Is anybody out there? Answering the question about where life in our solar system does – or could – exist is one of science’s biggest questions. But sometimes the answers to big questions come in the most unexpected places. It might look like something you could piece together in the kitchen, yet the fluxgate magnetometer has been behind some of the most astonishing discoveries of the space age.
Data recovered from magnetometers has revolutionised our ideas about where life might exist elsewhere in the solar system and beyond, revealed the structure of the Earth’s magnetic field, and helped us understand how the solar wind – the charged particles that stream from the Sun – can have such a devastating effect on life on Earth.
“What makes magnetometers so fundamental is that most of outer space has a magnetic field linked to it,” says Professor Michele Dougherty, Professor of Space Physics.
“To have a chance of understanding the environment there, you need to understand its magnetic field – it’s a fundamental quantity. If you don’t understand the magnetic field, then you can’t understand how the different processes that take place in the atmosphere and environment around other planets work.”
Developed during the 1930s, fluxgate magnetometers were widely used during the Second World War to protect ships from submarine attack. Nearly 90 years later, the essential principles remain the same.
Made from a doughnut-shaped magnetic core wrapped in two lengths of copper wire, an electrical current pushes the core into magnetic saturation – first one way, then the other – thus revealing the size and direction of a magnetic field.
But, instead of hunting for the magnetic signatures of submarines, today’s magnetometers are routinely launched into space in search of more interesting quarry.
Ulysses was a joint ESA-NASA mission launched in 1990 on the Space Shuttle Discovery, and was the first spacecraft to traverse the north and south poles of the Sun. Imperial's Space and Atmospheric Physics Group had interests in two instruments on Ulysses: the magnetic field experiment and the Anisotropy Telescope.
After its cruise to Jupiter, Ulysses' orbit over the poles of the Sun allowed the spacecraft to measure the solar wind flowing from very high solar latitudes, which had not been achieved previously.
Ulysses found that the solar magnetic field at the Sun's poles is much weaker than previously thought.
In more than 18 years in service, Ulysses made almost three complete orbits of the Sun and revolutionised our understanding of the heliosphere, the region of space surrounding the Sun.
Since its launch in October 1990 to the end of the mission in 2009, the spacecraft travelled more than 5,400,000,000 miles.
The spacecraft's May 1996 encounter with the comet Hyakutake revealed the tail was far longer than expected, providing unique information about the conditions within cometary ion tails.
Professor David Southwood (PhD Physics 1969), Senior Research Investigator and former President of the Royal Astronomical Society, explains: “Most objects – from the Sun to many of the planets – have either their own magnetic field, or interact with the solar environment in such a way that you get a lot of magnetic disturbances around them. So, a magnetometer is going to be required for almost any mission leaving Earth.”
And some of the most high-profile missions in recent times have been heavily influenced by Imperial scientists such as Professor Southwood and, earlier, Professor Andre Balogh. Described as the “godfather of the instrumentation side of the group”, Professor Balogh helped establish the College’s stellar reputation for magnetometer science – he founded Imperial’s Space Magnetometer Laboratory in the 1980s and paved the way for all future work, including the very latest mission, the Solar Orbiter.
If you don’t understand the magnetic field, then you can’t understand how the different processes that take place in the atmosphere work
In February, Senior Instrument Manager Helen O’Brien and her team oversaw the launch of the Solar Orbiter magnetometer, which blasted off from Cape Canaveral and is heading to the Sun to investigate the development of planets and how life begins.
“Although the technology has been around for a long time, the big difference now is the performance we’re trying to squeeze out of them,” says O’Brien.
“We’re working at temperatures and in high radiation environments that are breaking new ground. The fields we want to measure with Solar Orbiter, for example, are 50,000 times the equivalent we measure on the surface of the Earth. So, we’re getting much better at extracting small resolution from the instruments we have.”
Making major discoveries, including the unexpected, is in the Space Magnetometer Laboratory’s DNA. The ESA Cluster mission – a quartet of spacecraft launched in 2000 to study the Sun’s impact on the Earth’s space environment – was the first to study the Earth’s magnetosphere (the region of space surrounding an astronomical object dominated by its own magnetic field) in 3D.
