In the last two decades, humans have finally observed some of the most interesting places in our solar system—the ice worlds. The Galileo spacecraft visited Jupiter and it’s moons, including Europa . The Cassini spacecraft visited Saturn and its moons, including Titan and Enceladus.
These moons are as large as small planets and due to tidal forces from orbiting their giant planets, are likely to have liquid oceans with as much water (or liquid methane) as Earth’s oceans.
Titan has an atmosphere, with clouds, and possibly rivers and lakes. Europa has a huge ocean of water under an icy crust. Enceladus, too, seems to have a liquid ocean under ice.
Energy + liquid? Sounds like life could happen.
Of course, the data from recent missions is still being analyzed, so even before the next visit we can learn more.
This summer an international team reported more findings from the Cassini spacecraft which measured particles as it flew near Enceladus (more than ten years ago now). [2]. Enceladus has a rocky core, a large ocean, and a thin ice crust. Cracks in the crust emit water from below, and one ‘volcano’ is spewing vapor and ice crystals out into space. Cassini flew through this plume and observed some of the particles.
Initial study identified the plume as mainly gasses and ice particles. The new study extends the results, demonstrating that many of the observations appear to be ice crystals with traces of complex organic molecules embedded. Given the probably origin of the plume, this strongly suggests that the ocean has a soup of organic compounds. As the BBC confusingly put it, “a step closer to hosting life“.
The paper discusses the complexities of low temperature, low pressure ice, and argue that the hypothesized ‘dirty ice’ could only form from complex processes. They offer a scenario involving a thin film of organics, which bubble up through a crack, becoming coated with ice, which is then ejected. I didn’t follow all of the argument here, but there is an important point: it is a mistake to assume that organic chemistry works in familiar ways in such a cold place. Energy + water + complex chemistry does not mean “just like my back yard”.
Revisiting these ice worlds has become a top priority, at least for actual scientists (if not necessarily for funding agencies). If and when we visit them, we should find one of three possibilities:
- there is no sign of life, even though the environment likely could support life. This may tell us something about the probability of life emerging in the universe.
- there is recognizable life, and it is related to Earth. If we find some variation of DNA/RNA or whatever, that will open the questions of how a common ancestor got to two different places in the solar system. Got Panspermia?
- there is recognizable life, but it is clearly not related to Earth. This “second example” will tell us something about what “life” is, and how it emerges.
(There is a fourth possibility: there might be something so different we need new concepts. There may even be life, but we won’t recognize it, or may disagree about it.)
Any and all of these outcomes will be breathtaking! We have to go there!
Editorial aside: So, why are people wasting money on space tourism and suicide missions to Mars, when the most exciting discovery in the history of science is sitting right there, if we can just get our act together.
- Mary Halton, Saturn moon a step closer to hosting life, in BBC News Science & Environment. 2018. https://www.bbc.com/news/science-environment-44630121
- Frank Postberg, Nozair Khawaja, Bernd Abel, Gael Choblet, Christopher R. Glein, Murthy S. Gudipati, Bryana L. Henderson, Hsiang-Wen Hsu, Sascha Kempf, Fabian Klenner, Georg Moragas-Klostermeyer, Brian Magee, Lenz Nölle, Mark Perry, René Reviol, Jürgen Schmidt, Ralf Srama, Ferdinand Stolz, Gabriel Tobie, Mario Trieloff, and J. Hunter Waite, Macromolecular organic compounds from the depths of Enceladus. Nature, 558 (7711):564-568, 2018/06/01 2018. https://doi.org/10.1038/s41586-018-0246-4
Ice Worlds, Ho!
Robert McGrath's Blog 