active volcanic activity in the solar system. Future observations of the planet’s atmosphere may yield important discoveries regarding how crustal activity affects the planetary atmosphere.

Like Earth’s Moon, Planet d has a synchronous rotation period due to tidal forces, meaning it always keeps the same face toward the star LP 791-18. Consequently, the day side is extremely hot, reaching 300–400 K, and it is highly likely that water has evaporated there. On the other hand, since the night side is thought to be sufficiently cool, if volcanic activity is occurring, Planet D may have an atmosphere, and water vapor could condense in the atmosphere on the night side, potentially resulting in the presence of liquid water.

Furthermore, Planet D’s active volcanic activity may play a role in releasing substances into the atmosphere that would otherwise be trapped within the planet’s crust. These substances include carbon, which is essential for life. If we can successfully detect the composition of this planet’s atmosphere, it will be possible to conduct a detailed investigation into the effects of the planet’s crustal activity on its atmosphere. This could lead to research on the origins of life and is significant from the perspective of astrobiology.

The findings of this study were published in the British scientific journal *Nature* on May 17, 2023 (BST). An international research team, including Professor Noriyasu Narita (Visiting Professor at the Center for Astrobiology, National Institutes of Natural Sciences) from the Graduate School of Arts and Sciences at the University of Tokyo, Specially Appointed Assistant Professor Akihiko Fukui, and Specially Appointed Researcher Mayuko Mori, utilized NASA’s Transiting Exoplanet Survey Satellite (TESS), NASA’s Spitzer Space Telescope, and numerous ground-based telescopes—including the multi-color simultaneous imaging cameras MuSCAT and MuSCAT2, developed by researchers at the University of Tokyo and the Center for Astrobiology.

〈References〉Article Information

・東京大学 大学院総合文化研究科・教養学部：火山活動の可能性がある地球サイズの惑星を発見 ー 潮汐力により加熱された系外惑星 LP 791-18d

・Spitzer Space Telescope：NASA’s Spitzer, TESS Find Potentially Volcano-Covered Earth-Size World

・NASA JPL

・IAC：Astronomers find Earth-sized world potentially covered in volcanoes

・Nature：A temperate Earth-sized planet with tidal heating transiting an M6 star 論文: 2023年5月17日

（文責：日置）

Click here for detailed information on LP 791-18 d

http://www.exoplanetkyoto.org/exohtml/LP_791-18_dJP.html

HD 104985 b

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HD 104985 b is an exoplanet orbiting the star HD 104985, located 316.7 light-years (parsecs) from the Solar System, and was announced in 2003. The star HD 104985 has an apparent magnitude of 5.8 and an absolute magnitude of 0.9. This star has 1.6 times the mass of the Sun, a radius 10.9 times that of the Sun, a surface temperature of 4,786 K, and a spectral type of G9 III. In this star’s planetary system, HD 104985 b orbits the star with an orbital period of 199.5 days and a semi-major axis of 0.95 astronomical units (142,117,977.2 km).

[HD 104985 b Overview]

HD 104985 is a 6th-magnitude star (apparent magnitude) in the constellation Camelopardalis, located approximately 317 light-years from Earth. HD 104985 b is a planet with an orbit slightly less than one astronomical unit from this star. HD 104985 b has a radius nearly identical to Jupiter’s and a mass 8.3 times that of Jupiter. To draw an analogy with our solar system, HD 104985 b is a Jupiter-sized planet located between the orbits of Venus and Earth. Although it orbits at a distance roughly equivalent to Earth’s, the central star is extremely massive, so the environment is believed to be scorching hot.

[The First Exoplanet Detected in Japan: Demonstrating Japan’s Unique Contribution to the World]

HD 104985 b was detected using the radial velocity method with the 188-cm reflecting telescope owned by the Okayama Astrophysical Observatory and was announced in 2003 by Fumie Sato (then affiliated with the National Astronomical Observatory of Japan; now at Tokyo Institute of Technology) and his colleagues. This was the first detection of an exoplanet in Japan and attracted significant attention both domestically and internationally. Since the world’s first observation of an exoplanet in 1995, a fierce “planet-hunting race” had been underway worldwide, and Japan had now joined the fray.

While previous observations had targeted stars similar to the Sun, Sato and his team began searching for planets around giant stars—stars that have evolved and expanded significantly in size. In fact, HD 104985 has a radius 10.6 times that of the Sun and was one of the giant stars Sato and his team had identified as a candidate for observation. After two years of persistent observation, they successfully proved that exoplanets exist even around giant stars, demonstrating Japan’s unique contribution to exoplanet research.

[The Okayama Astrophysical Observatory’s 188-cm Reflecting Telescope: A Telescope That Supported Astronomical Observations in Japan for Half a Century]

The Okayama Astrophysical Observatory, one of the projects of the National Astronomical Observatory of Japan, began operations in Asakuchi City, Okayama Prefecture, in 1962. Until 2018, when operations as a project came to an end, it served as an outstanding optical and infrared astronomical observatory for approximately 56 years, utilized by many researchers. The observatory’s largest telescope is the 188-cm reflector, which has contributed to numerous significant discoveries. Its contributions to the discovery of exoplanets have been particularly notable; including joint observations with other telescopes, it has contributed to the discovery of 58 new exoplanets to date.

(For details on the 188cm telescope’s overview and achievements, please refer to this page.)

188-cm reflector telescope（https://www.nao.ac.jp/research/telescope/188cm.html）

After the project concluded, the telescopes at the Okayama Astrophysical Observatory were transferred to researchers from the participating universities to serve as their dedicated instruments. Currently, the 188-cm reflecting telescope is out of service due to a dome malfunction. Let’s look forward to the day when restoration work is complete and we can once again see the 188-cm reflecting telescope back in action.

[Kyoto University Okayama Astronomical Observatory’s Seimei Telescope: One of the Largest Telescopes in East Asia]

Following in the footsteps of the 188-cm telescope, a new telescope began operations in Okayama in 2019. This is the Seimei Telescope, owned by Kyoto University. With a primary mirror consisting of an 18-element composite mirror with a diameter of 3.8 meters, it is the largest telescope in East Asia. (There are differing opinions as to whether it is the “largest” or “one of the largest.” Please refer here for details.)

Seimei Telescope (Photo by the author)

The name “Seimei Telescope” is derived from Abe no Seimei, a Onmyōji (master of divination) from the Heian period. Abe no Seimei, who conducted astronomical observations throughout the country, is said to have established a residence for astronomical observation near the summit of Mt. Abe, located northwest of the current Okayama Astronomical Observatory. The telescope was named “Seimei Telescope” in honor of Abe no Seimei, a pioneer in astronomical research with ties to Okayama.

The Seimei Telescope is also used for the search for and observation of exoplanets, and a new high-dispersion spectrograph called GAOES-RV will begin operations in the second half of fiscal year 2023. A high-dispersion spectrograph is a device that separates the light collected by the telescope into its component wavelengths for detection; it is indispensable for observing exoplanets using the radial velocity method. With improved performance compared to previous high-dispersion spectrographs, GAOES-RV is expected to enable the observation of exoplanets around fainter stars.

(For more information on GAOES-RV, please click here.)

From Japan’s first detection of an exoplanet to the latest observational equipment, we’ve traced the history of exoplanet exploration. While the allure of exoplanets is endless, the telescopes and instruments used to discover them hold a unique charm of their own. If this has piqued your interest even a little, why not turn your attention not only to the star-studded night sky but also to the “big eyes” set up on the ground?

（文責：渡邊新）

Click here for detailed information on HD 104985 b

http://www.exoplanetkyoto.org/exohtml/HD_104985_bJP.html