daniel carrera | Universidad del Azuay (original) (raw)

Papers by daniel carrera

Monthly Notices of the Royal Astronomical Society

The distribution of exoplanet masses is not primordial. After the initial stage of planet formati... more The distribution of exoplanet masses is not primordial. After the initial stage of planet formation is complete, the gravitational interactions between planets can lead to the physical collision of two planets, or the ejection of one or more planets from the system. When this occurs, the remaining planets are typically left in more eccentric orbits. Here we use present-day eccentricities of the observed exoplanet population to reconstruct the initial mass function of exoplanets before the onset of dynamical instability. We developed a Bayesian framework that combines data from N-body simulations with present-day observations to compute a probability distribution for the planets that were ejected or collided in the past. Integrating across the exoplanet population, we obtained an estimate of the initial mass function of exoplanets. We find that the ejected planets are primarily sub-Saturn type planets. While the presentday distribution appears to be bimodal, with peaks around ∼ 1M J and ∼ 20M ⊕ , this bimodality does not seem to be primordial. Instead, planets around ∼ 60M ⊕ appear to be preferentially removed by dynamical instabilities. Attempts to reproduce exoplanet populations using population synthesis codes should be mindful of the fact that the present population has been depleted of intermediate-mass planets. Future work should explore how the system architecture and multiplicity might alter our results.

The Astrophysical Journal

We present empirical evidence, supported by a planet formation model, to show that the curve R R ... more We present empirical evidence, supported by a planet formation model, to show that the curve R R F F 1.05 0.11 = Å Å () approximates the location of the so-called photo-evaporation valley. Planets below that curve are likely to have experienced complete photo-evaporation, and planets just above it appear to have inflated radii; thus we identify a new population of inflated super-Earths and mini-Neptunes. Our N-body simulations are set within an evolving protoplanetary disk and include prescriptions for orbital migration, gas accretion, and atmospheric loss due to giant impacts. Our simulated systems broadly match the sizes and periods of super-Earths in the Kepler catalog. They also reproduce the relative sizes of adjacent planets in the same system, with the exception of planet pairs that straddle the photo-evaporation valley. This latter group is populated by planet pairs with either very large or very small size ratios (R out /R in ?1 or R out /R in =1) and a dearth of size ratios near unity. It appears that this feature could be reproduced if the planet outside the photo-evaporation valley (typically the outer planet, but sometimes not) has its atmosphere significantly expanded by stellar irradiation. This new population of planets may be ideal targets for future transit spectroscopy observations with the upcoming James Webb Space Telescope.

Monthly Notices of the Royal Astronomical Society

Protoplanetary discs are thought to be truncated at orbital periods of around 10 d. Therefore, th... more Protoplanetary discs are thought to be truncated at orbital periods of around 10 d. Therefore, the origin of rocky short-period planets with P < 10 d is a puzzle. We propose that many of these planets may form through the Type-I migration of planets locked into a chain of mutual mean motion resonances. We ran N-body simulations of planetary embryos embedded in a protoplanetary disc. The embryos experienced gravitational scatterings, collisions, disc torques, and dampening of orbital eccentricity and inclination. We then modelled Kepler observations of these planets using a forward model of both the transit probability and the detection efficiency of the Kepler pipeline. We found that planets become locked into long chains of mean motion resonances that migrate in unison. When the chain reaches the edge of the disc, the inner planets are pushed past the edge due to the disc torques acting on the planets farther out in the chain. Our simulated systems successfully reproduce the obs...

