HAT-P-2b

Physical properties

The planet's mass has been estimated to be 8.7 times that of Jupiter, while its diameter is 1.157 times Jupiter's. Its small size, despite the bloating of the planet's atmosphere, is caused by the strong gravity of the planet. The planetary atmosphere has indeed the smallest scale height, equal to 26km, among exoplanets with measurable atmospheres as of 2021.

This indicates its mean density is twice that of Earth and its surface gravity approximately 24 times that of Earth, almost equal to the Sun.

In addition to heat from its primary star, tidal heating is thought to have played a significant role in this planet's evolution.

Orbit

The planetary orbital period is 5 days 15 hours, and its inclination is such that it crosses directly in front of the star as viewed from Earth. The orbit is very eccentric, ranging from 4.90 million to 15.36 million miles from the star.

As of August 2008, the most recent calculation of HAT-P-2b's Rossiter–McLaughlin effect and so spin-orbit angle was that of Winn in 2007 but Loeillet has in 2008 disputed it. For Winn, this is +1 ± 13 degrees. The study in 2012 determined the planetary orbit is probably aligned with the equatorial plane of the star, with misalignment equal to 9°.

Other planets in the system

It has been suggested that there is a second outer planet perturbing HAT-P-2b. In 2023, the presence of a second planet, HAT-P-2c, was confirmed.

References

References

1. "Approved names".
2. "International Astronomical Union {{!}} IAU".
3. (2021). "Evidence for disequilibrium chemistry from vertical mixing in hot Jupiter atmospheres". Astronomy & Astrophysics.
4. Jackson, Brian. (2008). "Tidal Heating of Extra-Solar Planets". Astrophysical Journal.
5. Joshua N. Winn. (2008). "Measuring accurate transit parameters". Proceedings of the International Astronomical Union.
6. Winn. (2007). "Spin-Orbit Alignment for the Eccentric Exoplanet HD 147506b". Astrophysical Journal Letters.
7. (2012). "Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments". The Astrophysical Journal.
8. (2007). "HD 147506b: A Supermassive Planet in an Eccentric Orbit Transiting a Bright Star". The Astrophysical Journal.
9. (2017). "The GAPS Programme with HARPS-N at TNG . XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets". Astronomy and Astrophysics.
10. (2007-05-01). "Astronomers find super-massive planet". [[Harvard-Smithsonian Center for Astrophysics]].
11. de Beurs, Zoë L.. (October 2023). "Revisiting Orbital Evolution in HAT-P-2 b and Confirmation of HAT-P-2 c". The Astronomical Journal.
12. (2013). "Orbital Phase Variations of the Eccentric Giant Planet HAT-P-2b". The Astrophysical Journal.
13. (2008). "Refined parameters and spectroscopic transit of the super-massive planet HD 147506b". Astronomy and Astrophysics.
14. (2010). "Refined stellar, orbital and planetary parameters of the eccentric HAT-P-2 planetary system". Monthly Notices of the Royal Astronomical Society.