K2-22b: a hot, Disintegrating Terrestrial World With a Cometary Head and Leading Tail

THE K2-ESPRINT PROJECT. I. DISCOVERY OF THE DISINTEGRATING ROCKY PLANET K2-22b WITH A COMETARY HEAD AND LEADING TAIL

Authors:

Sanchis-Ojeda et al

Abstract:

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from ~0% to 1.3%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with Teff sime 3800 K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant "bump" just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo "Roche lobe overflow," even though the planet's surface is likely underfilling its Roche lobe by a factor of 2.

The Effects of Wakes on Dense Planetary Rings

Dynamics of Self-Gravity Wakes in Dense Planetary Rings I. Pitch Angle

Authors:

Michikoshi et al

Abstract:

We investigate the dynamics of self-gravity wakes in dense planetary rings. In particular, we examine how the pitch angle of self-gravity wakes depend on ring parameters using N-body simulations. We calculate the pitch angles using the two-dimensional autocorrelation function of the ring surface density. We obtain the pitch angles for the inner and outer parts of the autocorrelation function separately. We confirm that the pitch angles are 15 to 30 degrees for reasonable ring parameters, which are consistent with previous studies. We find that the inner pitch angle increases with the Saturnicentric distance, while it barely depends on the optical depth and the restitution coefficient of ring particles. The increase of the inner pitch angle with the Saturnicentric distance is consistent with the observations of the A ring. The outer pitch angle does not have the clear dependence on any ring parameters and is about 10 - 15 degrees. This value is consistent with the pitch angle of spiral arms in collisionless systems.

Migration and Disturbances in Multiplanetary S Type Circumbinary Systems

Migration into a Companion's Trap: Disruption of Multiplanet Systems in Binaries

Authors:

Touma et al

Abstract:

Most exoplanetary systems in binary stars are of S--type, and consist of one or more planets orbiting a primary star with a wide binary stellar companion. Gravitational forcing of a single planet by a sufficiently inclined binary orbit can induce large amplitude oscillations of the planet's eccentricity and inclination through the Kozai-Lidov (KL) instability. KL cycling was invoked to explain: the large eccentricities of planetary orbits; the family of close--in hot Jupiters; and the retrograde planetary orbits in eccentric binary systems. However, several kinds of perturbations can quench the KL instability, by inducing fast periapse precessions which stabilize circular orbits of all inclinations: these could be a Jupiter--mass planet, a massive remnant disc or general relativistic precession. Indeed, mutual gravitational perturbations in multiplanet S--type systems can be strong enough to lend a certain dynamical rigidity to their orbital planes. Here we present a new and faster process that is driven by this very agent inhibiting KL cycling. Planetary perturbations enable secular oscillations of planetary eccentricities and inclinations, also called Laplace--Lagrange (LL) eigenmodes. Interactions with a remnant disc of planetesimals can make planets migrate, causing a drift of LL mode periods which can bring one or more LL modes into resonance with binary orbital motion. The results can be dramatic, ranging from excitation of large eccentricities and mutual inclinations to total disruption. Not requiring special physical or initial conditions, binary resonant driving is generic and could have profoundly altered the architecture of many S--type multiplanet systems. It can also weaken the multiplanet occurrence rate in wide binaries, and affect planet formation in close binaries.

Relationship Between ExoPlanet Occurance and Wide Binary Host Stars

A Pan-STARRS1 study of the relationship between wide binarity and planet occurrence in the Kepler field

Authors:

Deacon et al

Abstract:

The NASA Kepler mission has revolutionised time-domain astronomy and has massively expanded the number of known extrasolar planets. However, the effect of wide multiplicity on exoplanet occurrence has not been tested with this dataset. We present a sample of 401 wide multiple systems containing at least one Kepler target star. Our method uses Pan-STARRS1 and archival data to produce an accurate proper motion catalogue of the Kepler field. Combined with Pan-STARRS1 SED fits and archival proper motions for bright stars, we use a newly developed probabilistic algorithm to identify likely wide binary pairs which are not chance associations. As by-products of this we present stellar SED templates in the Pan-STARRS1 photometric system and conversions from this system to Kepler magnitudes. We find that Kepler target stars in our binary sample with separations above 6 arcseconds are no more or less likely to be identified as confirmed or candidate planet hosts than a weighted comparison sample of Kepler targets of similar brightness and spectral type. Therefore we find no evidence that binaries with projected separations greater than 3,000AU affect the occurrence rate of planets with P less than 300days around FGK stars.

Testing the Zoo Hypothesis for the Fermi Paradox

A direct communication proposal to test the Zoo Hypothesis

Author:

de Magalhaes

Abstract:

Whether we are alone in the universe is one of the greatest mysteries facing humankind. Given the greater than 100 billion stars in our galaxy, many have argued that it is statistically unlikely that life, including intelligent life, has not emerged anywhere else. The lack of any sign of extraterrestrial intelligence, even though on a cosmic timescale extraterrestrial civilizations would have enough time to cross the galaxy, is known as Fermi's Paradox. One possible explanation for Fermi's Paradox is the Zoo Hypothesis which states that one or more extraterrestrial civilizations know of our existence and can reach us, but have chosen not to disturb us or even make their existence known to us. I propose here a proactive test of the Zoo Hypothesis. Specifically, I propose to send a message using television and radio channels to any extraterrestrial civilization(s) that might be listening and inviting them to respond. Even though I accept this is unlikely to be successful in the sense of resulting in a response from extraterrestrial intelligences, the possibility that extraterrestrial civilizations are monitoring us cannot be dismissed and my proposal is consistent with current scientific knowledge. Besides, issuing an invitation is technically feasible, cheap and safe, and few would deny the profound importance of establishing contact with one or more extraterrestrial intelligences. A website has been set up (this http URL) to encourage discussion of this proposal and for drafting the invitation message.

Rapid Water Loss can Extend the Lifetime of the Planetary Habitability

Rapid Water Loss can Extend the Lifetime of the Planetary Habitability

Authors:

Kodama et al

Abstract:

Two habitable planetary states are proposed: an aqua planet like the Earth and a land planet that has a small amount of water. Land planets keep liquid water under larger solar radiation compared to aqua planets. Water loss may change an aqua planet into a land planet, and the planet can remain habitable for a longer time than had it stayed an aqua planet. We calculate planetary evolution with hydrogen escape for different initial water inventories and different distances from the central star. We find that there are two conditions to evolve an aqua planet into a land planet: the critical amount of water on the surface M_ml consistent with a planet being a land planet, and the critical amount of water vapor in the atmosphere M_cv that defines the onset of the runaway greenhouse state. We find that Earth-size aqua planets with initial oceans < 10 % of the Earth's can evolve into land planets if M_cv = 3 m in precipitable water and M_ml = 5 % of the Earth's ocean mass. Such planets can keep liquid water on their surface for another 2 Gyrs. The initial amount of water and M_cv are shown to be important dividing parameters of the planetary evolution path. Our results indicate that massive hydrogen escape could give a fresh start as another kind of habitable planet rather than the end of its habitability.

Titanium(IV) Oxide (Titania) can Produce Oxygen Rich Habitable Zone Atmospheres WITHOUT Life

Titania may produce abiotic oxygen atmospheres on habitable exoplanets

Authors:

Narita et al

Abstract:

The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium(IV) oxide (titania) can produce abiotic oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of abiotic oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this abiotic mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets.