Two spacecraft on a nearly decade-long voyage to Mercury separated from their mother ship on Thursday, entering the final phase of their journey to the solar system's innermost planet. The conjoined European and Japanese probes, known as BepiColombo, detached as planned, though mission controllers had to wait two hours to receive confirmation via radio signals from over 124 million miles (200 million kilometers) away.

“It’s a brilliant moment,” said lead project scientist Geraint Jones. BepiColombo is scheduled to enter orbit around Mercury in November and then split into two separate spacecraft in December. Once separated, they will map and study the entire planet from different altitudes. As of Thursday, the spacecraft still had 2 million miles (3.3 million kilometers) remaining before reaching their destination.

Launched in 2018, the BepiColombo mission is named for the Italian mathematician who contributed to NASA’s Mariner 10 mission to Mercury in the 1970s. To date, only one other spacecraft, NASA’s Messenger, has explored Mercury, a planet slightly larger than Earth's moon.

“How tiny Mercury is and still it holds some of the biggest mysteries of our solar system,” mission manager Santa Martinez stated earlier this week. Mission scientists anticipate there is still a great deal to learn about the planet.

BepiColombo has already traveled over 6 billion miles (10 billion kilometers) on its indirect route. The mission required nine planetary flybys to reduce its energy sufficiently to be captured by Mercury’s orbit. The most recent flyby occurred in January 2025, providing detailed images of Mercury’s impact craters and volcanic plains.

Beginning next spring, the science instruments on board the two spacecraft will commence studies of Mercury’s magnetic field, its dense interior, and surface geological processes. Scientists are particularly interested in features known as hollows, which are believed to be formed by the vaporization of minerals from rocks.

Mercury presents a world of extremes. While surface temperatures can exceed 800 degrees Fahrenheit (427 degrees Celsius), the planet's poles remain frigid, with deep craters permanently in shadow containing ice. The spacecraft were engineered to withstand these harsh conditions due to Mercury's proximity to the sun.

Science observations are expected to begin next spring. The European Space Agency is funding the majority of the mission's approximately $2 billion cost.