Putting Exoplanets into Perspective
With the first science data downlink from the Kepler Mission supposed to be happening just these days, I thought I’d take a minute to put all the apparently uninteresting things we know about exoplanets into perspective.
According to The Extrasolar Planets Encyclopaedia, we are currently aware of 353 exoplanets and most of them are lonely giants outside their stars’ habitable zones. Close to 90% of the discovered planet systems contain a single planet and about two thirds of the rest contain only two. We currently know of only two systems (Gliese 581 and Mu Arae) containing four planets and only one (55 Cancri) containing five.
If we compare that to the eight planets and several other recognized dwarf planets from our own solar system, our current knowledge paints a rather boring picture of the galaxy through numbers alone. And if you also add the other things we know about exoplanets, such as size, likely composition and distance from their host star, things look even worse.
But the problem isn’t what’s out there, but what we can see. I wondered if anybody tried to figure out how much would an observer located on a habitable planet from one of these boring systems we have discovered and using our current technology be able to make out from our own solar system and I found exactly what I thought I would: “The only object in the Solar System available for detection by a team of planet hunters at the distance of the 55 Cancri system (using early 21st century technology) would be Jupiter, placidly circling our Sun at 5.2 AU.”
Granted that 55 Cancri is by far one of the least boring systems we have discovered so far, but bear with me. What matters is the distance, and that’s of only about 13 parsecs. If we could only detect Jupiter from 55 Cancri but detected five of its planets from here, what else could be there? How many Earths could be around all those lonely gas giants we have discovered? In fact, how many of anything could be anywhere, seeing as, even with our primitive technology, we could detect a planet roughly 6600 parsecs away, close to the center of the galaxy?
No matter what you think about what we already see, consider what we can’t (yet) see…
