NASA’s Juno spacecraft could perform the first close flights since the early 2000s of three of Jupiter’s largest moons, including Europa, if the space agency grants the mission an extension, the chief scientist said recently. by Juno.
Since entering orbit around Jupiter in July 2016, the Juno spacecraft’s suite of science instruments has probed the giant planet’s atmosphere and internal structure, revealing new insights into Jupiter’s cyclonic storms and detecting evidence of a potentially large core. dissolved in its center.
“We went out to find a core, whether or not there was a compact core inside Jupiter,” said Scott Bolton, Juno’s principal investigator at the Southwest Research Institute. “We were surprised because it is a large, diluted core.”
Juno’s five-year primary mission phase ends in July 2021 and mission leaders have proposed an extension that will continue operations until September 2025. The spacecraft’s additional orbits around Jupiter will bring Juno closer to the planet’s moons, allowing for a more diverse series of objective scientific data.
“One of the exciting things about the (extension) mission is that we’re going to visit the satellites and the rings,” Bolton said at a meeting of NASA’s Outer Planets Advisory Group last month. “It really becomes a complete explorer of the system, not as focused as the main mission, so it potentially feeds a more diverse (scientific) community because the satellite geologists, the people of the ring will all receive data that I think is very interesting and unique. “
The solar-powered Juno probe was launched in August 2011, starting a five-year cruise on Jupiter. Juno became the second spacecraft to orbit Jupiter when it arrived on July 4, 2016.
Juno’s nine scientific instruments include a microwave radiometer for atmospheric probes, ultraviolet and infrared spectrometers, particle detectors, a magnetometer, and a radio wave and plasma experiment. The Jupiter orbiter also carries a color camera known as the JunoCam, which collects image data for processing and analysis by an army of citizen scientists around the world.
Juno’s science team last month submitted a proposal to NASA for an extended mission that would continue spacecraft operations for another four years until 2025. Bolton said the extended mission will allow Juno to tackle further scientific goals.
“We have more close passes than Io, Europa and Ganymede,” Bolton said.
NASA officials are expected to decide by the end of the year whether to grant funding for the Juno team’s extended mission proposal. It’s part of a regular process called senior review, in which independent scientists rank the merits of continuing to run NASA’s robotic science missions beyond their original planned lives.
When considering senior review recommendations, NASA balances the scientific productivity of older missions with priorities for developing and launching new spacecraft.
The close passages of Jupiter’s moons will be made possible by Juno’s changing orbit. Jupiter’s asymmetrical gravitational field is gradually disrupting Juno’s trajectory and moving the closest point of the spacecraft’s elliptical, or egg-shaped, orbit north over time, according to Bolton.
The northward migration of Juno’s perijove, or the closest approach to Jupiter, will allow the spacecraft to take a closer look at the planet’s north pole. Juno was the first mission to glimpse Jupiter’s poles, and now the spacecraft could see the north pole and its cyclonic storms in more detail.
“This gives us close proximity to the northern parts of Jupiter, which is a new frontier,” Bolton said. “We saw a lot of activity there, so we will be able to explore them very closely, while in the main mission we were limited to the lower latitudes.”
In an extended mission, the spacecraft will also be able to quantify how much water is bound inside Jupiter’s atmosphere, Bolton said.
Juno has flown in a 53-day elliptical orbit since it landed on Jupiter more than four years ago. By the end of its main mission next year, the spacecraft will have completed 34 laps around Jupiter.
Built by Lockheed Martin, the spacecraft was originally supposed to maneuver in a tighter 14-day orbit in late 2016, but mission leaders chose not to run the rocket due to a problem with Juno’s main engine.
This decision meant that Juno needed more time to collect the scientific data required by the mission. The spacecraft’s instruments collect most of the data as they pass by the planet once every 53 days, not the originally planned 14-day cadence.
Scientists planned to have Juno complete 32 14-day scientific orbits until February 2018, when its main mission was due to end. At the time, ground controllers planned to intentionally crash the spacecraft into Jupiter’s atmosphere, avoiding the possibility of contaminating one of Jupiter’s potentially habitable moons.
The 53-day orbit meant that Juno operated at a slower scientific cadence, but the longer orbit is what allows the mission to venture close to Jupiter’s moons in the 2020s, Bolton said. Another benefit of the longer orbit was that Juno was exposed to less severe radiation around Jupiter, allowing the $ 1.1 billion mission to operate longer than originally anticipated.
“It’s a saving grace,” Bolton said. “I think the lesson is that we have been flexible, and this is good in the missions. So when you are planning a mission try to be flexible because you don’t know which curveball will be thrown at you. “
Juno’s naturally evolving orbit is also what will allow the probe to pass close to Jupiter’s moons and rings.
Lunar flybies would begin in mid-2021 with an encounter with Ganymede, Jupiter’s largest moon, at a distance of about 600 miles (1,000 kilometers), according to Bolton.
After a series of distant passes, Juno would fly just 200 miles (320 kilometers) above Europe in late 2022 for a high-speed flyby. Only NASA’s Galileo probe, which ended its mission in 2003, has come close to Europe.
There are two encounters with Jupiter’s volcanic moon Io, planned for 2024 at distances of around 900 miles (1,500 kilometers), according to the flight plan presented by Bolton last month.
Assuming NASA approves the mission extension, Juno will be able to look for changes on the surface of Jupiter’s moons since they were last seen up close by NASA’s Voyager and Galileo spacecraft.
In Ganymede, Juno was able to map the composition of the lunar surface and investigate 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 would be able to probe the thickness of Europa’s global ice shell, which covers an ocean of liquid water. “We will see where the ice is thin and where it is thick,” Bolton said.
The visit to Europe would give scientists a glimpse of what’s to come with NASA’s Europa Clipper mission, which could be launched in 2024. Europa Clipper will carry more powerful radar – among other tools – to measure the moon’s ice shell through a series of targeted flybys.
Juno’s spectrometers also map concentrations of water ice, carbon dioxide and organic molecules across 40 percent of Europa’s surface, Bolton said.
The JunoCam imager would be able to take photos of Europa with a surface resolution of between 1 and 2 kilometers, well below the details visible in the Europa maps of the Galileo probe. But JunoCam will return the clearest views of Europe in more than 20 years.
The images from JunoCam and Juno’s star tracker cameras would look for evidence of plumes erupting from the surface of Europa. The spacecraft’s other instruments would be tuned to look for particles raised by Europa in possible plumes. Signs of recurrent eruptions from Europe have been detected by the Hubble Space Telescope.
During his flybys with Io, Juno may be looking for evidence of a global magma ocean feeding Io’s volcanoes. Juno would also be able to observe active volcanoes in the polar regions of Io.
Juno also allegedly photographed Jupiter’s faint rings during a potential extended mission. The spacecraft’s dust detector could also record the impacts of the ring particles, Bolton said.
“We will really be able to look at the rings in a much better way with remote sensing, as well as in situ instruments,” Bolton said.
Email the author.
Follow Stephen Clark on Twitter: @ StephenClark1.