Most planets and moons in the Solar System are clearly dead and totally unsuitable for life. Earth is the only exception. But there are a few worlds where there are intriguing possibilities of life.
Chief among them is Jupiter’s moon Europa, and the JWST just discovered carbon there. That makes the moon and its subsurface ocean an even more desirable target in the search for life.
Life needs chemical diversity, and among that diversity, carbon is a necessity. The JWST detected abundant carbon dioxide in a specific location on Europa’s surface called Tara Regio, a region full of what’s called chaos terrain. The location is important.
Finding carbon dioxide on Europa’s surface doesn’t necessarily mean there’s carbon in the moon’s subsurface ocean, which is where it needs to be to bolster the possibility of life. Surface carbon dioxide could’ve been delivered to the surface from an external source, maybe by meteorites. If that’s the case, it doesn’t indicate there’s any carbon in the ocean where the action is.
But finding it in chaos terrain is an important piece of evidence.
Image of Europa’s ice shell, taken by the Galileo spacecraft, of fractured “chaos terrain.” Image Credit: NASA/JPL-CaltechChaos terrain is a disrupted region on Europa’s ice shell where ridges, cracks, bumps, and smooth regions are all jumbled together chaotically. These are regions of upheaval, where material can potentially move back and forth between the surface and the ocean. So finding carbon dioxide there is a strong indication that the carbon came from the ocean.
“On Earth, life likes chemical diversity — the more diversity, the better. We’re carbon-based life. Understanding the chemistry of Europa’s ocean will help us determine whether it’s hostile to life as we know it, or whether it might be a good place for life,” said Geronimo Villanueva of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Carbon is the backbone of life because it readily forms bonds with many other different types of atoms. It needs diverse chemicals around it to form more types of molecules. Diversity means potential in the chemical world, so finding carbon that came from the ocean is an exciting hint at what types of molecules might form in Europa’s ocean.
“We now think that we have observational evidence that the carbon we see on Europa’s surface came from the ocean. That’s not a trivial thing. Carbon is a biologically essential element,” added Samantha Trumbo of Cornell University.
This graphic shows a map of Europa’s surface with the JWST’s NIRCam in the first panel and compositional maps derived from NIRSpec/IFU (Near Infrared Spectrograph’s Integral Field Unit) data in the following three panels. In the compositional maps, the white pixels correspond to carbon dioxide in the large-scale region of disrupted chaos terrain known as Tara Regio (centre and right), with additional concentrations within portions of the chaos region Powys Regio (left). The second and third panels show evidence of crystalline carbon dioxide, while the fourth panel indicates a complex and amorphous form of carbon dioxide. Astronomers using Webb have found carbon on the chaos terrain of Tara Regio and Powys Regio. Image Credit: NASA, ESA, CSA, G. Villanueva (NASA/GSFC), S. Trumbo (Cornell Univ.), A. Pagan (STScI)The Hubble Space Telescope found salt on Europa’s surface, also in Tara Regio, in 2019. That’s a strong indication that the ocean is salty. That, along with other evidence, suggests that Europa has a warm salty ocean with a rocky seafloor. Scientists think that an interface between water and rock is an important precursor to life.
Adding carbon into the mix just ramps up the excitement. The discovery checks off another box in favour of life. It also helps shape future exploration, including by the ESA’s JUICE mission and NASA’s Europa Clipper.
Artist concept of JUICE, a Jupiter moons orbiter mission. Credit: ESAThe ultimate mission to Europa will somehow melt or drill through the ice to sample the ocean directly. But that’s for the future. JUICE and the Europa Clipper won’t even land on Europa, let alone tackle the tens-of-kilometres-thick ice sheet. So the JWST is doing what it can from a distance to help us understand what’s buried beneath all that ice, and if it has the potential to support life.
A critical piece of the Europa question is whether or not there’s interplay between the surface and the ocean, and these results are more proof that there is.
