Speculative Fact #150: Alpha Centauri Has a Planet

12/27/2013

Perhaps due to its relative proximity to Earth (a little over four light years, a modest leap in galactic terms) the binary star system of Alpha Centauri A&B has long held our attentions from ancient astronomers to speculative fiction writers. The almost romantic premise of reaching such a tantalizingly close system tempts the wander-lusting ape in each of us.
           In 2012 a European team discovered that Alpha Centauri B has a planet, currently known as Bb. The planet, while similar to Earth in terms of mass, orbits much too close to its star to be habitable (surface temperature of 1200 degrees Celsius, more than twice the temperature of Venus, the hottest planet in our system).
                The discovery has nonetheless opened the door of possibilities. If Alpha Centauri B has a planet there may be other Earth-mass planets waiting to be detected. It took over three years of observation to detect Alpha Centauri Bb, using an advanced and complicated technique (radial velocity).
                If the Alpha Centauri AB system has Earthlike planets they might make a logical destination for future spacefarers. While methods for reaching the nearby binary system are only theoretical they have been explored by private visionaries and even the US naval academy and NASA (project Longshot). Next stop…Alpha Centauri!

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Speculative Fact contributions are researched and written by Jonathan Hernandez and Rob Cameron

The Muse Tweets

Mark Salzwedel link

1/6/2014 12:25:21 pm

Radial velocity isn't really that complicated. Because of the Doppler Effect, stars’ spectra shift toward red as they recede from us, toward
blue as they approach us. A planet orbiting a star exerts enough gravimetric force on the star to cause it to wobble slightly. If we notice
a shift in a star’s spectrum at regular intervals, we can infer that it is caused by a planet or another dim star orbiting the star pulling it
slightly. The limitation is that we can only determine a minimum mass for the orbiting body, since we can’t tell if it’s a smaller planet orbiting
close to our line of sight or a larger planet orbiting at a greater angle.

More complex is gravitational microlensing. When a star with an orbiting planet, passes between us and another star, the eect of the
star’s and its planet’s gravity can act like a lens on the background star which makes it brighter during the time their edges pass in front of
the background star. With this method, we can more easily detect planets around stars we view pole on, such as Vega, but it requires
careful planning to make sure several observatories are ready and focused on the right part of the sky when the microlensing event
occurs.