Josep M. Trigo-Rodríguez

Impact Features on Stardust: Implications for Comet 81P/Wild 2 Dust

Particles emanating from comet 81P/Wild 2 collided with the Stardust spacecraft at 6.1 kilometers per second, producing hypervelocity impact features on the collector surfaces that were returned to Earth. The morphologies of these surprisingly diverse features were created by particles varying from dense mineral grains to loosely bound, polymineralic aggregates ranging from tens of nanometers to hundreds of micrometers in size. The cumulative size distribution of Wild 2 dust is shallower than that of comet Halley, yet steeper than that of comet Grigg-Skjellerup.

THE PHYSICS OF PROTOPLANETESIMAL DUST AGGLOMERATES. I. MECHANICAL PROPERTIES AND RELATIONS TO PRIMITIVE BODIES IN THE SOLAR SYSTEM

We present laboratory experiments on the formation of macroscopic dust aggregates. The centimeter-sized highly porous bodies are produced by random ballistic deposition from individual micrometer-sized dust particles. We find packing densities between 0.07 and 0.15 for uncompressed samples, dependent on the shape and size distribution of the constituent dust grains. Impacts into these bodies are simulated by uniaxial compression experiments. We find that the maximum compression, equivalent to the highest protoplanetary impact velocities of ~50 m s-1, increases the packing density to 0.20-0.33. Tensile strength measurements with our laboratory samples yield values in the range 200-1100 Pa for slightly compressed samples. We review packing densities and tensile strengths found for primitive solar system bodies, e.g., for comets, primitive meteorites, and meteoroids. We find a consistency between packing densities and tensile strengths of our laboratory samples with those from cometary origin.

Outburst activity in comets – II. A multiband photometric monitoring of comet 29P/Schwassmann–Wachmann 1

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.

Outburst activity in comets I. Continuous monitoring of comet 29P/Schwassmann-Wachmann 1

Aims. We carried out a continuous monitoring of comet 29P/Schwassmann-Wachmann 1 by using medium aperture telescopes with the aim of studying the activity and outburst mechanisms of this comet on the basis of photometric variations. Methods. We used a standardized method to obtain the coma photometry in the R filter of the Johnson-Kron-Cousins system. Some abrupt changes observed in the brightness of SW1 suggest important variations in surface activity with time. Results. During our 2002-2007 observational campaign we detected 28 outbursts (of 1 mag or larger) in 29P/Schwassmann-Wachmann 1. A typical outburst is characterized by a rapid increase towards maximum (in a few hours) and a slower decrease toward the quiescent level (in 3-4 days). Given the effective observing time, the average outburst rate is 7.3 events per year. Despite well-sampled data, no signs of a clear periodicity in the outburst occurrence has been found, thus confirming the unpredictability of the activity of this comet.

The role of massive AGB stars in the early solar system composition

We demonstrate that a massive asymptotic giant branch (AGB) star is a good candidate as the main source of short-lived radionuclides in the early solar system. Recent identification of massive (48 M) AGB stars in the galaxy, which are both lithium- and rubidium-rich, demonstrates that these stars experience proton captures at the base of the convective envelope (hot bottom burning), together with high-neutron density nucleosynthesis with 22Ne as a neutron source in the He shell and efficient dredge-up of the processed material. A model of a 6.5 Mʘ star of solar metallicity can simultaneously match the abundances of 26Al, 41Ca, 60Fe, and 107Pd inferred to have been present in the solar nebula by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material, and taking into account a time interval between injection of the short-lived nuclides and consolidation of the first meteorites equal to 0.53 Myr. Such a polluting source does not overproduce 53Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements. It is usually argued that it is unlikely that the short-lived radionuclides in the early solar system came from an AGB star because these stars are rarely found in star forming regions, however, we think that further interdisciplinary studies are needed to address the fundamental problem of the birth of our solar system.

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.

