Is There Life on Earth?

Hello, friends!

Let’s imagine some space aliens are cruising by our Solar System.  They turn their scanners on our planet and see… what?

Among other things, they’d notice that Earth’s landmasses are partially covered with a strange, green-colored substance.  Of course, you and I know what that green substance is.  It’s chlorophyll.  But would those extraterrestrial observers, who have no prior knowledge of our planet, be able to figure that out?  Even if they did, would they realize what chlorophyll is used for?  Maybe.  Probably not, though.

Which brings me to my all-time favorite scientific paper: “A search for life on Earth from the Galileo spacecraft,” by Carl Sagan et al.  I love this paper in part because it’s so clearly and concisely written, with jargon kept to a minimum.  Sagan was, after all, a talented science communicator.  But I also love this paper because its conclusions are so shocking, so eye-opening.

In 1990, NASA’s Galileo spacecraft turned all its high-tech instruments toward Earth and detected… not much, actually.  Galileo did pick up radio broadcasts emanating from the planet’s surface.  Aside from that, though, Galileo’s data offered highly suggestive (but also highly circumstantial) evidence on Earthly life.  The lesson: finding life on other planets is hard.  Even using our very best equipment, it was hard for NASA to detect signs of life right here on Earth!

At least that’s what I got out of reading Sagan’s Galileo experiment paper.  And based on various commentaries I’ve read or heard about this paper, that seems to be the lesson other people got out of it too.  So I was surprised to hear Sagan himself, approximately seven-and-a-half minutes into this interview, saying the exact opposite.

We’ve flown by some sixty worlds.  We claim that we haven’t found life anywhere, and that that is a significant result.  That is, that we would have found life had it been there.  But this has never been calibrated.  We’ve never flown by the Earth with a modern interplanetary spacecraft, all instruments on, and detected life here.  And so Galileo, because of this peculiar gravity assist VEEGA trajectory, permits us to do that.  And as I’ll describe tomorrow, we find life five or six different ways, including intelligent life.  And this then means that the negative results that we find elsewhere are, in fact, significant.

I’ve been puzzled by this for a while now, but I think I’ve finally figured out why Sagan would say this.  It’s politics.

On the one hand, scientists need to understand the challenges they’ll face (including the limitations of their own equipment) in searching for life on other worlds.  That really is, I think, the purpose of the Galileo experiment paper.  On the other hand, it would not do to say on public television, to cantankerous taxpayers and the listening ears of Congress, that NASA spends millions of dollars on space probes that are not even capable of detecting life right here on Earth.

Space exploration is expensive.  And like all expensive types of research, sooner or later the researchers involved have to learn how to play politics.