* Astronomy

Earth-Like Planet Discovery

An international team of astronomers has confirmed the existence of a planet that could have perfect conditions for life, outside our solar system. The discovery of planets in a habitable zone rises the hope that astronomers could soon answer the question of whether we are alone in the universe (Apr '12)
Guillem Anglada-Escudé from the University Göttingen, Germany, is one of the main astronomers, who helped to confirm the existence of the new planet. It is called Gliese 667Cc and is orbiting around a red dwarf star, 22 light years away from the earth. Red dwarf stars are the most common stars in the neighbourhood of the sun. Usually they host planets called gas giants which are not primarily composed of rock matter.
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Title: The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample
Authors: X. Bonfils, X. Delfosse, S. Udry, T. Forveille, M. Mayor, C. Perrier, F. Bouchy, M. Gillon, C. Lovis, F. Pepe, D. Queloz, N. C. Santos, D. Ségransan, J.-L. Bertaux
21 Nov 2011

Searching for planets around stars with different masses probes the outcome of planetary formation for different initial conditions. This drives observations of a sample of 102 southern nearby M dwarfs, using a fraction of our guaranteed time on the ESO/HARPS spectrograph (Feb. 11th, 2003 to Apr. 1st 2009). This paper makes available the sample's time series, presents their precision and variability. We apply systematic searches and diagnostics to discriminate whether the observed Doppler shifts are caused by stellar surface inhomogeneities or by the radial pull of orbiting planets. We recover the planetary signals corresponding to 9 planets already announced by our group (Gl176b, Gl581b, c, d & e, Gl674b, Gl433b, Gl 667Cb and c). We present radial velocities that confirm GJ 849 hosts a Jupiter-mass planet, plus a long-term radial-velocity variation. We also present RVs that precise the planetary mass and period of Gl 832b. We detect long-term RV changes for Gl 367, Gl 680 and Gl 880 betraying yet unknown long-period companions. We identify candidate signals in the radial-velocity time series and demonstrate they are most probably caused by stellar surface inhomogeneities. Finally, we derive a first estimate of the occurrence of M-dwarf planets as a function of their minimum mass and orbital period. In particular, we find that giant planets (m sin i = 100-1,000 Mearth) have a low frequency (e.g. f<1% for P=1-10 d and f=0.02^{+0.03}_{-0.01} for P=10-100 d), whereas super-Earths (m sin i = 1-10 Mearth) are likely very abundant (f=0.36^{+0.25}_{-0.10} for P=1-10 d and f=0.35^{+0.45}_{-0.11} for P=10-100 d). We also obtained eta_earth=0.41^{+0.54}_{-0.13}, the frequency of habitable planets orbiting M dwarfs (1<m sin i<10 Mearth). For the first time, eta_earth is a direct measure and not a number extrapolated from the statistic of more massive and/or shorter-period planets.

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Title: A planetary system around the nearby M dwarf GJ 667C with at least one super-Earth in its habitable zone
Authors: Guillem Anglada-Escudé, Pamela Arriagada, Steven S. Vogt, Eugenio J. Rivera, R. Paul Butler, Jeffrey D. Crane, Stephen A. Shectman, Ian B. Thompson, Dante Minniti, Nader Haghighipour, Brad D. Carter, C. G. Tinney, Robert A. Wittenmyer, Jeremy A. Bailey, Simon J. O'Toole, Hugh R.A. Jones, James S. Jenkins

We re-analyse 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the ESO public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported 7.2-day candidate, with periods of 28 days, 75 days, and a secular trend consistent with the presence of a gas giant (Period sim 10 years). The 28-day signal implies a planet candidate with a minimum mass of 4.5 Mearth orbiting well within the canonical definition of the star's liquid water habitable zone, this is, the region around the star at which an Earth-like planet could sustain liquid water on its surface. Still, the ultimate water supporting capability of this candidate depends on properties that are unknown such as its albedo, atmospheric composition and interior dynamics. The 75-day signal is less certain, being significantly affected by aliasing interactions among a potential 91-day signal, and the likely rotation period of the star at 105 days detected in two activity indices. GJ 667C is the common proper motion companion to the GJ 667AB binary, which is metal poor compared to the Sun. The presence of a super-Earth in the habitable zone of a metal poor M dwarf in a triple star system, supports the evidence that such worlds should be ubiquitous in the Galaxy.

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Newfound Alien Planet is Best Candidate Yet to Support Life 

A potentially habitable alien planet - one that scientists say is the best candidate yet to harbour water, and possibly even life, on its surface - has been found around a nearby star.
The planet is located in the habitable zone of its host star, which is a narrow circumstellar region where temperatures are neither too hot nor too cold for liquid water to exist on the planet's surface.
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