 Size comparison of HAT-P-7b (gray) with Jupiter. | |
| Discovery[1] | |
|---|---|
| Discovered by | HATNet Project |
| Discovery site | HAT-7 telescope atFred Lawrence Whipple Observatory and HAT-8 atMauna Kea Observatory |
| Discovery date | March 5, 2008 |
| Transit | |
| Designations | |
| Kepler-2b,KOI-2.01[2] | |
| Orbital characteristics | |
| 0.03813±0.00036AU | |
| Eccentricity | <0.0040[3] |
| 2.204737±0.000017[4]d | |
| Inclination | 85.7+3.5 −3.1 |
| Star | HAT-P-7 |
| Physical characteristics | |
| 1.64±0.11RJ[5] | |
| Mass | 1.806±0.036[3]MJ |
Meandensity | 0.54gcm−3 |
| 17.36 m/s2 (57.0 ft/s2) 1.77g | |
| Temperature | 2730+150 −100K |
HAT-P-7b (orKepler-2b) is anextrasolar planet discovered in 2008. It orbits very close toits host star and is larger and more massive than Jupiter. Due to the extreme heat that it receives from its star, the dayside temperature is predicted to be 2,630–2,880 K (4,270–4,720 °F; 2,360–2,610 °C), while nightside temperatures are 2,211–2,238 K (3,520–3,569 °F; 1,938–1,965 °C).[6] HAT-P-7b is also one of the darkest planets ever observed, with analbedo of less than 0.03—meaning it absorbs more than 97% of the visible light that strikes it.[7]
TheHATNet Project telescopes HAT-7, located at theSmithsonian Astrophysical Observatory'sFred Lawrence Whipple Observatory inArizona, and HAT-8, installed on the rooftop of Smithsonian Astrophysical Observatory'sSubmillimeter Array building atopMauna 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 fortransit signals and a very significant periodic drop in brightness was detected in the star GSC 03547–01402 (HAT-P-7), with a depth of approximately 7.0millimagnitude, a period of 2.2047 days, and a duration of 4.1 hours.[1]
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 (Arizona) and HAT-9 (Hawaii) telescopes which observed the neighboring 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.[1]
The GSC 03547-01402 system was within the initialfield of view of theKepler Mission spacecraft,[1] which confirmed thetransit and orbital properties of the planet with significantly improved confidence and observedoccultation and light curve characteristics consistent with a strongly absorbing atmosphere with limitedadvection to the night side. In testing itself on HAT-P-7b, Kepler proved it was sensitive enough to detect Earth-like exoplanets.[8]
On July 4, 2011, HAT-P-7b was the subject of theHubble Space Telescope's one millionth scientific observation.[9]
In August 2009, it was announced that HAT-P-7b may have aretrograde orbit, based upon measurements of theRossiter–McLaughlin effect.[10][11][12] This announcement came only a day after the announcement of the first planet discovered with such an orbit,WASP-17b. A study in 2012, utilizing the Rossiter–McLaughlin effect, determined the planetary orbit inclination with respect to the rotational axis of the star, equal to 155±37°.[13]
It is believed HAT-P-7b origined in a much wider orbit around its host star (around 3 AU) but was doomed to its current close and retograde orbit due to gravitational interactions with HAT-P-7 C, ared dwarf which orbits HAT-P-7 A at an orbital separation of 32 astronomical units in a highly-eccentric orbit. HAT-P-7 A also has a wider companion, HAT-P-7 B, at a separation of 700 AU. This outer star may have started aKozai mechanism by exciting the eccentricity of the inner companion, which on its turn excited the eccentricity of the primordial planet, untiltidal forces circularized the planet's orbit and HAT-P-7b migrated to its current position.[14]
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 is tidally distorted by the planet.[15]
In December 2016, a letter published inNature Astronomy by Dr. David Armstrong and his colleagues described evidence of strong wind jets of variable speed on HAT-P-7b.[16] 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 Al2O3 (corundum) on the night side of the planet's atmosphere. The clouds themselves are likely made up ofcorundum, the mineral which formsrubies andsapphires.[16][17]
Media related toHAT-P-7b at Wikimedia Commons