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Register a new userProspecting for exo-Earths in multiple planet systems with a gas giant
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In this work, we hunt for the best places to find exo-Earths in the currently known exoplanet population. While it is still unclear whether Jupiter had a beneficial or detrimental effect on the creation of the right environment for a habitable Earth to develop, we focus on the 51 multiple planet systems that have at least one Jupiter-like planet and aim to identify which would be good candidates to host an exo-Earth. We conduct a series of numerical simulations to identify dynamically stable regions of the habitable zone of the multiple exoplanet systems capable of hosting an Earth-mass planet. We produce a candidate list of 16 systems that could host such a stable exo-Earth in their habitable zone, and for which the induced radial velocity signal of a hypothetical one, two or four Earth-mass planet on the host star would be detectable with the ESPRESSO spectrograph. We find that whilst the gravitational interactions with the massive planet nearest the habitable zone are critical in determining stability, the secular resonant interactions between multiple planets can also have a dramatic influence on the overall stability of the habitable zone.
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We simulate a Kepler-like observation of a theoretical exoplanet population and we show that the observed orbital period distribution of the Kepler giant planet candidates is best matched by an average stellar specific dissipation function Q_* in the interval 10^6 ~< Q_* ~< 10^7. In that situation, the few super-Earths that are driven to orbital periods P < 1 day by dynamical interactions in multiple-planet systems will survive tidal disruption for a significant fraction of the main-sequence lifetimes of their stellar hosts. Consequently, though these very-hot super-Earths are not characteristic of the overall super-Earth population, their substantial transit probability implies that they should be significant contributors to the full super-Earth population uncovered by Kepler. As a result, the CoRoT-7 system may be the first representative of a population of very-hot super-Earths that we suggest should be found in multiple-planet systems preferentially orbiting the least-dissipative stellar hosts in the Kepler sample.
We study the long term orbital evolution of a terrestrial planet under the gravitational perturbations of a giant planet. In particular, we are interested in situations where the two planets are in the same plane and are relatively close. We examine both possible configurations: the giant planet orbit being either outside or inside the orbit of the smaller planet. The perturbing potential is expanded to high orders and an analytical solution of the terrestrial planetary orbit is derived. The analytical estimates are then compared against results from the numerical integration of the full equations of motion and we find that the analytical solution works reasonably well. An interesting finding is that the new analytical estimates improve greatly the predictions for the timescales of the orbital evolution of the terrestrial planet compared to an octupole order expansion. Finally, we briefly discuss possible applications of the analytical estimates in astrophysical problems.
The SIM Lite mission will undertake several planet surveys. One of them, the Deep Planet Survey, is designed to detect Earth-mass exoplanets in the habitable zones of nearby main sequence stars. A double blind study has been conducted to assess the capability of SIM to detect such small planets in a multi-planet system where several giant planets might be present. One of the tools which helped in deciding if the detected planets were actual was an orbit integrator using the publicly available HNBody code so that the orbit solutions could be analyzed in terms of temporal stability over many orbits. In this contribution, we describe the implementation of this integrator and analyze the different blind test solutions. We discuss also the usefulness of this method given that some planets might be not detected but still affect the overall stability of the system.
The nearest exoplanets to the Sun are our best possibilities for detailed characterization. We report the discovery of a compact multi-planet system of super-Earths orbiting the nearby red dwarf GJ 887, using radial velocity measurements. The planets have orbital periods of 9.3 and 21.8~days. Assuming an Earth-like albedo, the equilibrium temperature of the 21.8 day planet is approx 350 K; which is interior, but close to the inner edge, of the liquid-water habitable zone. We also detect a further unconfirmed signal with a period of 50 days which could correspond to a third super-Earth in a more temperate orbit. GJ 887 is an unusually magnetically quiet red dwarf with a photometric variability below 500 parts-per-million, making its planets amenable to phase-resolved photometric characterization.
Inferring the climate and surface conditions of terrestrial exoplanets in the habitable zone is a major goal for the field of exoplanet science. This pursuit will require both statistical analyses of the population of habitable planets as well as in-depth analyses of the climates of individual planets. Given the close relationship between habitability and surface liquid water, it is important to ask whether the fraction of a planets surface where water can be a liquid, $chi_text{hab}$, can be inferred from observations. We have produced a diverse bank of 1,874 3D climate models and computed the full-phase reflectance and emission spectrum for each model to investigate whether surface climate inference is feasible with high-quality direct imaging or secondary eclipse spectroscopy. These models represent the outcome of approximately 200,000 total simulated years of climate and over 50,000 CPU-hours, and the roughly-100 GB model bank and its associated spectra are being made publicly-available for community use. We find that there are correlations between spectra and $chi_text{hab}$ that will permit statistical approaches. However, spectral degeneracies in the climate observables produced by our model bank indicate that inference of individual climates is likely to be model-dependent, and inference will likely be impossible without exhaustive explorations of the climate parameter space. The diversity of potential climates on habitable planets therefore poses fundamental challenges to remote sensing efforts targeting exo-Earths.
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