“Scientists are debating to what extent Europa’s ocean connects to its surface. I think that question has been a big driver of Europa exploration,” said Villanueva. “This suggests that we may be able to learn some basic things about the ocean’s composition even before we drill through the ice to get the full picture.”
The nature of carbon dioxide indicates that the carbon was deposited on Europa’s surface relatively recently. It isn’t stable on Europa’s surface, so that, along with finding it in a young surface area, bolsters the idea that it came from Europa in a geologically recent event.
It’s remarkable how little observing time it took for the JWST to find the carbon dioxide. The powerful space telescope only needed a few minutes of its precious observing time to detect the carbon. Hopefully, that’s an indication of future observations in the Solar System.
“These observations only took a few minutes of the observatory’s time,” said Heidi Hammel of the Association of Universities for Research in Astronomy. Hammel is also a Webb interdisciplinary scientist leading Webb’s Cycle 1 Guaranteed Time Observations of the Solar System. Cycle 1 GTO devotes about 400 hours of observing time to studying our Solar System, so using only a few minutes to detect carbon is an impressive accomplishment. “Even in this short period of time, we were able to do really big science. This work gives a first hint of all the amazing Solar System science we’ll be able to do with Webb,” Hammel said.
JWST’s Europa observations led to two new papers in the journal Science. Though the authors of both papers are clearly excited by the findings, they also urge caution. “We interpret these observations as indicating that carbon is sourced from within Europa,” they write in one. In the other, they write “We propose that the CO2 formed in the internal ocean, although we cannot rule out formation on the surface through radiolytic conversion of ocean-derived organics or carbonates.”
Plumes of water could be responsible for delivering material from Europa’s ocean to its surface. The Hubble spotted some years ago and also watched as Europa transited across Jupiter’s disk ten times to find them again. Hubble found water plumes in three out of those ten images. Scientists hoped that the more powerful JWST would see them again. If they could find them, then they could begin to set an upper limit for how much carbon is being deposited on the surface.
They weren’t able to find the plumes with the JWST, but that doesn’t mean they’re not there. They could easily be intermittent and variable.
“There is always a possibility that these plumes are variable and that you can only see them at certain times. All we can say with 100% confidence is that we did not detect a plume at Europa when we made these observations with Webb,” said Hammel.
“This is a great first result of what Webb will bring to the study of Jupiter’s moons,” said Guillaume Cruz-Mermy, current ESA Research Fellow at the European Space Astronomy Centre. “I’m looking forward to seeing what else we can learn about their surface properties from these and future observations.”
While the JWST routinely makes headlines for its study of our Universe’s most ancient, most distant objects, these results show that it can also tell us a lot about our own solar neighbourhood. In fact, the powerful space telescope already found water plumes on Saturn’s moon Enceladus, another water moon with a frozen shell.
Images from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) show a water vapour plume jetting from the south pole of Saturn’s moon Enceladus, extending out 40 times the size of the moon itself. The inset, an image from the Cassini orbiter, emphasises how small Enceladus appears in the JWST image compared to the water plume. Credit: NASA, ESA, CSA, STScI, G. Villanueva (NASA’s Goddard Space Flight Center), A. Pagan (STScI).The ESA’s JUICE (Jupiter Icy Moons Explorer) launched in April 2023 and is currently on its long journey to the Jupiter system. It’ll study Europa and two of the gas giant’s other moons, Ganymede and Callisto. Ganymede is the Solar System’s largest moon and its buried ocean might contain more water than all of Earth. Callisto is the Solar System’s third-largest moon. It’s an intriguing object, though scientists aren’t convinced it has an ocean.
NASA’s Europa Clipper is due to launch a year from now. The Clipper is directly aimed at studying Europa. The spacecraft should arrive in the Jupiter system in 2030, while JUICE should arrive there in 2031.
But thanks to the JWST, scientists can look forward to more Solar System discoveries while we wait for the early 2030s. These new results are part of 10 hours of observing time dedicated to the subsurface oceans of Europa and Saturn’s moon Enceladus.
That means there are still 390 hours of JWST observing time dedicated to our Solar System. What else will it find?
