Field of Science

Planets in Binary Systems, Planets Everywhere

A few weeks ago Debra Fischer from San Francisco State University gave a colloquium here at UW on the 'Formation of Planets in Binary Star Systems'. It was entertaining, enlightening, and involved our closest of friends the, Alpha Centauri binary. I didn't know how to explain how cool this subject or the project was at the time, but now SEED magazine has done the job for me here. Her talk at UW was tagged as
The theory of planet formation has evolved significantly with the detection of more than 300 planets orbiting nearby stars. However, half of stars similar to the Sun are members of binary or multiple star systems. A function of the binary star separation, evolution from the planetesimal to planet embryo stage faces some significant dynamical challenges and is not expected to occur for binary stars with close separations. Contradicting standard theory, a few planets have now been discovered even in close binary systems and provides an impetus to reconsider mechanisms for planet formation in these challenging environments.
The problem observers often face is finding a suitable target to invest intensive observing resources towards (and of course the other problem is having too many targets). There are clues from where past planets have been found, as mentioned above, and from theories of planet formation as the article explains
No one yet knows for certain precisely how planets form, but the process seems to be a complex chain reaction that is highly dependent upon initial conditions. It begins with the creation of a star, which forms from a gravitationally collapsing cloud of gas and dust. The leftovers flatten out, due to the conservation of angular momentum, forming a spinning disk of material. To create a rocky world like Earth, dust must condense in the disk to form grains, grains must settle to form pebbles and rocks, and rocks must collide to form planetesimals, kilometer-sized objects that can gravitationally attract each other. These planetesimals must collide to form embryos, Moon-sized objects that collide in turn to finally form a planet.
Fischer and many others (a team including Greg Laughlin who runs a blog on exoplanets, Systemic) have realized that the Alpha Centauri system's proximity make it a serendipitously excellent target for observing. There remain doubts as to whether a suitable planet can form in this particular binary system, but regardless the observing has begun. The team will be looking for doppler shifts in the motion of the two stars to determine if other massive bodies (a planet) are perturbing the orbit of the stars. It will be a cosmic starring contest lasting several years.

CTIO 1.5-meter telescope where the search happens every night (Copyright NOAO).

If I was a betting man I would bet that we will find an earth size object in the Alpha Centauri system, but I don't bet I count the cards. I claim astronomers will find an earth size object around a distant star within the next ten years, yeah, it is a longshot.

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