How a Theory Helped Mariner 10 Reach the Planet Mercury

In ‘This Week in History,’ the last of NASA’s Mariner missions pursued the impossible task of reaching the elusive planet Mercury.

An artist's impression of the Mariner 10 mission. It used a flyby of the planet Venus to increase its chance of reaching Mercury when it was furthest from the sun. This would allow the spacecraft to meet Mercury on three occasions in 1974 and 1975. Public Domain

Nicolaus Copernicus once said of the planet Mercury that “the planet has tortured us with its many riddles and with the painstaking labor involved as we explored its wanderings,” according to Dava Sobel’s “The Planets.”

Copernicus, arguably history’s greatest astronomer, published his “De Revolutionibus Orbium Coelestium“ (”On the Revolutions of the Heavenly Spheres") in 1543, the same year of his death. His work established the heliocentric model of the planetary system, which upended the longstanding geocentric model.