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Every 8.5h, the star Kepler-78 (first known as TYC3147-188-1 and later designated KIC 8435766) presents to the Earth a shallow eclipse consistent (8) with the passage of an orbiting planet [...], Recent analyses (1-4) of data from the NASA Kepler spacecraft (5) have established that planets with radii within 25 per cent of the Earth's (R⊕) are commonplace throughout the Galaxy, orbiting at least 16.5 per cent of Sun-like stars (1). Because these studies were sensitive to the sizes of the planets but not their masses, the question remains whether these Earth-sized planets are indeed similar to the Earth in bulk composition. The smallest planets for which masses have been accurately determined (6, 7) are Kepler-10b (1.42R⊕) and Kepler-36b (1.49R⊕), which are both significantly larger than the Earth. Recently, the planet Kepler-78b was discovered (8) and found to have a radius of only 1.16R⊕. Here we report that the mass of this planet is 1.86 Earth masses. The resulting mean density of the planet is 5.57 g [cm.sup.-3], which is similar to that of the Earth and implies a composition of iron and rock.

Author(s): C. H. Blake [1]; J. S. Bloom (corresponding author) [1, 2]; D. L. Starr [13]; E. E. Falco [3]; M. Skrutskie [9]; E. E. Fenimore [7]; G. Duchêne [12]; [...]

The explosion that results in a cosmic?-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks,?-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks. [ABSTRACT FROM AUTHOR]

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s-1 (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of ∼5 cm s-1 is necessary. The combination of a laser frequency comb with a Fabry–Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (∼1-Å) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or ‘astro-comb’, is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s-1 in astronomical radial velocity measurements. [ABSTRACT FROM AUTHOR]