Smallest exoplanet ever found to have water vapour<\/em><\/p>\n Astronomers using data from the NASA\/ESA Hubble Space Telescope, the Spitzer Space Telescope, and the Kepler Space Telescope have discovered clear skies and steamy water vapour on a planet outside our Solar System. The planet, known as HAT-P-11b, is about the size of Neptune, making it the smallest exoplanet ever on which water vapour has been detected. The results will appear in the online version of the journal Nature on 24 September 2014.<\/p>\n This is an artist’s concept of the silhouette of the extrasolar planet HAT-P-11b In this method, known as transmission or absorption spectroscopy<\/a>, starlight filters\u00a0through the rim of the planet’s atmosphere and into the telescope. If molecules like\u00a0water vapour are present, they absorb some of the starlight, leaving distinct signatures\u00a0in the light that reaches our telescopes. Using this technique, astronomers\u00a0discovered clear skies and steamy water vapour on the planet.<\/em><\/p>\n The discovery is a milestone on the road to eventually finding molecules in the atmospheres of smaller, rocky planets more akin to Earth. Clouds in the atmospheres of planets can block the view of what lies beneath them. The molecular makeup of these lower regions can reveal important information about the composition and history of a planet.\u00a0Finding clear skies on a Neptune-size planet is a good sign that some smaller planets might also have similarly good visibility.<\/p>\n “When astronomers go observing at night with telescopes, they say ‘clear skies’ to mean good luck,”<\/em> said Jonathan Fraine of the University of Maryland, USA, lead author of the study. “In this case, we found clear skies on a distant planet. That’s lucky for us because it means clouds didn’t block our view of water molecules.”<\/em><\/p>\n This image, taken with the NASA\/ESA Hubble Space Telescope’s\u00a0<\/em>Wide Field Camera 3, shows the star HAT-P-11.<\/em><\/p>\n Not visible here is a Neptune-sized planet named HAT-P-11b\u00a0<\/em>which orbits the star. \u00a0Astronomers have discovered clear skies and steamy\u00a0<\/em>water vapour on the planet. It is the smallest planet ever for which\u00a0<\/em>water vapour has been detected.<\/em><\/p>\n The small bright object next to the star is not the planet in question;\u00a0<\/em>in fact it is not a planet at all, but another star.<\/em><\/p>\n The reason for the graininess in this image is that it is a very short exposure.\u00a0<\/em>The star itself is so bright that it is saturated, it would otherwise be a small dot \u00a0<\/em>like the faint star next to it. The rings and the cross are caused by the diffraction\u00a0<\/em>\u2014 the bouncing of light \u2014 inside the telescope.<\/em><\/p>\n HAT-P-11b is a so-called exo-Neptune \u2014 a Neptune-sized planet that orbits another star. It is located 120 light-years away in the constellation of Cygnus<\/a> (The Swan). Unlike Neptune, this planet orbits closer to its star, making one lap roughly every five days. It is a warm world thought to have a rocky core, a mantle of fluid and ice, and a thick gaseous atmosphere. Not much else was known about the composition of the planet, or other exo-Neptunes like it, until now.<\/p>\n Part of the challenge in analysing the atmospheres of planets like this is their size. Larger Jupiter-like planets are easier to observe and researchers have already been able to detect water vapour in the atmospheres of some of these giant planets. Smaller planets are more difficult to probe \u2014 and all the smaller ones observed to date have appeared to be cloudy.<\/p>\n The team used Hubble’s Wide Field Camera 3 and a technique called transmission spectroscopy, in which a planet is observed as it crosses in front of its parent star. Starlight filters through the rim of the planet’s atmosphere and into the telescope. If molecules like water vapour are present, they absorb some of the starlight, leaving distinct signatures in the light that reaches our telescopes.<\/p>\n “We set out to look at the atmosphere of HAT-P-11b without knowing if its weather would be cloudy or not,”<\/em> said Nikku Madhusudhan, from the University of Cambridge, UK, part of the study team. “By using transmission spectroscopy<\/a>, we could use Hubble to detect water vapour in the planet. This told us that the planet didn’t have thick clouds blocking the view and is a very hopeful sign that we can find and analyse more cloudless, smaller, planets in the future. It is groundbreaking!”<\/em><\/p>\n Before the team could celebrate they had to be sure that the water vapour was from the planet and not from cool starspots \u2014 “freckles” on the face of stars \u2014 on the parent star. Luckily, Kepler<\/a> had been observing the patch of sky in which HAT-P-11b happens to lie for years. Those visible-light data were combined with targeted infraredSpitzer<\/a> observations. By comparing the datasets the astronomers could confirm that the starspots were too hot to contain any water vapour, and so the vapour detected must belong to the planet.<\/p>\n The results from all three telescopes demonstrate that HAT-P-11b is blanketed in water vapour, hydrogen gas, and other yet-to-be-identified molecules. So in fact it is not only the smallest planet to have water vapour found in its atmosphere but is also the smallest planet for which molecules of any kind have been directly detected using spectroscopy [1]<\/a>. Theorists will be drawing up new models to explain the planet’s makeup and origins.<\/p>\n Zoom in on the star:<\/p>\n![\"Artist](\"http:\/\/hobbyspace.com\/Blog\/wp-content\/uploads\/2014\/09\/heic1420a1-1024x576.jpg\")
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\nas it passes its parent star. The planet was observed as it crossed in\u00a0front of its star in order to learn more about its atmosphere.<\/em><\/p>\n![\"Parent](\"http:\/\/hobbyspace.com\/Blog\/wp-content\/uploads\/2014\/09\/heic1420c1-300x257.jpg\")
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