\n<\/p>\n
For nearly two decades Enceladus, a 500-kilometer-wide moon of Saturn, has been a top target in the hunt for extraterrestrial life. In 2005, shortly after arriving in orbit around the ringed planet, the joint NASA\u2013European Space Agency (ESA) Cassini mission found clinching evidence that Enceladus harbored a liquid-water ocean beneath its bright-white icy crust\u2014plumes of seawater spraying up from the moon\u2019s south pole. Astrobiologists have become ever more enthralled by Enceladus ever since, as further studies of the ice grains in the plumes have revealed multiple molecular building blocks of life blasting out from the hidden ocean.<\/p>\n
Now scientists revisiting data from Cassini\u2014which ended its mission in 2017\u2014have spied even more tantalizing ingredients in the plumes: suites of complex organic molecules which, on Earth, are involved in the chemistry associated with even bigger molecules considered essential for biology. Published Wednesday in Nature Astronomy, the discovery bolsters the case for follow-up missions to search for signs of life within Saturn\u2019s enigmatic, ocean-bearing moon.<\/p>\n
The findings show \u201cthere is chemical complexity in Enceladus\u2019s subsurface ocean,\u201d says Nozair Khawaja, a planetary scientist at the Free University of Berlin in Germany, who led the Nature Astronomy study.<\/p>\n
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\u201cThese new results are very intriguing and raise the question of what, exactly, is the true nature and origin of organics within Enceladus\u2019s ocean,\u201d says Kevin Hand, a planetary scientist and director of the Ocean Worlds Lab at NASA\u2019s Jet Propulsion Laboratory, who was not involved in the study.<\/p>\n
Besides its remoteness from Earth, Enceladus has kept so many of its secrets for so long because the Cassini orbiter wasn\u2019t really designed for such deep scrutiny of a single, specific object. \u201cThe goal of the mission was to understand Saturn, its rings and its moon systems,\u201d Khawaja says. Cassini launched nearly 30 years ago carrying instruments built in the 1980s or 1990s, back when the moon\u2019s subsurface ocean and south polar plumes were unknown. Repurposing that vintage kit for in-depth astrobiology was difficult\u2014not least of all because of how hard the resulting data were to work with.<\/p>\n
\u201cCassini\u2019s instruments were made to analyze the chemical composition of dust and ice particles, but they weren\u2019t meant to explore the subsurface material of Enceladus,\u201d Khawaja says. One particular problem was the relatively low resolution available from a mass spectrometer on Cassini called the Cosmic Dust Analyzer (CDA), which parsed the chemical composition of puffs of dust from ice grains striking its detectors each time the spacecraft swooped through a plume. The plumes proved so thick with material, Khawaja explains, that the CDA would be overwhelmed during Cassini\u2019s Enceladus flybys.<\/p>\n
The result was that countless different types of particles with similar masses blurred together in the CDA\u2019s detections, making it nearly impossible for scientists back on Earth to discern them. They could clearly see that ordinary water molecules comprised the vast majority of collected material\u2014nearly 98 percent, Khawaja says. Piecing together the nature of the remaining 2 percent, however, required many carefully choreographed flybys and tweaks to the CDA\u2019s operations across several years. The flyby that eventually hit a bull\u2019s-eye was a maneuver on October 9, 2008, code-named E5. It wasn\u2019t the first and it wasn\u2019t the closest, but E5 was special because of its higher-than-average speed and a fortuitously timed eruption from Enceladus.<\/p>\n
Cassini\u2019s speed during E5 was nearly 18 kilometers per second (km\/s)\u2014about 6 km\/s faster than most other flybys\u2014which translated into massive improvements in the CDA data. \u201cThe impact speed was higher, and at such high speeds, water molecules shatter. They don\u2019t survive. But other species like organics remain,\u201d Khawaja explains. E5 was also lucky because it sent Cassini plowing through a plume that had been ejected mere minutes beforehand. This ensured the material came fresh out of Enceladus\u2019s subsurface and had not been altered or degraded by cosmic radiation. \u201cThe curtain went up,\u201d Khawaja says. But years of painstaking data analysis were still to come.<\/p>\n
A view of Enceladus against the backdrop of Saturn.<\/p>\n
NASA’s Goddard Space Flight Center<\/p>\n
Some of the co-authors of the new study published a paper in 2011 analyzing the E5 flyby results. \u201cBack then, we clearly saw the features of organic molecules in the mass spectra produced by the CDA, but we were unable to nail down the type of these organics. We just knew they were there,\u201d Khawaja says. Based on exhaustive experiments examining how differences in the ice grain impact speeds affect the CDA data, he and his colleagues think they\u2019ve now tracked down most of what\u2019s within the plumes, with major implications for the moon\u2019s possibility of hosting life.<\/p>\n
\u201cI think it makes a lot of sense that it would take diligence and patience to fully understand the CDA data. I applaud them for taking such care in their analyses,\u201d says Shannon MacKenzie, a planetary scientist at Johns Hopkins University, who wasn\u2019t involved in the study.<\/p>\n
