HD 240237 b is a super-Jupiter exoplanet orbiting the K-type giant star HD 240237 about 4,900 light-years (1,500 parsecs, or nearly 4.6×1016 km) away from Earth in the constellation Cassiopeia. It orbits outside of the habitable zone of its star at a distance of 1.9 AU. The exoplanet was found by using the radial velocity method, from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star. The planet has a mildly eccentric orbit.
| Discovery | |
|---|---|
| Discovery date | 9 October 2011 |
Detection method | Doppler spectroscopy |
| Orbital characteristics | |
Semi-major axis | 1.9 AU (280,000,000 km) |
| Eccentricity | 0.4 (± 0.1) |
Orbital period (sidereal) | 745.7 (± 13.8) d |
Time of periastron | 54,292 ± 28.3 |
Argument of periastron | 108.1 ± 21.8 |
| Semi-amplitude | 91.5 ± 12.8 |
| Star | HD 240237 (BD+57° 2714) |
| Physical characteristics | |
Mean radius | ~1.11 RJ |
| Mass | 5.3[1] MJ |
| Temperature | 781 K (508 °C; 946 °F) |
HD 240237 b is a "super-Jupiter", an exoplanet that has a radius and mass larger than that of the gas giants Jupiter and Saturn. It has a temperature of 781 K (508 °C; 946 °F), around that of the surface temperature of Venus.[2] It has an estimated mass of around 5.3 MJ and a potential radius of around 9% larger than Jupiter (1.11 RJ, or 12.2 REarth) based on its mass, since it is more massive than the jovian planet.
The planet orbits a (K-type) giant star named HD 240237. It has exhausted the hydrogen supply in its core and is currently fusing helium. The star has a mass of 1.69 M☉ and a radius of around 32 R☉. It has a surface temperature of 4361K and is likely 2 billion years old based on its mass and evolution. In comparison, the Sun is about 4.6 billion years old[3] and has a surface temperature of 5778 K.[4]
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 8.19. Therefore, HD 240237 is too dim to be seen with the naked eye.
HD 240237 b orbits its star with nearly 331 times the Sun's luminosity (331 L☉) every 746 days at a distance of 1.9 AU (compared to Mars' orbital distance from the Sun, which is 1.52 AU). It has a mildly eccentric orbit, with an eccentricity of 0.4.
The planet was detected through Doppler spectroscopy, the method of observing exoplanets through the measurement of radial velocities of a star. If there is a wobble, it could mean that there is a possible planetary companion orbiting it.
Observations were taken with the Hobby–Eberly Telescope equipped with the High-Resolution Spectrograph in a queue-scheduled mode.[1] From July 2004 to October 2009, 40 epochs were measured, with SNR values ranging from 161–450. These observations eventually led the team to conclude that there was in fact a planetary companion orbiting around HD 240237, and they estimated its parameters to be a mass of 5.3 times that of Jupiter, an orbital period of 746 days, an eccentricity of 0.4, and a semi-major axis of 1.9 AU. The discovery, along with 2 other exoplanets, were announced on October 9, 2011.[1]
