Title: Kepler-16b: safe in a resonance cell Author: E. A. Popova, I. I. Shevchenko
The planet Kepler-16b is known to follow a circumbinary orbit around a system of two main-sequence stars. We construct stability diagrams in the "pericentric distance - eccentricity" plane, which show that Kepler-16b is in a hazardous vicinity to the chaos domain - just between the instability "teeth" in the space of orbital parameters. Kepler-16b survives, because it is close to the stable half-integer 11/2 orbital resonance with the central binary, safe inside a resonance cell bounded by the unstable 5/1 and 6/1 resonances. The neighbouring resonance cells are vacant, because they are "purged" by Kepler-16b, due to overlap of first-order resonances with the planet. The newly discovered planets Kepler-34b and Kepler-35b are also safe inside resonance cells at the chaos border.
Title: Planetesimal accumulation in 16 Kepler B Authors: Francesco Marzari, Philippe Thebault, Hans Scholl, G. Picogna, Clement Baruteau
Recent observations from NASA's Kepler mission detected the first planets in circumbinary orbits. The question we try to answer is where these planets formed in the circumbinary disk and how far inside they migrated to reach their present location. We investigate the first and more delicate phase of planet formation when planetesimals accumulate to form planetary embryos. We use the hydrodynamical code FARGO to study the evolution of the disk and of a test population of planetesimals embedded in it. With this hybrid hydrodynamical--N--body code we can properly account for the gas drag force on the planetesimals and for the gravitational force of the disk on them. The numerical simulations show that the gravity of the eccentric disk on the planetesimal swarm excites their eccentricities to values much larger than those induced by the binary perturbations only within 10 AU from the stars. Moreover, the disk gravity prevents a full alignment of the planetesimal pericenters. Both these effects lead to large impact velocities, beyond the critical value for erosion. Planetesimals accumulation in circumbinary disks appears to be prevented close to the stellar pair by the gravitational perturbations of the circumbinary disk. The observed planets possibly formed in the outer regions of the disk and then migrated inside by tidal interaction with the disk.
Hobby-Eberly Telescope measures two stars with one orbiting planet
A team of Penn State University astronomers has obtained very precise measurements of a pair of stars that are orbited by a planet -- like the stellar system of the fictional planet Tatooine in the movie Star Wars. The orbits of the stars and planet in the system, named Kepler-16, are aligned so that they eclipse or transit each other when observed from Earth. These new measurements will aid astronomers in understanding how stars and planetary systems form. The Penn State astronomers used the spectroscopic capabilities of the Hobby-Eberly Telescope at McDonald Observatory to separate the light from the two Kepler-16 stars into individual wavelengths, which allowed them to precisely measure the masses of the stars. Read more
Title: Circumbinary Planet Formation in the Kepler-16 system. I. N-body Simulations Authors: Stefano Meschiari
The recently discovered circumbinary planets (Kepler-16 b, Kepler-34 b, Kepler-35 b) represent the first direct evidence of the viability of planet formation in circumbinary orbits. We report on the results of N-body simulations investigating planetesimal accretion in the Kepler-16 b system, focusing on the range of impact velocities under the influence of both stars' gravitational perturbation and friction from a putative protoplanetary disk. Our results show that planet formation might be effectively inhibited for a large range in semi-major axis (1.75 < a_P < 4 AU), suggesting that the planetary core must have either migrated from outside 4 AU, or formed in situ very close to its current location.
Title: Habitability of Earth-type Planets and Moons in the Kepler-16 System Authors: Billy Quarles, Zdzislaw E. Musielak, Manfred Cúntz
We demonstrate that habitable Earth-type planets and moons can exist in the Kepler-16 system by investigating their orbital stability in the standard and extended habitable zone (HZ). We find that Earth-type planets in S-type orbits are possible within the standard HZ in direct vicinity of Kepler-16b, thus constituting habitable exomoons. However, Earth-mass planets cannot exist in P-type orbits around the two stellar components within the standard HZ. Yet, P-type Earth-mass planets can exist superior to the giant planet in the extended HZ pertaining to considerably enhanced back-warming in the planetary atmosphere if facilitated. We briefly discuss the potential detectability of such habitable Earth-type moons and planets positioned in S-type and P-type orbits, respectively.
Title: Kepler 16: A System of Potential Interest to Astrobiologists Authors: Martin J. Heath, Laurance R. Doyle
We use the circumbinary planetary system Kepler-16b as an example to specify some considerations that may be of interest to astrobiologists regarding the dynamic nature of habitable zones around close double star systems.
NASA'S Kepler Discovery Confirms First Planet Orbiting Two Stars
The existence of a world with a double sunset, as portrayed in the film Star Wars more than 30 years ago, is now scientific fact. NASA's Kepler mission has made the first unambiguous detection of a circumbinary planet -- a planet orbiting two stars -- 200 light-years from Earth. Read more
Tatooine Found? -- Planet With Twin Suns Discovered
Although cold and gaseous rather than a desert world, the newfound planet Kepler-16b is still the closest astronomers have come to discovering Luke Skywalker's home world of Tatooine. Like Tatooine, Kepler-16b enjoys a double sunset as it circles a pair of stars approximately 200 light-years from Earth. It's not thought to harbour life, but its discovery demonstrates the diversity of planets in our galaxy.
"Kepler-16b is the first confirmed, unambiguous example of a circumbinary planet - a planet orbiting not one, but two stars. Once again, we're finding that our solar system is only one example of the variety of planetary systems Nature can create" - Josh Carter of the Harvard-Smithsonian Center for Astrophysics (CfA).