The Astrophysical Journal, 2017

Recent years have seen growing interest in the streaming instability as a candidate mechanism to ... more Recent years have seen growing interest in the streaming instability as a candidate mechanism to produce planetesimals. However, these investigations have been limited to small-scale simulations. We now present the results of a global protoplanetary disk evolution model that incorporates planetesimal formation by the streaming instability, along with viscous accretion, photoevaporation by EUV, FUV, and X-ray photons, dust evolution, the water ice line, and stratified turbulence. Our simulations produce massive (60-130 M ⊕) planetesimal belts beyond 100 au and up to ∼ 20M ⊕ of planetesimals in the middle regions (3-100 au). Our most comprehensive model forms 8 M ⊕ of planetesimals inside 3 au, where they can give rise to terrestrial planets. The planetesimal mass formed in the inner disk depends critically on the timing of the formation of an inner cavity in the disk by high-energy photons. Our results show that the combination of photoevaporation and the streaming instability are efficient at converting the solid component of protoplanetary disks into planetesimals. Our model, however, does not form enough early planetesimals in the inner and middle regions of the disk to give rise to giant planets and super-Earths with gaseous envelopes. Additional processes such as particle pileups and mass loss driven by MHD winds may be needed to drive the formation of early planetesimal generations in the planet forming regions of protoplanetary disks.

Monthly Notices of the Royal Astronomical Society, 2016

Many observed giant planets lie on eccentric orbits. Such orbits could be the result of strong sc... more Many observed giant planets lie on eccentric orbits. Such orbits could be the result of strong scatterings with other giant planets. The same dynamical instability that produces these scatterings may also cause habitable planets in interior orbits to become ejected, destroyed, or be transported out of the habitable zone. We say that a habitable planet has resilient habitability if it is able to avoid ejections and collisions and its orbit remains inside the habitable zone. Here we model the orbital evolution of rocky planets in planetary systems where giant planets become dynamically unstable. 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 planetary systems are far more destructive than systems with giant planets of unequal masses. We also establish a link with observation; we find that giant planets with present-day eccentricities higher than 0.4 almost never have a habitable interior planet. For a giant planet with an present-day eccentricity of 0.2 and semimajor axis of 5 AU orbiting a Sun-like star, 50% of the orbits in the habitable zone are resilient to the instability. As semimajor axis increases and eccentricity decreases, a higher fraction of habitable planets survive and remain habitable. However, if the habitable planet has rocky siblings, there is a significant risk of rocky planet collisions that would sterilize the planet.

Lund Observatory Examensarbeten, 2012

WIMPs, or Weakly Interacting Massive Particles, are a popular dark matter candidate, but their de... more WIMPs, or Weakly Interacting Massive Particles, are a popular dark matter candidate, but their detection remains elusive. At its core, this project is an effort to bridge the gap between the theory of WIMPs, and astronomical observation.

Astronomy & Astrophysics, 2015

The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to re... more 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 ∼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. In this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. We use a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from sub-millimeter-sized chondrules to meter-sized rocks. We find that particles down to millimeter sizes can form dense particle clouds through the runaway convergence of radial drift known as the streaming instability. We make a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) which are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculate the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ∼10 5 years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (∼10 6 − 10 7 years). Our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. We speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. This clumping, in turn reduces collision speeds and enhances coagulation. Future simulations should model coagulation and the streaming instability together to explore this feedback loop further.

Toxic cyanobacteria and wildlife conservation: proposal of a procedure to demonstrate waterbird m... more Toxic cyanobacteria and wildlife conservation: proposal of a procedure to demonstrate waterbird mass mortalities by microcystin. The role of toxic cyanobacteria in wildlife conservation is poorly known. However, toxic cyanobacteria blooms could have a very important effect on wildlife. In particular, mass mortalities of waterbirds are receiving improved attention in recent years because of their increased occurrence. Cyanobacteria toxicosis by microcystins (potent hepatotoxic cyclic peptides) should be taken in account as a significant cause of such mortalities in eutrophic inland water systems. A suitable procedure to diagnose waterbird mortalities due to toxin-producing cyanobacteria (microcystins) should be based on five sequential steps: i) macroscopic in situ evaluation searching evidences of cyanobacteria blooms; ii) identification of toxic cyanobacteria species; iii) analysis of water samples searching for microcystin detection; iv) epidemiology and clinical sings; and v) post-mortem examination of waterbirds to verify that microcystins reach to digestive system of birds. This procedure was employed to analyze recent mortalities of waterbirds in Doñana National Park (S Spain), revealing that toxicosis by microcystins was the main cause of the worst mass mortality.

