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Post Info TOPIC: KIC 12557548
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Direct Evidence for an Evolving Dust Cloud from an Exoplanet

Exoplanetology has progressed in several leaps. Initially, astronomers concentrated on simply discovering new planets outside our own Solar System. Having found over a thousand such bodies, and measured basic properties indicating their likely masses and for some of them, their sizes, the next step was to characterise them. This characterisation initially focused on the planets' atmospheres, as generally only the atmospheres emit and reflect light. Now, we are on the brink of the new era, where characterisation of exoplanetary surfaces and interiors could become feasible.
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Title: Direct evidence for an evolving dust cloud from the exoplanet KIC 12557548 b
Author: Jakub J. Bochinski, Carole A. Haswell, Tom R. Marsh, Vikram S. Dhillon, Stuart P. Littlefair

We present simultaneous multi-colour optical photometry using ULTRACAM of the transiting exoplanet KIC 12557548 b (also known as KIC 1255 b). This reveals, for the first time, the colour dependence of the transit depth. Our g and z transits are similar in shape to the average Kepler short-cadence profile, and constitute the highest-quality extant coverage of individual transits. Our Night 1 transit depths are 0.85 ± 0.04% in z; 1.00 ± 0.03% in g; and 1.1 ± 0.3% in u. We employ a residual-permutation method to assess the impact of correlated noise on the depth difference between the z and g bands and calculate the significance of the colour dependence at 3.2{\sigma}. The Night 1 depths are consistent with dust extinction as observed in the ISM, but require grain sizes comparable to the largest found in the ISM: 0.25-1µm. This provides direct evidence in favour of this object being a disrupting low-mass rocky planet, feeding a transiting dust cloud. On the remaining four nights of observations the object was in a rare shallow-transit phase. If the grain size in the transiting dust cloud changes as the transit depth changes, the extinction efficiency is expected to change in a wavelength- and composition-dependent way. Observing a change in the wavelength-dependent transit depth would offer an unprecedented opportunity to determine the composition of the disintegrating rocky body KIC 12557548 b. We detected four out-of-transit u band events consistent with stellar flares.

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Blobrana


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Title: Evidence for the disintegration of KIC 12557548 b
Authors: M. Brogi, C. U. Keller, M. de Juan Ovelar, M. A. Kenworthy, R. J. de Kok, M. Min, I. A. G. Snellen

Context. The Kepler object KIC 12557548 b is peculiar. It exhibits transit-like features every 15.7 hours that vary in depth between 0.2% and 1.2%. Rappaport et al. (2012) explain the observations in terms of a disintegrating, rocky planet that has a trailing cloud of dust created and constantly replenished by thermal surface erosion. The variability of the transit depth is then a consequence of changes in the cloud optical depth.
Aims. We aim to validate the disintegrating-planet scenario by modelling the detailed shape of the observed light curve, and thereby constrain the cloud particle properties to better understand the nature of this intriguing object.
Methods. We analysed the six publicly-available quarters of raw Kepler data, phase-folded the light curve and fitted it to a model for the trailing dust cloud. Constraints on the particle properties were investigated with a light-scattering code.
Results. The light curve exhibits clear signatures of light scattering and absorption by dust, including a brightening in flux just before ingress correlated with the transit depth and explained by forward scattering, and an asymmetry in the transit light curve shape, which is easily reproduced by an exponentially decaying distribution of optically thin dust, with a typical grain size of 0.1 micron.
Conclusions. Our quantitative analysis supports the hypothesis that the transit signal of KIC 12557548 b is due to a variable cloud of dust, most likely originating from a disintegrating object.

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 Newfound exoplanet may turn to dust

Researchers at MIT, NASA and elsewhere have detected a possible planet, some 1,500 light years away, that appears to be evaporating under the blistering heat of its parent star. The scientists infer that a long tail of debris - much like the tail of a comet - is following the planet, and that this tail may tell the story of the planet's disintegration. According to the team's calculations, the tiny exoplanet, not much larger than Mercury, will completely disintegrate within 100 million years.
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First subliming planet foreshadows Mercury's fate

A rocky exoplanet about the size of Mercury appears to be evaporating before our eyes. If confirmed, this would be the first time a rocky planet has been found turning to gas, demonstrating just how wacky alien planets can be. The provocative suggestion may also foreshadow the fate of Mercury.
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Title: Possible Disintegrating Short-Period Super-Mercury Orbiting KIC 12557548
Authors: S. Rappaport, A. Levine, E. Chiang, I. El Mellah, J. Jenkins, B. Kalomeni, M. Kotson, L. Nelson, L. Rousseau-Nepton, K. Tran

We report here on the discovery of stellar occultations, observed with Kepler, that recur periodically at 15.685 hour intervals, but which vary in depth from a maximum of 1.2% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a V = 16 magnitude K dwarf with T_eff = 4400 K. The out-of-occultation behaviour shows no evidence for ellipsoidal light variations, indicating that the mass of the orbiting object is less than ~3 Jupiter masses. Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. This scenario seems ruled out by the dynamical instability that would result from such a configuration. The much more likely explanation involves macroscopic particles - e.g., dust, possibly in the form of micron-sized pyroxene grains - escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury in size. The planetary surface is hot enough to sublimate; the resultant silicate vapour accelerates off the planet via a Parker-type thermal wind, dragging dust grains with it. We infer a mass loss rate from the observations of order ~1 Earth masses/Gyr, with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1 Earth mass planet (twice the mass of Mercury), the evaporation timescale may be ~0.2 Gyr. Smaller mass planets are disfavoured because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail.

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