HAT-P-2b
Encyclopedia
HAT-P-2b is an extrasolar planet
detected by the HATNet Project
in May 2007. It orbits a class F star
, (bigger and hotter than the Sun
), located about 440 light-year
s away in the constellation Hercules
. Every 5 days 15 hours, it crosses directly in front of the star
as viewed from Earth.
, while its radius is 0.951 times (135,978 km) that of Jupiter which is not uncommon for a superjovian. Its small size despite the bloating of planet's atmosphere
is caused by the strong gravitational pull of the massive planet pulling towards the center. This indicates that the planet's mean density is two times that of Earth and its surface gravity
is approximately 24 times that on Earth, almost equal to the Sun. The orbit is very eccentric, ranging from 4.90 million miles to 15.36 million miles from the star; if Earth's orbit were as eccentric its distance from the sun would vary from a distance of 0.4837 AU to a distance equivalent to Mars
(1.5163 AU).
In addition to heat from its primary star, tidal heating is thought to have played a significant role in this planet's evolution.
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.
It has been suggested that there is a second outer planet perturbing HAT-P-2 b. This has not so far been proved or disproved.
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
detected by the HATNet Project
HATNet Project
The Hungarian Automated Telescope Network project is a network of six small fully automated "HAT" telescopes. The scientific goal of the project is to detect and characterize extrasolar planets using the transit method. This network is used also to find and follow bright variable stars...
in May 2007. It orbits a class F star
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
, (bigger and hotter than the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
), located about 440 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation Hercules
Hercules (constellation)
Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. Every 5 days 15 hours, it crosses directly in front of the star
Astronomical transit
The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...
as viewed from Earth.
Orbit and mass
The planet's mass has been estimated to be 8.65 times that of JupiterJupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, while its radius is 0.951 times (135,978 km) that of Jupiter which is not uncommon for a superjovian. Its small size despite the bloating of planet's atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
is caused by the strong gravitational pull of the massive planet pulling towards the center. This indicates that the planet's mean density is two times that of Earth and its surface gravity
Surface gravity
The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in...
is approximately 24 times that on Earth, almost equal to the Sun. The orbit is very eccentric, ranging from 4.90 million miles to 15.36 million miles from the star; if Earth's orbit were as eccentric its distance from the sun would vary from a distance of 0.4837 AU to a distance equivalent to Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
(1.5163 AU).
In addition to heat from its primary star, tidal heating is thought to have played a significant role in this planet's evolution.
Rotation
As of August 2008, the most recent calculation of HAT-P-2b's Rossiter-McLaughlin effectRossiter-McLaughlin effect
The Rossiter–McLaughlin effect is a spectroscopic phenomenon observed when either an eclipsing binary's secondary star or an extrasolar planet is seen to transit across the face of the primary or parent star. As the main star rotates on its axis, one quadrant of its photosphere will be seen to be...
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.
It has been suggested that there is a second outer planet perturbing HAT-P-2 b. This has not so far been proved or disproved.