NASA’s Cassini spacecraft has successfully completed its most daring flyby yet of Saturn’s icy moon Enceladus. At 11:22 a.m. EDT (4:22 p.m. GMT) on October 28, the spacecraft flew 49 kilometers (30 miles) above the snowball-like moon’s south polar region, passing through its icy geysers that may originate from a subsurface ocean. Today we see the first raw images from this historic encounter.
"Cassini's stunning images are providing us a quick look at Enceladus from this ultra-close flyby, but some of the most exciting science is yet to come," said Linda Spilker, the mission's project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, in the announcement.
The flyby, officially titled E21, is the deepest dive through Enceladus’ plumes ever completed by Cassini. Earlier on in its mission, the spacecraft flew closer to the moon’s surface, but never this low through a plume before. From both a science and engineering perspective, 49 kilometers was the ideal altitude for this pass in order to conserve fuel and prolong the flyby — if only for a few tens of seconds — allowing for more science at the end of the mission in 2017.
"The joy of Enceladus is that you don’t need to land on it," said Curt Niebur, Cassini program scientist during a pre-flyby news conference. "It’s spewing samples into space all the time. We just have to fly by at the right time and the right trajectory."
Cassini cannot directly detect life on Enceladus, but it can provide some major clues as to how habitable the moon is. The team will be looking for the presence of molecular hydrogen within the data as the amount of hydrogen present in the plumes will tell us how active possible hydrothermal vents at the bottom of the ocean are.
"Confirmation of molecular hydrogen in the plume would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean, on the seafloor," said Hunter Waite, INMS (Ion and Neutral Mass Spectrometer) team lead at Southwest Research Institute in San Antonio. "The amount of hydrogen would reveal how much hydrothermal activity is going on."
The spacecraft also sampled the plume as it flew through, hopefully allowing scientists to determine its chemical composition. In order for the moon to be habitable, any potential life would need more than just water — energy from active hydrothermal vents and the right chemical ingredients are also necessary.
This stunning view of Enceladus was snapped by Cassini on October 28. NASA/JPL-Caltech/Space Science Institute.
The flyby will ultimately help solve the mystery of whether the plume is composed of column-like, individual jets, or sinuous, icy curtain eruptions – or a combination of both. The answer would tell us how the subsurface ocean is interacting with the surface, if the surface fractures are individual conduits that extend all the way to the ocean, and how much thermal energy is radiating from the cracks.
Researchers are also not sure how much icy material the plumes are actually spewing into space. The amount of material could reveal how long Enceladus has been active.
"Cassini truly has been a discovery machine for more than a decade," said Niebur. "This incredible plunge through the Enceladus plume is an amazing opportunity for NASA and its international partners on the Cassini mission to ask, 'Can an icy ocean world host the ingredients for life?'"
These observations are of significant astrobiological importance, so the science team says it may be weeks before we see the first science results from the flyby. If the moon proves to be habitable and we see signs that point to life, it could have major implications for the rest of the universe. “If life happens twice in one solar system, that would be really profound,” Spilker said in a news conference.
