24 January 2011

Rhea’s “Breathable” Atmosphere

Posted by Ryan Anderson

A Cassini mosaic of Saturn's moon Rhea. NASA/JPL/Space Science Institute

Yesterday I came across this article, proclaiming to the world that “Saturn’s icy moon Rhea has an oxygen and carbon dioxide atmosphere that is very similar to Earth’s. Even better, the carbon dioxide suggests there’s life – and that possibly humans could breathe the air.”

Say what? Ok. There’s so much badness packed into those two lede sentences that I feel dirty just reprinting them here. First of all, an oxygen and carbon dioxide atmosphere would be very different from our own. Last I checked we lived on a planet with a 78% nitrogen atmosphere with a decent amount (21%) of oxygen and traces of CO2 (.04%).  So, no, an oxygen and CO2 atmosphere would be very different from ours.

Second, where do they get off claiming that CO2 suggests that there is life? In the Science paper that they link to, it says that the CO2 is probably from reactions between oxidants and organics or from outgassing of CO2 trapped in the ice. Maybe the mention of organics is what led to the idea that this is some sort of evidence for life? For the record, “organics” means “molecules with carbon in them”. It does not mean “aliens”. The Science paper makes no attempt to tie this discovery to life on Rhea because it doesn’t make any sense at all to do so.

And finally, since when does the presence of CO2 suggest that “possibly humans could breathe the air”? CO2 is harmful to humans, that’s why we exhale it. It is a waste product. That’s why in Apollo 13 they had to “make a square peg fit in a round hole” – their CO2 levels were getting dangerously high, so they had to get a new scrubber installed to get it out of the air. Even if Rhea’s atmosphere was Earth-like in composition, we still couldn’t breathe it! The Science paper doesn’t even talk about a pressure for the “atmosphere” on Rhea because it is so tenuous that pressure is essentially meaningless. Rhea’s atmosphere is so thin that it is considered “collisionless” – in other words, the molecules never hit each other. Needless to say, we cannot breathe a vacuum, and that’s essentially what we’re talking about on Rhea. It is really really not breathable.

It really annoys me to read irresponsible headlines and intros like the one highlighted here. The article goes on to parrot the Science paper’s abstract, and talk about irradiation and decomposition of organics, but the damage is already done. Most people will just read the headline and go away thinking that there’s a moon of Saturn out there with a breathable atmosphere. An if they do read the article, those intro sentences will be the most memorable, so the take-home message will be that there is a breathable atmosphere and maybe life on Rhea. As cool as that would be, it’s not what the Science paper was about at all! The paper was about the discovery of a tenuous atmosphere and the possible ways that atmosphere could be formed. Is it as exciting as a habitable, inhabited moon: No! But it’s awesome that we are still learning new things about the moons in our solar system, and it does a disservice to readers and to the scientists who did the work to portray it as something it’s not.
This post was chosen as an Editor's Selection for ResearchBlogging.org
Teolis BD, Jones GH, Miles PF, Tokar RL, Magee BA, Waite JH, Roussos E, Young DT, Crary FJ, Coates AJ, Johnson RE, Tseng WL, & Baragiola RA (2010). Cassini finds an oxygen-carbon dioxide atmosphere at Saturn’s icy moon Rhea. Science (New York, N.Y.), 330 (6012), 1813-5 PMID: 21109635