Image of Mariner 10 Courtesy of NASA/JPL

Mariner 10 was launched on Nov. 3, 1973, intended as a flyby of planets Venus and Mercury.

It passed Venus in February of 1974, returning over 4000 photographs of it's thick cloud cover and information on the atmosphere composition. Mariner 10 then used Venus's gravity to gain speed and travel to Mercury, passing by the planet three times over the next year.

From the Mariner 10 mission, 57% of Mercury's surface was mapped, revealing many craters similar to those on our Moon. The last Mariner spacecraft is now out of energy and in orbit around the sun.

Image of Mariner 10 Courtesy of NASA/JPL

Mariner 10 was launched on Nov. 3, 1973, intended as a flyby of planets Venus and Mercury. It passed Venus in February of 1974, returning over 4000 photographs of the thick cloud cover which surrounds the planet, and information on the atmosphere composition.

Mariner 10 then used the gravitational pull of Venus to accelerate itself toward Mercury, becoming the first spacecraft to visit that planet, on March 29, 1974. During the next year, two more flybys produced a total of 10,000 images, revealing a heavily-cratered surface similar to that on our Moon.

After mapping 57% of Mercury, Mariner 10 ran out of energy and is now in an orbit around the Sun.

Image of Mariner 10 Courtesy of NASA/JPL

Mariner 10 was launched on Nov. 3, 1973, intended as a flyby of planets Venus and Mercury. It passed Venus in February of 1974, returning over 4000 photographs of the thick cloud cover which surrounds the planet, and information on the atmosphere composition.

Mariner 10 then used the gravitational pull of Venus to accelerate itself toward Mercury, becoming the first spacecraft to visit that planet, on March 29, 1974. During the next year, two more flybys were possible, at an altitude as low as 705 kilometers (438 miles). They produced a total of 10,000 images, revealing a heavily-cratered landscape similar to that on our Moon, and mapped 57% of the Mercury's surface.

The Mariner 10 mission developed many complications and several course corrections were necessary. It became the first spacecraft to use its solar panels as sails, riding the solar wind to conserve energy. Today, the last Mariner installment is in a solar orbit, no longer transmitting.