Scientists have detected water vapor features around the hot Jupiter Tau Bootis b.
Cowboys & Aliens are Coming!
July 29, 2011 --
If aliens are going out of their way to kick up dust in the Wild West, as they do in the upcoming movie "Cowboys & Aliens," they must be coming from somewhere. Life could take root on a moon or a meteorite. But to nurture the kind of life that could destroy our saloons and harass our livestock, a planet might be the most suitable. So far, Kepler, a NASA orbiting telescope that searches for planets beyond our solar system, has detected over 1,200 exoplanets. Surely there must be a few candidates among this group that could meet some of the most basic requirements to host life? Explore some far-out worlds that could support aliens, be they cattle-rustling characters or a more peaceful people.
First, let's lay out some basic criteria. Kepler hasn't identified many rocky worlds and a solid surface is essential for life to take root. Size matters: The mass of the planet helps astrophysicists infer what it's made of. Some planets are Earth-sized. Others are several times the size of our planet. And then there are gas giants, which can range from "Neptune sized" to "super-Jupiters." Orbit: To support life, a planet must be in a stable orbit around its star -- no planets with wonky orbits that will eventually dump them into their star for a fiery death. Goldilocks Zone: This is a region not too hot or too cold that gives the planet enough distance from its parent star to have liquid water, key for life. Loner Stars: Single stars make better parents. In 2010, a pair of closely orbiting binary stars was spotted surrounded by what could be the debris of former planets. Unknowns: Some factors for life can't be confirmed one way or the other from the data available about extrasolar planets. These include: water, chemical compounds such as ammonia; a nitrogen-rich atmosphere; a magnetic field to repel solar and cosmic radiation; and more. BUT, some planets do have a head-start, beginning with Gliese 581D.
Located a mere 20 light-years away, practically our backyard in cosmic terms, Gliese 581d is situated on the "outer fringes" of the Goldilocks zone, orbiting a red dwarf star. The planet may be warm enough and wet enough to support life in much the same manner as Earth. It might also contain a thick carbon atmosphere. If we ever need a new Earth and have the means to get there, Gliese 581d may be our best bet for now.
When it was first detected and reported last year in Astrophysical Journal, Gliese 581g appeared to be the perfect candidate for a true "Earth-like" planet. Located in the same star system as Gliese 581d (and detected earlier), Gliese 581g seemed to be the right size and located within a habitable zone away from its parent star. Gliese 581g was said to have three times the mass of Earth, making it possible for the planet to hold an atmosphere. However, since its discovery, follow-up studies have alleged that Gliese 581g might have been a false alarm. In other words, the planet might not exist at all.
Dubbed a "waterworld" and located a mere 42 light-years from Earth, GJ 1214b orbits near a red dwarf star about one-fifth the size of our sun. What makes this planet unique is that it appears to be primarily composed of water, although GJ 1214b is 6.5 times the mass of Earth and 2.7 times wider, which classifies it as a "super-Earth." This planet also has a steamy atmosphere composed of thick, dense clouds of hydrogen, which, although it might not the case with this planet, could incubate life.
Situated 150 light-years from Earth, HD 209458b is a planet that holds traces of water vapor in its atmosphere, and also contains basic organic compounds that, on Earth, foster the development of life. But there are two factors working against HD 209458b as a suitable habitat. The planet is very hot due to its close proximity to its parents star, and it's a gas giant, so no solid surfaces.
If Kepler-10b were located further from its parent star, it might have had a chance of hosting life. Kepler-10b was the first "iron-clad proof of a rocky planet beyond our solar system" back in 2001. It was even dubbed the "missing link" of extrasolar planetary research. When it comes to the search for life, though, Kepler 10-b is missing a lot of other ingredients -- just minor things like water or an atmosphere.
When venturing to a new star system to explore the possibility of extraterrestrial life, trying a star that has already shown itself to nurture planets -- even if they're not the kind you're looking for -- could be a promising strategy. Project Icarus, an ambitious five-year study into launching an unmanned spacecraft to an interstellar destination, has identified two stars located within 15 light-years that might fit the bill: "epsilon Eridani, a single K star 10.5 light-years away, and the red dwarf GJ 674, 14.8 light-years away." Indirect evidence has also shown that epsilon Eridani may already hold smaller worlds scientists simply haven't detected yet. Also, red dwarf star systems generally may be a safe haven for life.