The team\u2019s work revealed the plumes contain several chemical compounds Cassini previously detected in the E ring, a torus of ice and dust Enceladus makes as it spews material in its orbit around Saturn. \u201cThere were complex organics in the signal which had a benzenelike structure, with many compartments connected with side chains with some oxygen and nitrogen plugged in. They were like hydrocarbons\u2014massive and complex,\u201d Khawaja says. The analysis found other materials that had been seen in the E ring as well: amines, aromatics and oxygen-bearing molecules. Their presence in the freshly ejected plumes, Khawaja argues, confirms they all originated in Enceladus\u2019s subsurface ocean. Most excitingly, the study also revealed new, never-before-seen compounds lurking in the plume, sourced from somewhere within the moon.<\/p>\n
\u201cIn these fresh grains, we\u2019ve got molecules like esters and ethers, which were carrying oxygen in themselves and had double bonds,\u201d Khawaja says. Another new finding was the presence of compounds where oxygen and nitrogen were probably combined. \u201cWe suspect these are sort of intermediates to make further, complex organics, maybe potentially organics that are biologically relevant,\u201d he adds. Certainty is elusive because the organics collected by CDA were shattered into multiple tiny fragments; researchers are still figuring out how to piece these fragments back together.<\/p>\n
\u201cThis work shows that some of the fragments are indeed derived from quite large and complex organic compounds,\u201d Hand says. \u201cBut maybe those compounds originated from even larger compounds. What exactly would we find if we dove into the ocean below\u2014are the compounds reported here just the tip of the astrobiological iceberg?\u201d<\/p>\n
Khawaja already has ideas about what follow-up missions might find by delving deeper with better, state-of-the-art instruments. The newly revealed cocktail of compounds, he says, could feed into a \u201cnetwork of reactions\u201d to create pyrimidines\u2014a class of molecules necessary for the formation of DNA. (And, here on Earth, DNA is what leads to fish, lions, humans and life as we know it.) This network of reactions could yield lipids, too\u2014molecules that can arrange themselves into cell membranes. Even so, Khawaja notes, \u201cwe don\u2019t have a clue about any actual biological relevance yet.\u201d<\/p>\n
For now, in the absence of a follow-up mission at or en route to Enceladus, the team is developing an advanced computer model of the entire Enceladus subsurface system in hopes of pinpointing the probable sources and interactions of the moon\u2019s rich assortment of chemical compounds. There\u2019s also some room left for discovery in the Cassini data. \u201cThere are still certain spectral types that I see and don\u2019t understand,\u201d Khawaja says.<\/p>\n
Ultimately, most of the hope for definitive answers about life on Enceladus in the near term lies with a mission still on the drawing board at ESA. Such a mission would most likely include an orbiter, albeit one far more advanced than Cassini, with a lander as a possible addition. \u201cIn a mission like that, a lander and an orbiter should complement each other,\u201d Khawaja says.<\/p>\n
But not all are equally sold out on the lander idea. \u201cThe results of this study corroborate mission concepts that don\u2019t even need to land\u2014we could just continually fly through the plumes and collect fresh material,\u201d Hand says. \u201cWhy risk landing when Enceladus is handing out free samples?\u201d<\/p>\n
Regardless of such logistical debates, what\u2019s clear is that Enceladus remains one of the most alluring destinations to look for extraterrestrial life.<\/p>\n
\u201cWater, energy and the right chemicals\u2014all three keystones of habitability are there,\u201d Khawaja says. Even if future studies fail to find life, he argues, the implications would be enormous. \u201cIf it\u2019s not there despite those three keystones, it would mean that life needs something more.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
For nearly two decades Enceladus, a 500-kilometer-wide moon of Saturn, has been a top target in the hunt for extraterrestrial life. In 2005, shortly after arriving in orbit around the ringed planet, the joint NASA\u2013European Space Agency (ESA) Cassini mission found clinching evidence that Enceladus harbored a liquid-water ocean beneath its bright-white icy crust\u2014plumes of<\/p>\n","protected":false},"author":1,"featured_media":25123,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[50],"tags":[15203,15008,2830,15202,337,1615,11002,15179,4626,15204],"class_list":{"0":"post-25122","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-environment","8":"tag-cassini","9":"tag-chemistry","10":"tag-complex","11":"tag-enceladus","12":"tag-life","13":"tag-moon","14":"tag-ocean","15":"tag-organic","16":"tag-saturns","17":"tag-uncovers"},"_links":{"self":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/25122","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=25122"}],"version-history":[{"count":0,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/25122\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/media\/25123"}],"wp:attachment":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=25122"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=25122"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=25122"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}