Mercury, one of the least-explored rocky planets in our solar system, will shortly welcome a new visitor to its scorching part of the celestial neighborhood.
BepiColombo, a joint European and Japanese spacecraft comprised of two satellites, was successfully launched in late October on a mission to study Mercury and help uncover the science behind some of its more puzzling characteristics. Some 25 years in the making, the mission is considered a "cornerstone" in the long-term science program of the European Space Agency or ESA. It's also one of the most difficult and problematic exploration missions ever undertaken by the agency.
"We're flying into a pizza oven," ESA project manager Ulrich Reininghaus, referencing temperatures around Mercury in excess of 750 degrees F, quipped to the BBC. "We had to test materials at different, very high temperature regimes, sometimes with very unwanted results."
Despite its relative proximity to Earth, getting BepiColombo to Mercury will take a surprising seven years. The reason behind this extreme timeline has not so much to do with distance and everything to do with speed. In order for the spacecraft to slow down and achieve orbit, it will need to complete a number of gravity-assist maneuvers around Earth, Venus and its eventual host planet. This tricky orbital dance through our inner solar system is the reason the mission was named after Giuseppe "Bepi" Colombo, an Italian scientist who pioneered the use of interplanetary gravity-assist maneuvers during the 1974 Mariner 10 mission.
"You can get to Mercury quite quickly if you don't want to stop, but we have a swing-by the Earth and two swing-bys of Venus," planetary geologist David Rothery told The Naked Scientists. "And then half a dozen flybys of Mercury each time passing it more slowly until, eventually, it catches up with us with such a small relative speed difference that we can get captured into orbit and start doing science from orbit."
Once in orbit, a milestone that won't be crossed until December 2025, the spacecraft will separate into two satellites — the Mercury Planet Orbiter built by the ESA and the Mercury Magnetospheric Orbiter built by the Japanese Space Agency (JAXA). A total of 16 instruments on board both satellites will allow for a comprehensive study of Mercury, including its magnetic field, magnetosphere and both interior and surface structure.
A focus on key mysteries
One of the more interesting mysteries surrounding Mercury is its outsized iron core. NASA's Messenger probe, which orbited Mercury from 2011 to 2015, discovered that the planet's iron core occupies up to 60 percent of its volume. By comparison, Earth's core is only 17 percent of its volume. And then there's Mercury's surface, which was found to contain large amounts of volatile substances.
"For me, as a geologist, it's what the heck are all these volatiles doing there?" Rothery added. "We haven't identified exactly what they are; we can tell they're volatile substances. They shouldn't be there if Mercury began that close to the Sun. So we'll be finding out what's making the interesting recently active geological processes, and where the blooming planet formed, because it may have formed further from the Sun and found it's way inwards."
Still others are interested in using BepiColombo to analyze Mercury's global magnetic field, the only other planet in our solar system to generate one outside of Earth. And then there's the mystery surrounding its ice, which — despite the planet's close proximity to the sun — surprisingly exists in large volumes in permanently dark craters on its north pole.
Above all, scientists are hopeful that BepiColombo's rich array of instruments will help shed light on not only Mercury's past, but also our own beginnings.
"This wonderful spacecraft will let us learn more about how the Solar System began, where we all came from, and how, on our own planet, you and I came to be,” Bill Nye of the Planetary Society said.