Monthly Notices of the Royal Astronomical Society

The distribution of exoplanet masses is not primordial. After the initial stage of planet formati... more The distribution of exoplanet masses is not primordial. After the initial stage of planet formation is complete, the gravitational interactions between planets can lead to the physical collision of two planets, or the ejection of one or more planets from the system. When this occurs, the remaining planets are typically left in more eccentric orbits. Here we use present-day eccentricities of the observed exoplanet population to reconstruct the initial mass function of exoplanets before the onset of dynamical instability. We developed a Bayesian framework that combines data from N-body simulations with present-day observations to compute a probability distribution for the planets that were ejected or collided in the past. Integrating across the exoplanet population, we obtained an estimate of the initial mass function of exoplanets. We find that the ejected planets are primarily sub-Saturn type planets. While the presentday distribution appears to be bimodal, with peaks around ∼ 1M J and ∼ 20M ⊕ , this bimodality does not seem to be primordial. Instead, planets around ∼ 60M ⊕ appear to be preferentially removed by dynamical instabilities. Attempts to reproduce exoplanet populations using population synthesis codes should be mindful of the fact that the present population has been depleted of intermediate-mass planets. Future work should explore how the system architecture and multiplicity might alter our results.

The Astrophysical Journal

We present empirical evidence, supported by a planet formation model, to show that the curve R R ... more We present empirical evidence, supported by a planet formation model, to show that the curve R R F F 1.05 0.11 = Å Å () approximates the location of the so-called photo-evaporation valley. Planets below that curve are likely to have experienced complete photo-evaporation, and planets just above it appear to have inflated radii; thus we identify a new population of inflated super-Earths and mini-Neptunes. Our N-body simulations are set within an evolving protoplanetary disk and include prescriptions for orbital migration, gas accretion, and atmospheric loss due to giant impacts. Our simulated systems broadly match the sizes and periods of super-Earths in the Kepler catalog. They also reproduce the relative sizes of adjacent planets in the same system, with the exception of planet pairs that straddle the photo-evaporation valley. This latter group is populated by planet pairs with either very large or very small size ratios (R out /R in ?1 or R out /R in =1) and a dearth of size ratios near unity. It appears that this feature could be reproduced if the planet outside the photo-evaporation valley (typically the outer planet, but sometimes not) has its atmosphere significantly expanded by stellar irradiation. This new population of planets may be ideal targets for future transit spectroscopy observations with the upcoming James Webb Space Telescope.

Monthly Notices of the Royal Astronomical Society

Protoplanetary discs are thought to be truncated at orbital periods of around 10 d. Therefore, th... more Protoplanetary discs are thought to be truncated at orbital periods of around 10 d. Therefore, the origin of rocky short-period planets with P < 10 d is a puzzle. We propose that many of these planets may form through the Type-I migration of planets locked into a chain of mutual mean motion resonances. We ran N-body simulations of planetary embryos embedded in a protoplanetary disc. The embryos experienced gravitational scatterings, collisions, disc torques, and dampening of orbital eccentricity and inclination. We then modelled Kepler observations of these planets using a forward model of both the transit probability and the detection efficiency of the Kepler pipeline. We found that planets become locked into long chains of mean motion resonances that migrate in unison. When the chain reaches the edge of the disc, the inner planets are pushed past the edge due to the disc torques acting on the planets farther out in the chain. Our simulated systems successfully reproduce the obs...

