Two spacecraft bound for Mercury left their mother ship behind on Thursday and headed down the final stretch of a nearly decade-long voyage to the solar system's smallest planet. The linked European and Japanese craft separated as planned from their cruiser, but controllers had to wait two anxious hours for confirmation via radio signals. The operation was broadcast from the European Space Agency's control center in Germany, more than 124 million miles, or 200 million kilometers, away.
Home stretch after nine flybys
"It's a brilliant moment," said Geraint Jones, the mission's lead project scientist. The mission, known as BepiColombo, launched in 2018 and has already traveled more than 6 billion miles, or 10 billion kilometers, on a roundabout route. It needed nine planetary flybys to slow down enough to be captured by Mercury's gravity. The last flyby, in January 2025, produced close-up photos of the planet's impact craters and volcanic plains. As of Thursday, the spacecraft still had about 2 million miles, or 3.3 million kilometers, to go.
A world of extremes
Mercury is a planet of harsh contrasts. Daytime temperatures can top 800 degrees Fahrenheit, or 427 degrees Celsius, while the poles hold deep, permanently shadowed craters packed with ice. Engineers had to design the mission to withstand punishing conditions. "It's essentially equivalent to operating with a very hot pizza oven running right on your back," said Ignacio Tanco, a mission operations chief at the European Space Agency. Only one other spacecraft, NASA's Messenger, has ever explored the planet, which is only a little bigger than our moon. The mission is named for Giuseppe Colombo, an Italian mathematician who worked on NASA's Mariner 10 Mercury mission in the 1970s.
Orbit and first science
If all goes well, the conjoined spacecraft will enter Mercury's orbit in November and separate from each other in December to map and study the planet from different altitudes. Beginning next spring, science instruments on both craft will examine Mercury's magnetic field, its dense interior, and its surface geology, including mysterious hollows that scientists believe are carved by minerals vaporizing from rocks. The European Space Agency covers most of the mission's cost, estimated at about $2 billion, or 1.7 billion euros.