Pluto Status Non-Update

Jun 25, 2015 | Uncategorized

PlutoMemeAbout once a day, someone here at the SIUE location for CosmoQuest gets an email, Facebook inquiry, or Tweet asking, “Is it true Pluto’s a planet again?”

No. Nope. Nah ah. Seriously dude, no.  …

We’re starting to run out of new ways to say the exact same thing. (I’m starting to respond, “Have you heard of Former Planet Ceres?”)

People are deeply passionate about Pluto’s loss of planet status and every good marketeer knows that speaking to your audience’s passions is a good way to get them to click. Whether you think Pluto should or should not be a planet, savvy people can make you click with a sensationalistic “Pluto Status is Now …” clink bait title. In some cases, they are trying to lure you in to educator you (Hi there! I do this!), and in some cases they are luring you in because Solent Green revenue is people. Anytime you follow any link on the Internet, ask yourself, “Who benefits (and in what way) when I click?” With NASA projects, the answer is you; you are the one who benefits. Sure, the web master for whatever page you went to will have your pageview stat to report and that will help justify their job and keeping the page up and running, but… Really, your brain is what should be getting the most reward.

At the end of the day, anyone can call any rocky/gasy/icy lump whatever they want. At the European Planetary Science Conference last year the Dawn team were calling Vesta a planet. This is fun, but just like your kid won’t become a princess if you call her one, Pluto will not become a planet just because some dude on the internet calls it one. This isn’t to say Pluto will never again be a planet, or that your kid will never be a princess. Both things can happen, but both require getting the right people in the same room and doing paperwork (one more than the other).

For Pluto’s status to be changed, the International Astronomical Union (IAU) would need to revise its definition of what it means to be a planet. You can read the definition in its gory details here.  Pluto fails the “has cleared the neighborhood around its orbit” requirement. While its ok for Jupiter (the dominant mass) to have Trojan Asteroids in its orbit, and for Neptune (the dominant mass) to have Pluto and other small icy blobs in its orbit… it is not okay for Pluto to have Neptune (and a myriad of other not significantly smaller icy blobs) in its orbit.

The IAU definition isn’t perfect. To call extrasolar planets “planets,” it requires us to assume that astronomers assume that by “the Sun” its authors actually meant “a star.” It also ignores issues of geology that many of us wish had found their way in. At some point, this definition is going to need to be rewritten.

For now though, isn’t it all kinds of awesome that we are learning new things everyday about former planet Ceres while we orbit it? And aren’t you watching your social media feeds for the newest “best image of Pluto ever” to appear? Isn’t it the data – those images – that we are waiting for that matter so much more than the definition of “planet”?


While we know things need rewritten, we also know it’s not happening at this year’s IAU in August. we will all have at least until 2018 to say, “No, Pluto is still not a planet.” Until then, can we all agree to just call it a world, and stop arguing?


  1. P.C. Haring

    As todays Dunce, please accept my apologies for being “that guy” when i forwarded you the clipping, i honestly thought I might have missed something coming out of official channels.

    Thank you for this post and thank you for setting me straight.

  2. Cameron lavergne

    Lol I love this:)

  3. StarStryder

    P.C., Consider yourself part of the inspiration 🙂

  4. Jim Meeker

    But..but…Nibiru is still a planet right? 😉 (j/k)

  5. Adrian Morgan

    Mike Brown’s standard rebuke to the argument that the IAU definition doesn’t account for extrasolar planets is that it doesn’t purport to. The title of the resolution is “Definition of a Planet in the Solar System“, which is tantamount to neutrality on the classification of any object outside the solar system.

  6. Empryean Trifle

    The “cleared the neighborhood around its orbit” definition was clearly an excuse to bump Pluto because (as Dr. Pamela points out) Jupiter was not “punished” for the Trojan asteroids. But the harm was done to the common person on the street who thinks of the solar system as sun, planets and leftover rubbish. The IAU – for that perspective – told the common folk that Pluto does not matter anymore. I know that was not their intent but certainly that was the consequence. And in an era when science funding is being threatened, it seems to me that the establishment should consider making astronomy more appealing to the general populace, not less, and remove the “Solar System stops here sign” at Neptune.

    (I don’t believe the solar system stops at Neptune but when common folk look at maps of the solar system (post-IAU) that’s where the solar system stops…)


Submit a Comment

Your email address will not be published. Required fields are marked *

Got Podcast?

A community podcast.

URL * RSS * iTunes

Astronomy Cast LogoTake a facts-based journey.

URL * RSS * iTunes * YouTube

Daily Space LogoSpace & astronomy news.

URL * RSS * iTunes * YouTube

Join the Crew!

URL * RSS * iTunes * YouTube

Un podcast en español de cosmología y astronomía.
Premiering in October!

Become a Patron!
CosmoQuest and all its programs exist thanks the generous donations of people like you! Become a patron & help plan for the future while getting exclusive content.