On March 17, 2012—MESSENGER completed its first extended yearlong mission—after capturing roughly 100,000 images of Mercury’s surface.
The space probe launched a Delta II rocket into space on August 3, 2004, from Cape Canaveral—and it became the first space mission to enter Mercury’s orbit—capturing extraordinary images of the planet sitting closest to the sun.
MESSENGER is the second probe that was designed to explore Mercury and was catapulted into space almost three decades after the first space probe to Mercury—Mariner 10—completed three close-range flybys and a whistle-stop tour between 1974 and 1975.
During MESSENGER’s mission in space, it captured images of the planet’s western hemisphere—almost unseen previously—showcasing 98% of Mercury’s surface—sparing only the polar regions. Keep scrolling to learn more about MESSENGER’s shocking discoveries on the broiling planet!
MESSENGER found water ice on the sun-scorched planet, and it was shocking because scientists did not expect a planet perched at the mouth of the sun to have water in any form. The average surface temperature of Mercury is 427°C, and it still has more than a trillion tonnes of ice—at its poles—in permanently shadowed areas.
The discovery of frozen water was unbelievable. It further revealed that Mercury had no water when it was formed—it likely arrived much later due to asteroid and comet bombardments that carried various other volatile elements.
MESSENGER helped unravel why Mercury has a vast iron core that covers nearly 50% of its total volume — double the size of Earth's core. Scientists were baffled by this oddity as the sun-scorched planet is very dense as opposed to the other planets of the solar system.
Some theories propose that Mercury was originally a much bigger planet, but a giant collision disintegrated its mantle. However, it appears that the planet originated the same way the other terrestrial planets—Mars, Venus, and Earth—did.
Scientists suggest that Mercury originated in such a sweltering region that the protoplanetary nebula only condenses out iron. Similar to the gas giants that lie between Mars and Jupiter— beyond the snow line—where the cooler temperature allows ice and water to condense, Mercury also developed at an iron line.
NASA’s Mariner 10 spacecraft provided hints of volcanoes, but the captured images failed to render anything conclusive. Three decades later, the first flyby of MESSENGER confirmed the speculations by discovering a mammoth volcano (larger than the state of Delaware). Scientists further claimed that Mercury was volcanically active for a billion years since its formation, but the activities ceased after that.
MESSENGER’s flybys also disclosed that more than half of Mercury’s surface comprises smooth plains, and its magnetic field is actively producing within its partly molten core. Experts have further revealed that volcanism was a long-term player, and plays a crucial role in mercurian geology.
It took aeons for Mercury to cool down, causing the planet to shrink over the years and its surface to crack. Currently, the diameter of Mercury is 3,032 miles, slightly bigger than our moon. Earlier, the planet was likely 14 miles wider.
Before MESSENGER, scientists presumed that the surface of Mercury likely contained volatile chemicals like potassium, sulphur, chlorine, and sodium. Theoretically, these chemicals cannot naturally occur on the planet due to its closeness to the Sun.
If the sun-scorched planet was iron-rich from the time of its formation, it could not have so many volatile elements. When MESSENGER surveyed Mercury's surface, it revealed that these chemicals have left traces only around comet and asteroid impact sites.
When these volatiles were examined—especially potassium—scientists discovered that the ratios of thorium to potassium were similar to those detected in Martian meteorites. Chances are, Mercury was initially an iron-rich celestial body—but was later pounded by comets and asteroids containing volatiles.
MESSENGER is one of NASA’s most accomplished and resilient spacecraft that travelled 14 billion kilometres and orbited Mercury 4,100 times while capturing roughly 300,000 images.
