An artist's rendition of Cassini-Huygens on Saturn's orbit

On January 4, 1959, the former Soviet Union launched Luna 1. The probe became the first spacecraft to successfully reach the vicinity of the moon.
Since then, a number of probes have visited every planet in the solar system. They have also reached moons, asteroids, and comets. Three probes are now even en route to the outer parts of the solar system.

The earliest probes in the United States (US) space program are the Mariner series. The program, which began in 1962, investigated the inner planets—Mars, Venus, and Mercury.

Another notable program was the Venera, a series of probes developed by the Soviet Union from 1961 to 1984 to study the planet Venus. The probes of the series accomplished a number of “firsts” in space exploration.

Venera 4 is the first man-made device to enter the atmosphere of another planet. Venera 7 made the first soft landing on another planet. Venera 9 is the first probe to return images from a planetary surface.

Meanwhile, the Pioneer series involves a number of probes which were sent to the moon, the sun, and the outer planets. The most notable probes in the series are Pioneer 10 and 11 which investigated Jupiter and Saturn. They are the first man-made objects to reach the outer solar system.

The Viking 1 and 2 space probes traveled to Mars during the 1970s. They mapped its surface and searched for signs of life.

Other highly successful Martian probes are the Mars Pathfinder and the Mars Global Surveyor. Both arrived in Mars in 1997. The former analyzed the planet’s surface while the latter mapped it.

In 2003, the twin rovers Spirit and Opportunity were launched toward Mars. The rovers landed on the Red Planet in January 2004. They are still working and have already found many pieces of evidence that water existed on Mars.

The probes Voyager 1 and 2, launched in 1977, took spectacular photographs and data from Jupiter, Saturn, Uranus, Neptune, and their moons. They are still receiving commands and transmitting information back to Earth. The sister probes are now on an extended mission to study the outer solar system.

The Cassini orbiter was launched on October 15, 1997. It entered Saturn’s orbit on July 1, 2004. It released the lander Huygens on December 25 of the same year. Huygens reached Saturn’s moon, Titan, on January 14, 2005. The Cassini-Huygens mission is the biggest and most expensive probe to ever visit another planet.

Solar probes are those sent into space to study the sun. The Ulysses, which was launched on October 6, 1990, returned data about the poles of the sun. The Solar and Heliospheric Observatory (SOHO) was sent to space on December 2, 1995 to investigate the sun’s core and corona. It is now on an extended mission which is expected to last until December 2012.

Probes also visit asteroids and comets. The probe Near Earth Asteroid Rendezvous (NEAR) Shoemaker flew by the asteroid Mathilde on June, 27, 1997. It made a flyby on the asteroid Eros in 1999, then landed on its surface in 2001. Meanwhile, probes that conducted missions on comets include the Deep Impact which was designed to study the composition of the interior of the comet Tempel 1.

The New Horizons spacecraft, launched on January 19, 2006, is set to make history when it flies by and studies the dwarf planet Pluto and its moons, Charon, Nix, and Hydra, in 2015. It will be the first spacecraft to visit a trans-Neptunian object. The New Horizons will continue into the Kuiper Belt and may also make a flyby on one or more Kuiper Belt object.

Some Asian nations are also joining the race in space exploration. On January 7, 1985, Japan launched Sakigake, its first interplanetary space probe. Sakigake made a flyby on Halley’s Comet.

Another Japanese probe, Hayabusa, was launched on May 9, 2003. It landed on the asteroid Itogawa in November 2005 to collect samples. It is scheduled to return to Earth in June 2010.

Other Japanese probes include the lunar orbiter SELENE (Kaguya) which was launched on September 14, 2007, and Japan’s first lunar probe, Hiten, which was launched on January 24, 1990.

India had launched its first lunar probe, the Chandrayaan-1 on October 22, 2008. It is planning to to send a second probe, Chandrayaan-2, in 2013.

Meanwhile, China launched Chang’e 1, a lunar orbiter/impactor, on October 24, 2007. The country is scheduled to launch Chang’e 1’s sister probe, Chang’e 2, in October 2010.