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article imageAstronomers could soon find squished out exoplanets

By Robert Myles     Dec 15, 2014 in Science
Fairfax - A group of American researchers suggest astronomers could soon discover exoplanets — planets orbiting other stars — so deformed by gravity that they appear stretched out.
In a paper published in the Monthly Notices of the Royal Astronomical Society, the team, headed by Prabal Saxena of the Astronomy Department at George Mason University, Fairfax, VA, say discovering rocky planets stretched out by the gravity of the stars they orbit is a distinct possibility to add to the array of exotic exoplanets already found.
Such discoveries have included the lightweight "super-Jupiter" TrES-4b, a low density giant planet that theoretically shouldn’t exist. Then, at the other end of the exoplanetary scale, CoRoT-7b is a possible remnant of a former gas-giant. As well as being the confirmed rocky world outside our solar system, CoRoT-7b looks distinctly inhospitable. Temperatures there are so hot, the rain may consist of molten rock. One of the weirdest discoveries to date, neither star nor planet, is Luhman 16B, a "brown dwarf" where molten iron rains, as earlier reported in Digital Journal.
Since the first exoplanet was discovered in 1992, in excess of 1,800 planets have been found orbiting other stars. The catalogue of exoplanets is likely to grow exponentially as ever more powerful telescopes, such as Gaia, the European Space Agency’s so-called billion star surveyor, become operational.
Exoplanets have already been found orbiting their parent stars at extreme distances varying from less than a million kilometers to more than 100 billion kilometers distant. By way of comparison, Mercury, the closest planet to our Sun, orbits at a distance of about 58 million kilometers while the solar system’s most distant planet, Neptune, orbits at a mean distance of 4.5 billion kilometers.
Planets orbiting in close proximity to their parent stars, in addition to extremes of temperature, experience a number of harsh conditions. Such planets are often stretched by the powerful tidal forces that are the result of their parent star’s gravitational field. This effect is most obvious with planets similar to Jupiter where the atmosphere is a major component — so-called "hot Jupiters" — but more difficult to detect with rocky worlds similar to Earth or Mars.
Prabal and colleagues modeled cases involving planets in close orbits around small red dwarf stars. Such stars are fainter than our Sun but are far and away the most common type of stars found in the Milky Way galaxy.
The researchers modelling looked at planets whose rotation is tidally locked, so that they keep the same face towards their parent star in much the same way as the Moon is tidally locked in its orbit around Earth. In such circumstances, say the researchers, the distortion suffered by such closely orbiting exoplanets ought to be detectable in transit events, the method commonly used to detect exoplanets as they move in front of their parent star blocking out a tiny fraction of the star’s light.
If astronomers can find these extreme exoplanets, it could give them a better understanding of the properties of Earth-like planets generally. As Prabal explained, “Imagine taking a planet like the Earth or Mars, placing it near a cool red star and stretching it out. Analyzing the new shape alone will tell us a lot about the otherwise impossible to see internal structure of the planet and how it changes over time.”
The subtle signals from stretched-out rocky planets may be detectable by some telescopes currently in use but when far more powerful observatories such as the space-based James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT) based in the Atacama desert in Chile, become operational over the course of the next few years, expect to see a whole range of worlds that no-one has even imagined before.
More about Exoplanets, squashed exoplanets, tidally locked planets, weird worlds, Space exploration
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