The British-built BepiColombo took off aboard an Ariane 5 rocket at about 2.45am United Kingdom time on Saturday.
BERLIN - Final preparations were underway Friday for the launch of a joint mission by European and Japanese space agencies to send twin probes to Mercury, the closest planet to the Sun.
Newly developed electrical ion thrusters will help nudge the spacecraft, which was named after Italian scientist Giuseppe "Bepi" Colombo, into the right orbit. During that time, the two spacecraft will investigate a range of questions about Mercury.
Scientists hope the mission will tell them more about how the solar system was made and give them a better idea about the potential for life on exoplanets, which are planets found orbiting other stars.
The BepiColombo spacecraft will have to follow an elliptical path that involves a fly-by of Earth, two of Venus and six of Mercury itself so it can slow down before arriving at its destination in December 2025.
This interplanetary mission comes hot on the heels of Ariane 5's 100th flight, placing two telecommunications satellites into orbit in the process - which are the bread and butter missions for this launch vehicle.
Designated VA245 in Arianespace's launcher family numbering system, this will be the 23rd major scientific mission performed by the company to date.
This mission will deploy two science orbiters, one European and one Japanese, to make complementary measurements of the planet's dynamic environment at the same time.
Ariane 5 will be lofting estimated payload mass of 4,241 kg from ELA-3, with spacecraft separation expected 27 minutes into the flight. It is the only solar system planet that has a spin-orbit resonance: It spins on its axis three times for every two orbits around the Sun.
This is only the third mission to Mercury, following NASA's Mariner 10 in 1974-1975 and Messenger in 2011-2015. JAXA's Mercury Magnetospheric Orbiter (MMO) hosts a magnetometer, a spectral imager, and plasma physics instruments to study the origin, strength, and extent of the planet's magnetic field and exosphere. NASA's Mariner 10 made three brief fly-bys in the 1970s, and the U.S. space agency's Messenger orbiter circled the planet between March 2011 and April 2015, when it ran out of fuel and crashed onto Mercury's surface.
NASA's Messenger spacecraft mapped the north polar topography of Mercury.
At top speed after launch, the spacecraft will be moving at 60km/s. Later, the monitoring cameras will be switched on.
Its distance from Earth also makes it hard to reach - more energy is required to allow BepiColombo to "fall" toward the planet than is needed when sending missions to Pluto.
Nonetheless, it will be possible to operate or partially operate as many as eight of the 11 instruments on the MPO during the flybys, along with three of the five instrument packages onboard JAXA's Mercury Magnetospheric Orbiter. This will afford some unique data collection opportunities at Venus, for example. One year on Mercury is only 88 Earth days long, but a day-night cycle on the smallest planet lasts more than twice as long.