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NASA telescope finds 10 more planets that could have life

NASA's planet-hunting telescope has found 10 new planets outside our solar system that are likely the right size and temperature to potentially have life on them, broadly hinting that we are probably not alone.
After four years of searching, the Kepler telescope has detected a total of 49 planets in the Goldilocks zone. And it only looked in a tiny part of the galaxy, one quarter of one percent of a galaxy that holds about 200 billion of stars.
Seven of the 10 newfound Earth-size planets circle stars that are just like ours, not cool dwarf ones that require a planet be quite close to its star for the right temperature.
That doesn't mean the planets have life, but some of the most basic requirements that life needs are there, upping the chances for life.

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Preferentially Earth-sized planets with lots of water

Computer simulations by astrophysicists at the University of Bern of the formation of planets orbiting in the habitable zone of low mass stars such as Proxima Centauri show that these planets are most likely to be roughly the size of the Earth and to contain large amounts of water.
In August 2016, the announcement of the discovery of a terrestrial exoplanet orbiting in the habitable zone of Proxima Centauri stimulated the imagination of the experts and the general public. After all this star is the nearest star to our sun even though it is ten times less massive and 500 times less luminous. This discovery together with the one in May 2016 of a similar planet orbiting an even lower mass star (Trappist-1) convinced astronomers that such red dwarfs (as these low mass stars are called) might be hosts to a large population of Earth-like planets.

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Circular orbits identified for small exoplanets

In a paper published in the Astrophysical Journal, researchers from MIT and Aarhus University in Denmark report that 74 exoplanets, located hundreds of light-years away, orbit their respective stars in circular patterns, much like the planets of our solar system.
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Title: Atmospheric dynamics of terrestrial exoplanets over a wide range of orbital and atmospheric parameters
Author: Yohai Kaspi, Adam P. Showman

The recent discoveries of terrestrial exoplanets and super-Earths extending over a broad range of orbital and physical parameters suggest that these planets will span a wide range of climatic regimes. Characterization of the atmospheres of warm super-Earths has already begun and will be extended to smaller and more distant planets over the coming decade. The habitability of these worlds may be strongly affected by their three-dimensional atmospheric circulation regimes, since the global climate feedbacks that control the inner and outer edges of the habitable zone including transitions to Snowball-like states and runaway-greenhouse feedbacks depend on the equator-to-pole temperature differences, patterns of relative humidity, and other aspects of the dynamics. Here, using an idealized moist atmospheric general circulation model including a hydrological cycle, we study the dynamical principles governing the atmospheric dynamics on such planets. We show how the planetary rotation rate, stellar flux, atmospheric mass, surface gravity, optical thickness, and planetary radius affect the atmospheric circulation and temperature distribution on such planets. Our simulations demonstrate that equator-to-pole temperature differences, meridional heat transport rates, structure and strength of the winds, and the hydrological cycle vary strongly with these parameters, implying that the sensitivity of the planet to global climate feedbacks will depend significantly on the atmospheric circulation. We elucidate the possible climatic regimes and diagnose the mechanisms controlling the formation of atmospheric jet streams, Hadley and Ferrel cells, and latitudinal temperature differences. Finally, we discuss the implications for understanding how the atmospheric circulation influences the global climate.

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Title: Better Than Earth
Author: René Heller

Do We Inhabit The Best O All Possible Worlds? German mathematician Gottfried Leibniz thought so, writing in 1710 that our planet, warts and all, must be the most optimal one imaginable. Leibniz's idea was roundly scorned as unscientific wishful thinking, most notably by French author Voltaire in his magnum opus, Candide. Yet Leibniz might find sympathy from at least one group of scientists - the astronomers who have for decades treated Earth as a golden standard as they search for worlds beyond our own solar system. Because earthlings still know of just one living world - our own - it makes some sense to use Earth as a template in the search for life elsewhere, such as in the most Earth-like regions of Mars or Jupiter's watery moon Europa. Now, however, discoveries of potentially habitable planets orbiting stars other than our sun - exoplanets, that is - are challenging that geocentric approach.

