The Mariner 10 probe.

Mariner 10 was the last spacecraft of the Mariner program, launched on November 3 1973.

An unmanned space mission it was launched approximately 2 years after Mariner 9 and its mission was to explore Mercury and Venus.

Mariner 10 made use of a "gravitational slingshot", using Venus to bend its flight path. It also had its solar panels tilted to use the solar wind as a major means of spacecraft orientation during flight. Using a near-ultraviolet filter, it produced photographs of the Venusian chevron clouds and performed other atmospheric studies.

On March 29 and September 21, 1974, and March 16, 1975; Mariner 10 passed by Mercury and after a mid-course correction on March 16, 1974, and was able to map 40-45% of the planet. Its radiometer readings suggested Mercury has a nighttime temperatures of -297°F (–183°C) and maximum daytime temperatures of 368°F (187°C). The closest encounter was at 20:47 UT on March 29, 1974 at a range of 436.5 miles (703 kilometers). Having looped around the Sun, Mariner 10 flew by Mercury once more on September 21, 1974 at a more distant range of 29,850 miles (48,069 kilometers). The spacecraft used solar pressure on its solar panels and high-gain antenna for attitude control. A third and final encounter, the closest to Mercury, took place on March 16, 1975 at a range of 203 miles (327 kilometers). Contact with the spacecraft was terminated on March 24, 1975.

Among the mysteries from the data collected, scientists have developed a theory that the planet is shrinking, contracting in on itself as its core slowly freezes. Mariner was unable to provide more information on that question.

However, based on the data gathered, scientists hope to find out more from the latest mission to Mercury, MESSENGER, which was launched August 3, 2004 and will arrive at Mercury in March, 2011 for a year long orbit.

Mariner 11 and Mariner 12 were redesignated as Voyager 1 and Voyager 2.

External links

• The Voyage of Mariner 10: Mission to Venus and Mercury (NASA SP-424) 1978 This is an entire book about Mariner 10, with all pictures and diagrams, on-line! Scroll down to click on the "Table of Contents" link. PDF version
• 'Mariner 10', NASA's 1973-75 Venus/Mercury Mission
• NASA-JPL Guide to Mariner 10