New website for exoplanet app

Today I made a new website for the exoplanet app for iPhone/iPad/iPod.

More pictures and video will be added soon.

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Exoplanet HR Diagram

Inspired by Stuart, I created this HR Diagram for exoplanet researchers. The position on the x-axis is determined by the number of peer reviewed paper, as given by ADS. The position on the y-axis is given by the number of website returned by google when searched for the full name in quotes.

Of course, these numbers don’t necessarily mean anything. There are large errors if a person has a common name or alternative spellings. However, it’s interesting to see that there is indeed a correlation (which is labeled main sequence in the plot).

Update: I’ve made anĀ improved version in which the google searches include the words “exoplanet”, “astronomy” and “astrophysics”. The sum of the number of results is used in the plot. This should avoid most of the issues for people with common names. You can download the scripts to create these plots here and fine tune all parameters.

If you feel that someone is missing from the list let me know and I’ll add him/her. If you’re unhappy with your score, please send me bribes in forms of cakes or iPhones.

PS: Stephen, beware! I’m heading towards you!

Exoplanet HR Diagram (follow link for an svg version)

(original version)

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Japan Photos

Here are some photos from Ishigaki and from Tokyo in Japan.

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Stochastic migration of small bodies in Saturn’s rings


Hanno Rein, John C. B. Papaloizou

Many small moonlets, creating propeller structures, have been found in Saturn’s rings by the Cassini spacecraft. We study the dynamical evolution of such 20-50m sized bodies which are embedded in Saturn’s rings. We estimate the importance of various interaction processes with the ring particles on the moonlet’s eccentricity and semi-major axis analytically. For low ring surface densities, the main effects on the evolution of the eccentricity and the semi-major axis are found to be due to collisions and the gravitational interaction with particles in the vicinity of the moonlet. For large surface densities, the gravitational interaction with self-gravitating wakes becomes important.
We also perform realistic three dimensional, collisional N-body simulations with up to a quarter of a million particles. A new set of pseudo shear periodic boundary conditions is used which reduces the computational costs by an order of magnitude compared to previous studies. Our analytic estimates are confirmed to within a factor of two.

On short timescales the evolution is always dominated by stochastic effects caused by collisions and gravitational interaction with self-gravitating ring particles. These result in a random walk of the moonlet’s semi-major axis. The eccentricity of the moonlet quickly reaches an equilibrium value due to collisional damping. The average change in semi-major axis of the moonlet after 100 orbital periods is 10-100m. This translates to an offset in the azimuthal direction of several hundred kilometres. We expect that such a shift is easily observable.



Simulation EQ40050DT:

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Publications on the orbital migration of moonlets in Saturn’s rings

My research group published several papers on Saturn’s rings last week. I’m an author on two of them:

This is a video of one of the simulations (EQ40050DT, to be precise). Make sure you watch it in HD if possible.

It shows a three dimensional simulation of a small moonlet which is embedded in the rings. Due to collisions and gravitational interactions with ring particles, it will eventually undergo a random walk.

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