NASA’s Juno spacecraft could make the first close flights since the early 2000s from three of Jupiter’s largest moons, including Europe, if the space agency grants the mission an extension, Juno’s lead scientist recently said.
Since entering orbit around Jupiter in July 2016, the Juno spacecraft’s array of scientific instruments has examined the giant planet’s atmosphere and internal structure, gaining new insights into Jupiter’s cyclone storms, and finding evidence of a large, possibly dissolved core at its center.
“We went out to find a nucleus, whether or not there was a compact nucleus in Jupiter,” said Scott Bolton, Juno’s lead researcher at the Southwest Research Institute. “We were surprised because it’s a big, thinned core.”
Juno’s five-year primary mission phase ends in July 2021, and mission managers have proposed an extension that will continue operations through September 2025. The spacecraft’s additional orbits around Jupiter will bring Juno closer to the planet’s moons and allow a wider range of scientific knowledge to target.
“One of the exciting things about the mission (expansion) is that we’re visiting the satellites and rings,” Bolton said at a meeting of NASA’s Outer Planets Advisory Group last month. “It really becomes a complete systems researcher who is not as focused as the main task and therefore serves a potentially more diverse (scientific) community as the satellite geologists and ring people get all the data that I find very interesting and unique. ”
The solar-powered Juno spacecraft launched in August 2011 and embarked on a five-year cruise to Jupiter. Juno was the second spacecraft to orbit Jupiter when it arrived on July 4, 2016.
Juno’s nine scientific instruments include a microwave radiometer for atmospheric measurements, ultraviolet and infrared spectrometers, particle detectors, a magnetometer, and a radio and plasma wave experiment. The Jupiter orbiter also has a color camera called the JunoCam that gathers image data for processing and analysis by an army of citizen scientists around the world.
The Juno science team last month presented a proposal to NASA for an expanded mission that is expected to continue spacecraft operations for four years through 2025. Bolton said the expanded mission would allow Juno to achieve additional scientific goals.
“We have several fly-bys from Io, Europa and Ganymede,” said Bolton.
NASA officials are expected to decide by the end of the year whether to provide funding for the Juno team’s expanded mission proposal. It is part of a regular process called the Senior Review, which involves independent scientists assessing the merits of continuing to operate NASA’s robotic missions beyond their originally planned lifetimes.
In reviewing the recommendations for senior review, NASA balances the scientific productivity of older missions with priorities for the development and launch of new spacecraft.
The flyby of Jupiter’s moons is made possible by Juno’s alternating orbit. Jupiter’s asymmetrical gravitational field gradually disrupts Juno’s trajectory, drawing the closest point of the spacecraft’s elliptical or egg-shaped orbit north, according to Bolton.
The north migration from Junos Perijove, or the closest approach to Jupiter, allows the spaceship to take a closer look at the north pole of the planet. Juno was the first mission to see Jupiter’s Pole, and now the spaceship could see the North Pole and its cyclone storms more closely.
“This gives us proximity to the northern parts of Jupiter, which is a new frontier,” said Bolton. “We saw a lot of activity there so we can explore it up close, while we limited ourselves to the lower latitudes in the main mission.”
In an expanded mission, the spaceship will also be able to quantify how much water is trapped in Jupiter’s atmosphere, Bolton said.
Since Juno arrived in Jupiter more than four years ago, it has been in an elliptical orbit of 53 days. By the end of its main mission next year, the spaceship will have made 34 laps around Jupiter.
The Lockheed Martin-built spacecraft was originally scheduled to maneuver into a tighter 14-day orbit in late 2016, but mission managers decided not to perform the rocket combustion due to a problem with Juno’s main engine.
This decision meant that Juno needed more time to gather the necessary scientific data from the mission. The spacecraft’s instruments collect most of their data as they pass near the planet every 53 days, not the originally planned 14-day cadence.
Scientists planned to have Juno complete 32 of the 14-day scientific orbits by February 2018, when the main mission should be completed. At the time, ground controllers planned to purposely dump the spaceship into Jupiter’s atmosphere to avoid the possibility of contaminating any of Jupiter’s potentially habitable moons.
The 53-day orbit meant Juno was operating at a slower scientific cadence, but the longer orbit will allow the mission to venture close to Jupiter’s moons in the 2020s, Bolton said. Another benefit of the longer orbit was that Juno received less exposure to radiation around Jupiter, allowing the $ 1.1 billion mission to operate longer than originally planned.
“It’s a saving grace,” said Bolton. “I think the lesson is that we’ve been flexible, and that’s good in missions. So when you’re designing a mission try to be flexible because you don’t know which curveball you are going to throw. ”
Juno’s naturally evolving orbit also allows the spaceship to pass close to Jupiter’s moons and rings.
The lunar fly-bys would begin in mid-2021 with an encounter with Ganymede, Jupiter’s largest moon, about 1,000 kilometers away, Bolton said.
After a series of distant passes, Juno would only fly 200 miles over Europe by the end of 2022 to do a high-speed flyby. Only NASA’s Galileo spacecraft, which completed its mission in 2003, has come closer to Europe.
There are two encounters with Jupiter’s volcanic moon Io, planned to be around 1,500 kilometers away in 2024. This is evident from the flight plan that Bolton submitted last month.
Assuming NASA approves the mission expansion, Juno can look for changes on the surfaces of Jupiter’s moons since they were last seen up close by NASA’s Voyager and Galileo probes.
In Ganymede, Juno was able to map the surface composition of the moon and study the 3D structure of Ganymede’s magnetosphere. Ganymede is the only moon in the solar system known to have its own magnetic field.
Juno’s microwave radiometer could study the thickness of Europe’s global ice sheet, which covers an ocean of liquid water. “We’ll see where the ice is thin and where it’s thick,” said Bolton.
The visit to Europe would give scientists a taste of the future of NASA’s Europa Clipper mission, which could start as early as 2024. Europa Clipper will, among other things, carry a more powerful radar to measure the ice sheet of the moon through a series of targeted flybys.
Juno’s spectrometers would also map concentrations of water ice, carbon dioxide and organic molecules on 40 percent of Europe’s surface, Bolton said.
The JunoCam imager could take pictures of Europe with a surface resolution of 1 to 2 kilometers, which lags far behind the details visible on the Europe maps of the Galileo spacecraft. But JunoCam would return the sharpest views of Europe in more than 20 years.
Images from JunoCam and Juno’s Star-Tracker cameras would look for clues of feathers erupting from Europe’s surface. The other instruments of the spacecraft would be tuned to look for particles in the possible springs from Europe. The Hubble Space Telescope detected signs of recurring eruptions from Europe.
During his flybys with Io, Juno was able to search for evidence of a global ocean of magma feeding Io’s volcanoes. Juno could also observe active volcanoes in Io’s polar regions.
Juno also photographed Jupiter’s thin rings during a possible extended mission. The spacecraft’s dust detector could also register impacts from ring particles, Bolton said.
“We’re really going to be able to get a much better look at the rings with remote sensing and the in-situ instruments,” said Bolton.
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