Sophie Deam’s Journey with Near-Earth Objects
Impact
The hall is long, and my footsteps are heavy. My hand falls upon the door of the DFN headquarters. I am allowed entry into a veritable cacophony of furniture, photos, shelves and hardware, some of which I can’t identify. Sophie Deam stands there, a fireball herself.
The Drop
‘My PhD is looking at the journey of near-earth objects (NEOs), which are asteroids or comets in the solar system. I look at where they come from, how they get close to the earth, what they’re made of and what happens to them on that journey. I’m contributing a drop of knowledge in a giant well. My drop is characterising a size range of NEOs that are quite difficult to observe. We don’t have any observations of them. These are a centimetre to a meter in diameter. It’s the size range that specifically the Desert Fireball Network observes well with their cameras.’
It’s important for scientists to understand where asteroids and meteoroids are coming from for many crucial reasons, such as understanding the history of our Solar System. When scientists recover meteorites, they perform tests to find out the age and composition of the meteorite. These tests give vital clues on how our Solar System formed.
Sophie searches for important information about meteoroids still sprinting around our solar system. ‘It’s broad characterising. It’s asking, for example, about the heating mechanism when they get close to the sun, is it the same or not as other asteroids? How I analyse this information is through comparing data sets. So, I’m comparing what a computer tells us these objects will look like, where these objects will be and where our DFN cameras tell us these objects are.’
I’m contributing a drop of knowledge in a giant well.
Calculations
Sophie asks the hard questions on meteoroids with a handful of numbers and some heavy hardware. ‘You can characterise something that’s orbiting far away and has a low chance of hitting the earth. We understand how our observations of these meteoroids are biased by the fact that we are only observing what’s hitting the earth. We can account for that in our data set.’ The DFN team runs computer simulations with pre-programmed equations to understand where the meteoroid might have come from in our Solar System. The equations are formulated by previous scientists, some of them rather well-known, such as Newton and Einstein.
‘The movement of the bodies in the solar system are defined by equations that we give the simulator. We tell the simulator; this is what gravity is. The simulator has all these equations and can move particles in the solar system orbiting the sun. Numerical simulations are a thing and what we can do is we can pretend that we have asteroids in this simulation. We can turn on and off those kinds of forces. Then we can compare what the simulations look like with and without.’ Scientists then compare the results from the different kinds of simulations. They choose the most likely candidate based on real-time observations of the Solar System. This gives scientists a much better idea as to what the dynamical forces of the Solar System are doing. For fireballs that enter Earth’s atmosphere, using triangulation, a method of defining trajectory using several cameras at different locations, the DFN can then work out where in our Solar System it originated from.
Dynamics
The rocks in the asteroid belt between Mars and Jupiter did not end up there by accident. ‘Originally, the Sun formed from a cloud of dust and gas, and it collapsed under gravity. The Sun shrunk in on itself. When things were coming in, they would have had angular momentum. They would have been spinning in any random way, but by conserving momentum, it is the path of least energy to come into a flat disk.’ This is not the only reason that the asteroid belt has ended up where it is. The space between Mars and Jupiter is a kind of gravitationally stable zone, meaning the asteroids can orbit the Sun without being pulled into planets or flung out of the solar system, at least most of the time.
However, we know this is not the full truth. At least one meteorite everyday lands in Australia. Sophie explains how the meteoroids end up here, way out whoop-whoop on an inner planet full of life. ‘Those mechanisms can be dynamical. That means gravity. The gravity of these big bodies can push and pull.’ This means asteroids and meteoroids can get perturbed, which is a scientific term for becoming unstable. ‘Jupiter is a massive body. If you and Jupiter orbit around at the same times, then there’s always a force acting on you outwards towards Jupiter and inwards towards our Sun. If you go around twice while Jupiter goes around once, then you kind of keep matching up in your orbits. When you’ve got orbital periods that are very similar, like either divisible by half or a third or a quarter or whatever you keep matching up, the asteroid or meteoroid will become perturbed. That is dynamically unstable.’ Mars and Saturn also play a role in perturbing the rocks in the asteroid belt. These are planets who are neighbours, and each has a large enough gravity to make the asteroids or meteoroids uncomfortable should they have too much in common.
The sun can push and pull asteroids and meteoroids in its own way by heating them.
The Heat is On
The gravity of Mars, Saturn and Jupiter are not the only forces at work. ‘The sun can push and pull asteroids and meteoroids in its own way by heating them.’ Asteroids and meteoroids are also turning in space. During the day, they face our Sun. They absorb heat, making them warm. As they rotate, the warm side faces away from the sun and radiates the heat, creating a form of propulsion. When coupled with the interplanetary dynamics, such as gravity, if they are in the right place at the wrong time, they fire off onto their journey to orbit the system and land on a planet, sometimes ours.
Journey’s End
Sophie unpacked a great deal with me on meteoroid characterisation, a field she orbits with her PhD. She’s a keen and gifted communicator, explaining complex ideas with clarity and using everyday metaphors that made the science accessible, even to someone without a background in it. I appreciated the time she took from her studies to speak with me, leaving to blaze an academic streak of fire in her wake.
Written by Louise Kaestner, 2025. For more, visit LinkedIn or head to her website: https://www.louisekaestnerwriter.com/