Potentially habitable planet discovered just 4 light-years away
A team of astronomers has discoveredclear evidence of a potentially habitable Earth-sized planet orbitingthe closest star to our solar system, Proxima Centauri. This newlydiscovered world, which lies only four light-years from Earth in thedirection of the constellation Centaurus, will become a key targetfor missions searching for life beyond the nurturing influence of ourSun.
Proxima Centauri is classified as a reddwarf. Considered to be relatively small and cool compared to our ownSun, red dwarfs are the most common form of star populatingthe Milky Way. Despite their diminutive nature, it is thought thatplanets orbiting in the habitable zones (HZs) of red dwarfs arecapable of sustaining life.
A HZ is essentially a region of spacesurrounding a star in which an orbiting rocky planet can maintainliquid water on its surface. Since water is thought to be one of thekey ingredients for the evolution of life, Earth-sized planetsorbiting in these regions are a prized target for astronomers lookingfor extraterrestrial life. The HZ of a red dwarf is much closer to the star's surfacewhen compared to that of a stellar body such as our own Sun.
The discovery of the exoplanet, whichhas been named Proxima b, was made thanks to an international effortknown as the Pale Red Dot campaign. Named in reference to the reddishhue of light thrown off by Proxima Centauri, and as a tribute to CarlSagan's moniker for Earth as the "pale blue dot," the campaign wasformed to keep an eye on our Sun's closest neighbor, in the hope ofspotting an orbiting Earth-like exoplanet.
For the first half of 2016, ProximaCentauri was regularly monitored by a host of observatories spreadacross the globe. These telescopes, including the ESO's 3.6 m (11.8ft) telescope located at theLa Scilla observatory, Chile, were searching for minute wobbles thatwould serve as proof that the red dwarf was being disturbed by thegravitational influence of an orbiting exoplanet.
The first detection of Proxima boccurred in 2013, however the evidence was not sufficient to clearlypoint to the existence of the exoplanet. The intensive observationscarried out in 2016 under the Pale Red Dot effort were moresuccessful, providing clear evidence that the star was indeedwobbling through space. At points, the red dwarf was observedtraveling back towards Earth at a rate of 5 km per hour (3.1 milesper hour), and then away from our planet at the same pace. This cyclecontinued once every 11.2 days.
An analysis of the 2013 readings inconjunction with the Pale Red Dot observations of Proxima Centauri'swobble and light signature, provided clear evidence for the existenceof Proxima b. It is estimated that the exoplanet has a mass 1.3 timesthat of Earth, and orbits its star at a distance of 7 million km (4.3million miles), placing it wellinside the HZ of a red dwarf star.
"I kept checking the consistency ofthe signal every single day during the 60 nights of the Pale Red Dotcampaign" commented Dr Guillem Anglada-Escudé, one of the leadastronomers behind the Pale Red Dot campaign hailing from Queen MaryUniversity, London. "The first 10 were promising, the first 20 wereconsistent with expectations, and at 30 days the result was prettymuch definitive, so we started drafting the paper!"
So, could this newfound planet, whichorbits its star at only 5 percent the distance between the Earth andSun actually be habitable?
Ultimately, we do not yet know. It isestimated that the surface temperature is conducive to the presenceof liquid water, but that the environment may have been radicallyaltered from anything we know here on Earth as a result of itsdisparate formation history, and the intense radiation pouring outfrom the nearby red dwarf.
Furthermore, it is possible that theplanet is rotationally locked to its star. This means that one faceof the world is bathed in perpetual daylight, and the other inconstant night. According to one of the papers published on thediscovery of Proxima b, if the exoplanet were to be rotationallylocked, liquid water would likely only exist on the side bathed insunlight. If the exoplanet's orbit is not locked, then it is thoughtthat water could only endure in a tropical belt.
There are numerous reasons that havebeen given as to why life could not evolve on the planet. It has beensuggested that Proxima b does not experience seasons, and that theatmosphere could be fundamentally different to our own, assuming thatit hasn't evaporated away into space. On the bright side, none ofthese doom-and-gloom scenarios can be proven without directobservation of the planet, and this can only occur in the unlikelyevent that the exoplanet passes between Proxima Centauri and Earth.
Although it is extremely doubtful thatthis will happen, current and future Earth-bound and orbitaltelescopes will watch for just such an occurrence, which would allowastronomers to glean an understanding of the composition of Proximab's atmosphere.
Scroll down to view a fly-through of the Proxima Centauri system.