Category: Introduction to Exoplanets

Ross 128 b (Proxima Virginis b)

(Imaginary Image of Ross-128b Image Credit 清水海羽 守山高校ハビタブル研究会)

(Imaginary Image of Ross-128b Image Credit: Yosuke Yamashiki, Ryusuke Kuroki)

Ross-128b is a new habitable planet has been discovered, located about 11 light years (3.4 parsecs) away from our solar system. Its mass is about 1.35 times that of the Earth (ExoKyoto estimates 1.31), but the exact radius is not known because of a lack of transit. However, according to the mass estimation module (Weiss & Marcy, 2014) by ExoKyoto, the radius is estimated to be 1.078 times that of the Earth. The planet’s host star is Mare Virgo, which is a small M-type star in the constellation Virgo, with an estimated temperature of 3192 K and a mass 0.16 times that of our sun. It is the second closest habitable planet to Earth after Proxima Cen b. A research team from Université Grenoble Alpes in France made the discovery using a 3.6-meter diameter telescope at the European Southern Observatory (ESC) in Chile and the exoplanet survey instrument HARPS*. Ross-128b orbits the star Ross 128 in around 9.9 days per orbit and blackbody temperatures of the planet are 269 K for an Earth albedo (281 K for ExoKyoto) and 213 K for a Venus albedo according to Bonfils et al. 2017, which is classified as habitable (Earth’s blackbody temperature is 255 K).
The star Ross 128, is a red dwarf with a rotation estimated to be more than 120 days, which means that there is only moderate activity and it is unlikely to produce frequent superflares. Becaus eof this, depending on the state of the atmosphere of the planet, liquid water may exist and there is a possiblity it could support life.

A massive telescope scheduled for completion in 2024 called the ELT will begins its observations soon, and it this should be able to study the composition of the planet’s atmosphere to tell us more.


For more information abour Ross-128b, please visit the ExoKyoto Database:

X. Bonfils et al. 2017. A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs. Astronomy & Astrophysics manuscript © ESO

Imaginary Image of Ross 128 b (Proxima Vir b) *With no tidal locking.

The Habitable Zone of Ross 128 b (Proxima Vir b)

The Habitable Zone Orbits of Ross 128 b (Proxima Vir b) (Kopparapu et al.)
According to ExoKyoto, Ross 128b is calculated to be slightly inside the habitable zone limits.

The Habitable Zone Orbits of Ross 128 b (Proxima Vir b) (Kopparapu et al.)
According to ExoKyoto, Ross 128b is calculated to be slightly inside the habitable zone limits.

Ross 128 b (Proxima Vir b) Size Comparison

Ross 128 b (Proxima Vir b) Stellar Window Location

Ross 128 b (Proxima Vir b) Stellar Window Location

55 Cancri e

55 Cancri e is a super-Earth — about twice our planet’s size — that zooms around its star in 18 days. It has a surface temperature of nearly 4,900 degrees Fahrenheit (2,700 degrees Celsius). For a while, it was dubbed the “diamond planet” because scientists suggested that it was composed of diamonds and graphite. While that theory is not as popular today, the planet still remains an interesting object of study due to its high density and its very close proximity to its parent star. Several follow-up studies have yielded more insights about its super-hot surface, as well as its atmosphere.

(Credit: Rina Maeda & SGH Moriyama High School)

Astronomers discovered the planet in 2004 after looking at the spectrum of its parent star, 55 Cancri A, one of two stars in a binary system about 40 light-years from Earth in the constellation Cancer. There are at least four other planets in the same system, mostly discovered before 55 Cancri e. The team (led by the University of Texas at Austin’s Barbara McArthur) discovered subtle tugs on the parent star that could be explained by the presence of yet another planet. While the planet’s existence was challenged by a second research team in 2005, a separate team in 2006 confirmed it.


For more information about 55 Cancri e, please visit the ExoKyoto Database:

Beta Pictoris b

<Imaginary image of Beta Pictoris b>

Beta Pictoris b is located in the Pictoris constellation about 63 light-years from Earth. It orbits the star Beta Pictoris at 13.18 astronomical units.

The planet is about 1.65 times the size and 7 times the mass of Jupiter, it was discovered by direct imaging using European Southern Observatory’s Very Large Telescope.

Beta Pictoris b was discovered by using the Doppler effect on its rotation. As the planet moves further away from the observer, the wavelength of light becomes longer, and as the planet moves closer, the wavelengths become shorter.

Observing this change in wavelength (Doppler shift), we know that Beta Pictoris’ rotation cycle is about 8 hours, and its speed is around 100,000km/hr.

In comparison, Earth’s rotation speed is 1,700km/hr, and Jupiter’s is 47,000km/hr, which is the fastest in the solar system.

Because the planets in Beta Pictoris b’s solar system all tend to be this fast, it is implied that the relationship of speed and mass for this planet could be universal.

