Artist's depiction听of the Cassini spacecraft passing through plumes from Enceladus. (Credit: NASA/JPL-Caltech)
New data collected from the听Cassini spacecraft have revealed complex organic molecules originating from Saturn鈥檚 icy moon Enceladus, strengthening the idea that this ocean听world hosts conditions suitable for life.
彩民宝典听Assistant Professor Sascha Kempf and research associate Sean Hsu, both in the (LASP), co-authored the study.
Very little was known about Enceladus prior to 2005鈥攖he year when Cassini first flew by. Since then, it has become a continuous source of surprises, with secrets still being revealed even now, after the mission end.听
Visualization showing how hydrothermal activity drives the ejection of icy plumes from oceans on Enceladus. (Credit:听NASA/JPL-Caltech)
During the mission鈥檚 incredible career, scientists discovered that 500 kilometer-wide Enceladus has a massive sub-surface ocean hidden underneath a thick icy crust, with evidence pointing to powerful hydrothermal vents on the seabed that mix up material from the moon鈥檚 water-filled, porous core with the ocean water.
They detected mighty geysers releasing a mixture of water vapour and ice grains from the oceans into space through cracks鈥攏icknamed "tiger stripes"鈥攊n the moon鈥檚 icy shell, providing material for one of Saturn鈥檚 rings.
Now, a team led by Frank Postberg and Nozair Khawaja of the University of Heidelberg, Germany, has identified fragments of large organic molecules in these ejected ice grains. The results are .
鈥淚t is the first ever detection of complex organics coming from an extraterrestrial water-world,鈥� says Frank.听
鈥淲e found large molecular fragments that show structures typical for very complex organic molecules,鈥� adds Nozair. 鈥淭he fragments, of up to 200 units of molecular mass, are created as the ice grains hit the scientific instruments on Cassini at speeds of about 30,000 kilometres per hour, but we believe that, prior to the collision, the grains contain the original, even larger molecules, which could have molecular weights of thousands of atomic mass units.鈥�
Scientists calculate molecular mass, or weight, as the sum of weights of individual atoms contained in the molecule. Previously, Cassini had only detected lightweight organic molecules at Enceladus much smaller than the most recently found fragments.
Such large molecules can only be created by complex chemical processes鈥攊ncluding those related to life. Alternatively, they could come from primordial material as found in some meteorites or, more likely, be generated by hydrothermal activity.
鈥淚n my opinion the fragments we found are of hydrothermal origin, having been processed inside the hydrothermally active core of Enceladus: in the high pressures and warm temperatures we expect there, it is possible that complex organic molecules can arise,鈥� says Frank.
The observations in this study were made using the Cosmic Dust Analyzer on the Cassini spacecraft. LASP researchers have a long history of probing dust in space鈥攕tudents at the university designed a dust detector on the New Horizons spacecraft, which made a close pass of Pluto in 2015. Scientists at LASP are also developing an instrument called the (SUDA) that will analyze dust around Jupiter鈥檚 moon Europa as part of NASA鈥檚 Europa Clipper mission.听
鈥淭he detection of the tiniest amounts of large organic molecules in ice particles demonstrates the power of听dust detectors such as SUDA, which is much more capable than the Cosmic Dust Analyzer," says Kempf.
