The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1 AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163 ± 6 kilometres, density 2.52 ± 0.05 grams per cm(3) and a high visible geometric albedo, Pv = 0.96(+0.09)(-0.04). No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ∼1 nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun.

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Al2O3−TiO2 materials were prepared by the sol−gel method using different additives (HNO3, NH4OH, and CH3COOH) and their physical properties were evaluated by various techniques. The materials at two compositions (Al/Ti atomic ratios = 2 and 25) were synthesized at 278 K and calcined at temperatures from 573 to 1173 K. The solids were characterized by TGA, DTA, XRD, BET, and SEM. The complexing (CH3COOH) and the basic (NH4OH) additives led to solids with high pore volumes and broad pore size distributions. On one hand, very high surface areas (525 m2/g for solids calcined at 773 K) were found for samples prepared with CH3COOH. On the other hand, high-temperature stability was obtained with NH4OH addition (200 m2/g, for Al2O3-rich samples at 1173 K). HNO3-catalyzed samples showed lower surface areas and pore volumes. Surface areas and sintering behavior were a function of TiO2 content. TiO2-rich samples showed higher surface areas (773 K) than Al2O3-rich oxides, but at more severe conditions they suffered a severe specific area loss. The alumina-rich formulations showed good stability in the whole range of temperatures studied.

We have carried out a continuous multiband photometric monitoring of the nuclear activity of comet 29P/Schwassmann–Wachmann 1 from 2008 to 2010. Our main aim has been to study the outburst mechanism on the basis of a follow‐up of the photometric variations associated with the release of dust. We have used a standardized method to obtain the 10‐arcsec nucleus photometry in the V, R and I filters of the Johnson–Kron–Cousins system, which are accurately calibrated with standard Landolt stars. The production of dust in the R and I bands during the 2010 February 3 outburst has been also computed. We conclude that the massive ejection of large (optically thin) particles from the surface at the time of the outburst is the triggering mechanism to produce the outburst. The ulterior sublimation of these ice‐rich dust particles during the following days induces fragmentation, generating micrometre‐sized grains, which increase the dust spatial density to produce the outburst in the optical range as a result of the scattering of sunlight. The material leaving the nucleus adopts a fan‐like dust feature, formed by micrometre‐sized particles that decay in brightness as it evolves outwards. By analysing the photometric signal measured in a standardized 10‐arcsec aperture using the phase dispersion minimization technique, we have found a clear periodicity of 50 d. Remarkably, this value is also consistent with an outburst frequency of 7.4 outbursts per yr deduced from the number of outbursts noticed during the effective observing time.