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Exploring the outer solar system with space robots Exploring the outer solar system requires patience. It took Voyager 2 two years to reach Jupiter, another two to reach Saturn – then another five and a half years to reach Uranus, finally reaching Neptune twelve years after it launched. Pluto was explored by the New Horizons spacecraft, which took nine years to reach it. Basically, if you launch something to beyond Jupiter you’ve a while to wait, and while the space robot is adventuring, life on Earth continues.
Professor Carly Howett joined the Hall in October 2020 as a Fellow and Tutor in Physics. Carly is a planetary physicist and an expert on the surfaces of icy worlds with a long track record in space instrumentation.
For example, I’m working on a mission that will hopefully go to Neptune’s moon, Triton. This mission was conceived right around the time my second daughter was. I worked on the proposal while pregnant, and I found out we were selected for further study while nursing her. If it is selected it will launch when she starts primary school, flyby Jupiter when she starts high school, and reach Neptune when she’s old enough to vote. This mission will literally last her childhood, and I hope the results will be analysed for a long time after that too. I’m not naturally a patient person, but for Triton I’m willing to wait. It’s a fascinating world, like nothing else we know of. We think it formed even further from the Sun than Neptune, in the Kuiper Belt, which is the same region of space inhabited by Pluto. Something happened (gravitational instability, or maybe an impact) which resulted in earlyTriton getting kicked out of the Kuiper Belt towards the Sun, where it was captured by Neptune’s gravity. Triton orbits Neptune in the reverse direction to other satellites (which is how we know it can’t have formed there), and at a very high angle. The
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capture event, plus its weird orbit, provides Triton with a lot of energy. So much so that several billion years after capture, Triton still has enough energy to power plumes that tower eight kilometres (five miles) above its surface and extend several hundreds of kilometres downwind. Maybe there’s even enough energy to make Triton habitable. To know, we have to go there. There’s an old adage in science that every discovery is made because we “stand on the shoulders of giants”. In planetary science younger generations don’t just stand on the shoulders of giants, we operate their instruments, analyse the data they never got to see, and then (hopefully) make sure there’s more for the generation that follows us. My personal ‘giants’ were those people that built, launched and operated NASA’s Cassini and New Horizons missions. Cassini’s thorough exploration of the Saturn-system provided data that changed my career. The observations that it took of Saturn’s moons revitalised my passion for science. I went from planning to leave research (and academia) to loving every second of it. Specifically, I became enthralled by the activity on Saturn’s moon, Enceladus. This moon is small, even by moon standards (it’s about the same width as the UK), but despite this plumes of water ice continuously erupt into space from its south pole. Some of this ice spreads away from Enceladus, coating its neighbouring satellites and brightening them too. The rest of the ice forms another ring around Saturn, known as the E-ring. Understanding these eruptions is what I’ve been working on for a
