SETI Re: "Lack of light makes Europan life unlikely" article

Larry Klaes (
Mon, 14 Jun 1999 10:33:12 -0400

>>>> <excerpt>From: "Bruce Moomaw" To: Subject: Re: "Lack of light makes Europan life unlikely" article Date: Sun, 13 Jun 1999 05:46:30 -0700 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.3155.0 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3155.0 Sender: Reply-To: <smaller> I've just seen the original article by Gaidos <underline>et</underline> <underline>al.</underline> in the June 4 <underline>Science</underline> ("Life in Ice-Covered Oceans"), and it seems to me to be very well thought-out. They aren't saying that microbial life based on geothermal energy sources is impossible on Europa; but they are saying that it must be even scarcer and more limited in variety than scientists had thought. Their reasoning is as follows: Virtually everyone is certain that the total amount of geothermal heat (from both tidal and radioactive sources) reaching each square kilometer of Europa's surface rocks must be, at absolute most, only about 1.5 times that of the Moon -- and only one-third that of Earth. This doesn't prove that Europa has no volcanic vents, but it does mean that they must be few and far-between. And it also makes it absolutely certain that Europa (like the Moon and Mars) doesn't have Earth crustal tectonics ("continental drift") -- which is the process that keeps dragging the oxidized minerals of Earth's crust back down into its mantle. Without this "crustal recycling", the minerals of Europa's mantle must have become highly depleted in oxygen by now. And that means that whatever volcanic vents it does have will be belching forth only hydrogen, methane and sulfides, and not carbon dioxide, sulfur dioxide or elemental sulfur -- which are by far the most important energy sources for chemosynthetic bacteria on Earth (including those found at our "black smokers"). As they say, the situation is by no means hopeless. It's possible that bacteria might have evolved that could pull oxygen out of the iron oxides in Europa's crustal rocks and react it with hydrogen, methane or hydrogen sulfide to gain metabolic energy. There are many types of Earth bacteria that react oxygen with hydrogen, methane or sulfides for that purpose, and "two groups" of bacteria that can extract oxygen from iron minerals (including some that react that oxygen with hydrogen). "These organisms may metabolically resemble those that could function in a Europan biogeochemical cycle." But it's a very weak source of metabolic energy. (By the way, they also think that the sulfate salts of magnesium and sodium that <underline>Galileo</underline> has apparently detected in Europa's surface ice were created when sulfides dissolved in the ice react with the traces of oxygen that are released when Jupiter's radiation or solar UV light breaks down some of that water ice.) Bruce Moomaw </smaller> </excerpt><<<<<<<<

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