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Title: Two massive rocky planets transiting a K-dwarf 6.5 parsecs away
Author: Michael Gillon, Brice-Olivier Demory, Valerie Van Grootel, Fatemeh Motalebi, Christophe Lovis, Andrew Collier Cameron, David Charbonneau, David Latham, Emilio Molinari, Francesco A. Pepe, Damien Segransan, Dimitar Sasselov, Stephane Udry, Michel Mayor, Giuseppina Micela, Giampaolo Piotto, Alessandro Sozzetti

HD 219134 is a K-dwarf star at a distance of 6.5 parsecs around which several low-mass planets were recently discovered. The Spitzer space telescope detected a transit of the innermost of these planets, HD 219134 b, whose mass and radius (4.5 MEarth and 1.6 REarth respectively) are consistent with a rocky composition. Here, we report new highprecision time-series photometry of the star acquired with Spitzer revealing that the second innermost planet of the system, HD 219134 c, is also transiting. A global analysis of the Spitzer transit light curves and the most up-to-date HARPS-N velocity data set yields mass and radius estimations of 4.740.19 MEarth and 1.6020.055 REarth for HD 219134 b, and of 4.360.22 MEarth and 1.5110.047 REarth for HD 219134 c. These values suggest rocky compositions for both planets. Thanks to the proximity and the small size of their host star (0.7780.005 Rsun), these two transiting exoplanets - the nearest to the Earth to date - are well-suited for a detailed characterization (precision of a few percent on mass and radius, constraints on the atmospheric properties...) that could give important constraints on the nature and formation mechanism of the ubiquitous short-period planets of a few Earth masses.

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HD 219134b
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Title: The HARPS-N Rocky Planet Search I. HD219134b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun
Author: F. Motalebi, S. Udry, M. Gillon, C. Lovis, D. Segransan, L. A. Buchhave, B. O. Demory, L. Malavolta, C. D. Dressing, D. Sasselov, K. Rice, D. Charbonneau, A. Collier Cameron, D. Latham, E. Molinari, F. Pepe, L. Affer, A. S. Bonomo, R. Cosentino, X. Dumusque, P. Figueira, A. F. M. Fiorenzano, S. Gettel, A. Harutyunyan, R. D. Haywood, J. Johnson, E. Lopez, M. Lopez-Morales, M. Mayor, G. Micela, A. Mortier, V. Nascimbeni, D. Philips, G. Piotto, D. Pollacco, D. Queloz, A. Sozzetti, A. Vanderburg, C. A. Watson

We present here the detection of a system of four low-mass planets around the bright (V=5.5) and close-by (6.5 pc) star HD219134. This is the first result of the Rocky Planet Search program with HARPS-N on the TNG in La Palma. The inner planet orbits the star in 3.0937 0.0004 days, on a quasi-circular orbit with a semi-major axis of 0.0382 0.0003 AU. Spitzer observations allowed us to detect the transit of the planet in front of the star making HD219134b the nearest known transiting planet to date. From the amplitude of the radial-velocity variation (2.33 0.24 m/s) and observed depth of the transit (359 38 ppm), the planet mass and radius are estimated to be 4.46 0.47 Earth masses and 1.606 0.086 Earth radii leading to a mean density of 5.89 1.17 g/cc, suggesting a rocky composition. One additional planet with minimum mass of 2.67 0.59 Earth masses moves on a close-in, quasi-circular orbit with a period of 6.765 0.005 days. The third planet in the system has a period of 46.78 0.16 days and a minimum mass of 8.7 1.1 Earth masses, at 0.234 0.002 AU from the star. Its eccentricity is 0.32 0.14. The period of this planet is close to the rotational period of the star estimated from variations of activity indicators (42.3 0.1 days). The planetary origin of the signal is, however, the preferred solution as no indication of variation at the corresponding frequency is observed for activity-sensitive parameters. Finally, a fourth additional longer-period planet of mass of 62 6 Earth masses orbits the star in 1190 days, on an eccentric orbit (e=0.27 0.11) at a distance of 2.14 0.27 AU.

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NASA's Spitzer Confirms Closest Rocky Exoplanet

Using NASA's Spitzer Space Telescope, astronomers have confirmed the discovery of the nearest rocky planet outside our solar system, larger than Earth and a potential gold mine of science data.
Dubbed HD 219134b, this exoplanet, which orbits too close to its star to sustain life, is a mere 21 light-years away. While the planet itself can't be seen directly, even by telescopes, the star it orbits is visible to the naked eye in dark skies in the Cassiopeia constellation, near the North Star.

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Cassiopeia's Hidden Gem: The Closest Rocky, Transiting Planet

Skygazers at northern latitudes are familiar with the W-shaped star pattern of Cassiopeia the Queen. This circumpolar constellation is visible year-round near the North Star. Tucked next to one leg of the W lies a modest 5th-magnitude star named HD 219134 that has been hiding a secret.
Astronomers have now teased out that secret: a planet in a 3-day orbit that transits, or crosses in front of its star. At a distance of just 21 light-years, it is by far the closest transiting planet to Earth, which makes it ideal for follow-up studies. Moreover, it is the nearest rocky planet confirmed outside our solar system. Its host star is visible to the unaided eye from dark skies, meaning anyone with a good star map can see this record-breaking system.

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