Gliese 832c: The closest potentially habitable exoplanet

This planet is only 16 light years away — could it harbor life? Recently discovered exoplanet Gliese 832c has been found in a close orbit around a star that is less bright than our Sun. An interesting coincidence, however, is that Gliese 832c receives just about the same average flux from its parent star as does the Earth. Since the planet was discovered only by a slight wobble in its parent star’s motion, the above illustration is just an artistic guess of the planet’s appearance — much remains unknown about Gliese 832c’s true mass, size, and atmosphere. If Gliese 832c has an atmosphere like Earth, it may be a super-Earth undergoing strong seasons but capable of supporting life. Alternatively, if Gliese 832c has a thick atmosphere like Venus, it may be a super-Venus and so unlikely to support life as we know it. The close 16-light year distance makes the Gliese 832 planetary system currently the nearest to Earth that could potentially support life. The proximity of the Gliese 832 system therefore lends itself to more detailed future examination and, in the most spectacularly optimistic scenario, actual communication — were intelligent life found there.

Image credit & copyright: The Planetary Habitability Laboratory @ UPR Arecibo; Discovery: Robert A. Wittenmyer (UNSW Australia) et al.

The Formation and Dynamics of Super-Earth Planets

Super-Earths, objects slightly larger than Earth and slightly smaller than Uranus, have found a special place in exoplanetary science. As a new class of planetary bodies, these objects have challenged models of planet formation at both ends of the spectrum and have triggered a great deal of research on the composition and interior dynamics of rocky planets in connection to their masses and radii.

Being relatively easier to detect than an Earth-sized planet at 1 AU around a G star, super-Earths have become the focus of worldwide observational campaigns to search for habitable planets. With a range of masses that allows these objects to retain moderate atmospheres and perhaps even plate tectonics, super-earths may be habitable if they maintain long-term orbits in the habitable zones of their host stars. Given that in the past two years a few such potentially habitable super-Earths have in fact been discovered, it is necessary to develop a deep understanding of the formation and dynamical evolution of these objects.

This article reviews the current state of research on the formation of super-Earths and discusses different models of their formation and dynamical evolution.

Image Credit: ESO/M. Kornmesser

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Gliese 667 Cc

An extrasolar planet, Gliese 667 Cc orbits Gliese 667 C, which is part of a triple-star system. It lies at a distance of 22.1 light years from Earth within the Scorpius constellation.

Gliese 667Cc was discovered in April 2012 by an international group of astronomers working at the European Southern Observatory in the Atacama Desert, northern Chile. It is a super-Earth, some 3.4 times the mass of Earth, orbiting a red dwarf star, Gliese 667 C. At the time of its discovery, scientists called it the most Earth-like object outside of the Solar System.

The discovery was made with the High Accuracy Radial Planetary Searcher (HARPS) telescope. Gliese 667 Cc receives 10% less light from its star than the Earth receives from the Sun, but as this light is mostly in the infra-red part of the electromagnetic spectrum, its effect is that the energy received at its surface is the same as Earth receives from the Sun.

The planet orbits its star over a four-week period at a distance of 0.12 AU (17.9 million kilometres). The likelihood is that it is tidally locked to the star, meaning that it always shows the same hemisphere to the surface of Gliese 667 C.

The temperature on Gliese 667 C is 3,400K (Kelvin) compared with the Sun’s 5,778K. Its habitable zone lies in an orbit between 0.11 astronomical units (AU) (16.4 million kilometres) and 0.23 AU (34.3 million kilometres) from the star. Gliese 667 Cc’s orbital distance seems to be comfortably within the habitable zone, should liquid water be present on its surface.

The surface temperature of Gliese 667 Cc could be approximately 30C in the presence of liquid water, but if the atmosphere consists of more massive molecules, the temperature will be higher, making surface conditions inhospitable to life. The tidal locking adds further complications as one hemisphere of the planet experiences constant daylight while the other is permanently dark. The temperature differences between the two hemispheres will have a strong influence on the planet’s global climate. In addition, the planet will receive frequent flares from its host star.

A further complication is that the Gliese 667 C star is part of a triple-star system. Gliese 667 A and Gliese 667 B are about 230 AU (34.2 billion kilometres) away. Despite the distance, they would be visible from the surface of the planet. The Sun could also be seen as a distant star from the surface of Gliese 667 Cc.

Credit: L. Calçada, Rory Barnes/ESO

Nearby Exoplanet Is Best Candidate For Supporting Life

by Lisa Winter

Finding new exoplanets is always awesome, but discovering exoplanets within the star’s habitable zone are exponentially more exciting.

A team led by Robert Wittenmyer of the University of New South Wales has announced the discovery of the Super-Earth Gliese 832 c, which could very well turn out to be the best candidate for extraterrestrial life discovered to date. It’s also fairly close, cosmologically speaking, which adds to the intrigue. The team’s paper has been accepted for publication in The Astrophysical Journal, but has been made available online in an open access format on arXiv.org.

Gliese 832 is a red dwarf star that is located 16.1 light-years away in the constellation Grus. Astronomers discovered a Jupiter analog orbiting the star back in 2009, but its orbit takes nine years to complete; far beyond the star’s habitable zone. Gliese 832 c looks much more promising. Though only two planets in the system are known, it appears to be organized quite similarly to our own solar system…

(read more: I Fucking Love Science)

illustration by PHL @ UPR Arecibo, NASA Hubble, Stellarium

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