Is Mercury’s core liquid or solid, and why — on the smallest planet in our solar system — is it so big? What can the planet closest to the sun tell us about how our solar system came into being?
An uncrewed European-Japanese space mission, dubbed BepiColombo, blasted off early yesterday morning from French Guiana to probe these and other mysteries.
“BepiColombo is coming like a white knight with better and more precise data,” Paris Observatory astronomer Alain Doressoundiram said.
Photo: Centre National d’Etudes Spatiales / EPA
“To understand how Earth was formed, we need to understand how all rocky planets formed,” he said. “Mercury stands apart and we don’t know why.”
First, the instruments on board the Ariane 5 rocket will have to travel seven years and 9 million kilometers to reach their destination.
In a statement after the launch, ArianeGroup said that the satellite had successfully escaped Earth’s gravity field and was beginning its long journey, during which it would reach speeds of up to 40,000kph.
According to Pierre Bousquet, an engineer at France’s National Centre for Space Research and head of the French team contributing to the mission, Mercury is “abnormally small,” leading to speculation that it survived a massive collision in its youth.
“A huge crater visible on its surface could be the scar left over from that encounter,” Bousquet said.
The scenario would explain why Mercury’s core accounts for a whopping 55 percent of its mass, compared with 30 percent for Earth.
Mercury is also the only rocky planet orbiting the sun beside our own to have a magnetic field.
Magnetic fields are generated by a liquid core, but given its size, Mercury’s should have grown cold and solid by now.
This anomaly might be due to some feature of the core’s composition, something BepiColombo’s instruments are to measure with much greater precision than has been possible so far.
On its surface, Mercury is a planet of extremes, vacillating between hot days of about 430°C to nights of minus-180°C. Those days and nights last nearly three Earth months each.
Earlier missions have detected evidence of ice in the deepest recesses of the planet’s polar craters.
Scientists speculate that this might have accumulated from comets crashing onto Mercury’s surface.
“If the presence of ice is confirmed, it means that some of those water samples date back nearly to the origin of the solar system,” Doressoundiram said.
Mercury is 58 million kilometers from the sun, nearly three times closer than Earth.
“The planet is whipped by solar winds,” a constant torrent of ionized particles bombarding the surface at 500 kilometers per second, Bousquet said.
The scientists are to be able to study the impact of these winds — 10 times stronger than the ones hitting Earth’s atmosphere.
The BepiColombo mission is to deploy two spacecraft: The Mercury Planet Orbiter would investigate the planet’s surface and interior composition, while the Mercury Magnetospheric Orbiter is to study the region of space around the planet that is influenced by its magnetic field.
The mission would also look for tectonic activity and seek to understand why spectroscopic observations show no iron, even if it is thought to be one of the planet’s major component elements.
Compared with Mars, Venus and Saturn, Mercury has barely been explored. Only two spacecraft have ever paid it a visit.
NASA’s Mariner 10 did three flybys in 1974 and 1975, providing the first up-close images. More than 30 years later, NASA’s Messenger did the same, before settling into orbit around Mercury in 2011.
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