Exoplanetary Scratchpad

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Hat-P-2b (aka HD 147506b) is the most massive measured exoplanet discovered that is clearly not a Brown Dwarf and the first transiting Hot Super Planet discovered. It is the first known transiting planet with a significantly eccentric orbit and experiences significant seasons. It briefly held the record of furthest out transiting planet.

HD Hat-P-2 System Web Pages

HD Hat-P-2 System Artwork

HD Hat-P-2 System In the News

Massive Planet Discovered (2007)
HAT-P-2b: A Super-Massive Planet in an Eccentric Orbit - Extrasolar Visions BBS Thread HAT-P-2b: ‘A Really Weird Planet’ - Centauri Dreams BLOG

Atmosphere Modelled (2007)

Parameters Refined (Jun 2007)

HD Hat-P-2 System Fun Links

System Factoids

  • 440 light years away
  • Hot star with one or two planets
  • In the constellation Hercules
  • 4th brightest star that has a transiting planet
  • Visual Magnitude of 8.7, visible in small 3 inch telescopes
  • 2.7 Giga years old
  • Almost twice as large as the Sun (1.8 RS)
  • Mass is 1.3 MS.

Hat-P-2 Star Factoids

  • Star is also known as HD 147506.
  • A hot White Main Sequence Star (F8 V)
  • Almost twice as big as the Sun.

Planet b Factoids

  • Planet so unusual that its discoverers at first thought it was a false alarm.

Physical Characteristics

  • The most massive measured planet discovered so far.
  • Nicknamed "the heavyweight champion of extrasolar planets".
  • When first discovered, it was thought its Mass was 8.17 MJ and Radius 1.18RJ.
  • When first discovered, it was believed its density was as great as a terrestrial planet (6.6 gcm^-3, even though it is likely made up of hydrogen and helium.
  • Updated measurements give it Mass of 8.64 Jupiter, radius of 0.954, and an even higher density of 12.41 g cm^-3.
  • Density is now between that of a typical hot jupiter (1 g cm^-3) and low mass star (50 g cm^-3).
  • Updated surface gravity is 227 m s^-1.
  • Its measurements conform to current theory
  • The first discovered transiting planet that is not a Hot Jupiter. This is much larger and denser than a Jupiter class planet.
  • If it had 50% more mass, it would start limited fusion and be a Brown Dwarf.
  • Has greatest surface gravity of any measured planet, 14 time's Earth's.
  • Per earlier measurements, a 150 pound person would weigh 2100 pounds on its cloud tops.
  • Per earlier measurements Surface gravity is 5 times that of any other transiting exoplanet.

Orbit Characteristics

  • If Earth's orbit was as eccentric, it would extend from Mercury to Mars.
  • Orbits in an eccentric orbit near its star (e = 0.5).
  • No other known planet is as close in with such a high eccentricity (all other transiting planets are rather circular).
  • Its short period of 5.63 days is actually the longest of all known transiting planets and its transits last longer than any other.
  • Ranges from 0.03 AU to 0.1 AU (a = 0.06 AU)
  • The difference in heat it receives from its star is 9 times from periastron to apastron.
  • Temperatures range from 1000 C to 2000 C.

Hypothetical Outer Planet

  • An outer planet could explain the great eccentricity of planet b
  • There is no other evidense supporting or refuting this planet's existance

Map of HD 147506 System

0.00 AU - <Star>
x.xx AU - <periapsis/semi-major-axis/apapsis of sample planet>
x.xx AU - <habitability zone/stability zone/disk feature positions>

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