The decadal survey, which is put together by scientists from the US National Academies of Sciences, Engineering, and Medicine, is released every 10 years to recommend space exploration projects for the next decade. “So getting going now is helpful for a Uranus mission, and would be absolutely essential for Neptune mission,” he says.The latest Planetary Decadal report argues that NASA should focus on sending an interplanetary probe to study the ice giant planet within the next decade. This potential mission, they say, could see an atmospheric probe and orbiter being sent to the seventh planet from the Sun with the hopes of deepening our knowledge of ice giants. For Neptune, however, after 2030 it is pretty barren, owing to a lack of Jupiter gravity assists, for another 12 years, to about 2041 or so,” says Mark Hofstadter at the NASA Jet Propulsion Laboratory. “For Uranus, although the frequency of good launch dates falls off after 2034, there are still good opportunities through 2036. But if NASA misses that launch time, the opportunity could be gone for a while. With luck, a Uranus missions would launch by 2034.
Starting in 2013, small amounts of enrichment were allowed again. The plutonium-238 powered atomic batteries used by NASA are in short supply, because international treaties prevented plutonium enrichment for many years. The journey would take at least 14 years, and would need to use nuclear power, because solar would be largely ineffective that far from the sun. “This might have implications for how you form a planet of that mass in exoplanet systems, for example,” she says. Simon says understanding how Uranus and Neptune formed could show how ice giants differ from gas giants, and why the former are more abundant. So why visit these ice giants at all? Of the exoplanets we’ve discovered to date, the Neptune-sized ones are the most plentiful. “Compared to Neptune, Uranus has a larger satellite system that likely formed in a disk around the planet (like the Jupiter and Saturn satellite systems) which is helpful for comparative planetary science, and I am excited to better understand the diversity of these small worlds,” says Jonathan Fortney at the University of California, Santa Cruz. A Neptune mission would also focus on its largest moon Triton, a likely captured Kuiper belt object with geysers and a tenuous atmosphere. Other goals include studying energy fields, weather and climate in-depth studies of the moons and finding out more about the composition and formation of the ring systems that orbit Neptune and Uranus like the rings of Saturn. It would also drop an atmospheric probe to take a dive into Uranus’s atmosphere to measure the levels of gas and heavy elements there. There are four proposed missions – three orbiters and a fly-by of Uranus, which would include a narrow angle camera to draw out details, especially of the ice giant’s moons. “The preferred mission is an orbiter with an atmospheric probe to either Uranus or Neptune – this provides the highest science value, and allows in depth study of all aspects of either planet’s system: rings, satellites, atmosphere, magnetosphere,” says Amy Simon, co-chair of the Ice Giants Pre-Decadal Study group. This should teach us about them and similar planets in other solar systems. A NASA group has now outlined possible missions to make it to one of these outer worlds to gather data on their composition. Uranus and Neptune have never got much attention from us – we’ve only passed each once and never hung around. NASA is planning to visit Uranus (left) or Neptune (right)