In 2004, these twin Mars Exploration Rovers landed on opposite sides of the planet and explored it for more than five years.

Among the major finds is evidence that the surface of Mars once had liquid water.

NASA's Viking 1 was the first man-made object that soft-landed on Mars in July 1976.

The Viking 1 lander is also the longest-running Mars surface mission, and sent the first color pictures back from the surface of Mars,

NASA's best space mission was the Apollo, taking humans along. The Apollo trips brought moonrocks home. The astronauts gathered data that helped us learn the likely age of the moon and what it's made of.

Pioneer 10 and Pioneer 11 were launched in 1972 and 1973. They were the first spacecraft to visit Jupiter and Saturn in a one-way voyage.

• Pioneer 10 traveled through the solar system's asteroid belt between Mars and Jupiter.
• A year-and-a-half after it's laun...

NASA/ESA spacecraft was launched in 1997 and reached Saturn in 2004. Since then its been orbiting around the planet and taking photos of the planets' rings, moons, and weather.

The Huygens and Cassini probes separated. Huygens made a trip to the moon Titan and landed on solid ground in 200...

The photos of the Hubble Space Telescope is recognized around the world. It has radically changed science.

NASA developed a tool that could reveal starts, planets, nebulae, and galaxies in detail.

The Spitzer Space Telescope observes the heavens through infrared light.

• It takes stunning photos of galaxies, nebulae, and stars.
• In 2005, Spitzer detected light from extrasolar planets.

The earth's atmosphere blocks out most X-rays and prevents astronomers from viewing the universe in X-ray light - a high-energy, short-wavelength light.

• In 1999, the Chandra X-ray Observatory was sent up to space. It scans the skies in X-ray light and can see X-ray sources 100 times ...