Hey, Sky Fans! Here we are midweek again. I’ve had this, and a couple of related posts, on my calendar for a while now. With all the scratch-outs and changes I’ve made with other things coming up, I’ve been sort of itching to get this one off the list. Anyone else keep an editorial calendar for their blog? I’m sure you can empathize.
In June, NASA announced some new findings in its hunt for planets around other stars. This was a group of over 200 new possible, candidate, exoplanets; some of them Earth-sized. People always seem to grab me to talk about this. So, if you asked and you’re reading, thanks; this one’s for you.
Remember that old Schoolhouse Rock cartoon about “Interplanet Janet,” that galaxy girl? Every time there’s news about exoplanets, I think of that song.
The prefix exo- comes from Greek, meaning outside, and planet from the Greek word for wanderer. So, an exoplanet is an “outside wanderer.” I love the way that sounds; an outside wanderer. For this I think it’s sufficient to say a planet is something directly orbiting a star (like Mars, but not like Mars’s moon, Phobos).
An exoplanet is a planet in another star system.
A simple word, but a fascinating topic. As time goes on, scientists discover more and more of them. Some are found with ground-based observatories like TRAPPIST or from orbiting ones, like Kepler. The news is just about the existence of a planet and sometimes what it’s made of. It’s not about whether those planets are habitable. We’re not talking about life, not yet.
I have to confess I’m not a huge fan of the word exoplanet. This, again, has nothing to do with all the struggle over the word planet itself. I’m emotional about plenty, ask my wife and kids, but not whether Pluto is a planet. I just want consistency. Truth be told, I actually love the fact that the science community is having a hard time settling on a definition of what a planet is.
It’s the scientific method, alive and working right before our eyes. First, we knew there were six planets. Then along came Uranus, then Neptune and then Pluto, and we knew it was nine. We, as scientists, acknowledged the new data, and changed to accommodate it. We didn’t change science to accommodate us. When far-flung Eris was found, we needed to change again. The difficulty with “planet” is a metaphor for the best of humanity. We have the ability to change when new information becomes available. We’ll get there. We’ll get it right.
As far as exoplanets go, deciding to call all of those planets exoplanets means they’re separate and different from these planets here. The word seems to cordon off and segregate them.
There’s not a lot of difference between the Sun’s planets and Gleise 538’s. Sure, the details, the sizes are different, the make-up, the orbital distances are different, but to say those things are in a category other than simply “planet” kind of feels needlessly geocentric, and by extension, anthrocentric to me. When explorers from Earth set foot on the planet at Proxima Centauri, is the planet right under their feet an exoplanet? That doesn’t make a lot of sense.
Am I just complaining? Is exoplanet just a convenient one-word shorthand? I admit, maybe, and honestly, what other frame of comparison do we have? Still, I prefer “planets at other stars” or “planets in other star systems,” which allows for all kinds of systems, ones with multiple stars, not just one, like ours, or even “extrasolar planets.”
The search for exoplanets is a relatively new corner of astronomy, but they’re everywhere, and diversity we’re finding in other systems is a lot like how diverse life here on Earth is. We’ve found Mini-Neptunes (gassy, icy ones up to about 10 Earth masses), and Super-Earths (rocky, cape-wearing ones up to about 13 Earth masses; Uranus’s mass). Hot Jupiters (dibs on the band name), are incredibly close to their parent star, but have somehow managed to not get their atmospheres cooked off. They’ve all changed our thinking of how planetary systems form, including our own. Like, wow.
What do you think? Exoplanet? Planet? Good words? Bad words?
Have a great day, and clear skies, everyone!