why i don’t care about kepler 22b: confessions of a former astronomer

If you were near a news source today, you probably heard that NASA announced the latest and greatest lump of matter to join the catalog of extrasolar planets.

Welcome, Kepler 22b.  I will celebrate your discovery with a hearty yawn.

I hear the outcry already.  What?! you screech, how can you not be excited about this?  It’s a planet that has a chance of carrying life!  You know, aliens!  Plus it’s IN SPACE! and if you know anything at all, it’s that SPACE IS AWESOME!

Yes, fine, go have a party, IN SPACE! if you like.  I stand by my yawn.  Here’s three reasons why I could care less (plus one reason that I actually am excited).

1. Kepler is finding hundreds of extrasolar planets, and it’s going to keep on finding hundreds more until the project’s funding runs out.  Kepler 22b is just the poster child for NASA’s announcement of more than 1,000 new planet candidates.*  If they didn’t have Kepler 22b, they’d have some other lump of matter to tell us about, which would no doubt be portrayed as equally exciting.  In September, it was Kepler 16b, a “real life Tatooine” (which is, amusingly, expected to be absolutely nothing like Tatooine, except for the two suns bit).

But this one’s cooler! declare the protesters.  Kepler 22b is in the “Goldilocks zone,” so its distance from its sun is “just right” for life.  Ah, but what you may not know is that …

2. The Goldilocks zone** (or less whimsically, the habitable zone) is arbitrarily defined, and it tells us very little about whether a planet can actually support life.  The habitable zone is defined as a belt around a star where water could exist in liquid form on the surface of an Earth-like planet.  Let’s dissect this.

First of all, the definition assumes that a planet can only support life if it has liquid water.  This is possibly true, but it’s not something we can be sure about. Biologists argue about these sorts of things all the time.  Remember arsenic life?  Just one (non)-example of the debates that happen about what exotic life really needs to survive.

Second of all, the definition assumes we’re only interested in surface life.  Anyone familiar with science fiction will tell you it stands to reason that surface life isn’t the only option (and exobiology may be the one field where science fiction is a permissible form of analysis).

Third of all, and most importantly in my opinion, the definition assumes that we’re talking about an Earth-like planet — a planet with Earth’s atmospheric conditions and basic geology.  There’s no guarantee that habitable-zone exoplanets like Kepler 22b are rocky like Earth, and there’s no guarantee that they’re not covered in volcanoes or surrounded by a toxic atmosphere (often these two come together).

Venus isn’t too far outside the habitable zone, so it stands to reason that it’s just a bit too hot for life, right, and could even harbor some really strange heat-loving critters?  Using the current definition of habitable zones, this is a totally valid way to look at it.

Of course, we know that it’s actually hot enough to melt lead on the surface.  Venus is not a nice place for life, but extraterrestrial astronomers would have no way to figure that out if they used the same technology as us.  Perhaps folks on Kepler 22b are giddy at the prospect of life on Venus.

3.We have no clear way to figure out whether Kepler 22b — or any other extrasolar planet — actually harbors life.  Because Kepler uses planetary transits to discover planets (it measures a dark spot crossing the disk of a star at regular intervals, effectively a mini-eclipse), there’s the off chance that someone with a very high-quality spectrometer could follow-up and guess at Kepler 22b’s atmospheric composition (this has been done before, at least for extrasolar gas giants).  But that’d be about the best we could do.

We could, I suppose, follow Drake and Sagan’s lead and beam out a message towards Kepler 22b, but it’d be 1,200 years before we got any reply.  And, of course, not hearing back doesn’t mean much.  Any 22b-ians out there may not be listening, may not understand, may not care, or may not exist at all.  We’re about at the limit of what we can hope to find out about Kepler 22b without a significant leap forward in technology.

Enough cynicism for now (it’s Monday, I can’t help it).  Why am I actually excited about Kepler 22b?

1. Discoveries like Kepler 22b get everyone excited about astronomy, and open up opportunities to teach folks (especially kids) about science.  This thrills me as a science writer, of course, but in addition to my past life as an astronomer, I also have a past life as an astronomy educator, at  Morehead Planetarium, so space topics have a special place in my heart.

Announcements like Kepler 22b would always get folks asking questions and open up great opportunities to challenge kids with all sorts of questions, from why we couldn’t survive on the moon*** to how solar systems form.  I will cheer anything that gets people to pay attention to science for a day, even if it’s something that otherwise irks me.

So hooray for science, even if I just burst your Kepler 22b bubble.

*This thousand-odd crop of planets is the real reason to get excited about NASA’s announcement.  Kepler 22b is the glitter and flash, but this is where the science happens.  It wasn’t too long ago that folks trying to understand how solar systems form had exactly one data point (our own eight nine who really cares? planets).  In the last few decades, a handful of exoplanets trickled in, but now that Kepler’s operational, there are literally thousands of data points with which to refine theories.  It’s a big deal.  My undergraduate thesis was effectively doing “by hand” what Kepler does, and believe me, automating the process is a godsend for folks who study planetary formation.  There’s a reason I left astronomy, and the tedium of my thesis work is pretty much it.

**A note on sources: I find Wikipedia to be pretty reliable on science matters that I’m qualified to comment on.  Even better, with a big story like this, there are going to be good fairies watching the relevant pages I linked here to make sure that they stay accurate (I may just be one of the fairies).  Plus, NASA’s Kepler pages are understandably running quite slowly tonight, so I didn’t want to dig through their stuff too much.  I linked TV Tropes and Wookipedia early on just to keep you on your toes (and because I secretly hope to destroy your productivity for hours).

***Best (or worst) answer I ever got to this question: “because there are no grocery stores on the moon, we couldn’t get food!”  Right idea … just wrong, in a hilarious but depressing way.