|
The significant number of giant planets that orbit their stars within the habitable zone is resulting in new possibilities in the search for life; the possibility of finding habitable moons. Until now the search has focused on Earth-like planets located within the habitable zone of their star, but there is no reason why a satellite of a giant planet could not be massive enough to retain an atmosphere, and, if temperatures permit, liquid water on the surface.
To look into this possibility more closely three different models (by David Kipping, Luis Tusnski with Adriana Valio, and
András Pál) have recently been proposed, that based on simulations, have provided useful information on what scenarios may lead to moons able to support life.
The minimum mass for a habitable moon should be around 1/3 the mass of the Earth, so at least three times the mass of Mars, otherwise the gravity is not strong enough to retain a sufficiently dense atmosphere. In addition, the distance between the super-moon and the planet needs to be sufficient so as not to generate devastating tides.
The way to detect such moons would be via the transits across the disk of the host star, in which case the moon would cause a small additional dimming of the star light on top of that caused by the primary occultation by the giant planet.
The models proposed are able to predict the various light curves that would result from the transits of giant planets with large moons, whether or not these have orbits in the same plane as that of the planet.
The main problem in detecting them is the possible presence of spots on the photosphere of the star, that could mimic the signal of a moon. As with the planets themselves, this can be overcome by correlating the light curves with the almost imperceptible motion of the star as a result of the gravitational influence of the planet/moon system. Prolonged observations of the light curve, such as those made by Kepler, help eliminate such spurious signals from the data.
|
|
|
by Michele Ferrara & Marcel
Clemens |
credit:
NASA/MNRAS |
|
