The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or near-future instruments. We discuss the orbital effects that govern exomoon evolution, we present a framework to characterize an exomoon's stellar plus planetary illumination as well as its tidal heating, and we address the techniques that have been proposed to search for exomoons. Most notably, we show that natural satellites in the range of 0.1-0.5 Earth mass (i) are potentially habitable, (ii) can form within the circumplanetary debris and gas disk or via capture from a binary, and (iii) are detectable with current technology.

We present the data reduction pipeline for CHARIS, a high-contrast integral-field spectrograph for the Subaru Telescope. The pipeline constructs a ramp from the raw reads using the measured nonlinear pixel response, and reconstructs the data cube using one of three extraction algorithms: aperture photometry, optimal extraction, or χ 2 fitting. We measure and apply both a detector flatfield and a lenslet flatfield and reconstruct the wavelength-and position-dependent lenslet point-spread function (PSF) from images taken with a tunable laser. We use these measured PSFs to implement a χ 2 -based extraction of the data cube, with typical residuals of ∼5% due to imperfect models of the undersampled lenslet PSFs. The full two-dimensional residual of the χ 2 extraction allows us to model and remove correlated read noise, dramatically improving CHARIS' performance. The χ 2 extraction produces a data cube that has been deconvolved with the line-spread function, and never performs any interpolations of either the data or the individual lenslet spectra. The extracted data cube also includes uncertainties for each spatial and spectral measurement. CHARIS' software is parallelized, written in Python and Cython, and freely available on github with a separate documentation page. Astrometric and spectrophotometric calibrations of the data cubes and PSF subtraction will be treated in a forthcoming paper.

The known population of exoplanets exhibits a much wider range of orbital eccentricities than Solar System planets and has a much higher average eccentricity. These facts have been widely interpreted to indicate that the Solar System is an atypical member of the overall population of planetary systems. We report here on a strong anticorrelation of orbital eccentricity with multiplicity (number of planets in the system) among cataloged radial velocity (RV) systems. The mean, median, and rough distribution of eccentricities of Solar System planets fits an extrapolation of this anticorrelation to the eight-planet case rather precisely despite the fact that no more than two Solar System planets would be detectable with RV data comparable to that in the exoplanet sample. Moreover, even if regarded as a single or double planetary system, the Solar System lies in a reasonably heavily populated region of eccentricity−multiplicity space. Thus, the Solar System is not anomalous among known exoplanetary systems with respect to eccentricities when its multiplicity is taken into account. Specifically, as the multiplicity of a system increases, the eccentricity decreases roughly as a power law of index -1.20. A simple and plausible but ad hoc and model-dependent interpretation of this relationship implies that ∼80% of the one-planet and 25% of the two-planet systems in our sample have additional, as yet undiscovered, members but that systems of higher observed multiplicity are largely complete (i.e., relatively rarely contain additional undiscovered planets). If low eccentricities indeed favor high multiplicities, habitability may be more common in systems with a larger number of planets.orbital eccentricities | dynamical evolution | Solar System | radial velocity S olar System orbital eccentricities are unusually low compared with those of exoplanets. This fact is one of the most frequently noted major surprises revealed by the discovery and early explorations of the exoplanet population orbiting Sun-like stars and has been widely interpreted to indicate that the Solar System is not a representative example of a planetary system (reviews by refs. 1-3 and references therein). Many planetary formation theories developed before the discovery of exoplanets suggested planets would have eccentricities similar to the Solar System planets (4, 5). Several attempts have been made to accurately model the dynamical evolution of planetary systems since then, with the goal of explaining the observed eccentricity distribution (6-10). These papers invoke planet−planet interactions as the primary mechanism determining the distribution of orbital eccentricities. The most recent of these papers (10) concludes that there would be a dependence of eccentricity on multiplicity (the number of planets in the system) in this scenario. We use existing radial velocity (RV) exoplanet data to test that prediction.Our dataset consists of 403 of the 441 cataloged RV exoplanets obtained since the 1990s (exoplanet.org). Of these, 127 are members of known mul...

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All-sky imaging surveys have identified several dozen isolated planetary-mass objects (IPMOs) far away from any star. Here we examine the prospects for detecting transiting moons around these objects. We expect transiting moons to be common, occurring around 10%-15% of IPMOs, given that close-orbiting moons have a high geometric transit probability and are expected to be a common outcome of giant planet formation. The IPMOs offer an advantage over other directly imaged planets in that high-contrast imaging is not necessary to detect the photometric transit signal. For at least 30 (>50%) of the currently known IPMOs, observations of a single transit with the James Webb Space Telescope would have low enough forecast noise levels to allow for the detection of an Io-or Titan-like moon. The intrinsic variability of the IPMOs will be an obstacle. Using archival time-series photometry of IPMOs with the Spitzer Space Telescope as a proof of concept, we found evidence for a fading event of 2MASS J1119-1137 AB that might have been caused by intrinsic variability but is also consistent with a single transit of a habitable-zone 1.7 R ⊕ exomoon. Although the interpretation of this particular event is inconclusive, the characteristics of the data and the candidate signal suggest that Earth-sized habitable-zone exomoons around IPMOs are detectable with existing instrumentation.Unified Astronomy Thesaurus concepts: Natural satellites (Extrasolar) (483); Free floating planets (549); Transits (1711); Exoplanets (498); Habitable zone (696)