Nuclear techniques are improving our understanding of the solar system, mainly the materials that make-up the surface of planets and moons, said Bragg Institute instrument scientist Helen Maynard-Casely at a Science at the Dome event in Canberra on 28 May 2015.
The event, which has been organised by the Australian Academy of Science highlights how crystallography is contributing to a wide range of studies from Minerals to Medicines. Crystallography is a discipline that uses neutrons and X-rays, and provides a very detailed look at the atomic arrangement of materials under a wide range of conditions. The Minerals to Medicine symposium coincides with the announcement of new fellows to the Academy and awards.
Maynard-Casely was a Symposium presenter who highlighted how crystallography can be used to explore the surfaces and interiors of planets and moons – recreating these extremely harsh conditions in the laboratory.
Many scientists use X-ray powder diffraction to identify the elements and analyse the minerals in rocks and soil. “But Earth is not the only planet where you can do diffraction experiments,” said Maynard-Casely.
NASA’s Ames Research Group developed a small, portable, and fast-processing X-ray diffractometer, CheMin, to sit inside the Curiosity Rover on the surface of Mars to measure the abundance of various minerals in Martian samples.
CheMin uses Curiosity’s mechanical arm to drill out rock or scoop up dust and then place it inside a well, where it is vibrated and data is collected.
CheMin uses Curiosity’s mechanical arm to drill out rock or scoop up dust and then place it inside a well, where it is vibrated and data is collected.
“You get fantastic, beautiful, very well-averaged powder patterns straight away,“ said Marnard-Casely. Interesting peaks in the data were very indicative of clay, a group of minerals which trap water molecules between their layers.
When the diffraction patterns were compared to measurements from sites on Earth, they saw similarities with Icelandic ash and the lava plains of Hawaii.
“With this benchmark and our extensive knowledge of earth minerals, we can build analogues to help us understand the Martian surface and atmosphere, and how it may have changed over time.”
In contrast to the rocky inner planets which are composed of silicates and metals, the outer frozen gas giants and their moons are made of very different materials.
“Because we don’t have instruments on the surface of these bodies, we have to do it all from space and rely on other techniques to determine their chemical make-up.”
Spacecraft, such as Galileo, can capture images from many thousands of kilometres from the surface of a planet. It is possible to pick out features and determine materials from spectroscopy, which analyses light reflected from the sun to reveal elements.
“The spectra from Europa, an icy moon of Jupiter, informs us how to recreate the chemistry and temperatures of the moon in the laboratory, then we can use diffraction instruments and attempt to identify materials that would be there.”
One of the big surprises about Europa was that it appears to have a significant component of non-icy materials. The exact composition of this material is the subject of significant academic debate.
“Exposing the identified elements to temperature changes under similar temperatures (to the moon’s surface), we identified known and unknown materials from diffraction patterns that could provide information about the surface.”
“Because clouds shield the surface of another moon, Titan, which orbits another gas giant, Saturn, you have to use radar information from the surface.”
“The biggest surprise about Titan was that there are bodies of liquid on the surface, not water though–these lakes and seas are composed of small hydrocarbons, methane and ethane. “
The Cassini spacecraft sent the probe Huygens to the strange surface of Titan and along with data from the orbiting Cassini revealed a hydrological cycle that is not based on water. The data suggested a new range of minerals and materials, but these still created features that are analogous to those found on Earth.
“We were particularly interested in finding out if ethane evaporated on the surface as part of the hydrological cycle”.
Scientists from the Jet Propulsion Laboratory travelled to the Australian Synchrotron to solve the problem of identifying the crystal structure of a new material created when mixing benzene and ethane at the chilly 90 K temperature found on the surface of Titan.
X-ray diffraction of the sample under those conditions showed that linear ethane atom sat within a bigger two-dimensional host structure made of benzene.
X-ray diffraction of the sample under those conditions showed that linear ethane atom sat within a bigger two-dimensional host structure made of benzene.
Diffraction has also been used to help understand the coldest place in the Solar System, Uranus, which is unusual in its rotation and magnetic alignment and hideous surface conditions.
Following a flyby by the Voyager spacecraft, planetary scientists determined the planet had a molecular gassy envelope around a hot dense icy mantle.
“We were searching for the noble gases on Uranus, which we expected to find but there were surprises in the planet’s envelope.”
“In recreating the extreme surface conditions on Uranus with temperature and pressure, using water xenon and platinum, we found two new materials, one of which is a xenon hydrate.” This suggests that all the xenon could be locked up in the planets interior.
Maynard-Casely said she is looking forward to new data that will come from the New Horizons spacecraft which is expected to reach Pluto in July. “If Pluto has an ice cap, there may be minerals there.”