Results from the solar-powered spacecraft provide a new measurement of the thickness of the ice shell encasing the\u00a0Jovian moon\u2019s\u00a0ocean.\u00a0<\/p>\n
Data from NASA\u2019s Juno mission has\u00a0provided\u00a0new insights into the thickness and subsurface structure of the icy shell encasing Jupiter\u2019s moon Europa. Using the spacecraft\u2019s Microwave Radiometer (MWR), mission scientists\u00a0determined\u00a0that the shell averages about 18 miles (29 kilometers) thick in the region\u00a0observed\u00a0during Juno\u2019s 2022 flyby of Europa. The Juno measurement is the first to discriminate between thin and thick shell models\u00a0that\u00a0have suggested the ice shell is anywhere from less than half a mile to tens of miles thick.\u00a0\u00a0<\/p>\n
Slightly smaller than Earth\u2019s moon, Europa is one of the solar system\u2019s\u00a0highest-priority\u00a0science targets<\/a>\u00a0for investigating habitability. Evidence suggests that the ingredients for life may exist in the\u00a0saltwater ocean that lies beneath its ice shell. Uncovering a variety of characteristics of the ice shell, including its thickness,\u00a0provides\u00a0crucial pieces of the puzzle for understanding the moon\u2019s internal workings and the potential for the existence of a habitable environment.\u00a0<\/p>\n The new\u00a0estimate\u00a0on the ice thickness in the near-surface icy crust\u00a0was\u00a0published<\/a>\u00a0on Dec. 17 in the journal\u00a0Nature Astronomy.\u00a0<\/p>\n Although the\u00a0MWR instrument<\/a>\u00a0was designed to investigate Jupiter\u2019s atmosphere below the cloud tops, the novel instrument has proven valuable for studying the gas giant\u2019s icy and volcanic moons as well.\u00a0<\/p>\n On Sept. 29, 2022,\u00a0Juno<\/a>\u00a0came within about 220 miles (360 kilometers) of Europa\u2019s frozen surface. During the flyby, MWR collected data on about half the moon\u2019s surface, peering beneath the ice to measure its temperatures at various depths.\u00a0\u00a0<\/p>\n \u201cThe 18-mile estimate relates to the cold, rigid, conductive outer-layer of a pure water ice shell,\u201d said Steve Levin, Juno project\u00a0scientist\u00a0and co-investigator from NASA\u2019s Jet Propulsion\u00a0Laboratory in Southern California, which manages the mission. \u201cIf an inner, slightly warmer convective layer also exists, which is possible, the total ice shell thickness would be even greater.\u00a0If the ice shell\u00a0contains\u00a0a modest amount of dissolved salt, as suggested by some models, then our estimate of the shell thickness would be reduced by about\u00a03\u00a0miles.\u201d\u00a0\u00a0<\/p>\n The thick shell, as suggested by the MWR data, implies a longer route that oxygen and nutrients would have to travel to connect Europa\u2019s surface with its subsurface ocean.\u00a0Understanding this process may be relevant to future studies\u00a0of\u00a0Europa\u2019s habitability.\u00a0\u00a0<\/p>\n The MWR data also\u00a0provides\u00a0new insights into the makeup of the ice just below Europa\u2019s surface. The instrument revealed the presence of \u201cscatterers\u201d \u2014 irregularities in the near-surface ice such as cracks, pores, and voids that scatter the instrument\u2019s microwaves reflecting off the ice (similar to\u00a0how visible light is scattered in ice cubes). These scatterers are estimated to be no bigger than a few inches in diameter and appear to extend to depths of hundreds of feet below Europa\u2019s surface.\u00a0<\/p>\n The small size and shallow depth of these features, as modeled in this study, suggest they are unlikely to be a significant pathway for oxygen and nutrients to travel from Europa\u2019s surface to its salty ocean.\u00a0<\/p>\n \u201cHow thick the ice shell is and the existence of cracks or pores within the ice shell are part of the complex puzzle for understanding Europa\u2019s potential habitability,\u201d said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. \u201cThey provide critical context for NASA\u2019s Europa Clipper and\u00a0the ESA\u00a0(European Space Agency)\u00a0Juice (JUpiter\u00a0ICy\u00a0moons Explorer) spacecraft \u2014 both\u00a0of which are\u00a0on their way to the Jovian system.\u201d Europa Clipper will arrive there in 2030, while Juice will arrive the year after.\u00a0\u00a0<\/p>\n Juno will carry out its 81st flyby of Jupiter on Feb. 25.\u202f\u00a0<\/p>\n A division of Caltech in Pasadena, California, JPL manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA\u2019s New Frontiers Program, managed at NASA\u2019s Marshall Space Flight Center in Huntsville, Alabama, for the agency\u2019s Science Mission Directorate in Washington.\u00a0<\/p>\n To learn more about Juno, go to:<\/p>\n