In 2013, the Hubble Space Telescope spotted water vapour on Jupiter\u2019s moon Europa. The vapour was evidence of plumes similar to the ones on Saturn\u2019s moon Enceladus. That, and other compelling evidence, showed that the moon has an ocean. That led to speculation that the ocean could harbour life. <\/p>\n
But the ocean is obscured under a thick, global layer of ice, making the plumes our only way of examining the ocean. The plumes are so difficult to detect they haven\u2019t been confirmed.<\/p>\n
<\/p>\n The lead author of the paper presenting Hubble\u2019s 2013 evidence is Lorenz Roth of Southwest Research Institute. He said, \u201cBy far, the simplest explanation for this water vapour is that it erupted from plumes on the surface of Europa. If those plumes are connected with the subsurface water ocean we are confident exists under Europa\u2019s crust, then this means that future investigations can directly investigate the chemical makeup of Europa\u2019s potentially habitable environment without drilling through layers of ice. And that is tremendously exciting.\u201d <\/p>\n It is, but first, scientists have to find the plumes.<\/p>\n \u201cWe pushed Hubble to its limits to see this very faint emission. These could be stealth plumes because they might be tenuous and difficult to observe in visible light,\u201d said Joachim Saur of the University of Cologne, co-author of the 2013 paper. <\/p>\n Describing them as tenuous stealth plumes turned out to be prophetic. <\/p>\n Recently, a team of researchers went looking for the plumes. Their results are in a presentation given to the IAU Symposium 383 titled \u201cALMA Spectroscopy of Europa: A Search for Active Plumes.\u201d The lead author is M.A. Cordiner from the Solar System Exploration Division at NASA\u2019s Goddard Space Flight Center.<\/p>\n \u201cThe subsurface ocean of Europa is a high-priority target in the search for extraterrestrial life, but direct investigations are hindered by the presence of a thick exterior ice shell,\u201d the authors write. The researchers used ALMA to search for molecular emissions from atmospheric plumes. They were investigating processes under the ice that could help them understand Europa\u2019s ocean and its chemistry. <\/p>\n The Solar System is full of icy bodies, including comets, Kuiper Belt Objects, dwarf planets, and moons like Europa. Europa has a high density compared to other icy bodies, indicating a substantial rocky interior. Its ocean makes up about 10% of the moon and is covered by an icy shell of uncertain thickness. It could be several tens of kilometres thick. Scientists learned much of this from NASA\u2019s Galileo mission.<\/p>\n In recent years, Europa and its ocean have leapt to the top of the list of targets in the search for life. The reasons aren\u2019t obscure: liquid water is an irresistible beacon in our search for habitable places. The plumes from Europa\u2019s ocean are our only way to study the ocean and its potential habitability.<\/p>\n Over the years, different telescopes have examined Europa, searching for more evidence of the plumes. They\u2019ve found potential intermittent plume activity near the moon\u2019s south pole. But confirmation of the plumes the Hubble spotted in 2013 is elusive. In 2023, the JWST examined Europa. Those observations \u201cfound no evidence for active plumes, indicating that any present-day activity must be localized and weak; robust confirmation of the initial HST plume results also remains challenging,\u201d the authors write. <\/p>\n In an attempt to find the plumes, the authors employed ALMA, the Atacama Large Millimeter\/submillimeter Array. They observed Europa on four separate days to cover the moon\u2019s surface. Unfortunately, they found no plumes.<\/p>\n \u201cDespite near-complete coverage of both Europa\u2019s leading and trailing hemispheres, we find no evidence for gas phase molecular absorption or emission in our ALMA data,\u201d the researchers write. \u201cUsing ALMA\u2019s unique combination of high spectral\/spatial resolution and sensitivity, our observations have enabled the first dedicated search for HCN, H2<\/sub>CO, SO2<\/sub> and CH3<\/sub>OH in Europa\u2019s exosphere and plumes. No evidence was found for the presence of these molecules.\u201d<\/p>\n Finding no evidence doesn\u2019t quite mean that those molecules aren\u2019t there. Rather, it means that if they are there, their concentrations are so low they\u2019re below the detection threshold. In this case, some concentrations would be lower than those detected in Enceladus\u2019 plumes, which are confirmed. <\/p>\n One chemical in particular illustrates this point: CH3<\/sub>OH (methanol.) \u201cFor the CH3<\/sub>OH abundance, on the There are some interesting relationships between Europa and other icy objects in the Solar System. It has to do with abundance limits. The researchers established upper limits for H2<\/sub>CO (formaldehyde) on Europa. \u201cIndeed, our H2<\/sub>CO abundance upper limit is significantly lower than measured by Cassini in the Enceladus plume, implying a possible chemical difference.\u201d<\/p>\n Despite the fact that it didn\u2019t find any plumes, the observations were still valuable. By setting detection limits it helps subsequent efforts to search for them. And this won\u2019t be scientists\u2019 final attempt at finding plumes. Anything that provides clues to Europa\u2019s ocean is too tantalizing to ignore, and this research shows that ALMA is suited to this type of investigation.<\/p>\n \u201cOur results show that ALMA is a powerful tool in the search for outgassing from icy bodies within the Solar System and that follow-up searches for other molecules at additional epochs (on Europa and other icy bodies) are justified,\u201d the researchers conclude. <\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2023\/05\/e-pia24477_final_europa-volcanism_new-pia-1041-750.jpg\")
![\"These](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/04\/ALMA-Europa-observations.png\")
other hand, our ALMA upper limit of < 0.86% would not have been sensitive enough to detect this molecule at the Enceladus plume abundance of 0.02%,\u201d the authors write.<\/p>\nLike this:<\/h3>\n