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Terrestrial Exoplanets
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Title: Tidally Heated Terrestrial Exoplanets: Viscoelastic Response Models
Authors: Wade G. Henning, Richard J. O'Connell, Dimitar D. Sasselov

Tidal friction in exoplanet systems, driven by orbits that allow for durable nonzero eccentricities at short heliocentric periods, can generate internal heating far in excess of the conditions observed in our own solar system. Secular perturbations or a notional 2:1 resonance between a Hot Earth and Hot Jupiter can be used as a baseline to consider the thermal evolution of convecting bodies subject to strong viscoelastic tidal heating. We compare results first from simple models using a fixed Quality factor and Love number, and then for three different viscoelastic rheologies: the Maxwell body, the Standard Anelastic Solid, and the Burgers body. The SAS and Burgers models are shown to alter the potential for extreme tidal heating by introducing the possibility of new equilibria and multiple response peaks. We find that tidal heating tends to exceed radionuclide heating at periods below 10-30 days, and exceed insolation only below 1-2 days. Extreme cases produce enough tidal heat to initiate global-scale partial melting, and an analysis of tidal limiting mechanisms such as advective cooling for earthlike planets is discussed. To explore long term behaviours, we map equilibria points between convective heat loss and tidal heat input as functions of eccentricity. For the periods and magnitudes discussed, we show that tidal heating, if significant, is generally detrimental to the width of habitable zones.

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Distant world 'has rocky surface'
Astronomers say they are now confident that a planet orbiting a star some 500 light-years away is rocky.
Detailed observations show the world, dubbed Corot-7b, to have a mass just five times that of the Earth.
Combined with the object's known radius, the measurement means the far-off world should be solid in nature.


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Earth-sized planets are just right for life
The discovery of extrasolar super-Earths - rocky planets about five to ten times the mass of Earth - has raised hopes that some may harbour life. Perhaps it's a vain hope though, since it now seems that Earth is just the right size to sustain life.

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Are there other Earths?
In all the wide and starry universe, are there other worlds like our own? Can we ever hope to find new Earths?
Or is our world somehow unique?
We know that none of the planets in our own solar system is very much like Earth. Mars comes closest, but its a frigid desert from pole to pole, where temperatures rarely get above freezing and overnight lows are usually 100 degrees below zero or worse.

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EPOXI Team Develops New Method to Find Alien Oceans
NASA-sponsored scientists looking back at Earth with the Deep Impact/EPOXI mission have developed a method to indicate whether Earth-like extrasolar worlds have oceans.

"A 'pale blue dot' is the best picture we will get of an Earth-like extrasolar world using even the most advanced telescopes planned for the next couple decades. So how do we find out if it is capable of supporting life? If we can determine that the planet has oceans of liquid water, it greatly increases the likelihood that it supports life. We used the High Resolution Imager telescope on Deep Impact to look at Earth from tens of millions of miles away -- an 'alien' point of view -- and developed a method to indicate the presence of oceans by analysing how Earth's light changes as the planet rotates. This method can be used to identify extrasolar ocean-bearing Earths" - Nicolas B. Cowan, of the University of Washington.

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In the search for Earth-like planets, astronomers zeroed in Tuesday on two places that look awfully familiar to home. One is close to the right size. The other is in the right place. European researchers said they not only found the smallest exoplanet ever, called Gliese 581 e, but realised that a neighbouring planet discovered earlier, Gliese 581 d, was in the prime habitable zone for potential life.

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A solar system more than six parsecs away from Earth may hold two planetary record-breakers: the lightest exoplanet ever spotted, and another planet just the right distance from its star to harbour liquid water.
Michel Mayor, from Switzerland's Geneva Observatory, announced the findings on 21 April at a meeting for the European Week of Astronomy and Space Science at the University of Hertfordshire, UK. Both discoveries boost the spirits of astronomers seeking Earth-like planets outside our Solar System.
The new lightest exoplanet, called Gliese 581e, is the fourth to be detected in the Gliese 581 star system.

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Astronomers from six major centers, including NASA and Harvard University may be on the verge of finding a second Earth-like planet,  according to the journal Science.

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There could be one hundred billion Earth-like planets in our galaxy, a US conference has heard.
Dr Alan Boss of the Carnegie Institution of Science said many of these worlds could be inhabited by simple lifeforms.
He was speaking at the annual meeting of the American Association for the Advancement of Science in Chicago.
So far, telescopes have been able to detect just over 300 planets outside our Solar System.

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