Venus has received particular attention, from NASA's "Pioneer Venus" and most recently "Magellan", which mapped it by radar; two French balloons were successfully deployed by the Russian "Galley" ("Halley"--no H in Russian) on its way to meet comet Halley, and sent back data about the Venusian atmosphere. The Soviet Union has landed several instrumented modules on the planet's surface (a hellish place of high pressure and temperature) and has returned photographs from there (above).
| "Sojourner" on Mars, its top
covered with solar cells.
Mars has received considerable attention too, including two US landers of project "Viking" and the current Mars Global Surveyor. Not long ago, "Mars Pathfinder" landed a small robotic vehicle Sojourner on Mars, controlled from Earth (on right).
Two more rover missions, were launched by NASA towards Mars in mid-2003 and arrived in January 2004, releasing twin rovers--"Spirit" (January 4) and "Opportunity" (January 24). They carry extensive instruments for studying Mars rocks and soil, and are guided from Earth to explore the Mars surface.
Actually, the first extraterrestrial rover was the "Lunokhod" of the Soviet Union, deployed on the Moon in 1970 and exploring it for close to a year. It had a tublike body supported by 8 wheels and a hinged lid lined with solar cells, which opened during the lunar day to soak up sunlight but closed at night to protect the inside. Its mission ended when the open lid accidentally brushed the side of a crater as the vehicle was climbing out, showering the cells with moondust.
Ulysses flew by Jupiter and used the planet's gravity to deflect its motion to an orbit steeply inclined to the ecliptic, passing above the Sun's poles; this region of interplanetary space had not been explored before and has quite different properties than the one around Earth.
Voyager 2 acquired sufficient velocity to escape the Sun's gravity, and among all spacecraft it is currently the one most distant from the Sun. According to theory, some time in the 21st century it will probably pass the limit of the solar wind. If its nuclear power sources hold out until then, it may even tell us about the interstellar space that lies beyond.
Questions from Users:
Picturing the Sun from a different distance
Blimps on Mars?