Red Eye

The "Red Eye" was a meteor-like device that threatened Beach City, and possibly the whole Earth in "Laser Light Cannon". In "Marble Madness", it is revealed that it was a device built, sent, and used by the Gem Homeworld, possibly by Peridot, to detect Earth-resident Gem life-forms.

Appearance
The Red Eye, as its name entails, is a massive, red-orange, eye-like device. As such, it is spherical in shape. The Red Eye has a light orange hexagonal iris with a red-orange, aperture-like "pupil" of the same shape. Its body (or sclera) is orange, and is covered by a cream colored segmented covering (or eyelid) that can close and open to protect the eye. It seems to have the same triangular patterns that are shown on the floor of the Gem Warship, meaning that it belongs to the Gem Homeworld. This is confirmed when Peridot states that its purpose was to scout out other Gems on Earth. It seems to be constantly emitting light, or in some cases glowing.

Abilities
Because of its planetary size, it has the ability to defy Earth's gravitational pull, freely levitating. It is also highly durable, having a very hard body which provides great defense against physical attackers, as seen when it withstood multiple attacks from Amethyst and Garnet without taking any sort of damage, only taking major damage from Rose Quartz's laser light cannon. The aperture-like pupil/iris can open up and create a powerful vacuum.

"Laser Light Cannon"
It threatens Beach City with its potential of colliding with the Earth, which would likely kill all of Beach City's residents. Garnet, Amethyst, and Pearl try multiple times to stop it by throwing Amethyst at it, but find no success in doing so. It is implied that it cannot be destroyed without Rose Quartz's Laser Light Cannon, which Steven finds. He and the Gems use it to destroy the Red Eye, causing it to explode violently.

"Keep Beach City Weird"
Fragments of the Red Eye are seen on the boardwalk.

"Marble Madness"
Peridot revealed that the Red Eye was a scout sent to Earth by Gems, presumably to ascertain as to whether or not there were Gems present on Earth.

Trivia

 * The Red Eye functions very similarly to the moon in The Legend of Zelda: Majora's Mask, where the moon is crashing down to the planet and there is a limited time to stop it.
 * The Red Eye is similar to Ramiel or Leliel, Angels from Neon Genesis Evangelion. It is spherical like Leliel and geometric like Ramiel, and shares both Angels' trait of being a large, slowly-floating object.
 * Ian Jones-Quartey, creative director of the show, stated on his blog that the Red Eye is not a Gem.
 * The Red Eye's "iris" resembles a Rupee from The Legend of Zelda series.
 * Steven has mistaken its name for Pink Eye (or conjunctivitis) which led to him believing that everyone would get infected with it.
 * If one looks at the designs, its actually orange, but the scenes use red tinting to make the red eye red.

Official Artwork
Ojo Rojo