Irk is the homeworld of the bloodthirsty Irken race, and capital planet of the Irken Empire. The view of Irk from space is unknown, but the capital city could be seen when Invader Zim was rampaging through it in the episode "The Nightmare Begins" when he mistook Irk for an enemy planet. A screen showing the Irken Empire in the same episode depicted a large, dark blue planet with thin red rings in the middle, identified as Irk. This coloring was probably for easier identification for the Irken military audience, and Irk is believed to be red, magenta or pink in color.
Irk's climate, geography, flora, fauna and topgraphy are unknown, though it is theorized that with the dominance of the planet by the Irken species, the entire planet has become covered in sprawling cities and metropolises or even completely converted into a 100% mechanical/Industrial world. There is even civilization deep under Irk's surface. The cities are largely purple/magenta in color, hinting that it is an Irken custom for things to be shades of purple or magenta. The sky on Irk is light pink in color, like on Foodcourtia and Conventia. The idea of rain puzzled Zim when he first saw it on Earth, indicating that it doesn't rain on Irk. It is also suggested in the episode "Walk of Doom" that Irk's sun does not emit ultraviolet rays, or that Irk's ozone layer is unusually thick.
The only known organisms of the planet are the Irkens themselves and the Control Brains, who dominate the planet in sprawling cities and metropolises. However, if Irk is or was anything like Earth, it will have other species native to it. Zim has made references to other species when speaking in metaphors, but it is not known if any of these creatures are native to his planet. Also, Irken Smeets are born presumably in a large "birthing facility" (known to be called the "Hatcheries") beneath the surface of Irk. Very few Irkens are taller than five feet, except the Tallest and a few exceptions.
The idea of Irk being distant from its star would suggest the planet has a very low temperature. However, this does not increase the likelihood of water, as water requires hydrogen and oxygen to be present on the planet, which Irk may be devoid of. However, this is again highly unlikely, since hydrogen is the single most common element in the universe, with oxygen being similarly common. Additionally, Irk's sun is presumed to have a very thick ozone layer, meaning that Irk must have oxygen in some form. Hence, why Zim can breathe while on Earth.
It has been confirmed that Irk has an atmosphere, since it has clouds and a pink sky, but the make-up of its air is unknown. It is presumed that it has contains a breathable gas also found on Earth, as Zim does not need his space suit to breathe on Earth. If this is true, it is conceivable that, conversely, humans can breathe unassisted on Irk.
Distance appears to be relative, changing for comic reasons quite regularly. Assuming that the conquered planet Conventia is anywhere near Irk, it takes about six months or less (depending on the speed of the ship) to journey from the Irken homeworld to Earth.
Of course, that being said, it may also be possible that Irken ships cannot jump to hyperspace without a specific destination having been set beforehand, and as such, it would take much longer to reach a planet that one did not know the exact location of. Further evidence of this claim being the relatively short time it took Zim to reach Hobo 13 from Earth, as his ship was shown jumping to lightspeed.
Multiple galaxies near Irk and far from Earth were seen on the holographic map in The Nightmare Begins, suggesting that Irk is not located in the Milky Way. This means Irk has to be millions of light years away from Earth. Another factor to note is Irkens being unfamiliar with races such as the Abductors and the Nhar-Gh'ok. This is likely due to these races being from Earth's galactic vicinity and not Irk's.
As seen on the holographic map in The Nightmare Begins, Irk is surrounded by rings, meaning Irk is likely high in gravity. However, unlike the ringed giants in this solar system (such as Saturn and Jupiter), Irk is a terrestrial planet like Earth and Mars rather than a gas giant. This is probably what gives Irkens their agility on Earth, similar to the enhanced abilities that Superman gains when separated from his home planet, Krypton. This might also be the reason why it is rare for an Irken to grow tall while on Irk, and why they now idolize tall beings.
View from SpaceEdit
As mentioned above, Irk's view from space is possibly unknown. However, in The Nightmare Begins, Irk is said to be the dark blue planet with thin red rings in the center of the holographic map. We can assume that this is a color-coded representation of the universe, rather than its natural color, as all the other planets are a white color.