HAT-P-1b
Encyclopedia
HAT-P-1b is an extrasolar planet
orbiting the Sun
like star
HAT-P-1, also known as ADS 16402 B
. HAT-P-1 is the dimmer component of the ADS 16402
binary star
system. It is located 453 light year
s away from Earth
in the constellation Lacerta
. HAT-P-1b is among the least dense of any of the known extrasolar planets.
s of the parent star by orbiting planets. As the planet passes in front of its parent star (as seen from Earth), it blocks a small amount of the light reaching us from the star. HAT-P-1b was first detected by a dip of 0.6% in the light from the star. This enabled determination of the planet's radius
and orbital period
. The discovery was made by the HATNet Project
(Hungarian Automated Telescope Network) using telescope
s in Arizona
and Hawaii
and announced on September 14, 2006.
s to complete. It therefore falls into the category of hot Jupiter
s. At only 8.27 million kilometers from the star, tidal force
s would circularise the orbit unless another perturbing body exists in the system. At the present time, the existing measurements are not sufficient to determine the orbital eccentricity
, so a perfectly circular orbit has been assumed by the discoverers. However, the eccentricity of the planet was calculated to be no greater than 0.067.
In order to determine the mass
of the planet, measurements of the star's radial velocity
variations were made by the N2K Consortium
. This was done by observing the Doppler shift in the star's spectrum
. Combined with the known inclination
of the orbit as determined by the transit observations, this revealed the mass of the planet to be 0.53±0.04 times that of Jupiter.
and so spin-orbit angle was that of Johnson. This is +3.6 ± 2.0 degrees.
, most likely composed primarily of hydrogen
and helium
. The planet would thus have no well-defined surface. Current theories predict that such planets formed in the outer regions of their solar systems and migrated
inwards to their present orbits.
HAT-P-1b is significantly larger than predicted by theoretical models. This may indicate the presence of an additional source of heat within the planet. One possible candidate is tidal heating from an eccentric orbit, a possibility which has not been ruled out from the available measurements. However, another planet with a significantly inflated radius, HD 209458 b
, is in a circular orbit.
An alternative possibility is that the planet has a high axial tilt
, like Uranus
in our solar system. The problem with this explanation is that it is thought to be quite difficult to get a planet into this configuration, so having two such planets among the set of known transiting planets is problematic.
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...
orbiting 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...
like star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
HAT-P-1, also known as ADS 16402 B
ADS 16402
ADS 16402 is a binary star system, composed of two sun-like stars located 450 light-years away in the constellation Lacerta. The two stars are separated by 1500 AUs. The star system is estimated to be 3.6 billion years old...
. HAT-P-1 is the dimmer component of the ADS 16402
ADS 16402
ADS 16402 is a binary star system, composed of two sun-like stars located 450 light-years away in the constellation Lacerta. The two stars are separated by 1500 AUs. The star system is estimated to be 3.6 billion years old...
binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
system. It is located 453 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 from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
in the constellation Lacerta
Lacerta
Lacerta is one of the 88 modern constellations defined by the International Astronomical Union. Its name is Latin for lizard. A small, faint constellation, it was created in 1687 by the astronomer Johannes Hevelius. Its brightest stars form a "W" shape similar to that of Cassiopeia, and it is thus...
. HAT-P-1b is among the least dense of any of the known extrasolar planets.
Discovery
HAT-P-1b was detected by searching for astronomical transitAstronomical 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...
s of the parent star by orbiting planets. As the planet passes in front of its parent star (as seen from Earth), it blocks a small amount of the light reaching us from the star. HAT-P-1b was first detected by a dip of 0.6% in the light from the star. This enabled determination of the planet's radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
and orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
. The discovery was made 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...
(Hungarian Automated Telescope Network) using telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s in Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
and announced on September 14, 2006.
Orbit and mass
HAT-P-1b is located in a very close orbit to its star, taking only 4.47 dayDay
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
s to complete. It therefore falls into the category of hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
s. At only 8.27 million kilometers from the star, tidal force
Tidal force
The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force per unit mass exerted on one body by a second body is not constant across its diameter, the side nearest to the second being more attracted by it than the side...
s would circularise the orbit unless another perturbing body exists in the system. At the present time, the existing measurements are not sufficient to determine the orbital eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
, so a perfectly circular orbit has been assumed by the discoverers. However, the eccentricity of the planet was calculated to be no greater than 0.067.
In order to determine the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the planet, measurements of the star's radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
variations were made by the N2K Consortium
N2K Consortium
The N2K Consortium is a collaborative multinational effort by American, Chilean and Japanese astronomers to find additional extrasolar planets around stars that are...
. This was done by observing the Doppler shift in the star's spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
. Combined with the known inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of the orbit as determined by the transit observations, this revealed the mass of the planet to be 0.53±0.04 times that of Jupiter.
Rotation
As of August 2008, the most recent calculation of HAT-P-1b'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 Johnson. This is +3.6 ± 2.0 degrees.
Characteristics
As evidenced by its high mass and planetary radius, HAT-P-1b is a gas giantGas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
, most likely composed primarily of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
. The planet would thus have no well-defined surface. Current theories predict that such planets formed in the outer regions of their solar systems and migrated
Planetary migration
Planetary migration occurs when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite's orbital parameters, especially its semi-major axis...
inwards to their present orbits.
HAT-P-1b is significantly larger than predicted by theoretical models. This may indicate the presence of an additional source of heat within the planet. One possible candidate is tidal heating from an eccentric orbit, a possibility which has not been ruled out from the available measurements. However, another planet with a significantly inflated radius, HD 209458 b
HD 209458 b
HD 209458 b is an extrasolar planet that orbits the Solar analog star HD 209458 in the constellation Pegasus, some 150 light-years from Earth's solar system, with evidence of water vapor....
, is in a circular orbit.
An alternative possibility is that the planet has a high axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
, like Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
in our solar system. The problem with this explanation is that it is thought to be quite difficult to get a planet into this configuration, so having two such planets among the set of known transiting planets is problematic.