Cluster was the first mission to study the magnetosphere in 3D. Since they were launched in 2000, these four identical spacecraft, flying in pyramid formation, have revealed a wealth of data about the Earth’s magnetosphere and its complex relationship with the solar wind.
The Cluster orbit took it deep into the solar wind. It enabled the investigation of the Earth's magnetic environment and its interaction with the solar wind in three dimensions.
The four spacecraft were arranged in a ‘pyramid’ shaped formation so as to allow 3D measurements of the plasma.
Output from Cluster greatly advances our knowledge of space plasma physics, space weather and the Sun-Earth connection, and has been key in improving the modelling of the magnetosphere and understanding its processes.
Impact on Earth
The cusps are where Earth’s magnetic shield is vulnerable to plasma from the solar wind leaking in to the magnetosphere, which drives effects such as the aurorae and potential disruption to communication and satellites on Earth.
Cluster provided the first 3D measurements of the structure and motion of the ‘magnetic boundaries’, which separate the magnetosphere from the impacting solar wind. This is important because the solar wind causes what’s known as ‘space weather’, the climatic conditions that can have an effect on Earth by knocking out satellites and power grids, for example.
And, in 2005, another Imperial-built magnetometer, this time on the Cassini mission to Saturn, made its greatest discovery so far. Less than a year after launch, Cassini’s magnetometer picked up strange signals from one of Saturn’s moons. The data seemed to suggest that icy plumes were issuing from Enceladus, so Professor Dougherty, who was the Principal Investigator for the magnetometer, flew out to NASA to argue the case for a closer fly-by.
“After they agreed I was so excited. Then as the fly-by approached I was terrified,” Professor Dougherty recalls. “If we hadn’t found anything, no-one would ever have believed me again. The team took a chance. It was based on the science, but we weren’t certain of what we were seeing. We were brave and it paid off.”
The fly-by revealed that beneath Enceladus’s icy crust lay a liquid ocean, a discovery that has revolutionised our understanding of where else life might be able to form. Until 30 years ago, scientists assumed the only place in our solar system that you’d find water was closer to the Sun. Hence the hunt for life, or evidence that it once existed, on Mars.
But the fact that Cassini’s magnetometer discovered liquid water on Enceladus – the moon of an outer planet – means life could form in lots of other places further from our Sun, and other suns.
Cassini was an international venture involving NASA, the European Space Agency (ESA), the Italian Space Agency (ASI), and several separate European academic and industrial partners.
Its mission was to explore Saturn and its moons.
The snow line
Cassini revealed that we should not simply focus on planets close to the Sun, where liquid water is found only on the surface, for potential habitability, but also beyond the ‘snow line’.
What Cassini found at Saturn prompted scientists to rethink their understanding of the solar system.
Before Cassini, scientists thought that to find life, they'd have to look much closer to the Sun. Cassini's magnetometer showed us that life might exist on moons orbiting outer planets like Saturn.
Icy plumes on Enceladus
The magnetometer found water vapour coming off Enceladus, one of Saturn's moons, revealing a liquid water ocean under the crust. It also discovered organic matter and a heat source – the remaining components for habitability.
Today, Professor Dougherty and a small team of engineers in the Space Magnetometer Laboratory are working on their biggest challenge yet – making the magnetometer for a new mission to Jupiter. Due for launch in 2022, the JUpiter ICy moons Explorer (JUICE) will explore the giant planet and three of its moons: Europa, Callisto and Ganymede.
JUICE will be the first spacecraft to go into orbit around an outer planetary moon and, although it will take more than eight years to get there, the prospect is tantalising. “I’m not renowned for my patience,” she admits, “but it’s essential if we’re to understand whether life might be able to form in the outer solar system. For habitability, you need liquid water, a heat source and organic material, and for all three to have been stable for a long enough period. We think that could be happening on Ganymede.”
Patrick Brown, Senior Instrument Manager on the JUICE magnetometer, is the engineer responsible for making it happen. Over the past 23 years at Imperial, Brown has worked on magnetometers for six missions, tailoring each for different environments. For JUICE, the challenges are hair-raising. To deliver Professor Dougherty’s data, the magnetometer must be tough enough to withstand huge variations in temperature and massive doses of radiation, yet sensitive enough to detect tiny changes in magnetic field.