Orbit and dynamic origin of the recently recovered Annama's H5 chondrite

We describe the fall of Annama meteorite occurred in the remote Kola Peninsula (Russia) close to Finnish border on April 19, 2014 (local time). The fireball was instrumentally observed by the Finnish Fireball Network. From these observations the strewnfield was computed and two first meteorites were found only a few hundred meters from the predicted landing site on May 29th and May 30th 2014, so that the meteorite (an H4-5 chondrite) experienced only minimal terrestrial alteration. The accuracy of the observations allowed a precise geocentric radiant to be obtained, and the heliocentric orbit for the progenitor meteoroid to be calculated. Backward integrations of the orbits of selected near-Earth asteroids and the Annama meteoroid showed that they rapidly diverged so that the Annama meteorites are unlikely related to them. The only exception seems to be the recently discovered 2014UR116 that shows a plausible dynamic relationship. Instead, analysis of the heliocentric orbit of the meteoroid suggests that the delivery of Annama onto an Earth-crossing Apollo type orbit occurred via the 4:1 mean motion resonance with Jupiter or the nu6 secular resonance, dynamic mechanisms that are responsible for delivering to Earth most meteorites studied so far.

Clues on the importance of comets in the origin and evolution of the atmospheres of Titan and Earth

Abstract Earth and Titan are two planetary bodies formed far from each other. Nevertheless the chemical composition of their atmospheres exhibits common indications of being produced by the accretion, plus ulterior in-situ processing of cometary materials. This is remarkable because while the Earth formed in the inner part of the disk, presumably from the accretion of rocky planetesimals depleted in oxygen and exhibiting a chemical similitude with enstatite chondrites, Titan formed within Saturns sub-nebula from oxygen- and volatile-rich bodies, called cometesimals. From a cosmochemical and astrobiological perspective, the study of the H, C, N, and O isotopes on Earth and Titan could be the key to decipher the processes occurred in the early stages of formation of both planetary bodies. The main goal of this paper is to quantify the presumable ways of chemical evolution of both planetary bodies, in particular the abundance of CO and N 2 in their early atmospheres. In order to do that the primeval atmospheres and evolution of Titan and Earth have been analyzed from a thermodynamic point of view. The most relevant chemical reactions involving these species and presumably important at their early stages are discussed. Then, we have interpreted the results of this study in light of the results obtained by the Cassini–Huygens mission on these species and their isotopes. Given that H, C, N, and O were preferentially depleted from inner disk materials that formed our planet, the observed similitude of their isotopic fractionation, and subsequent close evolution of Earths and Titans atmospheres point s towards a cometary origin of Earth atmosphere. Consequently, our scenario also supports the key role of late veneers (comets and water-rich carbonaceous asteroids) enriching the volatile content of the Earth at the time of the late heavy bombardment of terrestrial planets.

The Effect of Aqueous Alteration and Metamorphism in the Survival of Presolar Silicate Grains in Chondrites

Relatively small amounts (typically between 2 and 200 ppm) of presolar grains have been preserved in the matrices of chondritic meteorites. The measured abundances of the different types of grains are highly variable from one chondrite to another, but are higher in unequilibrated chondrites that have experienced little or no aqueous alteration and/or metamorphic heating than in processed meteorites. A general overview of the abundances measured in presolar grains (particularly the recently identified presolar silicates) contained in primitive chondrites is presented. Here we will focus on the most primitive chondrite groups, as typically the highest measured abundances of presolar grains occur in primitive chondrites that have experienced little thermal metamorphism. Looking at the most aqueously altered chondrite groups, we find a clear pattern of decreasing abundance of presolar silicate grains with increasing levels of aqueous alteration. We conclude that measured abundances of presolar grains in altered chondrites are strongly biased by their peculiar histories. Scales quantifying the intensity of aqueous alteration and shock metamorphism in chondrites could correlate with the content of presolar silicates. To do this it would be required to infer the degree of destruction or homogenization of presolar grains in the matrices of primitive meteorites. To get an unbiased picture of the relative abundance of presolar grains in the different regions of the protoplanetary disk where first meteorites consolidated, future dedicated studies of primitive meteorites, IDPs, and collected materials from sample-return missions (like e.g. the planned Marco Polo) are urgently required.