CoRoT 9b: A Temperate Jovian Exoplanet
An international team of astronomers has discovered a new exoplanet about 1500 light years away from us. The jovian planet (0,83 mJup) orbits his host star in the constellation of Serpent (snake), in a mercury-type, nearly circular orbit.
The scientist-team used CoRoT, the European Space Telescope designed to detect exoplanets by transit-method.
CoRoT (Convection, Rotation and planetary Transits), the European space telescope , hunting for exoplanets. Source: cnes
Every time an exoplanet passes by the line of sight between his host star and the telescope of CoRoT, the planet slightly impairs the star´s light. The time between this repetitive reductions in stellar luminosity indicates at the period of the planet, while the extent of these reductions gives a hint at the size of the planet.
Transit of CoRoT 9b in front of host star (left). Light-curve of transit (right). Sources: ESA, DLR
Although CoRoT 9b circulates its host star only about the distance of Mercury in our Solar System, it is by far the largest orbit of any transiting planet found up to the present day.
The discovery was verified byDoppler-method, using the high-resolution HARPS spectrometer on the European Southern Observatory (ESO) 3.6-metre telescope in Chile. In a planetary system star and planet are constantly revolving their balance point (combined center of gravity in planetary system). This balance point is almost always located inside the star itself, because usually a star is much more massive than its planet. The star´s small „inside-orbit“ around balance point is visible as a minimal wobble, going hand in hand with little variations in radial velocity (speed towards or away from telescope). These littel variations in radial velocity cause a tiny alternating shift of the star´s spectral lines due to the Doppler effect. The frequency of spectral lines is higher than normal during radial approach (blueshift) and it is lower during radial recession (redshift). That´s why during approach the electromagnetical waves are compressed, during recession they are stretched.
The Doppler-method allows to detect an exoplanet by measuring periodical variations in radial velocity of the host star. Source: ESO
Nowadays extremely small variations of radial velocity can be detected, allowing to find exoplanet down to only a few earth masses! If the orbit of the exoplanet is inclined to the line of sight, the Doppler method basically undervalues the mass of the detected exoplanet. Therefore this method can only estimate an exoplanet´s minimum mass.
But combining Transit- and Doppler-method, astromomers are able to determine accurately inclination and planet´s mass. With mass and size they calculate density and thereby even the probalble composition of the exoplanet.
The new exoplanet CoRoT 9b has a radius a little more than Jupiter, but only 84% of its mass. This results in a density of 0,9g/ccm, or two-thirds that of Jupiter.
CoRoT 9b is sufficiently far from its host star to prevent tidal-locked orbit. According to calculations of scientist-team the new exoplanet has a normal day-night cycle. Tidal forces are created by weakening of the star´s gravitantional field from the front to back of a planet. When the difference of gravity is great enough, the tidal forces brake planetary circumgyration until the planet shows one face to the star. Tidal forces can also heat the interior of a planet, increasing its vulcanism.
As a results of its distance to host star, its blanket of clouds and its normal circumgyration CoRoT 9b probably has moderate temperatures, so that the planet could hold water in liquid state.
More than 30 years ago, well-known american atronomer Carl Sagan (1934-1996) and astrophysicist Edwin Ernest Salpeter (1924-2008) speculated on bubble-life. That means gas-inflated organism, floating in well-temperated layers in dense atmospheres of jovian planets. These lifeforms might subsist on autotrophic microorganism, while floating hunters feed them for theit part.
Bubble-life in the atmospheres of jovian planets? Source: COSMOS, Carl Sagan (1980)
On Earth, life uses water not only as a medium for its enzyme facilitated metabolism but also as a medium for all associated transport-processes. In the case of jovian bubble-life, gas might partly fill the role of water: The reactants for metabolism move inside the bubble, while enzymes located at their inner surfaces catch them as they pass by.
In an atmosphere where liquid water exists only as droplets, enzymes might evolve specific sites where condensed water droplets could adhere. Thus the enzymes could work efficiently even without the permanent presence of liquid water. CoRoT 9b, might it be a candidate planet for bubble-life?
Jens Christian Heuer