Jose Luis Ortiz

A terrestrial planet candidate in a temperate orbit around Proxima Centauri

At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun’s closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.

Dust measurements in the coma of comet 67P/Churyumov-Gerasimenko inbound to the Sun

Critical measurements for understanding accretion and the dust/gas ratio in the solar nebula, where planets were forming 4.5 billion years ago, are being obtained by the GIADA (Grain Impact Analyser and Dust Accumulator) experiment on the European Space Agency’s Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko. Between 3.6 and 3.4 astronomical units inbound, GIADA and OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) detected 35 outflowing grains of mass 10−10 to 10−7 kilograms, and 48 grains of mass 10−5 to 10−2 kilograms, respectively. Combined with gas data from the MIRO (Microwave Instrument for the Rosetta Orbiter) and ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instruments, we find a dust/gas mass ratio of 4 ± 2 averaged over the sunlit nucleus surface. A cloud of larger grains also encircles the nucleus in bound orbits from the previous perihelion. The largest orbiting clumps are meter-sized, confirming the dust/gas ratio of 3 inferred at perihelion from models of dust comae and trails.

“TNOs are Cool”: a survey of the trans-Neptunian region - VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects

Trans-Neptunian objects (TNO) represent the leftovers of the formation of the Solar System. Their physical properties provide constraints to the models of formation and evolution of the various dynamical classes of objects in the outer Solar System. Based on a sample of 19 classical TNOs we determine radiometric sizes, geometric albedos and beaming parameters. Our sample is composed of both dynamically hot and cold classicals. We study the correlations of diameter and albedo of these two subsamples with each other and with orbital parameters, spectral slopes and colors. We have done three-band photometric observations with Herschel/PACS and we use a consistent method for data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70.0, 100.0 and 160.0 mu m. Additionally, we use Spitzer/MIPS flux densities at 23.68 and 71.42 mu m when available, and we present new Spitzer flux densities of eight targets. We derive diameters and albedos with the near-Earth asteroid thermal model (NEATM). As auxiliary data we use reexamined absolute visual magnitudes from the literature and data bases, part of which have been obtained by ground based programs in support of our Herschel key program. We have determined for the first time radiometric sizes and albedos of eight classical TNOs, and refined previous size and albedo estimates or limits of 11 other classicals. The new size estimates of 2002 MS4 and 120347 Salacia indicate that they are among the 10 largest TNOs known. Our new results confirm the recent findings that there are very diverse albedos among the classical TNOs and that cold classicals possess a high average albedo (0.17 +/- 0.04). Diameters of classical TNOs strongly correlate with orbital inclination in our sample. We also determine the bulk densities of six binary TNOs.

Optical detection of meteoroidal impacts on the Moon

Impacts of meteoroids on the Moon should cause detectable optical flashes, but the population of objects that are big enough is very low, and hitherto no unambiguous impact flashes have been recorded. The flux of meteoroids associated with the Leonid meteor shower of 18 November 1999 was predicted to produce observable flashes on the night side of the Moon. Here we report the unambiguous detection of five such impact flashes, three of which were seen simultaneously by other observers. We also observed a possible impact flash on 16 July 1999. All of the flashes were of very brief duration (<0.02u2009s), as expected for high-speed impacts.

Luminous Efficiency in Hypervelocity Impacts from the 1999 Lunar Leonids

An analysis of the optical flashes produced by Leonid meteoroids impacting the Moon in 1999 November is carried out in order to estimate the fraction of kinetic energy converted into radiation, the so-called luminous efficiency η. It is shown that the observational data are consistent with luminous efficiencies of 2 × 10-3 in the wavelength range of 400-900 nm with an uncertainty of about 1 order of magnitude. This experimental value of η is significantly larger than previous estimates for meteoroids of asteroidal composition based on numerical calculations and scaling laws from laboratory collisions. According to our results, the luminous efficiency might vary with mass, i.e., the smaller impactors converting less kinetic energy into light and vice versa. A comparison with recent numerical simulations for meteoroids of cometary composition is also carried out.

(596) Scheila in outburst: a probable collision event in the main asteroid belt

Images of asteroid (596) Scheila have been acquired at various dates after the discovery of the 2010 outburst. Assuming a short-duration event scenario, as suggested by the quick vanishing of the dust tail brightness with time, and numerically integrating the equation of motion of individual particles ejected from the surface, we have developed a tail model from which we estimate the parameters associated with the geometry of the ejection, the size distribution, and the velocity distribution of the ejected particles, as well as the total mass ejected. We found a weak inverse power-law dependence of ejection velocity versus particle radius, with velocities ranging from 50 to 80 m s{sup -1} for particle radii in the range from 5 cm to 8 x 10{sup -5} cm, respectively. These velocities are very different from those expected from ice sublimation at the asteroid heliocentric distance ({approx}3 AU) and suggest a collision scenario as a likely cause of the outburst. We found that the ejected particles are distributed in size following a power law of index -3, and, based on the ejecta mass and scaling laws, the impactor size is estimated at 30-90 m in radius, assuming an impact velocity of {approx}5 km s{supmorexa0» -1}, and the same density (1500 kg m{sup -3}) for the asteroid as for the projectile. We have inferred an asymmetry in the ejecta along the axis normal to the asteroid orbit plane, a likely indicator of an oblique impact. The impact is estimated to have occurred on November 27, with an accuracy not better than {+-}3 days.«xa0less

Observation and Interpretation of Leonid Impact Flashes on the Moon in 2001

We present observations of lunar Leonid impact flashes recorded in 2001 November from Spain. Four impact flashes were detected on November 18. Another flash was also recorded on the same night, which appears to be impact related, and two more on that night are possibly, but not unambiguously, of impact nature. On November 19 another flash was detected, which very likely resulted from an impact. The brightest impact flash reached a peak brightness of 5.2 ± 0.3 mag in V; it had a very dim precursor just 0.02 s prior to peak brightness and had a very long lasting afterglow that remained visible for more than 600 ms with oscillations in brightness; this unique and unexpected behavior challenges current models of impact flashes. The other flashes did not show such a behavior and remained visible for a few tens of milliseconds. Adopting the luminous efficiency derived for the 1999 lunar Leonids (2 × 10-3), our observations can be used to estimate meteoroid fluxes. The observations are compatible with a flux of 0.1 meteoroids of mass larger than 2 × 10-8 kg km-2 hr-1 on November 18 at 18:15 UT, provided that a mass index of 1.69 is used. Both the flux and the mass index agree with meteor observations carried out in 2001 from several locations on Earth.

The 2011 October Draconids outburst – II. Meteoroid chemical abundances from fireball spectroscopy

We acknowledge support from the Spanish Ministry of Science and Innovation (projects AYA2009-13227, AYA2009-14000-C03-01 and AYA2011-26522), Junta de Andalucia (project P09-FQM-4555) and CSIC (grant # 201050I043).

Robotic Systems for Meteor Observing and Moon Impact Flashes Detection in Spain

A robotic observatory has been setup in the south-west of Spain with the aim to study meteoroids interacting with the Earths atmosphere and meteoroids impacting on the Moons surface. This is achieved by using an array of high-sensitivity CCD video cameras and three automated Schmidt-Cassegrain telescopes. We summarize here the main characteristics of this new facility.

A large lunar impact blast on 2013 September 11

On 2013 September 11 at 20h07m28.68