In Europa's case, different models have yielded estimates of between 15 and 25 km (10 and 15 mi). The main challenge for exploring the interiors of these worlds is the thickness of their ice sheets, which can be up to 40 km (25 mi) deep. Further evidence of these oceans and activity includes surface plumes and striated features indicating exchanges between the surface and interior. These worlds are all believed to have interior oceans heated by tidal flexing due to gravitational interaction with their parent body or (in the case of Ceres and Pluto) the decay of radioactive elements. The list of ocean worlds is long and varied, ranging from Ceres in the Main Asteroid Belt, the moons of Jupiter (Callisto, Ganymede, and Europa), Saturn (Titan, Enceladus, and Dione), Neptune's largest moon (Triton), and Pluto and other bodies in the Kuiper Belt. This proposal was selected for Phase I development by the NASA Innovative Advanced Concepts (NIAC) program. Theresa Benyo (a physicist and the principal investigator of the lattice confinement fusion project at NASA's Glenn Research Center), a possible solution is to use a special reactor that relies on fission and fusion reactions. Investors, who have recently handed it $1.8bn, will be hoping it will.Įditor’s note (February 10th 2022): This piece has been updated since it was published.One of the many challenges for these missions is how to mine through the thick icy crusts and obtain samples from the interior ocean for analysis. CFS claims, for example, that it can achieve net positive fusion by 2025. Put together, the breakthroughs suggest that scientists and engineers are on the brink of something important-certainly the pace of development has been moving faster than ever before. And in September Commonwealth Fusion Systems (CFS), a startup that counts Jeff Bezos and Bill Gates among its backers, generated a powerful magnetic field that, in theory, could be used in a net-positive tokamak. In August, America’s National Ignition Facility using lasers came the closest yet to achieving net energy gain. In May 2021 a Chinese reactor sustained a fusion reaction at 120m☌ for 101 seconds, a new record. But recent developments have made some people optimistic that “net energy gain” reactions-the holy grail where a nuclear fusion reaction produces more energy than it consumes-could soon be achieved. So far every controlled fusion reaction on Earth has consumed more energy than it has released, making the process useless as an alternative to fossil fuels. One is trying “ magnetised target fusion”, which would use electrical pulses to create plasma and steam-powered pistons to compress it. Startups, attracted by the potential financial returns that could come from successful fusion, are developing new methods. Another popular approach, inertial-confinement fusion, uses powerful lasers to implode pellets containing hydrogen atoms, and compressing that fuel to the point of fusion. At its heart is a Soviet-designed system called a tokamak reactor. The method with the longest pedigree, and the one used at JET, traps the plasma within powerful, doughnut-shaped magnetic fields. They have so far struggled to find an energy-efficient way of doing so. In Oxfordshire, where such pressures are not available, reactions need temperatures closer to 100m☌.Īt such high temperatures solids and gases cannot exist and scientists must instead manipulate a fourth state of matter, plasma, a fluid consisting of individual ions and electrons. Even at the extreme pressures found in the sun, the nuclei need to be at 15m☌ to overcome their mutual repulsion. Because atomic nuclei repel each other they have to be moving very fast to fuse, which means you need a lot of energy to kickstart and sustain the process. But although individual fusion reactions have been achieved for many decades, power-generating plants remain elusive. Given those stellar characteristics, scientists have long wanted to develop power plants that use nuclear fusion. It is also a clean process, producing no greenhouse gases or long-term toxic nuclear waste. If done correctly, this fusion reaction can release almost 4m times more energy than burning the equivalent mass of oil, and four times as much energy as a nuclear fission reaction. In JET two different isotopes of hydrogen are fused to release a helium nucleus, a spare neutron and large amounts of energy.
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