Making alien worlds on Earth
Australian nuclear scientists are finding fresh ways to uncover the secrets of space, writes Belinda Smith.
Want to get up close to the swirling methane seas on Saturn’s satellite Titan or check out the subsurface salty oceans of Ganymede, Jupiter’s largest moon? For Helen Brand at ANSTO’s Australian Synchrotron in Melbourne and Helen Maynard-Casely at the Australian Centre for Neutron Scattering in Sydney, there’s no need to wait for a probe to dive or drill in. The planetary science pair explores alien worlds by making tiny bits of them on Earth.
Using a technique called powder diffraction, Brand and Maynard-Casely mix the compounds that are thought to comprise our companions in the solar system, squash them to mimic those otherworldly pressures and watch how their crystal structure changes. For work such as this, Brand and Maynard-Casely shared the 2017 ANSTO Early Career Award in Nuclear Science and Technology.
Their collaboration spans decades. They met at age 18 as undergraduates at University College London. “We’ve known each other for a very long time!” Maynard-Casely says. And even though both are London-born and work closely in Australia today, their journeys from childhood through school to university took different paths.
Maynard-Casely grew up in rural Cambridgeshire, her parents a mechanic and a teacher. But she had her sights set on space early on. At eight years old, she watched chemist Helen Sharman blast off and become the first British astronaut and first woman to visit the Mir space station. “Family legend is I walked up to dad and said, ‘I want to go to space because that’s what Helens do!’” Maynard-Casely laughs.
That drive for outer space was brought back to earth when, not long after, she discovered volcanoes. She became enamoured with the spate of volcano-disaster films of the time, such as the 1997 thrillers Volcano and Dante’s Peak. And at around 15 or 16 years old, she “found out about volcanoes made of ice [on other planets], and thought: ‘That’s where I want to be’.”
After high school, she enrolled in a planetary science degree at University College London, the first in her family to go to university. Meanwhile, Brand – with a physics teacher mother and maths teacher father – “had no chance” of not being a scientist, she says. Her dad, a hobby geologist, “took a geological hammer on his honeymoon, much to my mum’s annoyance!”
Luckily, the younger Brand liked geology too – not to mention space. Growing up in south London, she remembers frequenting the London Science Museum. There, she admired the bronze command module of Apollo 10, which flew around the moon in a dress rehearsal of the historic Apollo 11 landing in 1969.
It was a school trip to Iceland, led around the bleak, icy, otherworldly landscapes by a geologist teacher, that really glued her love of rocks and space together. She decided to apply for the general physical sciences degree at University College London.
“On the first day, they give you a timetable and tell you to choose eight subjects,” she says. But after around six weeks, she realised she was in the same classes as the planetary science students – including Maynard-Casely – so she transferred to their course.
After graduating, both embarked on PhDs. Brand stayed at University College London, unravelling the crystal structure of hydrated minerals in Jupiter’s four largest moons: Io, Europa, Ganymede and Callisto. Maynard-Casely’s studies took her to the University of Edinburgh in Scotland, where she examined how methane’s structure changes in the crushing pressures of gas giants Uranus and Neptune.
When Brand moved to Australia in 2009 to take up a position at CSIRO in Melbourne, she worked on a problem extremely relevant to the mining boom of the time: how a hydrated mineral called jarosite forms.
Ore dug from the ground is often a mix of loads of metals and impurities. To end up with pure zinc, for instance, a refinery must get rid of iron. This is done by mixing ore with water and adding an alkaline. The alkaline binds to iron, creating jarosite, which “precipitates and blobs to the top, and can then be scooped off,” Brand says.
X-ray powder diffraction can tell mining companies the best way to crystallise different types of jarosite and do it more efficiently.
“But the same thing happens on Mars,” Brand says – not in mines, of course, but naturally (as it does on Earth). In 2004, the Opportunity rover found jarosite on the Martian surface – the first hydrated mineral discovered on the red planet.
Jarosite needs lots of water to form. Its presence was another piece of evidence that, at some point, Mars had vast liquid oceans.
When Brand moved to the Australian Synchrotron powder diffraction beamline, she wanted to see how jarosite forms in conditions like the Martian crust and surface. The chemistry could be plugged into geological models of Martian evolution and help planetary scientists reveal the planet’s history.
Maynard-Casely made the move to Australia too, in 2011, first working with Brand at ANSTO’s Australian Synchrotron before moving to ANSTO in Sydney. (“She followed me!” Brand laughs. “I was here first.”)
Among other things, Maynard-Casely is looking at how the structure of small hydrocarbons and ices shift when placed under pressure. Recently, she’s taken an interest in the asteroid belt – a ring of asteroids and dwarf planets between Mars and Jupiter.
NASA’s Dawn spacecraft swung by asteroid Vesta before settling into orbit around Ceres, the largest body in the asteroid belt, last year. There, it found the topmost metre of Ceres’ surface to be hydrogen-rich, consistent with huge expanses of water ice tucked away below.
“We’ve gone from thinking these bodies are completely dry, there’s no water there, to the realisation that Ceres sits neatly on the ice line, which is the point where it got cold enough for water to condense straight away [when the solar system formed],” Maynard-Casely says.
She’ll try different combinations of salts to emulate Ceres conditions and see what structures appear. Then, she’ll compare her data with that taken by Dawn (which, like all NASA research, is open-access). It might tell us about the water situation on Ceres, she says, “but in reality, we’ll probably make it a bit more complicated!” At the very least, she will have accumulated a comprehensive diffraction catalogue of different salty solutions from minus 269 °C to room temperature.
Brand, too, has turned her attention to asteroids – but those that made it to Earth. Last year, a friend asked if she would use the X-ray diffractometer to examine sand-sized 2.7-billion-year-old meteorites found embedded in limestone in the Pilbara. What they found was evidence that the early Earth’s upper atmosphere’s oxygen levels were similar to that of today.
Since finishing their degrees, Maynard-Casely and Brand have forged their own paths using data that didn’t exist when they were at university.
And while they’ve been interested in science since childhood, neither had an idea of where it would take them – or the solar system’s secrets they’d reveal. They simply pursued what they loved.
“When people say to me, ‘I don’t know what to do’, I say, ‘do what you enjoy’,” Maynard-Casely says. “I tend to give that advice to a lot of people.”
Brand agrees. When enrolling in her general maths and physics undergraduate degree, “I didn’t really know what I was doing or where I was going to end up,” she says. “I just liked space and rocks – and here I am.”
To learn more about ANSTO visit www.ansto.gov.au