Juno, a NASA spacecraft, will make the closest approach of Jupiter's icy moon Europa in over 20 years on September 29 as part of an expedition to drill deep into Europa's ice in search of pockets of liquid water.
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Future missions, such as the Europa Clipper, which is scheduled for flight in 2024 to investigate the frozen moon, might benefit from such data. According to Juno's principal investigator, Scott Bolton of the Southwest Research Institute in San Antonio, “Europa is such an intriguing Jovian moon, it is the focus of its own future NASA mission. We’re happy to provide data that may help the Europa Clipper team with mission planning, as well as provide new scientific insights into this icy world.”
Europa is around 90% the size of Earth's Moon, with an equatorial diameter of 1,940 miles (3,100 kilometres). There is speculation among scientists that a salty ocean lurks under Europa's miles-thick ice cover, raising doubts about whether or not the subsurface environment might sustain life.
The course of Juno will be altered by the near flyby, shortening the time it takes to circle Jupiter from 43 days to 38 days. On January 3, 2000, NASA's Galileo spacecraft reached within 218 miles (351 kilometres) of Europa. This will be the closest a NASA mission has been to Europa since then. This is Juno's second contact with a Galilean moon during its extended mission, and it comes during this flyby. The probe visited Ganymede in June of 2021, and it will go quite near to Io in 2023 and 2024.
When the spacecraft is 83,397 kilometres (51,820 miles) from Europa, one hour before closest approach, data collecting will begin.
“The relative velocity between spacecraft and moon will be 14.7 miles per second (23.6 kilometers per second), so we are screaming by pretty fast,” said John Bordi, Juno deputy mission manager at the Jet Propulsion Laboratory. “All steps have to go like clockwork to successfully acquire our planned data, because soon after the flyby is complete, the spacecraft needs to be reoriented for our upcoming close approach of Jupiter, which happens only 7 ½ hours later.”
When approaching Europa, the spacecraft will use all of its equipment and sensors. The ionosphere of Europa will be studied by Juno's Jupiter Energetic-Particle Detector Instrument (JEDI) and its medium-gain (X-band) radio antenna. To investigate how Europa interacts with Jupiter's magnetosphere, Juno will use its Waves, Jovian Auroral Distributions Experiment (JADE), and Magnetometer (MAG) instruments to monitor plasma left behind by the moon.
A possible water plume above Europa's surface will also be searched for by MAG and Waves. “We have the right equipment to do the job, but to capture a plume will require a lot of luck,” said Bolton. “We have to be at the right place at just the right time, but if we are so fortunate, it’s a home run for sure.”
