It takes more energy to slow a spacecraft into orbit around Mercury than it does to fly directly to Pluto, because the Sun's gravity accelerates anything falling toward the inner solar system — a counterintuitive physics problem that forced BepiColombo to loop around nine planets across eight years just to slow down enough to stop

It takes more energy to slow a spacecraft into orbit around Mercury than it does to fly directly to Pluto, because the Sun's gravity accelerates anything falling toward the inner solar system — a counterintuitive physics problem that forced BepiColombo to loop around nine planets across eight years just to slow down enough to stop

Mercury is only one planet inward from Earth, yet stopping there is one of the hardest jobs in planetary exploration. The European Space Agency says that placing a spacecraft into a stable orbit around Mercury demands more energy than sending one to Pluto. That comparison needs one important qualification. It contrasts capture at Mercury with a flight to Pluto, such as the New Horizons flyby, not with stopping in orbit around Pluto. A Pluto orbi…