Field of Science

One planet, two stars

When we are going to approach to the binary system Kepler-16 (image source) we'll see two different stars: the largest of the couple, the star A, is a K dwarf with a mass of about 0.69 solar mass and about 0.65 Sun's radius, and a little red dwarf, the stra B, with a mass of about 0.2 solar mass and about 0.23 Sun's radius. But when we'll arrive at about 0.5 au from the gravitational centre of the binary system we'll see a great surprise: a little planet with a mass of 0.333 ± 0.016 and a radius of 0.7538 ± 0.0025 those of Jupiter(1).
In this momenti is very difficult to suppose the properties(2) (like composition and surface temperature) of Kepler-16b, but the most important thing is that Kepler can discover, using the transit technique, also a planet around a binary system! I think that this is the principle reason becuase the paper was accepted by Science. And it's clear that all nerd and sci-fi fan think about Skywalker family's planet, Tatooine:

Press release: Nasa, Kepler
Two interesting posts from SETI by Laurance Doyle and Franck Marchis
(1) Doyle, L., Carter, J., Fabrycky, D., Slawson, R., Howell, S., Winn, J., Orosz, J., Pr sa, A., Welsh, W., Quinn, S., Latham, D., Torres, G., Buchhave, L., Marcy, G., Fortney, J., Shporer, A., Ford, E., Lissauer, J., Ragozzine, D., Rucker, M., Batalha, N., Jenkins, J., Borucki, W., Koch, D., Middour, C., Hall, J., McCauliff, S., Fanelli, M., Quintana, E., Holman, M., Caldwell, D., Still, M., Stefanik, R., Brown, W., Esquerdo, G., Tang, S., Furesz, G., Geary, J., Berlind, P., Calkins, M., Short, D., Steffen, J., Sasselov, D., Dunham, E., Cochran, W., Boss, A., Haas, M., Buzasi, D., & Fischer, D. (2011). Kepler-16: A Transiting Circumbinary Planet Science, 333 (6049), 1602-1606 DOI: 10.1126/science.1210923 (pdf)
(2) In the paper we can read that the high density suggests a greater degree of enrichment by heavy elements. At the other hand
Nevertheless, for any age greater than 0.5 Gyr, the planet’s interior would include 40-60 Earth masses of heavy elements according to standard planetary models(3). This would imply a composition of approximately half gas (hydrogen and helium) and half heavy elements (presumably ice and rock).
So I think that is not so correct write in press release
Kepler-16b is cold, gaseous and not thought to harbor life
also because
it more difficult to estimate the age [of star A] with theoretical evolutionary models
The surface temperature (170-200 K), instead, seems more certain.
In every case Kepler-16b is a death planet...
(3) Fortney, J.J., et al., Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits, Astroph. J., 659, 1661-1672 (2007)

1 comment:

  1. This is pretty neat- but Kepler 16b is cold and gaseous. If it harbors any form of life, it cannot lifeforms we are accustomed too. Maybe it has moons similar to Europa that could have liquid oceans beneath their icy surface- but any forms of life their would never see the double stars. They would live in the inky blackness of a deep extrasolar sea, having only the flashing lights of strange deep-sea creatures to navigate by.

    I have a question for any astrophysics nerds reading this- is it possible for a planet to have a stable orbit in the habitable zone of the Kepler 16 system, or any other binary system? If it is, perhaps someday a human astronaut will see double suns in the sky of an alien world.

    Christopher Phoenix

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