Astronomers Predict a ‘Habitable Earth’ Twin Found in 2011

6a00e551c4c4d88833010535dae634970b-320wi Are Earth-like planets rare or common in the Universe? In September 2010, a truly exceptional find elated the planet's artonomy community: the first alien planet that could host life on its surface, Gliese 581 g, was discovered by a team led by Steven Vogt of the University of California, Santa Cruz. The new-found exo-planet inhabits a "Goldilocks" 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 -a key to the potential evolution of life.

Although a second team of astronomers failed to find signs of Gliese 581 g in their data, reported newscientist.com, if its existence is confirmed, it will be the most habitable exoplanet yet found.


When scientists confirmed in October that they had detected the first rocky planet outside our solar system, it advanced the longtime quest to find an Earth-like planet hospitable to life. The rocky planet CoRoT-7 b is, however, proving to be a forbidding place, undergoing continuous, fierce volcanic eruptions.

Rocky planets — Earth, Mercury, Venus and Mars — make up half the planets in our solar system. Rocky planets are considered better environments to support life than planets that are mainly gaseous, like the other half of the planets in our system: Jupiter, Saturn, Uranus and Neptune.

The rocky planet CoRoT-7 b was discovered circling a star some 480 light years from Earth. It is, however, unlikely to harbor life because it is so close to its star that temperatures might be above 4,000 degrees F (2,200 C) on the surface lit by its star and as low as minus 350 F (minus 210 C) on its dark side.

Now scientists led by a University of Washington astronomer say that if CoRoT-7 b's orbit is not almost perfectly circular, then the planet might also be undergoing fierce volcanic eruptions. It could be even more volcanically active than Jupiter's moon Io, which has more than 400 volcanoes and is the most geologically active object in our solar system.

"If conditions are what we speculate, then CoRoT-7 b could have multiple volcanoes going off continuously and magma flowing all over the surface," says Rory Barnes, a UW postdoctoral researcher of astronomy and astrobiology. Any planet where the surface is being remade at such a rate is a place nearly impossible for life to get a foothold, he says.

The next step to finding a planet that harbors life may have to wait until astronomers are better able to detect rocky planets that are farther from their stars, Barnes says. "Because it is easier to detect planets that orbit close to their host stars, a significant fraction of the first wave of rocky planets being found outside our solar system may be more Io-like than Earth-like."

Barnes and his colleagues suspect CoRoT-7 b is subject to extreme volcanism partly because it is so close to its sun, the distance between the two being about 1.6 million miles (2.5 million kilometers). That's about 60 times closer than the Earth is to the sun.

Volcanism is triggered by even a tiny deviation from a circular orbit. How tiny of a deviation? About 155 miles (250 kilometers), according to calculations done by Barnes based on how bodies in our solar system influence each other's orbits. That's about the distance from Washington, D.C., to Philadelphia. That amount of deviation, or more, could be caused by the gravitational pull of the next planet out from CoRoT-7 b.

Deviations in its orbit would set tidal forces in motion that flex and distort the whole shape of CoRoT-7 b. This is different from what happens on Earth, where oceans absorb the energy of tidal forces.

"CoRoT-7 b most certainly has no oceans. A planet on a non-circular orbit experiences different amounts of gravitational force at different points along the orbit, feeling the strongest gravitational pull when it is closest to the star and the weakest when it is most distant. As the planet moves between these two points, it stretches and relaxes. This flexing produces friction that heats the interior of the planet resulting in volcanism on the surface," Barnes says.

"This scenario is exactly what is occurring on Jupiter's moon Io. For planets like CoRoT-7 b, however, the heating may be much, much stronger than on Io."

So the search continues for a planet with the size and temperature of Earth. In early 2010 a metric of "habitability index" was created by Samuel Arbesman and  Greg Laughlin of the University of California, Santa Cruz. The  idex is based on estimates of a planet's average temperature and size. "Hot Jupiters", 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 – Gliese 581 g – was spotted although the detection is awaiting further confirmation.

New Scientist adapted the data to include Gliese 581 g's habitability index of 0.4, and come up with figures that suggest there is an 82 per cent chance that we will find a true doppelgänger for Earth by the close of 2011.

Exoplanet-hunters could strike gold in February, when NASA's Kepler Space Telescope is set to release a flood of newly discovered data. Even if Earth's twin doesn't emerge then, there are plenty of other exoplanet searches that could spot it too.

But there is still a contingent of "Rare Earth" belivers watchiing from the sidelines. The "Rare Earth" hypothesis is the idea that life is a staggeringly unlikely event, and that the reason we haven't seen hide nor hair (nor scale nor weird gel-layer) of aliens is that there aren't any.  It's had some time in the spotlight, it makes us sound very important, and it's wrong.

The Rare Earth argument ignores a number of essential factors, the first being how staggeringly huge the numbers involved are.  Even the Milky Way has 200 to 400 billion stars, and it's only one of a hundred billion galaxies in the observable universe, and there have been billions of years for things to happen.  Countering "it's really unlikely" with "but there are lots of things!" might sound weak, but it's the Rare Earthers who are taking the burden of proof – claiming that nothing happens anywhere else ever.  The more places there are, the worse their argument gets.

Geologist Peter Ward and astrobiologist Donald Brownlee, both of the University of Washington have outlined a short list of conditions needed: Right distance from a star; habitat for complex life; liquid water near surface; far enough to avoid tidal lock; right mass of star with long enough lifetime and not too much ultraviolet; stable planetary orbits; right planet mass to maintain atmosphere and ocean with a solid molten core and enough heat for plate tectonics; a Jupiter-like neighbor to clear out comets and asteroids; plate tectonics to build up land mass, enhance bio-diversity, and enable a magnetic field; not too much, nor too little ocean; a large moon at the right distance to stabilize tilt; a small Mars-like neighbor as possible source to seed Earth-like planet; maintenance of adequate temperature, composition and pressure for plants and animals; a galaxy with enough heavy elements, not too small, ellipitcal or irregular; right position the galaxy; few giant impacts like had 65 million years ago; enough carbon for life, but not enough for runaway greenhouse effect; evolution of oxygen and photosynthesis; and, of course, biological evolution.

Claims that there aren't many suitable planets over all these stars are like hiding in a closet and claiming there's no such thing as coffee tables – we're now detecting planets at an ever-increasing rate, because now we have technology actually capable of detecting planets.  Almost as soon as we try any new planet-detecting technique it detects a whole bunch of the things.  We're even edging into the ability to find Earth-size planets, and what do you know?  There they are!  And some even have water!

The second slip-up is ignoring the suitability of the laws of physics to life – or rather, the suitability of our form of life to the laws of physics. The idea of someone sitting in pre-existence limbo and tuning the weak nuclear force in order to create bald monkeys is patently ridiculous, as is the idea that only a tiny range of values could give rise to any repeating pattern – our pattern, DNA, is just the one that happened to work for the collection of constants we call reality.

Once life is possible in a universe, expecting it to occur in one place only is like leaving a loaf of bread and expecting exactly one slice to go moldy.  Life just happens here – thermodynamic math has shown that amino acids simply will be built anywhere their components can be found.  Since those components are on the periodic table, the literal "this is what happens in this universe" list, they're going to be all over.  Assuming aliens don't come up with another pattern anyway (increasing the odds again).

Claiming that we're the only life in existence is a combination of ignorance and self-importance that should have a livejournal, not a scientific journal. 

Daily Galaxy via University of Washington and newscientist.com

 

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