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Title: Atmospheric Circulation of Terrestrial Exoplanets
Authors: Adam P. Showman, Robin D. Wordsworth, Timothy M. Merlis, Yohai Kaspi

The investigation of planets around other stars began with the study of gas giants, but is now extending to the discovery and characterisation of super-Earths and terrestrial planets. Motivated by this observational tide, we survey the basic dynamical principles governing the atmospheric circulation of terrestrial exoplanets, and discuss the interaction of their circulation with the hydrological cycle and global-scale climate feedbacks. Terrestrial exoplanets occupy a wide range of physical and dynamical conditions, only a small fraction of which have yet been explored in detail. Our approach is to lay out the fundamental dynamical principles governing the atmospheric circulation on terrestrial planets--broadly defined--and show how they can provide a foundation for understanding the atmospheric behaviour of these worlds. We first survey basic atmospheric dynamics, including the role of geostrophy, baroclinic instabilities, and jets in the strongly rotating regime (the "extratropics") and the role of the Hadley circulation, wave adjustment of the thermal structure, and the tendency toward equatorial superrotation in the slowly rotating regime (the "tropics"). We then survey key elements of the hydrological cycle, including the factors that control precipitation, humidity, and cloudiness. Next, we summarise key mechanisms by which the circulation affects the global-mean climate, and hence planetary habitability. In particular, we discuss the runaway greenhouse, transitions to snowball states, atmospheric collapse, and the links between atmospheric circulation and CO2 weathering rates. We finish by summarising the key questions and challenges for this emerging field in the future.

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Title: Magnetodynamo Lifetimes for Rocky, Earth-Mass Exoplanets with Contrasting Mantle Convection Regimes
Authors: Joost van Summeren, Eric Gaidos, Clinton P. Conrad

We used a thermal model of an iron core to calculate magnetodynamo evolution in Earth-mass rocky planets to determine the sensitivity of dynamo lifetime and intensity to planets with different mantle tectonic regimes, surface temperatures, and core properties. The heat flow at the core-mantle boundary (CMB) is derived from numerical models of mantle convection with a viscous/pseudo-plastic rheology that captures the phenomenology of plate-like tectonics. Our thermal evolution models predict a long-lived (~8 Gyr) field for Earth and similar dynamo evolution for Earth-mass exoplanets with plate tectonics. Both elevated surface temperature and pressure-dependent mantle viscosity reduce the CMB heat flow but produce only slightly longer-lived dynamos (~8-9.5 Gyr). Single-plate ("stagnant lid") planets with relatively low CMB heat flow produce long-lived (~10.5 Gyr) dynamos. These weaker dynamos can cease for several billions of years and subsequently reactivate due to the additional entropy production associated with inner core growth, a possible explanation for the absence of a magnetic field on present-day Venus. We also show that dynamo operation is sensitive to the initial temperature, size, and solidus of a planet's core. These dependencies would severely challenge any attempt to distinguish exoplanets with plate tectonics and stagnant lids based on the presence or absence of a magnetic field.

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Title: A Plateau in the Planet Population Below Twice the Size of Earth
Authors: Erik A. Petigura, Geoffrey W. Marcy, Andrew W. Howard

We carry out an independent search of Kepler photometry for small transiting planets with sizes 0.5--8.0 times that of Earth and orbital periods between 5 and 50 days, with the goal of measuring the fraction of stars harbouring such planets. We use a new transit search algorithm, TERRA, optimised to detect small planets. We restrict our stellar sample to include the 12,000 stars having the lowest photometric noise in the Kepler survey. We report 129 planet candidates having radii less than 6 Earth-radii found in 3 years of Kepler photometry. Forty-seven of these candidates are not in Batalha et al. (2012). We gather Keck HIRES spectra for the majority of these targets leading to precise stellar radii and hence precise planet radii. We inject synthetic dimmings from mock transiting planets into the actual Kepler photometry and analyse that photometry with TERRA to assess detection completeness. We compute the occurrence of planets as a function of planet radius and period, correcting for the detection completeness. The resulting distribution of planet sizes exhibits a power law rise in occurrence from 5.7 Earth-radii down to 2 Earth-radii, as found in Howard et al. (2012). That rise clearly ends at 2 Earth-radii. The occurrence of planets is consistent with constant from 2 Earth-radii toward 1 Earth-radius. This unexpected plateau in planet occurrence at 2 Earth-radii suggests distinct planet formation processes for planets above and below 2 Earth-radii. We find 15.1% of solar type stars---roughly one in six---has a 1--2 Earth-radii planet with P = 5--50 days.

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Earth-sized planets in habitable zones are more common than previously thought

The number of potentially habitable planets is greater than previously thought, according to a new analysis by a Penn State researcher, and some of those planets are likely lurking around nearby stars.
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At Least One in Six Stars Has an Earth-sized Planet

The quest for a twin Earth is heating up. Using NASA's Kepler spacecraft, astronomers are beginning to find Earth-sized planets orbiting distant stars. A new analysis of Kepler data shows that about 17 percent of stars have an Earth-sized planet in an orbit closer than Mercury. Since the Milky Way has about 100 billion stars, there are at least 17 billion Earth-sized worlds out there.
Francois Fressin, of the Harvard-Smithsonian Centre for Astrophysics (CfA), presented the analysis today in a press conference at a meeting of the American Astronomical Society in Long Beach, Calif. A paper detailing the research has been accepted for publication in The Astrophysical Journal.

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