Aten asteroids are a group of Near-Earth Asteroids that are Earth-crossing. Their semi-major axis (average distance from the Sun) is less than 1 Astronomical Unit (AU), meaning they spend the majority of their time closer to the Sun than Earth does, but their orbit stretches out far enough to intersect Earth's path.
Because they cross Earth's orbit and have similar orbital periods, certain Atens offer incredibly low Delta-V requirements for rendezvous missions, making them ideal early targets for automated mining rigs.
The fact that their orbits cross Earth's makes Atens inherently dangerous. Many Potentially Hazardous Asteroids (PHAs) belong to this class. Mining these could double as planetary defense operations.
Like Atiras, they spend a lot of time in the daytime sky. Ground-based telescopes typically only catch them when they are approaching their furthest point from the Sun (aphelion) near Earth's orbit.
Atens make up roughly 8% of the known Near-Earth Asteroid population. Here are some of the most famous and economically interesting targets:
| Designation | Type | Diameter (Est.) | Significance |
|---|---|---|---|
| 2062 Aten | S-Type | ~0.9 km | The namesake of the class, discovered in 1976. It proved that Earth-crossing asteroids with orbits smaller than Earth's could exist. |
| 3554 Amun | M-Type | ~2.5 km | A massive metallic asteroid. It is highly theorized to be an exposed iron-nickel core of a shattered planetesimal, containing trillions of dollars in platinum-group metals. |
| 99942 Apophis | S-Type | ~0.37 km | Infamous for its incredibly close approach to Earth scheduled for Friday, April 13, 2029. Gravitational interactions with Earth during this pass will actually alter its orbit, turning it from an Aten into an Apollo class! |