BepiColombo: Europe's mission to Mercury returns first picture
The mission's first picture of Mercury was snapped by a low-resolution monitoring camera on the side of the probe. At the moment, Bepi is not ready to deploy its high-resolution science cameras
Europe's BepiColombo mission has returned its first picture of Mercury, the Solar System's innermost planet.
The probe took the image shortly after it zipped over the little world at an altitude of just 200km (125 miles), says BBC.
Controllers have planned a further five such flybys, each time using the gravitational tug of Mercury to help control the speed of the spacecraft.
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The aim is for Bepi to be moving slow enough that eventually it can take up a stable orbit around the planet.
This should happen by the end of 2025.
The mission's first picture of Mercury was snapped by a low-resolution monitoring camera on the side of the probe. At the moment, Bepi is not ready to deploy its high-resolution science cameras.
These are tucked away inside what is referred to as the spacecraft stack.
Bepi is essentially two spacecraft in one.
One part has been developed by the European Space Agency (Esa), the other part by the Japanese space agency (Jaxa). The way these two components have been packed for the journey to Mercury obstructs the apertures of the main cameras.
This means the mission's first images of Mercury were acquired by a couple of monitoring, or engineering, cameras mounted on the outside of the craft - "selfie" cameras - that were still good enough to pick out recognisable features on the planet's surface.
These simple black-and-white photos started filtering back to Earth on Saturday, and Esa is expected to release more images over the weekend. Come Monday, there should be enough to make a short film.
Although Bepi is a long way from beginning proper science operations, quite a few of the probe's instruments were switched on for the flyby. Phenomena such as magnetic fields and some particles can still be sensed, even in the stack configuration.
"We'll get data back," Dr Suzie Imber, from Leicester University, UK, said, "but the purpose of the flyby, and the six flybys in total at Mercury, is to help us change our trajectory and slow us down.
"Eventually, in a few years from now in December 2025, our spacecraft and Mercury will be in the same place going in the same direction. And so, finally, we can separate our spacecraft, and get into orbit," the mission scientist told the BBC.
Even at this early stage, there was still some data-taking during this first flyby.
For the scientists behind the UK's Mercury Imaging X-ray Spectrometer, or MIXS, it was an opportunity to better understand the performance of their instrument.
MIXS's detectors pick up a general background noise of energetic particles known as cosmic rays.
"As we go really close to Mercury and one half of the sky is blocked by the planet, then we should see a dip in some of this noise that we've been getting, and that will help us to pinpoint the fact that it is galactic cosmic rays we've been detecting," explained Dr Suzie Imber from Leicester University.
The exercise will ensure the mission team gets the most out of MIXS when eventually it does start observing the planet later in the decade.
This first flyby will have put Bepi in a two-to-three resonance with Mercury. That's to say, as Mercury goes three times around the Sun, Bepi will go around twice.
The next flyby in June next year, will slow this to a three-to-four resonance: Bepi will circle the Sun three times compared with Mercury's four circuits.
Further passes in June 2023, September 2024, December 2024, and January 2025 should see Bepi in a regular orbit to begin full science operations in 2026.
What science will BepiColombo do at Mercury?
The European and Japanese elements of the mission will separate when they get into orbit at Mercury and perform different roles.
Europe's Mercury Planetary Orbiter (MPO) is designed to map Mercury's terrain, generate height profiles, collect data on the planet's surface structure and composition, as well as sensing its interior.
Japan's Mercury Magnetospheric Orbiter (MMO) will make as its priority the study of Mercury's magnetic field. It will investigate the field's behaviour and its interaction with the "solar wind", the billowing mass of particles that stream away from the Sun. This wind interacts with Mercury's super-tenuous atmosphere, whipping atoms into a tail that reaches far into space.
It's hoped the satellites' parallel observations can finally resolve the many puzzles about the hot little world.
One of the key ones concerns the object's oversized iron core, which represents 60% of Mercury's mass. Science cannot yet explain why the planet only has a thin veneer of rocks.
"When we get into orbit, we'll then start studying the magnetic field at Mercury, and the surface of Mercury, which has huge temperatures of 450C, the temperature of a pizza oven, and yet it has water on the surface in some places," said Prof Mark McCaughrean, Esa's senior advisor for science and exploration.
"Mercury has a huge metal core. It's very much denser than it should be for its size. We just don't understand how Mercury got to be the way it is. So, there are huge mysteries about the origin of Mercury and that's what BepiColombo is designed to study," he told BBC News.
Europe's MPO was largely assembled in the UK by Airbus.
