Hubble, Galileo data provide more evidence of plumes over Europa
After reviewing data from a previous mission to the Jovian system, scientists found evidence of a plume erupting from Jupiter’s moon Europa, which NASA said indicates that the moon’s subsurface ocean may indeed be venting water vapor through cracks in its icy surface.
In 2012, NASA revealed ultraviolet images captured by the Hubble Space Telescope that suggested the presence of plumes that erupted from the surface of Europa. It was the first strong evidence of such eruptions from the icy world.
However, after recently re-examining magnetometer data from a 1997 Europa flyby that saw the Galileo spacecraft, which orbited Jupiter between 1995 and 2003, fly within about 124 miles (200 kilometers) of the surface of the moon, scientists put that information through “new and advanced computer models” to better understand an unexplained “bend” in the planet’s magnetic field. The new analysis, combined with 2012 Hubble images, is considered “strong and corroborating support for plumes,” NASA said.
Old data provides new insights
Scientists say Europa is an important exploration destination because it could contain the three ingredients known to be required for life: liquid water; chemistry necessary for life, including carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur; and energy. The presence of plumes on Europa offers evidence for the third ingredient—energy—in the form of heat.
The scientists sharing the recent findings via a May 14, 2018, “Science Chat” included Lori Glaze, acting director of NASA’s Planetary Science Division; Xianzhe Jia, associate professor in the Department of Climate and Space Sciences and Engineering at the University of Michigan, Ann Arbor; Elizabeth Turtle, research scientist at Johns Hopkins Applied Physics Laboratory in Laurel, Maryland; and Margaret Kivelson, professor emerita of Space Physics in the Department of Earth and Space Sciences at the University of California, Los Angeles.
Kivelson served as principal investigator on the magnetometer instrument for the Galileo spacecraft, which orbited Jupiter and made 11 flybys of Europa between 1995 and 2003.
The science team for the upcoming Europa Clipper mission became interested in reviewing the Galileo data after Hubble captured ultraviolet images of what appeared to be plumes over Europa.
Based on the Hubble images, as well as the discoveries made by the Cassini spacecraft, which orbited Saturn between 2004 and 2017, showing that materials from plumes on its moon Enceladus interacted with the magnetic field of the ringed planet, the team decided to review the previously-unexplained magnetometer readings from Galileo’s Europa flybys using new, more advanced computer algorithms.
Through this analysis, they detected disruptions of the magnetic field happening at Europa, indicating that Galileo had flown through a plume of some sort in 1997.
Europa’s icy surface, which could be as much as 10-15 miles (16-24 kilometers) thick, is suspected of concealing a global ocean. Like Earth, Europa is thought to have an iron core, a rocky mantle and an ocean of salty water. However, Europa’s ocean could have an estimated depth of 40-100 miles (65-160 kilometers), making it twice the volume of all of Earth’s oceans combined.
Moreover, Europa’s ice is broken into numerous linear fractures where the ice has cracked. There, material from below could rise up into the fissure. Any plumes shooting up from the moon’s surface are likely caused by cryovolcanism, scientists say.
Cryovolcanism is what happens when materials are shot into space by the force of Jupiter’s gravity flexing the moon’s surface. However, instead of releasing lava, these cryovolcanoes emit liquid water or other volatile materials.
The suspected Europa plume was identified above a thermal anomaly on the surface. Jia said that the “area seems to have elevated temperature compared to its surroundings.” However, he pointed out that the exact reason why this plume-producing region of Europa appears to be warmer than other parts of the moon is not well understood. He said that the heat for the plumes could be the result of internal mechanisms, surface material, or other processes.
Evidence of life?
As to whether this finding strengthened the case for potential life on Europa, none of the scientists on the chat would state that directly.
“We know life exists in Lake Vostok in Antarctica, and the temperature there is like minus 80 degrees Celsius [minus 112 degrees Fahrenheit],” said JoAnna Wendel, the Planetary Science division’s communications lead.
The surface temperature at Europa is around minus 274 degrees Fahrenheit (minus 170 degrees Celsius), but if the water beneath the surface ice is liquid, that would make it much warmer than that. Even if the water in Europa’s icy seas contains a large amount of salts, bringing the freezing temperature lower than it is on Earth, it would still be warm enough to be liquid.
Implications for future missions
NASA is in the planning phase for the Europa Clipper mission, which is slated to launch toward Jupiter in 2022, possibly aboard the Space Launch System (SLS). While the spacecraft is not designed specifically to search for life, it is expected to provide a detailed examination of Europa to determine if conditions exist that favor Earth-like life. The findings released May 14 suggest specific areas the mission could fly by when it arrives.
Turtle told Spaceflight Insider that Europa Clipper will make 44 close flybys of the moon, many within 62 miles (100 kilometers) of the surface and several within 15 miles (25 kilometers).
“That allows us to look at the surface in very close detail and makes it easier to study the atmosphere because there will be more material closer to the surface,” Turtle said. “It’s also better for measuring the magnetic field.”
Europa Clipper, like Cassini, should be able to fly through the moon’s plumes without much danger to the spacecraft. Turtle described the plumes as very tenuous, but not “optically thick.” Also like Cassini, the spacecraft is expected to look at the Sun through plumes at a variety of wavelengths using an ultraviolet spectrograph and thermal imager to characterize the gases and particles that comprise them.
The spacecraft is being designed to carry a suite of instruments, including cameras and spectrometers for capturing observations at a distance as well as on-site measurements with a magnetometer and mass spectrometer. It is also is slated to carry a sounding radar, which should allow Europa Clipper to see the structure of the ice kilometers beneath the surface.
Video courtesy of NASA JPL
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.