Water found on an alien world
Astronomers on Wednesday announced they had spotted the first planet beyond the solar system that has water, the precious ingredient for life. The watery world, though, is far beyond the reach of our puny chemically-powered rockets – and in any case is quite uninhabitable.
It is made of gas rather than rock and its atmosphere reaches temperatures hot enough to melt steel, which means the water exists only as superheated steam. The find, named HD189733b, is about 15% bigger than our Jupiter and orbits a star in the constellation of Vulpecula the Fox.
It was spotted by a team led by Giovanna Tinetti of the European Space Agency (ESA) and University College London. As HD189733b swung in front of its star, it absorbed part of the spectrum of starlight in a telltale way that can only be explained by the presence of water in its atmosphere.
Extrasolar worlds – also called exoplanets – were first spotted in 1995.
So far, 245 of them have been spotted, according to the Extrasolar Planets Encyclopaedia (http://exoplanet.eu/), and the tally is growing at the rate of three or four a month.
Planet would be hell for humans
Virtually all of the discoveries have been made indirectly, mainly by a “wobble” in light, seen from Earth, when the planet swings around its star.
The change in light is a fingerprint that can yield many clues about the planet’s size, orbit and atmosphere. But this is the first time that astronomers have been able to confirm that water is present.
“Although HD189733b is far from being habitable and actually provides a rather hostile environment, our discovery shows that water might be more common out there than previously thought,” said Tinetti.
“Our method can be used in the future to study more ‘life-friendly’ environments.”
The planet’s star, HD 189733, is similar in size to our Sun, but a bit cooler.
But the planet itself would be hell for humans.
Orbiting cheek by jowel to the star, at a distance that is 30 times closer than that between the Earth and the Sun, parts of the planet’s atmosphere reach 2 000 degrees Celsius.
This seething temperature is reached on the side of the planet that always faces the star. By comparison, the other side of the planet is relatively balmy, with a low of 500 C.
Tinetti’s team used Nasa’s Spitzer orbiting telescope, using its infrared sensors to pick out the tiny signature that occurs when water vapour absorbs light from a star.
The big prize is to spot a rocky planet that lies in the so-called Goldilocks Zone, where the temperature is not so hot that water evaporates, nor so cold that it is perpetually frozen, but “just right”, enabling water to exist in liquid form.
“The ‘Holy Grail’ for today’s planet-hunters is to find an Earth-like planet that also has water in its atmosphere,” explained Tinetti.
“When it happens, the discovery will provide real evidence that planets outside our solar system might harbour life. Finding the existence of water on an extra-solar gas giant is a vital milestone along that road of discovery.”
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