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Thread: Disintegrating Planets - some recent news

  1. #31
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    More on ultrahot gas giants losing their atmospheres.


    https://phys.org/news/2018-12-exopla...here-tail.html

    An exoplanet loses its atmosphere in the form of a tail

    December 6, 2018, Instituto de Astrofísica de Canarias

    A new study led by scientists from the Instituto de Astrofísica de Canarias (IAC) reveals that the giant exoplanet WASP-69b carries a comet-like tail made up of helium particles escaping from its gravitational field and propelled by the ultraviolet radiation of its star. The results of this work are published today in the journal Science.

    The planet was observed during a transit, when it passed in front of its host star. During this event, the planet and its atmosphere eclipse part of the starlight. "We observed a stronger and longer-lasting dimming of the starlight in a region of the spectrum where helium gas absorbs light," says Lisa Nortmann, a researcher at the IAC and lead author of the article published today in the journal Science. "The longer duration of this absorption allows us to infer the presence of a tail," she adds.

    But this is not the only result described in the article. The authors have also analyzed four other planets in a similar way. These are the hot exoplanets HD 189733b and HD 209458b, which have a mass similar to that of Jupiter, the extremely hot giant planet KELT-9b and the warm Neptune-sized exoplanet GJ 436b. The analysis does not show extensive helium exospheres around the last three planets, which defies previous theoretical predictions. The hot Jupiter HD 189733b, on the other hand, does reveal a clear signal of absorbing helium, although here, the helium envelope is more compact and does not form a tail.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  2. #32
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    Our hot disintegrating friend KELT-9b is back in the news.

    https://arxiv.org/abs/1812.02773

    A ground-based NUV secondary eclipse observation of KELT-9b

    Matthew J. Hooton, Christopher A. Watson, Ernst J. W. de Mooij, Neale P. Gibson, Daniel Kitzmann (Submitted on 6 Dec 2018)

    KELT-9b is a recently discovered exoplanet with a 1.49 d orbit around a B9.5/A0-type star. The unparalleled levels of UV irradiation it receives from its host star put KELT-9b in its own unique class of ultra-hot Jupiters, with an equilibrium temperature > 4000 K. The high quantities of dissociated hydrogen and atomic metals present in the dayside atmosphere of KELT-9b bear more resemblance to a K-type star than a gas giant. We present a single observation of KELT-9b during its secondary eclipse, taken with the Wide Field Camera on the Isaac Newton Telescope (INT). This observation was taken in the U-band, a window particularly sensitive to Rayleigh scattering. We do not detect a secondary eclipse signal, but our 3σ upper limit of 181 ppm on the depth allows us to constrain the dayside temperature of KELT-9b at pressures of ~30 mbar to 4995 K (3σ ). Although we can place an observational constraint of A g < 0.14, our models suggest that the actual value is considerably lower than this due to H − opacity. This places KELT-9b squarely in the albedo regime populated by its cooler cousins, almost all of which reflect very small components of the light incident on their daysides. This work demonstrates the ability of ground-based 2m-class telescopes like the INT to perform secondary eclipse studies in the NUV, which have previously only been conducted from space-based facilities.

    ===============

    I would think deformation comes before disintegration.

    https://arxiv.org/abs/1812.04538

    Detectability of shape deformation in short-period exoplanets

    B. Akinsanmi, S. C. C. Barros, N. C. Santos, A. C. M. Correia, P. F. L. Maxted, G. Boué, J. Laskar (Submitted on 11 Dec 2018)

    Short-period planets suffer from extreme tidal forces from their parent stars causing them to deform and attain non-spherical shapes. The planet shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light curves and the planetary parameters derived. We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We show how the detection of deformation from the light curve allows us to obtain an observational estimate of the second fluid Love number which gives valuable insight about the planet's internal structure. We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. Our model is parameterized by the Love number, hence for a given light curve we can derive the value of the Love number that best matches the observations. We simulated the known cases of WASP-103b and WASP-121b expected to be highly deformed. Our analyses showed that instrumental precision ≤ 50ppm/min is needed to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in ~40 transits using HST and in ~300 transits using the forthcoming CHEOPS. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST can permit the detection of deformation with a single transit. However, the effects of instrumental and astrophysical noise must be well-considered as they can increase the number of transits required to reach the 50 ppm/min detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the planet's shape thereby leading us to infer sphericity for a deformed planet.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  3. #33
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    A fast-boiling Neptune-type planet that will disappear before long...

    https://phys.org/news/2018-12-hubble...ay-planet.html

    Hubble finds far-away planet vanishing at record speed
    December 13, 2018, Johns Hopkins University

    The speed and distance at which planets orbit their respective blazing stars can determine each planet's fate—whether the planet remains a longstanding part of its solar system or evaporates into the universe's dark graveyard more quickly. In their quest to learn more about far-away planets beyond our own solar system, astronomers discovered that a medium-sized planet roughly the size of Neptune, GJ 3470b, is evaporating at a rate 100 times faster than a previously discovered planet of similar size, GJ 436b.

    The findings, published today in the journal of Astronomy & Astrophysics, advance astronomers' knowledge about how planets evolve. "This is the smoking gun that planets can lose a significant fraction of their entire mass. GJ 3470b is losing more of its mass than any other planet we seen so far; in only a few billion years from now, half of the planet may be gone," said David Sing, Bloomberg Distinguished Professor at Johns Hopkins and an author on the study.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  4. #34
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    More on same "evaporating" exoplanet.

    Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b

    V.Bourrier, et al. (Submitted on 12 Dec 2018)

    GJ 3470b is a warm Neptune transiting an M-dwarf star at the edge of the evaporation desert. It offers the possibility of investigating how low-mass, close-in exoplanets evolve under the irradiation from their host stars. We observed three transits of GJ 3470b in the Lyman-alpha line with the Hubble Space Telescope (HST) as part of the Panchromatic Comparative Exoplanet Treasury (PanCET) program. Absorption signatures are detected with similar properties in all three independent epochs, with absorption depths of 35+-7% in the blue wing of the line, and 23+-5% in the red wing. The repeatability of these signatures, their phasing with the planet transit, and the radial velocity of the absorbing gas allow us to conclude that there is an extended upper atmosphere of neutral hydrogen around GJ 3470 b. We determine from our observations the stellar radiation pressure and XUV irradiation from GJ 3470 and use them to perform numerical simulations of the upper atmosphere of GJ 3470b with the EVaporating Exoplanets (EVE) code. The unusual redshifted signature can be explained by the damping wings of dense layers of neutral hydrogen that extend beyond the Roche lobe and are elongated in the direction of the planet motion. This structure could correspond to a shocked layer of planetary material formed by the collision of the expanding thermosphere with the wind of the star. The blueshifted signature is well explained by neutral hydrogen atoms escaping at rates of about 1e10 g s-1 that are blown away from the star by its strong radiation pressure and are quickly photoionized, resulting in a smaller exosphere than that of the warm Neptune GJ 436b. The stronger escape from GJ 3470b, however, may have led to the loss of about 4-35% of its current mass over its 2 Gyr lifetime.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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