HAT-P-38b

HAT-P-38b, formally named Hiisi, is a transiting exoplanet orbiting the G-type star HAT-P-38 821 light-years from the Solar System in the constellation Triangulum.

Nomenclature

The planet's designation is derived from the host star's designation and the fact that it was the first planet to be discovered around the star, hence the "b" in its name. In 2019, it was selected for the second NameExoWorlds campaign for Finland as part of the IAU's 100th anniversary. The approved name for the planet is Hiisi, which represents sacred localities and later evil spirits from Finnic mythology.^[4] It shares this name with the binary companion of the trans-Neptunian object 47171 Lempo.

Discovery

The transits of HAT-P-38 were first observed between August and November 2010 by using two telescopes related to the HATNet Project: The HAT-6 telescope in Arizona and the HAT-8 telescope in Hawaii.^[1] Astronomers observed a transit curve with a period of 4.64033 days.^[1] Later observations of the star's radial velocity using the High Dispersion Spectrograph confirmed HAT-P-38b's planetary status and it also yielded its mass in the process.^[1]

Properties

HAT-P-38b is a hot Saturn that takes over 4 days to circle its host star in a relatively circular and tight orbit; it has a separation of 0.0519 astronomical units. HAT-P-38b has 26.6% the mass of Jupiter, which is similar to that of Saturn. However, tidal heating from HAT-P-38 causes the planet to bloat to 82.5% the radius of Jupiter. It has an equilibrium temperature of 1,082 K. The planet has a density of 590 kg/m³, which is half of that of water (the density of water is 1,000 kg/m³). The average gravitational acceleration of the planet is 9.77 m/s², which is slightly smaller compared to the gravitational acceleration at the surface of the Earth.

In 2017, the atmospheres of HAT-P-38b and WASP-67b were compared since both planets had similar properties.^[5] Giovanni Bruno and colleagues detected water vapor in both planets, with HAT-P-38b having the greater abundance in its atmosphere.^[5] This indicates that the atmosphere lacks clouds or hazes.^[6]

References

• v
• t
• e

Constellation of Triangulum

• List of stars in Triangulum
• Triangulum in Chinese astronomy

Stars

Bayer	α (Mothallah) β γ δ ε ι
Flamsteed	1 5 7 10 11 12 13 14 15
Variable	R V X RW XX
HR	490 523
HD	9446 13189
Other	B324 HAT-P-38 (Horna) LSPM J0207+3331 M33-013406.63 M33 X-7 Romano's Star Var 83

Exoplanets	HAT-P-38b (Hiisi) HD 9446 b c HD 13189 b

Nebulae	588 595 604

Galaxies

NGC	Triangulum Galaxy 608 634 669 670 672 684 688 736 739 740 750 751 769 777 784 804 805 819 855 860 861 890 925 931 940 941 953 959 970 973 1060
Numbered	I II
Other	Arp 166 RD1

Category