Research: Formation and evolution of planetary systems

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I am a finishing PhD student at Lund Observatory. I am interested in the formation and early dynamical evolution of planetary systems, especially in the context of rocky planets in the habitable zone. I work with Anders Johansen and Melvyn B. Davies. My strongest skills include programming, statistics, orbital dynamics, and dust-gas dynamics in a protoplanetary disk. I conduct hydrodynamic simulations with the Pencil Code and N-body simulations with MERCURY. I am currently looking for a postdoctoral position where I can continue to work on planet formation, protoplanetary disks, and/or planetary habitability.

In addition to my astronomy research, I have worked as a software developer in the private sector, I teach MATLAB, and I have taught the Masters course in statistics at Lund Observatory. I am interested in programming languages, robust statistics, and high-performance computing.

Survival of habitable planets in unstable planetary systems

Published: Carrera et al, 2016, MNRAS, 463, 3226 (also as arXiv:1605.01325)

Many observed giant planets lie on eccentric orbits. These orbits may be the result of strong scatterings with other giant planets at a time when the giant planets were dynamically unstable. In this work I investigate whether life in a habitable planet could survive this period of dynamical instability. In many cases, a habitable planet is ejected from the system or experiences a physical collision with another planet. In a few cases, the planet survives but acquires a new orbit that renders the planet uninhabitable.

We conducted 1,200 N-body simulations with MERCURY in which we modeled the orbital evolution of rocky planets and giant planets in various configurations. We measure the resilience of habitable planets as a function of the observed, present-day masses and orbits of the giant planets. We find that the survival rate of habitable planets depends strongly on the giant planet architecture; equal-mass giant planets are far more destructive than hierarchical systems where the giant planets have unequal masses. Our final result is shown in the figure below.

Final plot Click to Expand
We say that a habitable planet is resiliently habitable if it can avoid ejections, collisions, or orbital changes that would destroy life on the planet. The left plot shows the probability that a rocky planet in the habitable zone is resiliently habitable (colour scale) as a function of the present-day semimajor-axis and eccentricity of the observed giant planet. As a general rule, giant planets with eccentricity higher than 0.4 most likely came from a planet system where the giant planets had similar masses and experienced very strong scatterings. In these systems, rocky planets in the habitable zone are almost universally destroyed, mostly through ejection. If the present-day eccentricity is low, that indicates a dynamically quient past, that would have been conductive to the survival of habitable planets. The three white lines correspond to resilience probabilities of 25%, 50%, and 75%. The plot on the right shows the same three lines, now marked in red. The blue dots are the currently known exoplanets with a mass of at least 0.3 Jupiter masses and a stellar mass between 0.95 and 1.05 solar masses.

How to form planetesimals from mm-sized chondrules and chondrule aggregates

Published: Carrera et al, 2015, A&A, 579, A43 (also as arXiv:1501.05314)

The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to reconcile with a bottom-up formation scenario due to the observed scarcity of objects smaller than \( \sim \)100 km in size. Instead, planetesimals appear to form top-down, with large 100-1000 km bodies forming from the rapid gravitational collapse of dense clumps of small solid particles. We investigated the conditions under which solid particles can form dense clumps in a protoplanetary disk. We used the Pencil Code to model the interaction between solid particles and gas in a protoplanetary disk for a range of particle sizes. We found that particles down to millimeter sizes can form dense particle clouds through the streaming instability. We made a map of the range of conditions (particle size vs concentration) needed to form dense particle clumps.

Spacetime diagram Click to Expand
Spacetime diagrams for select runs showing the solid surface density \( \Sigma_{\rm solid} \) (shown by color) as a function of the radial coordinate \( x \) and simulation time. The right hand axis shows the mean solid concentration \( Z = \langle \Sigma_{\rm solid} \rangle / \langle \Sigma_{\rm total} \rangle \). Three of the runs form visible filaments.
Final results Click to Expand
Final results. The plot shows the range of particle sizes and concentration where particle clumps form (Green; Streaming regime). The particle concentration is \( Z = \langle \Sigma_{\rm solid} \rangle / \langle \Sigma_{\rm total} \rangle \). The particle size is measured in Stokes number.

Finally, we estimated the distribution of collision speeds between mm-sized particles. We calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ~105 years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale ( \( \sim \)106-107 years).