Juan Carlos Gómez Martín

Cosmic dust is a general term that encompasses different types of extraterrestrial particulate materials: interplanetary (or zodiacal) dust, cometary dust, asteroidal dust, interstellar dust, and even atmospheric aerosol in different planets and moons. Submillimeter sized debris orbiting the Sun are usually termed micrometeoroids. There is some confusion about these denominations and it is noted that the international astronomical union has published some recommendations. In general: dust is smaller than 30 μm, meteoroids 30 μm to 1 m, asteroids larger than 1 m. The term micrometeroid is currently discouraged by the IAU.

Dust particles ejected by comets approaching perihelion and released by collisions between asteroids feed the Zodiacal Cloud, a disk-shaped cloud of aged dust that pervades the interplanetary space around the Sun and scatters Sun light giving rise to the so-called Zodiacal Light. In situ analysis of pristine particles of comet 67P/Churyumov-Gerasimenko has been carried out by the Rosetta mission. Samples have been returned to Earth from asteroid Itokawa by the Hayabusa mission and from comet 81P/Wild by the Stardust mission (see figures). As planets orbit the sun, they sweep up tens of tons of these particles. Between 20 and 50 t d^-1 of zodiacal dust particles are captured by the gravity of Earth according to current estimates, dwarfing the input of larger meteorites. Because of the high relative speed (11-72 km s^-1), particles entering Earth’s and other planet's atmospheres are heated by collisions with atmospheric molecules and their elemental constituents sputter and vaporize (ablate). Depending on mass and speed, particles may vaporize completely, melt and solidify forming a cosmic spherule, melt partially forming an scoriaceous micrometeorite or suffer a minor degree of alteration, forming an unmelted micrometeorite.

Particles or residues surviving entry normally reach the ground and are collected from sea sediments, deserts, and specially from the polar ice and snow. Also, a dedicated NASA program collected over years an impressive collection of particles of extraterrestrial origin using collectors mounted in stratospheric research aircraft. These have been called traditionally interplanetary dust particles.

The main source of Zodiacal Dust appears to be the Jupiter Family of Comets (JFCs) according to dynamical modelling constrained with atmospheric observations. The fact that micrometeorite mineralogy and morphology statistics are more consistent with an asteroidal origin appears to be related to the mass and velocity distributions of the cometary dust particles, which tend to ablate more efficienty in the mesosphere.

Unmelted micrometeorites and interplanetary dust particles have average elemental abundances close to those of carbonaceous chondrites of type CI, which in turn are similar to the composition of the solar photosphere. This is at least true for refractory elements. Owing to the different volatility of the elemental constituents of zodiacal dust particles, micrometeorites that have experienced total or partial melting are usually depleted in the most volatile elements and even show isotopic mass fractionation. Conversely, the metal layers formed by meteoritic ablation are enriched in volatile elements such as sodium and potassium. This phenomenon known as differential ablation. There is near-live evidence of differential ablation from high performance large aperture radar measurements of meteor head echoes and from spectrally resolved high sensitivity cameras.

Cosmic dust has been proposed as a carrier of trace bioelements (C, S, P) to planetary surfaces in the early Solar System. Moreover, the input of extraterrestrial sulfur may have had paleoclimatic impacts

The objective of the ERC-AvG project Cosmic Dust in the Terrestrial Atmosphere (CODITA) was determining the total input of cosmic dust into Earth. In order to find an estimate of this number consistent with all available observations, the different biases of these had to be considered. In particular, ground based observations need to account for the effect of atmospheric entry and ablation. The chemical ablation model (CABMOD) was used for this purpose. A meteor ablation simulation (MASI) was developed to provide experimental support to the model. I led a team to design, build and run the instrument with cosmic dust analogs and compare the results with CABMOD predictions. The most important predictions of the model were validated and in particular we demonstrated the differential ablation of meteors in the laboratory for the first time.

Spectro-foto-polarimetric [1] [2] remote sensing is a source of information about cosmic dust complementary to the collections of micrometeorites [1] [2] and stratospheric IDPs, the in-situ observations of Rosetta and the samples returned by Stardust and Hayabusa. Currently, I work with Olga Muñoz and Fernando Moreno at the Cosmic Dust Laboratory of IAA-CSIC, a facility that has produced in the past excellent measurements of the light scattering properties of a large number of cosmic dust analogs.