Are We Alone?
Taking into account the number of exoplanets that have been detected, as well as the vastly greater number that are estimated to be out there, some astrophysicists are convinced that extraterrestrial life is inevitable. After all, the Milky Way may be loaded with as many as 50 billion alien worlds. Some even think we'll find alien life by 2020. Others, however, say it may not exist at all. Recently, astrophysicists David Spiegel of Princeton University and Edwin Turner from the University of Tokyo suggested we might be alone in the universe, based on their interpretation of the Drake equation, a formula meant to determine loosely the probability of the existence of life beyond Earth. According to their analysis, just because life on Earth took shape early, endured and prospered doesn't mean the same process would naturally and inevitably occur elsewhere in the universe. Discovering life elsewhere, however, would be the only means of settling this debate. Unless the aliens find us first, of course.
Water vapor has been detected in the atmosphere of one of the first alien planets ever identified by astronomers.
Advances in the technique used to scan the atmosphere of this "hot Jupiter" could help scientists determine how many of the billions of planets in the Milky Way contain water like Earth, researchers said.
The exoplanet Tau Boötis b was discovered in 1996, when the search for worlds outside our solar system was just kicking off. At about 51 light-years away, Tau Boötis b is one of the nearest known exoplanets to Earth. The planet is considered a "hot Jupiter" because it is a massive gas giant that orbits close to its parent star. [A Gallery of the Strangest Alien Planets]
To analyze the atmosphere surrounding Tau Boötis b, scientists looked at its faint glow. Different types of molecules emit different wavelengths of light, resulting in signatures known as spectra that reveal their chemical identify.
"The information we get from the spectrograph is like listening to an orchestra performance; you hear all of the music together, but if you listen carefully, you can pick out a trumpet or a violin or a cello, and you know that those instruments are present," study researcher Alexandra Lockwood, a graduate student at Caltech, explained in a statement.
"With the telescope, you see all of the light together, but the spectrograph allows you to pick out different pieces; like this wavelength of light means that there is sodium, or this one means that there’s water," Lockwood added.
Scientists have used spectrographic analyses to find water signatures on other alien planets before, but only when those worlds passed in front of their parent stars. Tau Boötis b does not transit in front of its parent star from our viewpoint on Earth, but Lockwood and colleagues were able to tease out the weak light emitted by the planet using the Near Infrared Echelle Spectrograph (NIRSPEC) at the Keck Observatory in Hawaii.
Researchers had previously used a similar technique to find carbon monoxide around Tau Boötis b. That compound is thought to be the second-most common gas in the atmospheres of hot Jupiters, after hydrogen.
The new analysis showed that the glow of the planet's atmosphere matches the distinct molecular signature of water, the researchers say.
The spectrographic technique is presently limited to big planets orbiting closely to bright stars, like hot Jupiters, but it could eventually be used to study super-Earths (planets slightly larger than Earth) and worlds in the "habitable zone" around their parent stars, where liquid water and perhaps life as we know it could exist.
"While the current state of the technique cannot detect Earth-like planets around stars like the sun, with Keck it should soon be possible to study the atmospheres of the so-called 'super-Earth' planets being discovered around nearby low-mass stars, many of which do not transit," Caltech professor Geoffrey Blake said in a statement.
"Future telescopes such as the James Webb Space Telescope and the Thirty Meter Telescope (TMT) will enable us to examine much cooler planets that are more distant from their host stars and where liquid water is more likely to exist," Blake added.
Astronomers found the first evidence of an exoplanet in 1992. Since then, more than 1,000 worlds have been discovered outside of our solar system, and many more await confirmation.
The new findings were detailed in the Feb. 24 online version of The Astrophysical Journal Letters. The results are also freely available on the preprint service Arxiv.
Originally published on Space.com.
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