Browsing by Author "Janković, Marija"

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    A guide to hunting periodic three-body orbits with non-vanishing angular momentum
    Janković, Marija; Dmitrašinović, Veljko; Šuvakov, Milovan
    A large number of periodic three-body orbits with vanishing angular momentum have been found in Newtonian gravity over the past 6 years due to a simple search method and to the contribution from practitioners outside the Celestial Mechanics community. Extension of such orbits to non-vanishing angular momentum has been lacking due to inter alia the absence of a sufficiently simple and widely known search method. We present a method, i.e., a general strategy plus detailed tactics (but not a specific algorithm, or a code), to numerically search for relative periodic orbits in the Newtonian three-body problem with three equal masses and non-vanishing angular momentum. We illustrate the method with an application to a specific, so-called Broucke–Hadjidemetriou–Hénon (BHH) family of periodic 3-body orbits: Our search yielded around 100 new “satellite” orbits, related to the original BHH orbits by a topological relation (defined in the text), with infinitely many orbits remaining to be discovered. We used the so-obtained orbits to test the period vs. topology relation that had previously been established, within a certain numerical accuracy, for orbits with vanishing angular momentum. Our method can be readily: (1) applied to families of periodic 3-body orbits other than the BHH one; (2) implemented using various standard algorithms for solving ordinary differential equations, such as the Bulirsch–Stoer and the Runge–Kutta–Fehlberg ones; (3) adapted to 3-body systems with distinct masses and/or coupling constants, including, but not limited to, Coulomb interaction. Our goal is to enable numerical searches for new orbits in as many families of orbits as possible, and thus to allow searches for other empirical relations, such as the aforementioned topology vs. period one.
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    Close-in Super-Earths: The first and the last stages of planet formation in an MRI-accreting disc
    Janković, Marija; Owen, James E.; Mohanty, Subhanjoy
    We explore in situ formation and subsequent evolution of close-in super-Earths and mini-Neptunes. We adopt a steady-state inner protoplanetary gas disc structure that arises from viscous accretion due to the magneto-rotational instability (MRI). We consider the evolution of dust in the inner disc, including growth, radial drift, and fragmentation, and find that dust particles that radially drift into the inner disc fragment severely due to the MRI-induced turbulence. This result has two consequences: (1) radial drift of grains within the inner disc is quenched, leading to an enhancement of dust in the inner regions that scales as dust-togas-mass-flux-ratio at ∼1 au; (2) however, despite this enhancement, planetesimal formation is impeded by the small grain size. Nevertheless, assuming that planetary cores are present in the inner disc, we then investigate the accretion of atmospheres on to cores and their subsequent photoevaporation. We then compare our results to the observed exoplanet mass-radius relationship. We find that (1) the low gas surface densities and high temperatures in the inner disc reduce gas accretion on to cores compared to the minimum mass solar nebula, preventing the cores from growing into hot Jupiters, in agreement with the data; (2) however, our predicted envelope masses are still typically larger than observed ones. Finally, we sketch a qualitative picture of how grains may grow and planetesimals form in the inner disc if grain effects on the ionization levels and the MRI and the back reaction of the dust on the gas (both neglected in our calculations) are accounted for.
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    MRI-active inner regions of protoplanetary discs. I. A detailed model of disc structure
    Janković, Marija; Owen, James; Mohanty, Subhanjoy; Tan, Jonathan C.
    Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magnetorotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization, and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate (dot M∼, 10-8 M· yr-1) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the mid-plane. As a result, both the disc mid-plane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges on to grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.
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    On the likely magnesium–iron silicate dusty tails of catastrophically evaporating rocky planets
    Campos Estrada, Beatriz; Owen, James E; Janković, Marija; Wilson, Anna; Helling, Christiane
    Catastrophically evaporating rocky planets provide a unique opportunity to study the composition of small planets. The surface composition of these planets can be constrained via modelling their comet-like tails of dust. In this work, we present a new self-consistent model of the dusty tails: we physically model the trajectory of the dust grains after they have left the gaseous outflow, including an on-the-fly calculation of the dust cloud’s optical depth. We model two catastrophically evaporating planets: KIC 1255 b and K2-22 b. For both planets, we find the dust is likely composed of magnesium–iron silicates (olivine and pyroxene), consistent with an Earth-like composition. We constrain the initial dust grain sizes to be ∼ 1.25–1.75 μm and the average (dusty) planetary mass-loss rate to be ∼ 3$\, M_{\oplus } \mathrm{Gyr^{-1}}$. Our model shows that the origin of the leading tail of dust of K2-22 b is likely a combination of the geometry of the outflow and a low radiation pressure force to stellar gravitational force ratio. We find the optical depth of the dust cloud to be a factor of a few in the vicinity of the planet. Our composition constraint supports the recently suggested idea that the dusty outflows of these planets go through a greenhouse effect–nuclear winter cycle, which gives origin to the observed transit depth time variability. Magnesium–iron silicates have the necessary visible-to-infrared opacity ratio to give origin to this cycle in the high mass-loss state.
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    The Effect of Sculpting Planets on the Steepness of Debris-disc Inner Edges
    Pearce, Tim; Krivov, Alexander; Sefilian, Antranik; Janković, Marija; Löhne, Torsten; Morgner, Tobias; Wyatt, Mark; Booth, Mark; Marino, Sebastian
    Debris discs are our best means to probe the outer regions of planetary systems. Many studies assume that planets lie at the inner edges of debris discs, akin to Neptune and the Kuiper Belt, and use the disc morphologies to constrain those otherwise-undetectable planets. However, this produces a degeneracy in planet mass and semimajor axis. We investigate the effect of a sculpting planet on the radial surface-density profile at the disc inner edge, and show that this degeneracy can be broken by considering the steepness of the edge profile. Like previous studies, we show that a planet on a circular orbit ejects unstable debris and excites surviving material through mean-motion resonances. For a non-migrating, circular-orbit planet, in the case where collisions are negligible, the steepness of the disc inner edge depends on the planet-to-star mass ratio and the initial-disc excitation level. We provide a simple analytic model to infer planet properties from the steepness of ALMA-resolved disc edges. We also perform a collisional analysis, showing that a purely planet-sculpted disc would be distinguishable from a purely collisional disc and that, whilst collisions flatten planet-sculpted edges, they are unlikely to fully erase a planet’s signature. Finally, we apply our results to ALMA-resolved debris discs and show that, whilst many inner edges are too steep to be explained by collisions alone, they are too flat to arise through completed sculpting by non-migrating, circular-orbit planets. We discuss implications of this for the architectures, histories, and dynamics in the outer regions of planetary systems.