Up until recently, only two spacecraft had ever visited Mercury: NASA’s Mariner 10, which accomplished three flybys between 1974 and 1975.
Mariner 10 was successful in using Venus’ gravity to speed towards Mercury and sent back fuzzy images of its heavily cratered surface. Meanwhile, MESSENGER proved more successful, mapping all of it and discovering water ice on Mercury.
Mariner 10
On March 29, 1974 Mariner 10 made its maiden close encounter with Mercury, passing just 438 miles above its surface. The spacecraft returned over 2,000 images plus data from other instruments.
These included spectrometers to assess Mercury’s rock composition. This mission revealed evidence of pockets of water ice surviving within craters at both poles – these may have come from comets or from inside Mercury as vapor which eventually condensed back into solid form.
Mariner 10 has also discovered shallow, irregular depressions called hollows within craters and on Mercury’s plains that appear unique to this planet and may form when sublimated material sublimates below its surface.
Between March 1974 & 1975, Mercury Express completed three flybys around Mercury collecting images & data that helped scientists develop theories regarding how small rocky planets like Mercury form.
MESSENGER
Mariner 10 provided Mariner 9 with an impressive image of Mercury’s landscape during three flybys, but due to Mercury’s closeness to the Sun its coal-black surface quickly heated to temperatures where humans would never survive. Therefore, NASA developed the MESSENGER mission (MErcury Surface, Space Environment Geochemistry and Ranging).
This spacecraft was first launched into space in 2004. Following launch, it conducted several gravity assist maneuvers at Earth, Venus and Mercury to reduce its speed before entering into an extremely elliptical orbit.
MESSENGER was equipped with seven instruments that conducted observations of Mercury from both its surface and interior. Dual imaging systems provided maps with resolutions up to 800 feet per pixel; while X-ray and neutron spectrometers searched for signs of polar ice formation.
MESSENGER was among the mission’s greatest discoveries, not least its revelation that, despite Mercury’s proximity to the Sun, ice may exist at the bottom of permanently shaded craters. Furthermore, its probe also detected massive chains of cliffs in Caloris basin and evidence of volcanic vents.
BepiColombo
BepiColombo, named in honor of Italian mathematician and engineer Giuseppe “Bepi” Colombo, will visit Mercury to help scientists address some key questions about its composition and history. The mission comprises two spacecraft with distinct missions – ESA’s Mercury Planetary Orbiter (MPO), with 11 instruments aboard it; and JAXA’s spin-stabilised Mercury Magnetospheric Orbiter which was produced in Britain by Airbus.
BepiColombo takes seven years to reach Mercury using gravity-assist maneuvers similar to what you might try if your car’s brakes fail; these include one Earth flyby, two Venus flybys and six Mercury flybys that allow it to side-swipe planets for additional braking power.
Once Mercury is reached, both orbiters will split off and study it from different perspectives. Both MPO and MMO feature high-resolution imaging systems – including one developed by UK space scientists at University of Leicester – equipped with colour imaging capability for enhanced observation of this planet.
The story of Mercury
Mercury is an intriguing planet with an intriguing past. Sitting so close to its star, Mercury has provided us with an accurate record of early Solar System events untouched by wind or water erosion.
Scientists are eager to better understand Mercury due to its odd magnetic field and unusual behavior, so the MESSENGER mission used spacecraft equipped with radar and other sensors to learn more. According to this data, some craters around Mercury’s poles may contain permanent shadowed regions containing water ice from comets or formed from solar vapor.
Mariner 10 and MESSENGER missions were the first to reach Mercury. Now, European-Japanese bepiColombo mission will reach Mercury by 2025 following nine flyby maneuvers – three at Earth, two at Venus and six at Mercury itself – designed to correct space probe trajectories against Sun’s pull. Colombo pioneered this method. These flybys allow spacecraft to enter stable orbits.