19 research outputs found
Two Earth-sized planets orbiting Kepler-20
Since the discovery of the first extrasolar giant planets around Sun-like
stars, evolving observational capabilities have brought us closer to the
detection of true Earth analogues. The size of an exoplanet can be determined
when it periodically passes in front of (transits) its parent star, causing a
decrease in starlight proportional to its radius. The smallest exoplanet
hitherto discovered has a radius 1.42 times that of the Earth's radius (R
Earth), and hence has 2.9 times its volume. Here we report the discovery of two
planets, one Earth-sized (1.03R Earth) and the other smaller than the Earth
(0.87R Earth), orbiting the star Kepler-20, which is already known to host
three other, larger, transiting planets. The gravitational pull of the new
planets on the parent star is too small to measure with current
instrumentation. We apply a statistical method to show that the likelihood of
the planetary interpretation of the transit signals is more than three orders
of magnitude larger than that of the alternative hypothesis that the signals
result from an eclipsing binary star. Theoretical considerations imply that
these planets are rocky, with a composition of iron and silicate. The outer
planet could have developed a thick water vapour atmosphere.Comment: Letter to Nature; Received 8 November; accepted 13 December 2011;
Published online 20 December 201
A planetary system as the origin of structure in Fomalhaut's dust belt
The Sun and >15 percent of nearby stars are surrounded by dusty debris disks
that must be collisionally replenished by asteroids and comets, as the dust
would otherwise be depleted on <10 Myr timescales (ref. 1). Theoretical studies
show that disk structure can be modified by the gravitational influence of
planets (ref. 2-4), but the observational evidence is incomplete, at least in
part because maps of the thermal infrared emission from disks have low linear
resolution (35 AU in the best case; ref. 5). Optical images provide higher
resolution, but the closest examples (AU Mic and Beta Pic) are edge-on (ref.
6,7), preventing the direct measurement of azimuthal and radial disk structure
that is required for fitting theoretical models of planetary perturbations.
Here we report the detection of optical light reflected from the dust grains
orbiting Fomalhaut (HD 216956). The system is inclined 24 degrees away from
edge-on, enabling the measurement of disk structure around its entire
circumference, at a linear resolution of 0.5 AU. The dust is distributed in a
belt 25 AU wide, with a very sharp inner edge at a radial distance of 133 AU,
and we measure an offset of 15 AU between the belt's geometric centre and
Fomalhaut. Taken together, the sharp inner edge and offset demonstrate the
presence of planet-mass objects orbiting Fomalhaut.Comment: 8 pages, 3 figures, 1 tabl
State-of-the-art models for the phase diagram of carbon and diamond nucleation
Contains fulltext :
72586.pdf (preprint version ) (Open Access)28 p
Disk Detective: Discovery of new circumstellar disk candidates through citizen science
The Disk Detective citizen science project aims to find new stars with 22 ÎŒm excess emission from circumstellar dust using data from NASA's Wide-field Infrared Survey Explorer (WISE) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 ÎŒm excess around the previously known debris disk host star HD 22128