HATS-17b

HATS-17b is a warm planet with a mass close to that of  Jupiter, that orbits around a Sun-like star about once every 16.255 days. The host star of HATS-17b has ~1.13 times the mass and ~1.09 times the radius of the Sun. Additionally, the host star’s surface temperature is estimated to be 5846 ± 78 K and the luminosity is about 25 percent greater than the Sun. By measuring how much light the plant blocks when it transits its host star, the radius of HATS-17b is estimated to be 0.777 ± 0.056 times the radius of Jupiter.

When radial velocity measurements were used, HATS-17b seemed to be 1.338 ± 0.065 times the mass of Jupiter. Knowing the size and mass of the planet, the density of HATS-17b can be calculated and is found to be ~3.50 g/cm³, roughly 30 percent denser than aluminum. The density of HATS-17b is remarkably high for an object with its mass. For comparison, the mean density of Jupiter is 1.326 g/cm³.

Interior models of HATS-17b suggest that ~50 percent of the planet’s mass is composed of a massive core of heavier elements. This works out to be around 200 times the mass of Earth. The massive core of HATS-17b is consistent with the high metallicity of its parent star. A star’s metallicity refers to the abundance of elements heavier than hydrogen and helium. The host star of HATS-17b has roughly twice the metallicity of the Sun and a more metal-rich protoplanetary disk can form massive cores more efficiently.

The host star HATS-17 has an apparent magnitude of 12.4, with an absolute magnitude of 4.75. It is 1.13 times more massive and 1.09 times larger compared with our sun. The surface temperature is 5846 K with a spectral type of G. In this planetary system, the extrasolar planet HATS-17 b orbits around the star HATS-17 with its orbital distance of 0.1308.

Journal Articles

1.) HATS-17b: A TRANSITING COMPACT WARM JUPITER IN A 16.3 DAYS CIRCULAR ORBIT

WEB Articles

1.) HATS-17b is a Warm-Jupiter Denser than Aluminium

2.) Our research: HATS-17b: a transiting compact warm Jupiter in a 16.3 days circular orbit

HD 219134 b

While it may not have a catchy name, HD 219134 b is the nearest known rocky planet outside our solar system and it deserves our attention.

The planet orbits the star HD 219134, which is visible to the human eye near the constellation Cassiopeia, only 21 light-years from the sun. Like our own solar system with Mercury, Venus, Earth, and Mars, HD 219134 b has three planetary siblings.

What makes HD 219134 b special is how near it is to us – relatively speaking. We can learn a lot about these close exoplanets by using techniques that would be difficult or impossible for those at greater distances.

For example, using a technique called the radial velocity method it’s possible to deduce an exoplanet’s mass by measuring tiny movements of the star caused by the exoplanet’s gravitational pull. This reveals that HD 219134 b has a mass of between four and five times that of the Earth, making it a type of exoplanet known as a “Super-Earth.”

Journal Articles

1.) Bayesian analysis of interiors of HD 219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55 Cnc e, and HD 97658b using stellar abundance proxies

2.) The HARPS-N Rocky Planet Search I. HD 219134 b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun

3.) A SIX-PLANET SYSTEM ORBITING HD 219134

WEB Articles

1.) It’s not Earth 2.0, but our new rocky neighbour is a planet worth watching

HD219134 c

HD 219134 c is a Super-Earth exoplanet that orbits a K-type star. Its mass is about 4.36 times Earth’s, it takes 6.8 days to complete one orbit of its star, and it is 0.0653 AU from its host star. Its discovery was announced in 2015.

Journal Articles

1.) A 12-YEAR ACTIVITY CYCLE FOR THE NEARBY PLANET HOST STAR HD 219134

2.) A SIX-PLANET SYSTEM ORBITING HD 219134

3.) Secondary atmospheres on HD 219134 b and c

WEB Articles

1.) HD 219134: A Nearby System with Multiple Transits

2.) HD 219134 c

Kepler 442 b

<Imaginary Picture of Kepler-442 b     Credit:  M Masada, SGH Moriyama High School>

Kepler-442b orbits a red dwarf star that is smaller and cooler than our sun.

