Studies: Europa's Surface CO2 Emerges from Internal Ocean

A pair of independent studies, using recent James Webb Space Telescope (JWST) observations of carbon dioxide (CO₂) ice on Jupiter's moon Europa, indicate the CO₂ originates from a source within the icy body's subsurface ocean. The findings from both research groups provide new insights into the poorly known composition of Europa's internal ocean. Beneath a crust of solid water ice, Jupiter's moon Europa is thought to have a subsurface ocean of salty liquid water. Because of this, Europa is a prime target in the search for life elsewhere in the Solar System. Assessing this deep ocean's potential habitability depends on its chemistry, including the abundance of biologically essential elements like carbon. Previous research has identified the presence of solid CO₂ ice on Europa's surface, but it has not been possible to establish whether the CO₂ originated from the subsurface ocean, was delivered to the moon's surface by meteorite impacts, or was produced on the surface through interactions with Jupiter's magnetosphere. Determining the source of the CO₂ could constrain the chemistry of Europa's internal ocean.

In two separate studies, researchers analyze near-infrared spectroscopy of CO₂ on Europa's surface, obtained with JWST. In one study, Samantha Trumbo and Michael Brown used the JWST data to map the distribution of CO₂ on Europa and found the highest abundance of CO₂ is located in Tara Regio – a ~1,800 square kilometer region dominated by "chaos terrain," geologically disrupted resurfaced materials. According to Tumbo and Brown, the amount of CO₂ identified within this recently resurfaced region – some of the youngest terrain on Europa's surface – indicates that it was derived from an internal source of carbon. This implies that the CO₂ formed within Europa's subsurface ocean and was brought to the surface on a geologically recent timescale. However, the authors say that formation of CO₂ on the surface from ocean-derived organics or carbonates cannot be entirely ruled out. In either interpretation, the subsurface ocean contains carbon.

In an independent study of the same JWST data, Geronimo Villanueva and colleagues found that the CO₂ on Europa's surface is mixed with other compounds. Villanueva et al. also find the CO₂ is concentrated in Tara Regio and interpret that as demonstrating that the carbon on the moon's surface was sourced from within. The authors measured the ice's ¹²C/¹³C isotopic ratio, but could not distinguish between an abiotic or biogenic source. Moreover, Villanueva et al. searched for plumes of volatile material breaching moon's icy crust. Although previous studies have reported evidence of these features, the authors did not detect any plume activity during the JWST observations. They argue that plume activity on Europa could be infrequent, or sometimes does not contain the volatile gasses they included in their search. The results in both studies complement each other and reinforce the conclusion that Europa's subsurface ocean contains abundant carbon.