Pluto (bottom image) with various other non-planets.

Since everyone has their knickers in a knot over Pluto not being a planet, here are various different celestial objects who are also not classified as planets. You’ll notice, just because it’s not called a “planet” doesn’t mean it isn’t cool.

Let us be reminded, there is no heirarchy of celestial bodies. It wasn’t necessarily “demoted” from planethood, it was simply reclassified as something else. There’s literally no reason to be emotionally attatched to the idea of Pluto’s planetary classifaction.

But what “classifies” a planet anyway?

According to the International Astronomical Union, there are 3 basic requirements that it must meet:
1) It orbits the sun
2) Sufficient mass to assume a “hydrostatic equilibrium” (meaning it’s mostly shaped like a globe)
3) Has “cleared its neighborhood” in its orbit.

The third one is where Pluto fails. What they mean by “clearing the neighborhood” is that the orbital path is good and clear. Every planet will still collide with something now and then but their orbital paths are not occupied by anything that is similar to the size of the planet itself. They’re not really in danger of running into much of anything except maybe an asteroid or a comet that might enter their path and collide.

In addition, here is an image showcasing the dwarf planets of the solar system. Pluto isn’t alone in it’s classification.

So don’t be sad over Pluto not being a planet, you’re just being melodramatic. Wipe your tears away with some scientific literacy. ;)

This is Neptune’s moon, Triton, taken in 1989 by Voyager 2 - the only spacecraft ever to pass it. Triton has fascinating terrain, a thin atmosphere & even evidence for ice volcanoes on this world of peculiar orbit and spin. Ironically, Voyager 2 also confirmed the existence of complete thin rings around Neptune.


Planet Neptune and its largest Moon Triton

Neptune is the outer most planet in our solar system; it orbits the sun with a radius of 2,798,000,000 miles. Neptune is the 4th largest planet by diameter, 3rd largest planet by mass and densest of all the gas giants. Neptune has a great dark spot similar to that of Jupiter. Both spots are Anticyclonic storms, meaning the winds around the storm flow opposite to the direction dictated by the Coriolis effect. However, unlike Jupiter’s spots, Neptune’s dark spots appear to only last a few years (as opposed to a few hundred) and have relatively calm and cloudless centers. Observations have shown that Neptune spends about the same amount of time with and without its largest dark spot. The storms activity seems to cyclical.

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Neptune has 14 moons, Triton is the largest and composes more than 99.5% of all the mass that orbits the planet. Triton is roughly the same size as our moon: (Neptune’s Triton vs Earth’s moon)

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Triton has a retrograde orbit around Neptune, meaning that it orbits in the opposite of the planet’s rotation.

These images were taken by the Voyager 2 space probe and the Hubble space telescope, with the exception of the last image being an artists impression of Neptune seen from its moon Triton.

Credit: NASA/Hubble/JPL/wikipedia