BepiColombo’s first close-up photos of Mercury’s surface point to answers to planet’s mysteries

The BepiColombo spacecraft – a joint project by European and Japanese space agencies – swung by its destination planet Mercury in the early hours of 2 October 2021. Passing within 200 km of Mercury’s surface, it sent back some spectacular pictures.

For those of us who have worked on this mission for a decade or more, there is hardly a better way to celebrate the 101st birthday of the mission’s name, Italian mathematician and engineer Giuseppe Colombo. His groundbreaking work in this area earned him the title of the grandfather of planetary fly-by technology, now often referred to as “swing-by”.

BepiColombo’s cruise from Earth began in October 2018, and its journey is far from over. The amount of time it will take for Mercury to orbit the Sun three times (about 264 days), will orbit the Sun twice. This will allow it to rendezvous with the planet for another swing-by on 23 June 2022.

After a total of six orbits of Mercury, the cumulative effect of the planet’s gravity will reduce the spacecraft’s velocity to the point where it may fall into orbit with Mercury by the end of 2025.

The BepiColombo is actually made up of two connected spacecraft and a propulsion unit. During its cruise through interplanetary space, the European orbiter (referred to as the “Mercury Planetary Orbiter” or MPO) is attached to the Interplanetary Propulsion Unit (or “Mercury Transfer Module”) on one side. On the other hand, it has a Japanese orbiter called Mio (or “Mercury Magnetospheric Orbiter”), as well as a sunshield to protect Mio from overheating.

This stacked configuration constrains the openings through which the sophisticated visible, infrared and X-ray cameras inside the MPO – capable of imaging and analyzing Mercury’s surface in great detail – will once be able to reach the MPO’s eventual free-flight. Will work when In fact, most of BepiColombo’s science instruments will remain completely or partially inactive until each orbiter is freed, around December 2025.

adding cameras

Until a relatively late stage in mission planning, it was accepted that BepiColombo would be “flying blind” during its entire cruise from Earth, including during swing-by – meaning it would have achieved orbit around Mercury. Till date no image will be available.

But to the level of public interest sparked by images of Comet 67P from the Rosetta mission in 2015, BepiColombo engineers Kelly Galen and James Windsor proposed that low-cost lightweight cameras should be added to the spacecraft.

By the end of 2016, it was agreed that three small surveillance cameras – each just 6.5 cm in length – would be mounted on the craft. These will photograph the planets during swing-by.

It was decided to place these cameras on the Mercury Transfer Module, where they would be able to monitor the deployment of the solar panels that power the spacecraft, the magnetometer boom used to measure the magnetic field, and the communications antenna.

what did Bepi see

During BepiColombo’s first Mercury swing-by, fields two and three of the surveillance cameras tracked across the planet. Camera three showed us part of the Southern Hemisphere, beginning with a view of the sunrise on the Astrolabe Rups – a remarkable feature named after a French Antarctic exploration ship.

Astrolabe Rups is a 250 km long “lobate scarp” – a long, curved structure where a portion of the planet’s crust has been pushed into a nearby area as the entire planet shrinks and cools slowly. has gone.

There are some very small equivalent features on the Moon, but Mercury is the only celestial body known to have such massive lobate scarps.

Four minutes later, the perspective had changed enough to reveal a wider area: the 251 km-wide Hayden Crater and Pampu Facula, one of several bright spots formed by explosive volcanic eruptions, including the lava-flooded. Both of these features attest to the long volcanic history of Mercury, which is most active three billion years ago, but probably persisted until about a billion years ago.

Meanwhile, Camera Two focused on Mercury’s northern hemisphere, including the area around Calvino Crater: a key location for understanding what lies in the layers of Mercury’s crust.

It also showed Lermontov crater: a region that appears bright because it is host to both volcanic deposits and “hollows,” where an unknown volatile component of the crust is being lost to space through a mysterious process.

NASA’s MESSENGER mission orbited Mercury between 2011 and 2015, revealing a perplexing planet. We are still struggling to understand its composition, origin and history.

Why Mercury has features such as explosive volcanism and strange, unique hollows on its surface is one of the problems we hope further study will solve. Once in orbit, BepiColombo’s advanced payload of scientific instruments will help us better understand how Mercury formed and what it is made of.

Read more: The more we learn about Mercury, the weirder it seems

In the meantime, these extraordinary swing-by photos remind us at least that we have a healthy spacecraft headed for an exciting destination.