A new look at ‘ocean worlds’: James Webb Space Telescope will target Europa and Enceladus

An example of possible spectroscopy results from one of Europa’s water vapour plumes. Image Credit: NASA-GSFC/SVS/Hubble Space Telescope/Stefanie Milam/Geronimo Villanueva

NASA’s upcoming James Webb Space Telescope (JWST) will be used to study two of the most fascinating moons in our Solar System  – Europa and Enceladus, also known as “ocean worlds” since both have global oceans of water beneath their outer icy surfaces. The new observations will help scientists learn more about conditions on these worlds and guide the development of future robotic missions.

Both moons are exciting targets since Europa’s surface has deposits of minerals thought to have come up from the ocean below, and Enceladus has huge plumes of water vapour erupting through fissures in the icy surface, originating from the subsurface ocean. Europa may also have plumes, which have been tentatively identified but not confirmed yet. Enceladus’ plumes also contain organic compounds of various complexities, which were sampled directly by the Cassini spacecraft multiple times.

“We chose these two moons because of their potential to exhibit chemical signatures of astrobiological interest,” said astronomer Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy (AURA).

Astronomers will use Webb’s near-infrared camera (NIRCam) to take high-resolution images of Europa’s surface, to search for hot regions related to plumes and active geological processes. If a plume is found, they can then use Webb’s near-infrared spectrograph (NIRSpec) and mid-infrared instrument (MIRI) to analyze the plume’s composition.

“Are they made of water ice? Is hot water vapour being released? What is the temperature of the active regions and the emitted water?” asked Villanueva. “Webb telescope’s measurements will allow us to address these questions with unprecedented accuracy and precision.”

JWST will be able to study Enceladus’ plumes and surface in a similar manner, even though it is about 10 times smaller than Europa as seen by the telescope.

For both moons, a focus will be to search for organic signatures such as methane, methanol, and ethane in the plumes. Evidence of life itself, like microbes, would be more difficult since some life-like processes could also have a geological explanation.

Composite image showing the possible water vapour plumes near the south pole of Europa, at about the 7 o’clock position. The image of Europa, from the Galileo and Voyager missions, is superimposed on the Hubble data. Image Credit: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center
Diagram of an interior cross-section of the crust of Enceladus, showing how hydrothermal activity is thought to be causing the plumes of water vapour on the surface. Image Credit: NASA-GSFC/SVS/NASA/JPL-Caltech/Southwest Research Institute
The water vapour plumes of Enceladus, as seen by the Cassini spacecraft. Photo Credit: NASA/JPL-Caltech

“We only expect detections if the plumes are particularly active and if they are organic-rich,” Villanueva noted.

JWST is the successor to the Hubble Space Telescope (HST) and will be the most powerful space-based telescope ever built. It is an international project led by NASA, along with the European Space Agency (ESA) and the Canadian Space Agency (CSA).

Even if JWST isn’t able to find signs of life on either moon, it will be another huge step in understanding what conditions are like, both on their surfaces and below the ice in the oceans themselves, building on results from spacecraft such as Galileo and Cassini. It will help prepare the way for future, more advanced probes on the drawing boards now which may be able to answer that question of whether life has ever existed on (in) these far-off ocean worlds.

This article was first published on AmericaSpace.









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