Secrets of Stardust Studied at the ESRF
In February 1999 NASA launched the spacecraft "Stardust" for a twelve year mission to fly through the cloud of dust that surrounds the nucleus of a comet. In addition to the cometary grains, the spacecraft also collected dust particles from the interstellar space.
On the outer fringes of the solar system, astronomers estimate that perhaps a trillion dormant comets circle the sun. These frozen bodies of dust and ice are the most distant survivors of the disc of gas and dust that formed the Sun and planets about 4.6 billion years ago. Our own solar system is home to a constant flow of interstellar dust. These tiny particles are the initial building blocks of planetary systems like our own.
For the first time in history, the mission brought cometary and interstellar material back to Earth for analysis. The dust samples - in fact tiny, incredibly fast flying grains - were collected using silica-based aerogel blocks mounted in aluminium foil cells. Particle impacts, or craters in the aluminium foil covered by some particle residue, were also looked at.
The interstellar grains were found to be partly crystalline with a small carbon content. These findings deviate from the predictions of astronomical observations and modelling.
More than 30,000 international volunteers joined the search for interstellar dust impacts in a citizen science project known as Stardust@home.
Over one million field of view microscopy images were analysed in the course of the project, to zero in on the final 15 tracks of potential interstellar dust grains.
"The localization of the microscopic particulate material trapped within the glassy foam was such an extremely time consuming task that the whole world was asked to help", explained Professor Laszlo Vincze from Ghent University, Belgium.
The enthusiasm for the project is not surprising: Stardust was the first sample return mission to bring back solid samples from beyond the Moon, specifically cometary and interstellar grains. Of the thousands of particles collected and recorded in total, only seven dust particle impacts have been identified as having probable interstellar origin. More than 50 spacecraft debris particles or interplanetary particles were also identified.
Several impact tracks from the sampling tray of the Stardust mission were studied at the ESRF's ID13 and ID22-NI nano-focussing beamlines, using synchrotron X-ray fluorescence and diffraction techniques. These investigations were carried out at ID13 by Professor Frank Brenker from the Goethe University Frankfurt, Germany, (and Laszlo Vincze from the Ghent University, Belgium) and at ID22-NI by Professor Alexandre Simionovici from the J. Fourier University, Grenoble. ESRF staff and scientists involved in this research were Manfred Burghammer at ID13, Peter Cloetens, Juan-Angel Sans Tresseras at ID22-NI beamline (now ID16A) as well as Vicente A. Solé from the BLISS group. Members of the two team include Dr. Laurence Lemelle from ENS Lyon, France, Dr. Andrew Westphal from SSL, Univ. of California Berkeley, Dr. T. Schoonjans from Univ. of Sassari, Italy, Drs. G. Silversmit, B. Vekemans from Ghent Univ, Belgium.
Last year, the members of Brenker and Simionovici’s Stardust synchrotron groups were awarded NASA Achievement awards for their involvement in the project. They were presented to the four ESRF members in November 2013.
Read the results of the full study in Science.
Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft, A.J. Westphal et al., Science, 14 August 2014. dx.doi.org/10.1126/science.1252496