Movie: Talk at Kavli Institute of Theoretical Physics
Talk at the KITP, 26.3.2010, Santa Barbara, within the workshop Exoplanets Rising: Astronomy and Planetary Science at the Crossroads. ( Coordinators: Adam Burrows, Kristen Menou ) Talk KITP flash format movie Talk KITP mp4 format movie
Movie: Simulation of the diversity of extrasolar planets (Mordasini et al. 2009, A&A 501, 1139)
According to our current understanding form planets in circumstellar disks of dust and gas, where dust particles first accumulate to form kilometer sized planetesimals, and then continue to grow first to protoplanets and finally to planets with some mass and distance from the parent star. These model calculations show which planetary masses are expected at which distances from a solar like star. The numerical formation model contains our current knowledge about dust and gas disks around young stars as well as present-day theories about various planet formation processes.
Formation tracks
For each simulation of the formation of a planet, a small
protoplanet is initially placed at some randomly chose initial
distance from the young star inside a disk with some randomly
chosen properties. Each simulation run is represented by a solid,
multicolored line, the formation track in the mass-distance plane
which shows how the protoplanet grows and migrates. Masses are
measured in units of the Earth's mass and distances are in
astronomical units (Click on the link below for an
animation). The randomly chosen disk properties are drawn from
probability distributions that are derived from actual observed
properties of protoplanetary disks. The planetary seeds start to
grow at the lower boundary of the diagram by accreting first
planetesimals and later on also gas. Due to this growth in mass
they move upwards along vertical tracks. Then they start to migrate
inwards at a speed set by the mass of the planet and the gas
disk. Depending on the particular type of this migration process,
the formation tracks are plotted in red, blue or green. At the
moment when the protoplanetary disk finally disappears, the planets
reach their final position, indicated by a black symbol. One notes
that also planets similar to our gas giants are formed. As the
mechanism halting planetary migration close to the star is
currently poorly understood, simulations are also arbitrarily
stopped once a planet migrates to about 0.1 AU from the host
star.
Diversity in the population
synthesis
The final positions show that in the model
planets of great diversity form: There are Superjupiters with
masses higher than ten times the mass of Jupiter, there are
Neptunian planets and there is foremost a large number of small
planets with masses similar to the Earth. Such very low mass
planets can currently not yet be detected by astronomical
observations. Among the currently known extrasolar planets however,
a large diversity in their properties exist as in the model, a
partially surprising result, as it was for example originally
thought that all gas giants should be similar to Jupiter and not be
located very close to the star as it is sometimes the case. Thanks
to the high number of detected exoplanets it is now possible to
study the statistical properties of the whole population of planets
instead of just single examples. Simulating the formation of such a
population within a computer model is therefore called population
synthesis. It is a well established method in stellar astrophysics,
but was not yet often used for the study of exoplanets.
Parameters: Stellar mass: 1 Msun. Disk alpha: 7x10^-3. Isothermal migration with efficiency factor 0.001. 1 seed per disk.