Chris and the Middle Kingdom Chris Ormel

Research Group Leader
Anton Pannekoek Institute for Astronomy
University of Amsterdam (UvA)
The Netherlands

c.w.ormel AT uva DOT nl




News Flashes

August 2017
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Atmosphere recycling of super-Earths

How do super-Earth and mini-Neptunes "survive" in gas rich disks? The problem is that an early formation of a super-Earth is preferred (because they often harbor a massive hydrogen/helium-rich atmosphere), yet not too much gas can be accreted, as this would have converted them into hot-Jupiters. Since super-Earth planets are a factor 100 more frequent than hot-Jupiters there should be a robust process to prevent rapid gas accretion. We have previously suggested that the exchange of material between the super-Earth' atmosphere with the gas of the circumstellar disk is the key to solve the problem. In this work, led by (then) undergraduate student Nicolas Cimerman, we specifically tested this idea by running hydrodynamical simulations of the atmosphere of super-Earth planets, located at a distance of 0.1 au from their star. ...

[More...] [ADS] [ArXiv]

evolution of the entropy -- for a 1D bound, isolated atmosphere and a 3D "open" atmosphere


June 2017
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TRAPPIST-1 in the news

Right: Scale models of Trappist-I (red) and solar (yellow) planetary systems. The planets are placed on top of the surface of their respective stars. Sizes are to scale. 3D print design can be found here. (c) Ann Archibald.

EOS article by Shannon Hall

Astronomie.nl article (ook in Nederlands)



June 2017
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Formation of TRAPPIST-1

TRAPPIST-I, an M8-dwarf star, of mass 0.08x solar is tiny and dim — it barely is a star. Yet it harbors a magnificent planetary system of no less than seven(!) planets. The planetary system somewhat resembles the inner solar system: the planets are all about Earth size (or less), rocky or icy, and planet e, f, and g orbit within the habitable zone. The difference, however, is that the planets all orbit very close-in; the entire system fits in a circle of 0.06 au!

In this work, we offer a framework for the origin of the physical and dynamical properties of this system. ...

[More...] [ADS] [ArXiv]

stages in the formation of the TRAPPIST-1 system


March 2017
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Pebble accretion review chapter!

I wrote a review chapter about the pebble accretion mechanism, which will become part of a book on "Formation, Evolution, and Dynamics of Young Solar Systems" (Springer Verlag; edited by Oliver Gressel and Martin Pessah). It covers the physics of the process, assessing the cons- and pros, and reviews some recent applications. Enjoy!

[More...] [download]


February 2017
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Planetesimal formation: the snowline to the rescue.

How do planetesimals form from pebbles? According to the so-called Streaming Instability model this happens once the pebble-to-gas density is around unity. The problem with pebbles is, however, their mobility: they tend to drift towards the star in an inside-out-fashion, meaning that the inner disk is emptied first. Unfortunately, this behavior tends to decrease the pebble spatial density, instead of the desired increase. Something special is needed.

In this work we investigated the role of the water iceline. This is the place where ice comes off the pebbles in the form as H2O vapor. Through diffusion some of the H2O vapor is carried back, across the iceline, where it can re-condense on the incoming pebbles. Hence the density, as well as the size of the pebbles increases. As a result, as can be seen in the animation to the right, the solids-to-gas ratio increases over time. In this case, the ratio becomes around unity, which is a condition for the formation of planetesimals. ...

[More...] [ADS] [ArXiv]

Formation of a high solids-to-gas density ratio at the iceline


February 2017
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Planet dynamics with Magnetospheric Rebound

The Kepler spacecraft has discovered an enormous number of exoplanets of the super-Earth type: bigger than Earth, up to Neptune in sizes, orbiting very close to their host stars. Mostly, these planets are not alone: they are often part of a compact, multi-planetary system. Intriguingly, some of these planets are seen in resonance (a resonance is an integer commensurability in orbital periods, like 2:1 or 3:2); but most of them are not.

In this project, we offer an explanation for this complex architecture. First, the fact that at least some planets are seen in resonance suggests planet migration in gas-rich disks. But the fact that the planets obviously did not fall in the star, also suggests the gas disk was truncated. We postulate that this survival was due to the stellar magnetic field. ...

[More...] [ADS] [ArXiv]

Magnetospheric rebound.