Venus has received particular attention, from NASA's "Pioneer Venus" and more recently "Magellan", which mapped Venus 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 also landed several "Venera" 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" followed by the Mars Global Surveyor and also by "Mars Pathfinder", which landed a small robotic vehicle "Sojourner" on Mars, controlled from Earth (on right). The effort of exploring Mars from space has been long one
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 carried extensive instruments for studying Mars rocks and soil, and were guided from Earth to explore the Mars surface.Currently (2016) that program continues with the rover "Curiosity which landed on Mars in August 2012 and is still rolling.
The "Dawn" mission to the asteroid belt visited Vesta and ended in an orbit around Ceres, the largest member of the belt.
Mercury was also included in the planetary exploration program. The "Messenger" mission, launched 2011, successfully established an orbit around that small planet. It is not easyu to do so, since aprobe from Earth gains velocity as it "falls" towards the Sun, and unless that extra energy is somehow removed, it will pass the planet with too much speed to be captured. Orbital energy can be given up or gained by "planetary slingshot" encounters, and "Messenger" used 6 of those--one with Earth, two with Venus and 3 with Mercury itself (even then the orbit was quite elongated). The mission ended in 2015 when the spacecraft was deliberately crashed into the surface.
The "Rosetta" space probe was launched in 2004 towards comet Churmuyov-Gerasimenko, with an attached rover "Philae".
It took detailed photographs of the comet, also another one and two asteroids, and on 12 November 2014 its probe "Philae" landed on the comet itself. Unfortunately, the comet's gravity was too weak for a solid landing, and the lander bounced off its first landing, ending in deep shadow next to a cliff. With insufficient sunlight, its batteries ran down. "Rosetta" itself was deliberately crashed on its comet, before ir entered the outer part of their solar orbit, far enough from the sun to freeze and destroy the electric batteries.
Ulysses flew by Jupiter and used the planet's gravity to deflect its motion to a solar orbit steeply inclined to the ecliptic, passing above the Sun's poles (originally the mission started as "Solar Polar," with a pair of spacecraft above opposite poles of the Sun).The polar region of interplanetary space had not been explored before and has quite different properties than the one around Earth.
Both "Voyagers" acquired sufficient velocity to escape the Sun's gravity, and are currently the ones most distant from the Sun. Their nuclear power sources still operate (2016) and they have passed some of the outer boundaries of the Heliosphere, the region dominated by the solar wind.
Questions from Users:
Picturing the Sun from a different distance
Blimps on Mars?