Read more: 鈥淚n with the 快猫短视频: Our predictions for 2011鈥�
Earthlings will surely thrill at finding their planetary double: our calculation suggests the discovery could happen next year
In 2010, one new exoplanet appeared every four days or so; by the end of the year, the total topped 500. But in September, a truly exceptional find punctuated this steady drumbeat of discovery: the first alien planet that could host life on its surface.
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Gliese 581 g, spotted by a team led by Steven Vogt of the University of California, Santa Cruz, inhabits a 鈥淕oldilocks鈥� zone around its host star, a band just warm enough to boast liquid water. At 3.1 to 4.3 times the mass of Earth, it is also small enough that it should be made mostly of rock. Although a second team of astronomers failed to find signs of Gliese 581 g in their data, if its existence is confirmed, it will be the most habitable exoplanet yet found.
An even bigger prize awaits, however: a planet with the size and temperature of our own. We鈥檙e unlikely to be exceptional, so such a doppelg盲nger must be out there. Will it be found in 2011? See 鈥淧rediction: Get ready for Earth鈥檚 doppelg盲nger鈥�.
Prediction: Get ready for Earth鈥檚 doppelg盲nger
Like meeting an estranged twin you didn鈥檛 know you had, Earthlings will thrill at finding their planetary double.
To predict the timing of this momentous occasion, we turned to a measure of 鈥淓arth-like-ness鈥� devised earlier this year by one of us (Arbesman), along with Greg Laughlin of the University of California, Santa Cruz. This 鈥渉abitability index鈥� is based on estimates of a planet鈥檚 average temperature and size. 鈥淗ot Jupiters鈥�, searingly hot worlds that orbit their hosts in just days, score close to zero, while one with similar properties to Earth would get a value of 1.
In September, plotting the index of each planet against the date of its discovery and extrapolating the resulting curves predicted that an Earth-like planet would be found by May 2011. Two weeks later, such a planet 鈥� Gliese 581 g 鈥� was spotted although the detection is awaiting further confirmation.
Now we鈥檝e taken the same curves, adapted them to include Gliese 581 g鈥檚 habitability index of 0.4, and come up with a fresh prediction. Our figures suggest there is an 82 per cent chance that we will find a true doppelg盲nger for Earth by the close of 2011.
This exciting prediction is subject to uncertainty as the dates of exoplanet discoveries are only known to the year. What鈥檚 more, the habitability index does not account for a planet鈥檚 atmosphere, which could turn what would otherwise be a hospitable world into a hothouse like Venus.
Exoplanet-hunting may get a boost in February, when NASA鈥檚 is set to release a flood of data. Even if Earth鈥檚 twin doesn鈥檛 emerge then, there are plenty of other exoplanet searches that could spot it too. Samuel Arbesman and Rachel Courtland
