George's Cosmic Treasure Hunt (9 page)

 

NASA's Mars landers,
Viking 1
and
Viking 2
, which touched down on the red planet in 1976, gave us our first pictures from the surface of the planet, which had intrigued people on Earth for millennia. The
Viking
landers showed the reddish-brown plains scattered with rocks, the pink sky of Mars, and even frost on the ground in winter. Unfortunately, it is very difficult to land on Mars, and several probes sent to the red planet have crashed onto the surface.

Later missions to Mars sent the two rovers,
Spirit
and
Opportunity
. Designed to drive around for at least three months, they lasted for far longer and also, like other spacecraft sent to Mars, found evidence that Mars had been shaped by the presence of water. In 2007, NASA sent the Phoenix Mars Mission. Phoenix could not drive around Mars, but it had a robotic arm to dig into the soil and collect samples. It had an onboard laboratory to examine the soil and work out what it contains. Mars also has three operational orbiters around it—the
Mars Odyssey, Mars Express,
and
Mars Reconnaissance Orbiter
, showing us in detail the surface features.

Robotic space probes have also shown us the hellish world that lies beneath the thick atmosphere of Venus. It was once thought that dense tropical forests might lie under the Venusian clouds, but space probes have revealed the high temperatures, heavy carbon dioxide atmosphere, and dark brown clouds of sulfuric acid. In 1990 NASA's
Magellan
entered orbit around Venus. Using radar to penetrate the atmosphere,
Magellan
mapped the surface of Venus and found 167 volcanoes more than seventy miles wide! ESA's
Venus Express
has been in orbit around Venus since 2006. This mission is studying the atmosphere of Venus and trying to find out how Earth and Venus developed in such different ways. Several landers have returned information from the surface of Venus, a tremendous achievement given the challenges of landing on this most hostile of planets.

Robotic space probes have braved the scorched world of Mercury, a planet even closer to the Sun than Venus.
Mariner 10
, which flew by Mercury in 1974 and again in 1975, showed us that this bare little planet looks very similar to our Moon. It is a gray, dead planet with very little atmosphere. In 2008 the MESSENGER mission returned a space probe to Mercury and sent back the first new pictures of the Sun's nearest planet in thirty years.

Flying close to the Sun presents huge challenges for a robotic spacecraft, but probes sent to the Sun—
Helios 1, Helios 2, SOHO, TRACE, RHESSI
, and others—have sent back information that helped scientists to develop a far better understanding of the star at the very center of our Solar System.

Farther away in the Solar System is Jupiter, first seen in detail when the probe
Pioneer 10
flew by in 1973. Pictures captured by
Pioneer 10
also showed the Great Red Spot in great detail, a feature seen through
telescopes from Earth for centuries. After
Pioneer
, the
Voyager
probes revealed the surprising news about Jupiter's moons. Thanks to the
Voyager
probes, scientists on Earth learned that Jupiter's moons are all very different from one another. In 1995 the
Galileo
probe arrived at Jupiter and spent eight years investigating the giant gas planet and its moons.
Galileo
was the first space probe to do a flyby past an asteroid, the first to discover an asteroid with a moon, and the first to measure Jupiter over a long period of time. This amazing space probe also showed the volcanic activity on Jupiter's moon, Io, and found Europa to be covered in thick ice, underneath which may lie a gigantic ocean that could even harbor some form of life!

NASA's
Cassini
was not the first to visit Saturn—
Pioneer 11
and the
Voyager
probes had flown past on their long journey and sent back detailed images of Saturn's rings and more information about the thick atmosphere on Titan. But when
Cassini
arrived in 2004 after a seven-year journey, it showed us many more features of Saturn and the moons that orbit it.
Cassini
also released a probe, ESA's
Huygens,
which traveled through the thick atmosphere to land on the surface of Titan. The
Huygens
probe discovered that Titan's surface is covered in ice and that methane rains down from the dense clouds.

Voyager 2
flew by Uranus, even farther from Earth, and showed pictures of this frozen planet, tilted on its axis! Thanks to
Voyager 2
, we also know much more about the thin rings circling Uranus, which are very different to the rings of Saturn, as well as many other details of its moons.
Voyager 2
carried on to Neptune and revealed this planet is very windy—Neptune has the fastest moving storms in the Solar System.
Voyager 2
is now ten billion miles from Earth and
Voyager 1
is eleven billion miles away. They should be able to continue communicating with us until 2020.

 

The Stardust mission, during which a probe caught particles from a comet's tail and returned them to Earth in 2006, taught us far more about the very early Solar System from these fragments. Capturing these samples from comets, which formed at the center of the Solar System but have traveled to its very edge, has helped scientists to understand more about the origin of the Solar System itself.