Road to Pandora

Pandora of as seen in the movie Avatar

The world famous movie Avatar invented an exomoon, which had a story that took a worldwide fame and revenue. That exomoon was Pandora, an earth-like moon that orbits around a gas giant called Polyphemus. As said in avatar, this system lies in the habitable zone (zone where liquid water can exist) of Alpha Centauri A star. Therefore the moon Pandora is teeming with exotic life as you witnessed by watching the movie.

Alpha Centauri A is one of the stars of the Alpha Centauri star system, located at a distance of 4.37 light years away from the Earth. The stars Alpha Centauri A and Alpha Centauri B are orbiting each other, getting close as Saturn to the sun and getting far as Pluto and sun. Many planetary scientists proposed the possibility of a gas giant like Polyphemus is less, because the gravitational pull of the two stars will kick out such a large planet out of the system.  Therefore a terrestrial planet orbiting a star was expected to be found.

In 2009 computer simulations showed that a planet might have been able to form within a distance of 1.1 AU (160 million km) of Alpha Centauri B, and that the orbit of that planet may remain stable for at least 250 million years. Proving close to that simulation, a team of European scientists of the ESO (European Southern Observatory) have found confirmable evidence of an earth-like planet orbiting around Alpha Centauri B star. Then, the existence of Pandora is coming quite possible due to this discovery which was revealed on 16^th October 2012.

Artist's Conception of the newly discovered planet
CREDIT : ESO\L . Calcada

This is the closest exoplanet to Earth which has been ever discovered. Also it is the least massive exoplanet that was discovered orbiting a sun-like star.  This planet is named as Alpha Centauri Bb and it has a 1.13 times the mass of the earth. But don’t expect liquid water on it. Because this one orbits around its star at a stunning distance about 3.6 million miles (6 million kilometers or 0.04 AU) and orbits a round in just 3.6 days. That means its orbit is too much closer to the star than the mercury’s orbit to our sun. The gravitational force of the Alpha Centauri A has pulled the planet much forward to the star. Because of that it has a heat-blasted surface of 1200 ⁰C and it may be covered with molten rock or lava. (Watch the video about it by ESO.)

Although closest to the earth, it took a long time to discover this planet after the discoveries of more than 840 exoplanets. Because the star system is much complex to discover clues of an exoplanet. After high accurate measurements this discovery was made using the radial velocity technique with HARPS (High Accuracy Radial velocity Planet Searcher) at La Silla Observatory, Chile. The technique used is to measure the Doppler shifts in the spectrum of a star due to the gravitational pull of a planet. The highest precision of the HARPS instrument, magnitude of 51 centimeters per second was reported to make this important discovery.   More than 450 HARPS measurements taken over four years of observing have been needed to detect the planet's signal.

Top left : Dome of the telescope
Top right: The relescope
Lower: The HARPS Spectrograph 

The discovery team is composed of Xavier Dumusque (Observatoire de Genève, Switzerland; Centro de Astrofisica da Universidade do Porto, Portugal), Francesco Pepe (Observatoire de Genève), Christophe Lovis (Observatoire de Genève), Damien Ségransan (Observatoire de Genève), Johannes Sahlmann (Observatoire de Genève), Willy Benz (Universität Bern, Switzerland), François Bouchy (Observatoire de Genève; Institut d’Astrophysique de Paris, France), Michel Mayor (Observatoire de Genève), Didier Queloz (Observatoire de Genève), Nuno Santos (Centro de Astrofisica da Universidade do Porto) and Stéphane Udry (Observatoire de Genève).

 Many low-mass planets like Alpha Centauri Bb are in a system of two, three or even up to six, seven planets.  So, this has raised the possibility of a planet in the habitable zone or goldilock zone of Alpha Centauri B, located at 65 million miles from the star that a planet would take around 200 days to orbit. Many astronomers say there are more planets in this system definitely. Dr. Dumusque has said that it would need 8 to 10 years to find a planet at 200 days by using this instrument.

So this discovery makes a landmark in the goal of exoplanet hunters, finding an earth-like exoplanet, the so-called Earth 2.0.  With the advancement of the technology in the next decade, exoplanet hunters would discover a Pandora, orbiting around one of a star or both. Even without Polyphemus, it would be a science fiction Pandora becoming a fact. Some scientists have proposed to send a probe to Alpha Centauri system even it would take 100 years or more time to reach.  It seems like our closest neighbor star system has much more mysteries than we anticipated.

The position of Pandora as depicted in the Avatar game.

Want to know how James Cameron saw Pandora. Visit here for all scientific information about Pandora.