It’s been almost 10 years since the whole kerfuffle, but a lot of people still don’t
seem to be over the fact that Pluto isn’t a planet.
Back in 2006, the International Astronomical Union -- the organization that makes all the
rules when it comes to astronomy -- officially defined what makes a planet a planet, and
Pluto didn’t qualify.
Now, a researcher has come up with a new definition of a planet -- one that can be used to classify
planets around other stars, too.
But Pluto still doesn’t make the cut.
Currently, the official definition of a planet means it has to meet three criteria.
A planet has to be orbiting the Sun;
have enough mass to be generally spherical;
and its gravitation has to be strong enough for it to have its orbital path basically
to itself, clear of any other major objects.
Anything that meets the first two conditions, but not the third, is called a dwarf planet.
So Pluto is a dwarf planet.
But you’ll notice that the official definition includes orbiting the Sun, which means we
can’t classify anything we detect in another star system as a planet.
But in the past 30 years, we’ve discovered nearly 2,000 worlds orbiting other stars.
And with the telescopes we have right now, it’s pretty much impossible to tell whether
any of them is round, so that criterion isn’t really useful either.
So last week, at the 47th meeting of the American Astronomical Society, astronomer Jean-Luc
Margot proposed a new definition -- and used it to classify almost all of the exoplanets
we’ve found so far.
The new definition is simple: a planet has to orbit at least one star -- or the remains
of one -- have a clear orbital path to itself, and have less than 13 times the mass of Jupiter.
That last one is to make sure we don’t accidentally classify any of the tiny, failed brown dwarf
stars as planets.
If you test this new definition of our solar system, it still works -- all the planets
and dwarf planets fall into the right categories, including dwarf planet Pluto.
And these are all things we can measure in other star systems, by calculating things
like the masses of the star and exoplanet.
Turns out that if you apply this definition to all the exoplanets that have enough data
… they all count as full-fledged planets.
Which kinda makes sense, because our telescopes aren’t powerful enough to detect something
as small as a dwarf planet orbiting another star anyway.
The new definition hasn’t been adopted by the IAU, so it isn’t official. But the group
will eventually have to come up with a way to classify exoplanets, and according to at
least one of the higher-ups at the American Astronomical Society, Margot’s definition
might be a good place to start.
Closer to home, knowing how to classify new worlds is coming in handy, too.
Because at that same meeting, a group of astronomers announced that they’d discovered a new possible
dwarf planet in our solar system.
For now it’s going by the catchy name of V774104, and it’s the farthest object ever
detected in the solar system.
As our technology improves, astronomers have been finding more and more worlds beyond Neptune’s
orbit, including what used to be the most distant dwarf planet-sized object we knew
of: 2012VP113, informally known as Biden.
I say dwarf planet sized, because, along with a few other likely-looking candidates, it
hasn’t been officially confirmed as a dwarf planet yet.
Sometime in October, the same team that analyzed Biden’s orbit was using the Subaru telescope
in Hawaii to scan the distant reaches of the solar system, when they noticed a moving dot
that had never been seen before.
That was the new possible dwarf planet, and it was incredibly far away.
To give you some perspective, when Biden is closest to the Sun, it’s about 12 billion
kilometers away -- or around 80 times the distance from Earth to the Sun.
But this newly-found rock is about 15 billion kilometers from the Sun -- around 103 times
as far from the Sun as we are.
We just don’t know where exactly it is in its orbit, because there hasn’t been enough
time to track it yet -- that will take about another year.
For all we know, at some point it might end up closer to the Sun than Biden does.
Still, now we know that we can spot worlds more than a hundred times farther from the
Sun than we are.
And, at the very least, we might have a new dwarf planet to study.
So, welcome to the neighborhood!
Thanks for watching this episode of SciShow Space News, and thanks especially to our patrons
on Patreon.
You guys are awesome.