Uranus hasn't had a visitor since 1986 and Neptune's been neglected since 1989, but NASA is formulating a plan to return to the ice giant planets on the fringes of our Solar System. As one of the first steps, the agency has conducted a study to determine the scientific focus of these potential missions, the kinds of instruments needed and the logistics of how the spacecraft would get there.
NASA, ESA and other institutes are currently developing the next Planetary Science Decadal Survey, which will determine the scientific priorities for study between 2022 and 2032, and develop missions to help answer those questions. The mysterious ice giants Uranus and Neptune are great potential targets since we know so little about them and, according to the ever-growing haul of exoplanets reeled in by the Kepler program, they seem to be the most common type of planet in our galaxy.
"We do not know how these planets formed and why they and their moons look the way they do," says Amy Simon, co-chair of the team behind the report. "There are fundamental clues as to how our solar system formed and evolved that can only be found by a detailed study of one, or preferably both, of these planets."
According to the report, the two most important objectives in a trip to the ice giants would be to study the structure of the planets' interior, which appear to be mostly made up of huge subsurface oceans, and determine the abundance and composition of elements and gases. Other objectives include studying the planets' magnetosphere, weather, moons and rocky rings.
"This study argues the importance of exploring at least one of these planets and its entire environment, which includes surprisingly dynamic icy moons, rings and bizarre magnetic fields," says Mark Hofstadter, the other co-chair of the project.
The report also examines how these objectives could be met, with the right combination of spacecraft and instruments. The best case scenario would be to send an orbiter equipped with a narrow angle camera, Doppler imager and a magnetometer, along with a probe that can be launched into the planet's atmosphere to measure temperature, pressure and density. To keep costs down, an orbiter could be launched without a probe, or just swing past on a flyby mission.
If a trip to Uranus or Neptune is given the green light, the craft wouldn't be launched until 2030 at the earliest, and would take a further 10 years to arrive.
The full 529-page report has been published online, along with a much more digestible 12 page version.