The Astrophysical Journal, 2017

Recent years have seen growing interest in the streaming instability as a candidate mechanism to ... more Recent years have seen growing interest in the streaming instability as a candidate mechanism to produce planetesimals. However, these investigations have been limited to small-scale simulations. We now present the results of a global protoplanetary disk evolution model that incorporates planetesimal formation by the streaming instability, along with viscous accretion, photoevaporation by EUV, FUV, and X-ray photons, dust evolution, the water ice line, and stratified turbulence. Our simulations produce massive (60-130 M ⊕) planetesimal belts beyond 100 au and up to ∼ 20M ⊕ of planetesimals in the middle regions (3-100 au). Our most comprehensive model forms 8 M ⊕ of planetesimals inside 3 au, where they can give rise to terrestrial planets. The planetesimal mass formed in the inner disk depends critically on the timing of the formation of an inner cavity in the disk by high-energy photons. Our results show that the combination of photoevaporation and the streaming instability are efficient at converting the solid component of protoplanetary disks into planetesimals. Our model, however, does not form enough early planetesimals in the inner and middle regions of the disk to give rise to giant planets and super-Earths with gaseous envelopes. Additional processes such as particle pileups and mass loss driven by MHD winds may be needed to drive the formation of early planetesimal generations in the planet forming regions of protoplanetary disks.

Monthly Notices of the Royal Astronomical Society, 2016

Many observed giant planets lie on eccentric orbits. Such orbits could be the result of strong sc... more Many observed giant planets lie on eccentric orbits. Such orbits could be the result of strong scatterings with other giant planets. The same dynamical instability that produces these scatterings may also cause habitable planets in interior orbits to become ejected, destroyed, or be transported out of the habitable zone. We say that a habitable planet has resilient habitability if it is able to avoid ejections and collisions and its orbit remains inside the habitable zone. Here we model the orbital evolution of rocky planets in planetary systems where giant planets become dynamically unstable. 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 planetary systems are far more destructive than systems with giant planets of unequal masses. We also establish a link with observation; we find that giant planets with present-day eccentricities higher than 0.4 almost never have a habitable interior planet. For a giant planet with an present-day eccentricity of 0.2 and semimajor axis of 5 AU orbiting a Sun-like star, 50% of the orbits in the habitable zone are resilient to the instability. As semimajor axis increases and eccentricity decreases, a higher fraction of habitable planets survive and remain habitable. However, if the habitable planet has rocky siblings, there is a significant risk of rocky planet collisions that would sterilize the planet.

Lund Observatory Examensarbeten, 2012

WIMPs, or Weakly Interacting Massive Particles, are a popular dark matter candidate, but their de... more WIMPs, or Weakly Interacting Massive Particles, are a popular dark matter candidate, but their detection remains elusive. At its core, this project is an effort to bridge the gap between the theory of WIMPs, and astronomical observation.

Astronomy & Astrophysics, 2015

The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to re... more 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 ∼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. In this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. We use a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from sub-millimeter-sized chondrules to meter-sized rocks. We find that particles down to millimeter sizes can form dense particle clouds through the runaway convergence of radial drift known as the streaming instability. We make a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) which are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculate the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ∼10 5 years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (∼10 6 − 10 7 years). Our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. We speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. This clumping, in turn reduces collision speeds and enhances coagulation. Future simulations should model coagulation and the streaming instability together to explore this feedback loop further.

Toxic cyanobacteria and wildlife conservation: proposal of a procedure to demonstrate waterbird m... more Toxic cyanobacteria and wildlife conservation: proposal of a procedure to demonstrate waterbird mass mortalities by microcystin. The role of toxic cyanobacteria in wildlife conservation is poorly known. However, toxic cyanobacteria blooms could have a very important effect on wildlife. In particular, mass mortalities of waterbirds are receiving improved attention in recent years because of their increased occurrence. Cyanobacteria toxicosis by microcystins (potent hepatotoxic cyclic peptides) should be taken in account as a significant cause of such mortalities in eutrophic inland water systems. A suitable procedure to diagnose waterbird mortalities due to toxin-producing cyanobacteria (microcystins) should be based on five sequential steps: i) macroscopic in situ evaluation searching evidences of cyanobacteria blooms; ii) identification of toxic cyanobacteria species; iii) analysis of water samples searching for microcystin detection; iv) epidemiology and clinical sings; and v) post-mortem examination of waterbirds to verify that microcystins reach to digestive system of birds. This procedure was employed to analyze recent mortalities of waterbirds in Doñana National Park (S Spain), revealing that toxicosis by microcystins was the main cause of the worst mass mortality.