Back in 2005, the Cassini spacecraft -- the first to study Saturn's rings and moons from orbit -- detected a plume of water vapor and ice shooting into space from fissures near the south pole of Saturn's sixth largest moon, Enceladus (pronounced en-SELL-ah-dus). About two years later, using its ultraviolet imaging spectrograph, Cassini observed four high-density water vapor jets against the background of the plume. One of the interesting things about the jets is that they were in the same positions as dust jets seen earlier. Another is that additional analyses revealed the presence of organic compounds in the plume.
But perhaps the most interesting development so far is that the density and temperature of the jets are consistent with a model that identifies the source of the plume as liquid water, venting from within Enceladus into space at supersonic speed through narrow channels on its surface.
It isn't known yet if the geysers on Enceladus are really produced by a subsurface aquifer, or via some other source. Cassin's next passby won't occur until August 2009. Meanwhile, planetary scientists working with the data in hand are keeping plenty busy.
And occasionally publishing.
Last week a letter in the journal Nature reported what you just read here in brief summary, which made the news wires and produced stories pointing out that if the presence of liquid water is confimed, then Enceladus would be the third body in our solar system known to have it. Earth and Jupiter's moon, Europa, are the other two.
The possibilities are exciting. Joshua Colwell, a Cassini team member and one of the authors of the letter (as well as "comet advisor" to the film Deep Impact), puts it this way:
"Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary phenomenon, then it gets really interesting."
Yes it does.
But if tidal heating is confirmed on Enceladus, there's a long way to go (literally) before anyone can determine if the process is replicated, let alone common, on other planets and moons. And then there is the matter of the "ingredients" whose presence, along with tidal heating or something close to it, astrobiologists believe are likely necessary to support life. Another planetary scientist, David Grinspoon (see Lonely Planets in last post), reminds us there are important questions to ask along the way as we think about habitable zones on worlds beyond our own:
"Life may be something that frequently, or even ubiquitously, happens inside planets. Perhaps biology can be a purely internal planetary phenomenon. If life begins underground, it makes the origin of life anywhere else in the universe less dependent on surface conditions. If all you need is some internal energy and some liquid water, then most planets have the right combo at some point in their history, since planets are born hot and wet . . . Can a planetary biosphere that loses its surface water retreat inward and persist, subterranean and homesick, but still alive? In some cases an 'inhospitable' surface may be only the thick, protective skin covering a thriving underground world.
Astrobiologists agree that there are three essential ingredients for habitability: (1) organic molecules (the building blocks), (2) liquid water (the medium), and (3) a source of energy (the spark of life). Based on our studies of comparative paleontology, how rare might such a combination be? . . .The belief that water is necessary and sufficient rests on the assumption that suitable energy sources will be common. How reasonable is this? . . . is tidal energy sufficient to drive a biosphere, or does life need a sun?"
These are good questions waiting for answers.
Meanwhile, I'm reminded that a large part of my interest in the intersection of science, religion, and extraterrestrial life came from questions of my own that waited -- and in some cases, are still waiting -- for answers. My journey, which has been and will continue to be a combination of curiosity, background, experience, and personal relationships, eventually brought me into contact with statements and writings on these subjects from several world religions. One in particular caught my attention years ago. It's from Gleanings from the Writings of Baha'u'llah, a volume of tablets (letters) written by Baha'u'llah (1817-1892), the founder of the Baha'i Faith:
"Thou hast, moreover, asked Me concerning the nature of the celestial spheres. To comprehend their nature, it would be necessary to inquire into the meaning of the allusions that have been made in the Books of old to the celestial spheres and the heavens, and to discover the character of their relationship to this physical world, and the influence which they exert upon it. Every heart is filled with wonder at so bewildering a theme, and every mind is perplexed by its mystery. God, alone, can fathom its import . . . Know thou that every fixed star hath its own planets, and every planet its own creatures, whose number no man can compute." [Gleanings, pp. 162-163, italics mine]
The impact of this passage, an English translation from the original Arabic (or perhaps Farsi), depends on who is reading it and where they are on their own journey, spiritual or otherwise. But the fact that the principal figure of the youngest recognized independent world religion, a prophet whom Baha'is believe is the most recent Messenger of God sent to raise the spirit and potential of humanity, wrote this in the 19th Century, fascinates me as a matter of scripture unique in religious history. It also frequently inspires me to investigate the subjects I write about.
As I look at the artist's conception of the geysers on Enceladus venting into space, I'm gratified by the fact that at least some human beings on planet Earth now know they exist.
The knowledge we as a species acquire is always incremental.
Like steps on a journey.
Next stop: tbd
Artist's conception of Enceladus jets and Cassini orbiting craft copywrited by Karl Kofoed. For editorial use only.
Banner bus photo created by Dorothy Delina Porter