Whenever you are told to list the planets of our solar system, you start off with Mercury, don’t you? The planet closest to our sun, it is also now the smallest, since Pluto has been demoted to the status of a dwarf planet. Albert Einstein’s theory of relativity might have confirmed observations about Mercury’s anomalous orbit, but there was still plenty to be learnt about the planet.
Among the many firsts that Mariner 10 achieved, it was the first spacecraft to visit two planets. On its way to Mercury, Mariner 10 first passed by Venus on February 5, 1974, capturing close-up images of the same. Apart from enabling a better understanding of Venus’ magnetic field, the mission also discovered evidence of rotating clouds.
Gravity assist debut Mariner 10 was also the first probe to use gravity assist as a technique to move towards its final destination. A standard manoeuvre now, gravity assist involves employing the relative movement and gravity of a planet or other astronomical body to change the speed and path of a spacecraft.
Using Venus’ gravity, Mariner 10 achieved a slingshot effect to propel it towards Mercury. And on March 29, 1974, it made its first of three passes past Mercury. The first flyby, performed mainly to determine the presence of an atmosphere, occurred in Mercury’s dark side at an altitude of about 440 miles.
A second look The second flyby, which happened on September 21, 1974, was another first, as it marked the first time a spacecraft returned to its target to have a second look. More photographs were captured during this instance that took it across the sunlit side of the planet at a distance of nearly 30,000 miles.
The third and final flyby happened on March 16, 1975 at an altitude of about 200 miles in an attempt to further understand Mercury’s weak magnetic field, which was detected during the first phase. Being the closest approach, this also resulted in detailed images of Mercury’s bumpy surface.
By March 24, 1975, Mariner 10 had run out of fuel, leading the scientists to turn off its transmitters, effectively disconnecting communications with earth. The mission was able to discern Mercury’s moon-like surface, helium-rich atmosphere, iron-rich core and weak magnetic field, apart from obtaining close to 2,800 photos. Mariner 10’s equipment might have been scorched by this time due to the heat of the sun, but it is believed to be still in the orbit around the sun.
