A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation

in Nature (2011), 478

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 ... [more ▼]

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 (1AU 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+/-6kilometres, density 2.52+/-0.05 grams per cm[SUP]3[/SUP] and a high visible geometric albedo, . No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1nanobar, 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. [less ▲]

Dynamical Modeling of the Deep Impact Dust Ejecta Cloud

in Käufl, H. U.; Sterken, C. (Eds.) Deep Impact as a World Observatory Event: Synergies in Space, Time, and Wavelength (2009)

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its ... [more ▼]

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its position and shape are governed by the physical properties of the dust grains. We use a Monte Carlo model to describe the evolution of the post-impact dust plume. The results of our dynamical simulations are compared to the data obtained with FORS2footnote{FORS stands for \underline{FO}cal Reducer and low dispersion Spectrograph for the Very Large Telescope (VLT) of the European Southern Observatory (ESO).} to derive the particle size distribution and the total amount of material contained in the dust ejecta cloud. [less ▲]

Observations of Comet 73P/SW3 close to its closest approach to the Earth.

in European Planetary Science Congress 2006 (2006)

In May 2006 comet 73P/SW3 passed at less than 0.1 AU from Earth providing us an unique opportunity for high spatial resolution study of its coma. This event was expected to be particularly interesting ... [more ▼]

In May 2006 comet 73P/SW3 passed at less than 0.1 AU from Earth providing us an unique opportunity for high spatial resolution study of its coma. This event was expected to be particularly interesting because the comet had broken apart in 3-4 fragments in 1996. The 2006 apparition has been even more interesting because the fragments produced in 1996, when approaching the Sun, were continuously breaking apart. This process resulted in many small sub-fragments and in the injection in the coma of fresh material, coming from the interior of the nuclei, giving the possibility to study this uncontaminated material. The breaking fragments have been observed at ESO in the visible and near-IR with the aim of analyzing this fresh solid component of the coma in search of possible presence of organic solids. In the presentation we will report preliminary results of this campaign. [less ▲]

Comet C/2001 Q4 (NEAT) at its closest approach to the Earth

in American Astronomical Society, DPS meeting #36 (2004, November 01)

Comet C/2001 Q4 (NEAT) was observed at ESO (La Silla) for three consecutive nights at the beginning of May, 2004 at its closest approach to Earth. The observations consisted of quasi-simultaneous multi ... [more ▼]

Comet C/2001 Q4 (NEAT) was observed at ESO (La Silla) for three consecutive nights at the beginning of May, 2004 at its closest approach to Earth. The observations consisted of quasi-simultaneous multi-wavelength exposures in the visible, near-IR and thermal-IR in order to study different properties of the solid component that are responsible for the scattering and emission of radiation in different spectral ranges. The comet was observed with the 3.6m telescope, equipped with TIMMI2 for the thermal-IR region, the NTT, equipped with EMMI and SOFI for the visible and near-IR regions. Narrow band images and long slit spectra were recorded for each spectral region. In the near-IR range, polarimetric observations were also performed during the last night. The aim of the observations was the characterization of the solid component at small scalelength to search for possible short lifetime organic components, as those found in the comet C/2000 WM1 (Tozzi et al., 2004, A&A, 424, 235), dust fragmentation etc.. Here we report preliminary results of the analysis of these observations. [less ▲]

Spectral evolution of Rosetta target comet 46P/Wirtanen

in Astronomy and Astrophysics (1998), 335

The compositional evolution of the coma of Rosetta target comet 46P/Wirtanen was studied along its pre-perihelion orbit. At 2.34 AU the first gaseous species, CN and C_3, were detected. C_2 and NH_2 arose ... [more ▼]

The compositional evolution of the coma of Rosetta target comet 46P/Wirtanen was studied along its pre-perihelion orbit. At 2.34 AU the first gaseous species, CN and C_3, were detected. C_2 and NH_2 arose at 2.0 AU. The production rate curves of gas and dust show a steep increase between 1.8 AU and 1.6 AU indicating a distinct change of the outgassing conditions. The C_2 production increases more rapidly with decreasing solar distance than CN. As one consequence the C_2/CN ratio strongly varies with heliocentric distance. Due to this variation a classification of 46P/Wirtanen by the taxonomy introduced by A'Hearn et al. (\cite{AMSOB}) distinguishing comets with typical abundance ratios from carbon-chain depleted comets, is impossible. It would be classified as depleted beyond about 1.6 AU whereas it would be designated typical at smaller distances. The knowledge of the unexpected changes in the activity curves of 46P/Wirtanen will help to optimize the Rosetta mission scenario in particular with regard to science operations. based on observations obtained at ESO La Silla within ESO programmes No. 57.F-0290 and 58.F-0413 [less ▲]