HAT-P-7b is an extrasolar planet discovered in 2008. It orbits very close to its host star, and is both larger and more massive than Jupiter. Due to the extreme heat it receives from its star, the dayside temperature is predicted to be 2730 K, while nightside is at 2235 K. HAT-P-7b is also one of the darkest planets ever observed, with an albedo of less than 0.03—meaning it absorbs more than 97% of the visible light that strikes it.
Discovery
The HATNet Project telescopes HAT-7, located at the Smithsonian Astrophysical Observatory’sFred Lawrence Whipple Observatory in Arizona, and HAT-8, installed on the rooftop of Smithsonian Astrophysical Observatory’s Submillimeter Array building atop Mauna Kea, Hawaii, observed 33,000 stars in HATNet field G154, on nearly every night from late May to early August 2004. The light curves resulting from the 5140 exposures obtained were searched for transit signals and a very significant periodic drop in brightness was detected in the star GSC 03547–01402, with a depth of approximately 7.0, a period of 2.2047 days, and a duration of 4.1 hours. Fortunately HAT-P-7 was located in the overlapping area between fields G154 and G155 allowing the transit to be independently confirmed by the HAT-6 and HAT-9 telescopes which observed the neighbouring field G155. Field G155 was observed from late July 2004 to late September 2005 gathering an additional 11,480 exposures for a total of 16,620 data points.
History
The GSC 03547-01402 system was within the initial field of view of the Kepler Mission spacecraft, which confirmed the transit and orbital properties of the planet with significantly improved confidence and observed occultation and light curve characteristics consistent with a strongly absorbing atmosphere with limited advection to the night side. In testing itself on HAT-P-7b, Kepler proved it was sensitive enough to detect Earth-like exoplanets. On July 4, 2011, HAT-P-7b was the subject of the Hubble Space Telescope's one millionth scientific observation.
Physical characteristics
In August 2009, it was announced that HAT-P-7b may have a retrograde orbit, based upon measurements of the Rossiter–McLaughlin effect. This announcement came only a day after the announcement of the first planet discovered with such an orbit, WASP-17b. The study in 2012, utilizing a Rossiter–McLaughlin effect, have determined the planetary orbit inclination with the respect to the rotational axis of the star, equal to 155°. In January 2010, it was announced that ellipsoidal light variations were detected for HAT-P-7b, the first detection of such kind. This method analyses the brightness variation caused by the rotation of a star as its shape tidally distorted by the planet.
Weather
In December 2016, a letter published in Nature Astronomy by Dr. David Armstrong and his colleagues described evidence of strong wind jets of variable speed on HAT-P-7b. High variation in wind speed would explain similar variations in light reflected from HAT-P-7b's atmosphere. In particular, the brightest point on the planet shifts its phase or position on a timescale of only tens to hundreds of days, suggesting high variation in global wind speeds and cloud coverage. Condensation models of HAT-P-7b predict precipitation of Al2O3on the night side of the planet's atmosphere. Because corundum gems are rubies and sapphires, one can describe the hypothetical weather on the planet's night side as "raining rubies and sapphires."