Beta Pictoris is a young star at only around 20 million years old, there is a debris disk around the star at about 1000 astronomical units, leading scientists to believe the system is still in progress.

Taking into consideration the passage of time and the planet’s contractions due to cold, the rotation is expected to be very fast.

Also, the planetary systems have 493 exo-comets that were discovered by a research team in France, and each comet has various trajectories that are affected by the planet’s large size and gravitational field. It is thought that the comets were originally one celestial body that broke apart into two groups of comets.

One group of comets released gas and dust due to their vigorous movement, causing them to fly close to the host star, which means that any ice present would be dried up.

The other group of comets move the same way, orbiting the planet, which means they are thought to be from one celestial body that broke apart.

Beta Pictoris is a young system that is still evolving.

What could have been happening in our solar system 45 billion years ago? This is why Beta Pictoris a subject of extremely important research.



Kepler-35(AB) b

(Kepler-35AB bの想像図 前田理那 SGH守山高校ハビタブル研究会)










Kepler-35 bについての情報は こちらから


GJ 1132b

(GJ1132bの想像図   画:清水海羽 守山高校ハビタブル研究会)






GJ 1132 bについての詳しい情報

The Astronomical Journal (2017): “Detection of the Atmosphere of the 1.6 M_⊕ Exoplanet GJ1132b” John Southworth1, Luigi Mancini, Nikku Madhusudhan, Paul Mollière, Simona Ciceri, and Thomas Henning (
BBS NEWS, Science & Environment: Atmosphere found around Earth-sized planet GJ 1132b (,天文: 地球サイズの系外惑星「GJ1132b」に大気 水の存在の可能性も(

(ExoKyoto Stellar Mapを用いて表示したGJ 1132 bの位置)

(ExoKyoto Stellar Mapを用いて表示したGJ 1132 bの位置 Zoom Level 3)

KELT-9 b

(Imaginary Picture of KELT-9 b and its host star KELT-9 (HD195689), credit: Miu Shimizu, Habitable Research Unit – SGH Moriyama High School)
(KELT-9 b と主星KELT-9 (HD195689) の想像図 守山高校ハビタブル研究会 清水海羽 画)


KELT-9 bは、恒星に匹敵するほど熱い惑星として話題になりました。はくちょう座の方向、650光年先のA型星 KELT-9 の周りを周期1.48日で公転しており、質量と半径はそれぞれ木星の2.9倍と1.9倍ほどの、巨大ガス惑星です。約1万度という主星の表面温度の高さ(太陽でも約6千度)と、そこから0.03 au しか離れていない公転軌道の近さ(水星軌道の10分の1以下)ゆえ、この惑星の表面はかなりの高温になっていることが予想されます。

実際に、惑星が主星の後ろ側に隠れる場面を観測した結果、この惑星の昼側は4600 Kという、惑星のイメージを覆すほどの高温環境であることがわかりました。我々の太陽系を含む天の川銀河にある恒星の7割以上を占めると言われるM型星でも、その表面温度は4000度に達しません。つまり、KELT-9 b は惑星でありながら、多くの恒星よりも熱い大気を持っていることになります。この温度になると、水や酸素、二酸化炭素など、惑星の大気には馴染み深い “分子” が存在できないため、この惑星の大気は原子が主成分になっていると考えられます。これまで常識だった「分子を主成分とする惑星大気」とはまったく違う、しかし内側に熱源を持つ恒星の大気とも異なる、全く新しい未知の大気です。



今後、ハッブル宇宙望遠鏡 (HST) や、2018年に打ち上げが予定されるジェームズ・ウェッブ宇宙望遠鏡 (JWST) などの観測によって、大気流出の様子や大気の成分の調査が期待されます。これまであまり調べられてこなかった、高温の星を回る惑星の一生についての、新たな知見につながるかもしれません。

KELT-9 b を発見したKELTサーベイは、これまでのトランジット法による惑星探査計画では明るすぎて調べられなかった恒星をターゲットとし、小型の望遠鏡を用いて全天を探査するプロジェクトです。今回の発見には、日本の成田憲保氏と福井暁彦氏も参加しています。
(文責 石川 裕之 (総合研究大学院大学・国立天文台))
(修正担当 佐々木貴教)

KELT-9 bははくちょう座に位置し、Kepler観測領域の近くにある。主星KELT-9 (HD 195689) は視等級 7.6 スペクトル A0型の星で、太陽系から615 光年離れている。肉眼や双眼鏡でも観測できる星であるので、夏の大三角形とともに機会があれば探してみてはいかがだろうか?

(ExoKyoto Stellar Windowを用いて天球上に表示したKELT-9b & KELT-9 (HD195689), (Kepler領域の星も参考までに表示) )
KELT-9 b の詳しい情報はこちら。