NASA’s Juno will make a close flyby of Jupiter’s icy moon Europa

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. The solar-powered spacecraft is expected to collect some of the highest-resolution images ever recorded of parts of Europa’s surface, as well as valuable data on the Moon’s interior, surface composition and ionosphere along with its interaction with Jupiter’s magnetosphere.

Such information could benefit future missions, including the agency’s Europa Clipper, due to launch in 2024 to study the icy moon. “Europa is such a fascinating Jovian moon, it’s the focus of its own future NASA mission,” said Juno principal investigator Scott Bolton of the Southwest Research Institute in San Antonio. “We are excited to provide data that can help the Europa Clipper team with mission planning and provide new scientific insights into this frigid world.”

With an equatorial diameter of 3,100 kilometers, Europa is about 90% the size of the Earth’s moon. Scientists believe a salty ocean lies beneath a kilometer-thick sheet of ice, raising questions about possible conditions that could support life below Europa’s surface.

The close flyby will change Juno’s trajectory and shorten the time it takes to orbit Jupiter from 43 to 38 days. Since Galileo came within 218 miles (351 kilometers) of Europa on January 3, 2000, this will be NASA’s next spacecraft. This flyby also marks the second encounter with a Galilean moon during Juno’s extended mission. The mission explored Ganymede in June 2021 and plans to approach Io in 2023 and 2024.

Data collection will begin one hour before closest approach when the spacecraft will be 51,820 miles (83,397 kilometers) from Europa.

“The relative speed between the spacecraft and the moon will be 14.7 miles per second (23.6 kilometers per second), so we’re screaming by pretty quickly,” said John Bordi, Juno deputy mission manager at JPL. “All steps must run like clockwork to successfully capture our planned data, because shortly after the flyby is complete, the spacecraft must be realigned for our upcoming approach to Jupiter, which occurs just 7 ½ hours later.”

All spacecraft instrumentation and sensors will be activated for the Europa encounter. Juno’s Jupiter Energetic-Particle Detector Instrument (JEDI) and medium-gain (X-band) radio antenna will collect data over Europa’s ionosphere. Its Waves, Jovian Auroral Distributions Experiment (JADE) and Magnetometer (MAG) experiments will measure plasma in the Moon’s wake while Juno explores Europa’s interaction with Jupiter’s magnetosphere.

MAG and Waves will also look for possible water plumes over Europa’s surface. “We have the right gear to get the job done, but catching a cloud takes a lot of luck,” Bolton said. “We have to be in the right place at exactly the right time, but if we’re that lucky it’s definitely going to be a home game.”

Inside and outside

Juno’s microwave radiometer (MWR) will peer into Europa’s water-ice crust and obtain data on its composition and temperature. This is the first time such data has been collected to study the moon’s icy shell.

In addition, the mission expects to capture four visible-light images of the Moon with JunoCam (a public camera) during the flyby. The Juno science team will compare them to images from previous missions, looking for changes in Europa’s surface features that may have occurred over the past two decades. These visible light images have an expected resolution of better than 0.6 miles (1 kilometer) per pixel.

Although Juno will be in Europa’s shadow when it is closest to the moon, Jupiter’s atmosphere will reflect enough sunlight for Juno’s visible-light imagers to collect data. The mission’s star camera (dubbed the Stellar Reference Unit) is designed to capture images of star fields and look for bright stars with known positions to help orient Juno. It will take a high-resolution black and white image of the surface of Europe. In the meantime, the Jovian Infrared Auroral Mapper (JIRAM) will attempt to collect infrared images of its surface.

Juno’s close-up images and data from its MWR instrument will inform the Europa Clipper mission, which will conduct nearly 50 flybys after arriving in Europe in 2030. Europa Clipper will collect data on the moon’s atmosphere, surface and interior – information that scientists will use to better understand Europa’s global subsurface ocean, the thickness of its icy crust and possible plumes that may be venting subsurface water into space .