As the Juno spacecraft makes a close approach of the moon Europa, it is expected to provide valuable science – and remarkable imagery – for NASA’s upcoming Europa Clipper mission.
In less than three days, on Thursday, September 29, at 2:36 a.m. PDT (5:36 a.m. EDT), NASA’s Juno spacecraft will come within 222 miles (358 kilometers) of the surface of Jupiter’s ice-covered moon, Europa. During the close flyby, the solar-powered spacecraft is expected to obtain some of the highest-resolution images ever taken of portions of Europa’s surface. It will also collect valuable data on the moon’s interior, surface composition, and ionosphere, along with its interaction with Jupiter’s magnetosphere.
Future missions could benefit greatly from this detailed information. One such mission is Europa Clipper, which is set to launch in 2024 to study the icy moon. “Europa is such an intriguing Jovian moon, it is the focus of its own future NASA mission,” said Juno Principal Investigator Scott Bolton of the Southwest Research Institute in San Antonio. “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 about 90% the size of Earth’s Moon, with an equatorial diameter of 1,940 miles (3,100 kilometers). Researchers believe a salty ocean lies below a miles-thick ice shell, sparking questions about potential conditions capable of supporting life underneath Europa’s surface.
Gravitational forces from the close flyby will modify Juno’s trajectory, reducing the time it takes to orbit Jupiter from 43 to 38 days. It will be the closest a NASA spacecraft has approached Europa in over 22 years, since Galileo came within 218 miles (351 kilometers) on January 3, 2000. Additionally, this flyby marks the second encounter with a Galilean moon during Juno’s extended mission. In June 2021, the mission explored Ganymede and plans include making close approaches of Io in 2023 and 2024.
Data collection on the spacecraft will begin an hour prior to closest approach, when the Juno is 51,820 miles (83,397 kilometers) from Europa.
“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 JPL. “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.”
Juno’s full suite of instruments and sensors will be activated for the Europa encounter. The spacecraft’s Jupiter Energetic-Particle Detector Instrument (JEDI) and its medium-gain (X-band) radio antenna will collect data on Europa’s ionosphere. Its Waves, Jovian Auroral Distributions Experiment (JADE), and Magnetometer (MAG) experiments will measure plasma in the moon’s wake as Juno explores Europa’s interaction with Jupiter’s magnetosphere.
MAG and Waves will also search for possible water plumes above Europa’s surface. “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.”
Juno’s Microwave Radiometer (MWR) will gaze into Europa’s water-ice crust to obtain data on its composition and temperature. This is the first time that data like this will be gathered to study the moon’s icy shell.
Additionally, during the flyby the mission expects to take four visible-light images of the moon with JunoCam (a public-engagement camera). The Juno science team will compare them to images from previous missions, so they can find any changes in Europa’s surface features that might have occurred over the past two decades. These visible-light images will have an expected resolution of better than 0.6 miles (1 kilometer) per pixel.
This movie was generated using imagery collected on October 29, 2018, during Juno’s 16th perijove (the point at which an orbit comes closest to Jupiter’s center). Citizen scientists Gerald Eichstädt created this movie using data from the spacecraft’s JunoCam imager. Credit: Enhanced image by Gerald Eichstädt based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS
Juno will be in Europa’s shadow when closest to the moon. However, Jupiter’s atmosphere will reflect enough sunlight for Juno’s visible-light imagers to collect data. The mission’s star camera (called the Stellar Reference Unit) will take a high-resolution black-and-white image of Europa’s surface. It was designed to take images of star fields and search for bright stars with known positions to help Juno get its bearings. Meanwhile, the Jovian Infrared Auroral Mapper (JIRAM) will attempt to capture infrared images of its surface.
Juno’s closeup views and data from its MWR instrument will inform the Europa Clipper mission, which will perform almost 50 flybys of the icy moon after it arrives at Europa in 2030. Europa Clipper will gather data on the moon’s atmosphere, surface, and interior. With this information, scientists expect to better understand Europa’s global subsurface ocean, the thickness of its ice crust, and possible plumes that may be venting subsurface water into space.
More About the Mission
NASA’s Jet Propulsion Laboratory (JPL), a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott J. Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.