“Jupiter has the largest planetary magnetic field in the solar system, and it has these big moons, one of which is full of volcanoes spewing out material that gets accelerated and trapped in the magnetic field. That means an intense radiation environment – like going through a nuclear reactor,” says Brown.
If we hadn't found anything, no-one would have ever believed me again. The team took a chance. We were brave and it paid off
While Brown is in the maelstrom of the design and build phase, O’Brien and Professor Tim Horbury (BSc Physics 1992, PhD 1995), Principal Investigator of the Solar Orbiter magnetometer, can only watch and wait as their instrument heads for the Sun, closer than any previous European mission. “We’re going closer to the Sun than Mercury, so we’ll be able to measure the solar wind when it’s young and fresh,” says Professor Horbury. “That will give us a better understanding of how it’s formed – as well as the damage that space weather can do to satellites and electricity grids on Earth.”
The list of scientific successes highlights what makes the Space Magnetometer Laboratory special. The small, close-knit team has championed magnetometers since the start of the space age. Its degree of specialisation – it typically only builds one flight instrument per mission – is unusual, and its experience unrivalled. And its combination of world-class engineering with world-class science sets it apart.
“Our unique success is down to the fact that, at Imperial, we’re good at exploiting both the science and the instruments,” says Chris Carr, now head of the lab. “It keeps us at the heart of missions and it lets us produce great science. It’s a truly virtuous circle.”
Timeline of magnetometer technology at Imperial
“Developing magnetometers has been a flagship activity for Imperial for many decades,” says Professor David Southwood, the original Principal Investigator on Cassini.
“I’ve always felt the way we do things is special. As a mixture of scientists and engineers working together we get more out of it than we could alone.”
Here’s a potted history of Imperial’s role in magnetometer development.
Imperial’s Cosmic Ray and Space Physics Group builds the cosmic ray detector for Britain’s first satellite, Ariel 1. Harold Macmillan named the satellite, deciding on Ariel, the spirit of the air in Shakespeare’s The Tempest.
Europe’s first satellite ESRO 2 is launched with a trio of Imperial-built instruments.
The launch of HEOS-1, the first European spacecraft to venture beyond the Earth’s magnetosphere. The magnetometer, built by Imperial, makes a major contribution to mapping the Earth’s magnetosphere.
Imperial builds particle detectors for the NASA mission ISEE-3. Redirected to the comet Giacobini-Zinner in 1984, ISEE-3 performs the first fly-by of a comet by a spacecraft.
The NASA-ESA mission Ulysses launches from the Space Shuttle Discovery with an Imperial magnetometer. The first spacecraft to traverse the north and south poles of the Sun, Ulysses discovered that the Sun’s magnetic field flips from south to north every 11 years.
The Cluster mission – four identical spacecraft with four Imperial magnetometers – blows up 40 seconds after launch, dealing a near-fatal blow to magnetometer science at Imperial.
Cassini – the NASA-ESA mission to Saturn and its moons – launches. Cassini reaches Saturn in 2004 and the following year its magnetometer discovers water-rich plumes venting from the moon, Enceladus, allowing scientists to rethink their search for life beyond Earth.
Partly re-built from flight spares in four short years, Cluster is relaunched successfully. The first mission to use four spacecraft flying in formation – an idea developed by Professor Jim Dungey, former head of the Space and Atmospheric Physics Group at Imperial – Cluster is able to study the Earth’s magnetosphere in 3D. Thanks to Cluster, our model of the Earth’s magnetosphere is now based on data rather than theory, and Cluster is helping us defend satellites and power grids against damaging space weather.
Solar Orbiter launches on its long voyage to the Sun. The ESA mission is carrying ten instruments – including an Imperial magnetometer. Solar Orbiter will answer big questions about how the Sun creates and controls the giant bubble of plasma that fills our solar system.
JUICE due for launch. When it arrives in 2031, its Imperial-built magnetometer will hunt for signs of life on Jupiter’s moon, Ganymede.
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This story was published originally in Imperial 48/Summer 2020.