Juno

3 Juno feels like a classic "old school" discovery. It was the third asteroid ever found (in 1804), and for a few decades, it was actually considered the eleventh planet from the Sun.

The "Stony" Giant

Juno is one of the largest members of the S-type (stony) asteroids. While Ceres is icy and Vesta is volcanic, Juno is made mostly of silicate rocks mixed with iron and nickel.

• Massive but Small: It holds about 1% of the total mass of the entire asteroid belt.

• The "Maryland" Size: It is about 247 km (154 miles) in diameter—roughly the size of the state of Maryland.

A Wildly "Stretched" Orbit

Juno is famous for having a very eccentric (oval-shaped) orbit. It doesn't stay in a nice, neat circle.

• The Great Swing: Because its orbit is so stretched out, its distance from the Sun varies wildly. At its closest, it is closer to the Sun than Vesta; at its furthest, it travels even further out than Ceres.

• High-Speed Crashes: Because it crosses through different parts of the belt at an angle, it is prone to high-velocity collisions, which has left it with a very rugged surface.

The Giant Scar

In the late 1990s and early 2000s, astronomers used "adaptive optics" (technology that cancels out the blur of Earth’s atmosphere) to get a clear look at Juno.

• They discovered a massive impact crater about 100 km (62 miles) wide.

• This crater is geologically "young," and scientists believe it was caused by a violent collision that nearly shattered the asteroid. This impact likely created the "Juno family"—a group of hundreds of smaller rocks that travel in the same path as Juno.

Why it was Found So Early

You might wonder why Juno (the 10th or 11th largest) was found before much bigger asteroids like Hygiea.

1. It's Reflective: Juno has a high albedo, meaning it reflects a lot of sunlight. Its surface is much brighter than the dark, charcoal-like surface of Hygiea.

2. The "Spotlight" Effect: Because of its eccentric orbit, it occasionally gets much closer to Earth than other asteroids, making it appear exceptionally bright in the night sky.

Quick Facts

• Name: Named after the Roman goddess Juno, the queen of the gods and wife of Jupiter.

• Rotation: It spins once every 7.2 hours.

• Temperature: Surprisingly, when it's at its closest point to the Sun, its surface can reach 28°C (82°F)—basically a nice room temperature!