The Greatest Asteroid Encounters of All Time!

All-Time Greatest Asteroid Encounters

Illustration: Space.com; NASA

Asteroids are important building blocks of our solar system. When spacecraft study these small worlds, we learn more about how our neighborhood was formed — moons, planets and, of course, our own planet Earth. A flurry of spacecraft visited asteroids in recent decades. Here are some of the more notable of those spacecraft and the asteroids they studied.

FIRST STOP: Galileo at Gaspra and Ida!

Galileo, First to an Asteroid

NASA/JPL

NASA's Galileo spacecraft was the first craft to ever visit an asteroid; in fact, this probe flew by two. The mission launched Oct. 18, 1989, from space shuttle Atlantis and arrived at Jupiter on Dec. 7, 1995, where Galileo spent eight years studying the largest planet in our solar system. But before the probe reached Jupiter, it made several pit stops, including to the asteroids Gaspra and Ida.

NEXT: Asteroid Gaspra

Asteroid Gaspra

NASA/JPL

Humanity's first encounter with an asteroid occurred on Oct. 29, 1991, when Galileo flew by the asteroid Gaspra. During the historic encounter, Galileo approached within 997 miles (1,604 kilometers) of Gaspra (an S-type or siliceous asteroid) and revealed that the space rock had mysterious flat areas that may be due to impacts. They may also be scars from when Gaspra broke off from its parent asteroid.

NEXT: Hello, Ida!

Ida and Dactyl

NASA/JPL/USGS

Then, on Aug. 28, 1993, Galileo made history again, this time by flying by the first asteroid known to have a moon: Ida. The probe's photos revealed that this asteroid and its moon, Dactyl, are truly strange objects; both experience space weathering that has caused their surfaces to turn red over time. After Galileo's asteroid adventures, it went on to Jupiter, but NASA hadn't finished with space rocks.

NEXT: NEAR-Shoemaker to Eros

NEAR-Shoemaker

NASA

NASA's Near Earth Asteroid Rendezvous-Shoemaker (which was partially named after the planetary scientist Eugene Shoemaker) was designed to study the near-Earth asteroid 433 Eros for about a year. The probe launched on Feb. 17, 1996, and made a landing on the asteroid on Feb. 12, 2001, where the mission ended. (NEAR-Shoemaker was not designed for a landing, so the successful touchdown provided bonus science.) Before going to Eros, this spacecraft made a flyby of the asteroid 253 Mathilde.

NEXT: Asteroids Eros and Mathilde

Eros and Mathilde

NASA/JPL/JHUAPL

This picture of Mathilde (left) and Eros shows the two asteroids at the same scale as NEAR-Shoemaker imaged them, although Mathilde's brightness was exaggerated in this picture to make the asteroid easier to view. The two space rocks were both photographed from a distance of about 1,116 miles (1,800 km) on June 27, 1997, and Feb. 12, 2000, respectively. Mathilde is 35 miles (56 km) across, and Eros is 21 miles (33 km) across at its greatest extent.

NEXT: Meet Mathilde

Meet Mathilde

NASA

The asteroid Mathilde is located in the asteroid belt, between Mars and Jupiter, and has an orbital period of about 4.3 years. The asteroid has a slow rotation rate (17.4 days) and is made up of carbon-rich rock, making the object a C-type asteroid. NASA says the asteroid changed little since the solar system was formed 4.5 billion years ago.

NEXT: Asteroid Eros

Eros, Asteroid of Love

NASA

NEAR flew by Eros on Dec. 23, 1998, and performed an orbital insertion on Feb. 14, 2000, orbiting for almost exactly a year, until its 2001 touchdown on Eros' surface. NEAR's views of Eros revealed it to be an S-type (siliceous) asteroid, meaning it consists mainly of stony materials and nickel iron. It is a part of the Amor groups of near-Earth asteroids (NEAs), which cross Mars' orbit. NASA says that NEAs like Eros are probably dead comets or the leftovers of collisions of small bodies in the asteroid belt.

NEXT: Cassini's Asteroid Flyby

Cassini

NASA/JPL

The NASA and European Space Agency (ESA) Cassini mission lifted off from Earth in 1997 for an epic rendezvous with Saturn. Cassini orbited the planet and its moons between 2004 and 2017, making many remarkable discoveries — from learning that the icy moon Enceladus has plumes to imaging incredible methane and ethane lakes on the surface of Titan. (The spacecraft also released an ESA probe called Huygens, which landed on Titan and worked for a few hours there.) While the mission is famous for its discoveries at Saturn, it also contributed to asteroid science by flying by asteroid Masursky.

NEXT: Asteroid Masursky

Asteroid Masursky

NASA/JPL/Cassini Imaging Team

This picture is of asteroid Masursky on Jan. 23, 2000, taken during Cassini's asteroid belt flyby. Asteroid 2685 Masursky is about 6.8 miles (11 km) in diameter and is classified as an S-type asteroid. When Cassini flew by the asteroid from about 4 lunar distances (1 million miles, or 1.6 million km), the probe looked at the asteroid's composition and made an estimate of its diameter.

NEXT: Deep Space 1 in … Deep Space

Deep Space 1

NASA/JPL

Deep Space 1 was originally intended to test out ion engines, a form of spacecraft propulsion, but the mission was extended to fly by the asteroid 9969 Braille and Comet Borrelly. The spacecraft launched on Oct. 24, 1998, and flew by Braille on July 29, 1999. Its star tracker failed en route to Borrelly, but engineers still managed to keep on the trajectory and flew by the comet successfully in September 2001.

NEXT: Asteroid Braille

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