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Neptune is a windy, cool and confusing planet. Let's go!



It was just after midnight at the mission control center of NASA's Jet Propulsion Laboratory, and Carl Sagan was left out. The Voyager 2 spacecraft had just completed its ten-year mission by coming closest to Neptune before setting off into interstellar space. It was the first – and so far only – spaceship to visit the mysterious blue giant ice lurking at the edge of the solar system.

"We are looking at the boundary of the solar system, the last planet," said Sagan CNN television crew, who had gathered for the occasion. "The level of excitement is the highest I've ever seen here."

Before Voyager 2 passed just 3,000 miles over Neptune's atmosphere on August 25, 1

989, scientists knew almost nothing about the location. What they found was a planet covered with dense, methane-rich clouds that lashed Neptune at more than 1,000 miles an hour, making it the windiest point in the solar system. At that time, the planet had the Great Dark Spot, an earth-sized storm that has since disappeared. Voyager also looked at Triton, Neptune's largest moon, and saw geysers rising from its surface. This indicated that it was tectonically active and possibly harbored a huge subterranean ocean. In addition to Triton, Voyager 2 found six more moons and four lumpy rings circling the planet.

Voyager 2 captured this image of Neptune's Outer Ring, which is 39,000 miles away.

NASA / JPL

Encounter with Voyager Neptune asked as many questions as he answered. But in the last 30 years NASA was not back. Data from the Kepler Space Telescope suggest that ice giants such as Neptune and Uranus are among the most abundant planets in our galaxy, which is a strong argument for a visit. The return to Neptune could dramatically improve our understanding of planet formation and dynamics, but the window to organizing such a mission quickly closes.

About every 12 years, the planets align themselves to launch a Neptune-bound spacecraft from Earth. Jupiter can provide gravity support, reducing travel time to approximately 12 years. The window for Jupiter Gravity Support will only last a few years, and the next window will open in the late 2020s. The problem, says Mark Hofstadter, a planet scientist at the Jet Propulsion Laboratory, is that merging a flagship planetary exploration usually takes about a decade. That is, if NASA wants to open the next gravity support window, a Neptune mission must be launched yesterday.

According to Hofstadter, an ideal Neptune flagship mission would consist of a large spaceship with at least 10 scientific instruments and one atmospheric probe. These tools could answer some basic questions about Neptune. He notes that scientists believe that most of the mass of Neptune is water, but they are far from safe. In addition, Neptune defies our best models of planet formation. Based on these models, which accurately reflect the formation of all other planets, Neptune and Uranus should have had a balloon size like the gas giants Jupiter and Saturn. But they do not have it – and scientists can not explain why.

"Right now we are in a situation where we realize that these ice giants are somehow weird, but we do not understand what they are made of, how they are composed or why they even exist," says Hofstadter. "But they can be found everywhere in our galaxy, so if we learn some of these basic things, we can better understand how planets evolve and evolve."

Hofstadter hopes that a return to Neptune is possible in the next decade. In 2017, he co-authored a report that included several missionary proposals for Neptune and Uranus. The report will help inform NASA's next Planetary Science Decadal Survey, which sets the agency's exploration priorities for the coming decade. Work on the decade survey will begin next year and is expected to be completed in 2021 or 2022. But even if a flagship mission to Neptune is selected as a priority and receives the necessary funds, it will be completed by the conclusion of the decade-count, a Herculean effort to contract the mission in time to hit the window of gravity support.

Faced with this dilemma, some planetary scientists have already begun to discuss what a flagship mission to the outer solar system might look like when the One Decade Survey gives an ice giant the green light for a mission. He can start immediately. A particularly tempting plan is, according to Hofstadter, a collaboration between NASA and the European Space Agency. In January, the ESA completed a study on how it could contribute to a NASA-led mission to the ice giants, such as the creation of a spacecraft, a sister spacecraft to study Neptune and Uranus or a lander for Triton. "We started to work on the details," says Hofstadter. However, whether NASA joins the ESA plan depends on the results of the Decadal survey.

Given the time crisis, Hofstadter also recommends thinking about smaller missions Profiles. Louise Prockter, the director of the Lunar and Planetary Science Institute, could not agree anymore. In March, Prockter and her colleagues unveiled their plans for Trident, a flyby mission to Neptune's moon Triton, which was set to launch in 2026 and fly by the moon in 2038.

Prockter describes Triton as the "forgotten moon" of the solar system Too bad, she says, because Triton is very different than any other planetary body in the solar system. Many scientists believe that the moon actually comes from the Kuiper belt, a massive field of objects from the early solar system that lies beyond Neptune and is trapped in the orbit of the planet. Based on data from Voyager 2, it also appears to be geologically active and there is evidence that it could support a huge ocean below its surface. The ionosphere is ten times as intense as any other ionosphere in the solar system, which is difficult to explain since ionospheric activity is normally correlated with the interaction of a planet with the solar wind and Triton is quite far from the Sun.

Trident would spend about 10 days navigating the area around Neptune, during which time he would map almost the entire Triton area, examine his geysers, determine if it would harbor an ocean, and within 300 kilometers of the "bizarre "Moon surface fly to investigate its ionosphere. She says the mission could cost around $ 500 million, well below the cost of flagship missions, which typically cost around $ 1 billion. "We try to do something bold that nobody believes could be done," says Prockter.

In July, Prockter will submit the Trident Proposal for consideration as part of NASA's Discovery Program. If approved, the arrival of Trident in Triton will coincide almost perfectly with the 50th anniversary of Voyager's visit.

The justification of large planetary missions is always difficult, and the periods associated with missions to the outer solar system only increase the burden on the scientists who make the case for them. The special thing about space exploration, however, is that the most exciting discoveries are rarely anticipated in advance. Neptune has a lot of well-known science, but we'll never know what we'll miss until we get there.


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