The exoplanet completes one orbit every 112 days and gets about two-thirds as much light as Earth. Scientists give it a 97 percent chance of being in the habitable zone.

Kepler-442b is 1,100 light-years away and about one-third larger than Earth; its chance of being rocky is 60 percent.

The host star Kepler 442 has an apparent magnitude of 15.3, with an absolute magnitude of 7.63. It is 0.61 times more massive and 0.60 times larger than our sun. The surface temperature is 4402 K with a spectral type of K5. The exoplanet Kepler-442 b orbits around the star Kepler 442 at an orbital distance of 0.4090.

Journal Articles

1.) VALIDATION OF TWELVE SMALL KEPLER TRANSITING PLANETS IN THE HABITABLE ZONE

2.) Exosolar photovoltaics: Exploring the detailed balance of other star and planetary systems

WEB Articles

1.) Kepler-442b is more habitable than Earth

2.) Kepler-438b and 442b: Are These the Planets We’re Looking For?

3.) HIRAETH: KEPLER-442B

Kepler 438 b

Discovered in January 2015, Kepler-438b looked like an excellent candidate for a habitable planet. The planet fits the two key characteristics for a Kepler candidate to a T. The first of these is that the planet has to be rocky, like Earth or Mars, rather than gaseous, like Jupiter or Saturn. The second is that it has to orbit its star in the habitable zone, where temperatures are neither too hot nor too cold to support life.

Kepler-438b It is only 12 percent bigger than Earth and receives about 40 percent more light. Kepler-438b is similar in temperature to the Earth, but it is much closer to its star, a cooler Red Dwarf called Kepler-438. Kepler-438b orbits Kepler-438 every 35 days.

The research team, led by David Armstrong of the University of Warwick’s Astrophysics Group, has discovered that this star is very active, shooting superflares and associated coronal mass ejections every few hundred days. Using photometry, the team detected excess radiation caused by the star’s flares.

The coronal mass ejections from the star, 10 times more powerful than any on record made by our sun, may have stripped the planet of its atmosphere.

Kepler 438 b orbits the star Kepler 438, which is located 472.9 (145 parsecs) away from our solar system. Its apparent magnitude is 15 and its absolute magnitude is 9.2. It is 0.5 times the mass and 0.5 times the radius of our sun, it is also an M1 type star, at 3748 degrees kelvin.

Kepler-438系は、こと座に位置し地球から約470光年の位置にある惑星系で、主星はK型主系列星(温度3748K、質量0.54太陽質量、半径0.62太陽半径)に分類されます。星の年齢は約44億歳と考えられていて、太陽とほぼ同年齢です。なお、この星は磁気活動が強く、Kepler宇宙望遠鏡の測光観測データの解析からスーパーフレアが多数観測されています。 この系では2015年1月にKepler宇宙望遠鏡のトランジット観測により、惑星Kepler-438bが発見されました。Kepler-438bは、軌道周期が35日、半径が1.12地球半径・1.3地球半径であり、惑星の表面に液体の水が存在できるハビタブルゾーン内に存在する岩石惑星の可能性がかなり高いと考えられています。一方で前述の様にこの系の主星は超巨大なフレア(スーパーフレア)を頻発しているため、大気中に強い紫外線・放射線が降り注いだり、フレアに付随するコロナ質量放出衝突で放出されたガス・プラズマが大気衝突に頻繁に衝突する事が考えられ、大気散逸過程や詳細なはビタビリティに関しては、今後の詳しい観測・理論研究が大変重要と考えられます。

論文：https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stv2419

ジャーナル記事

1.) VALIDATION OF TWELVE SMALL KEPLER TRANSITING PLANETS IN THE HABITABLE ZONE

2.) Where are they?

WEB記事

1.) Farewell to hope of life on Kepler-438b

2.) Kepler-438b and 442b: Are These the Planets We’re Looking For?

3.) Could Humans Survive On Kepler-438b?