BepiColombo mission captures Mercury in unprecedented detail

The ESA/JAXA BepiColombo mission has successfully completed its fourth of six scheduled gravity-assist flybys of Mercury, capturing impressive images of two notable impact craters.

By utilizing Mercury’s gravitational pull, the spacecraft is fine-tuning its trajectory to eventually enter Mercury’s orbit in November 2026.

BepiColombo mission to Mercury

BepiColombo made its closest pass to Mercury at 23:48 CEST (21:48 UTC) on September 4, 2024, coming within just 165 kilometers of the planet’s surface.

For the first time, this flyby provided the spacecraft with a clear view of Mercury’s south pole.

“The main aim of the flyby was to reduce BepiColombo’s speed relative to the Sun, so that the spacecraft has an orbital period around the Sun of 88 days, very close to the orbital period of Mercury,” said Frank Budnik, BepiColombo Flight Dynamics Manager. 

“In this regard, it was a huge success, and we are right where we wanted to be at this moment. But it also gave us the chance to take photos and carry out science measurements, from locations and perspectives that we will never reach once we are in orbit.”

Viewing Mercury from different angles

Three monitoring cameras onboard the spacecraft captured unique views of Mercury from different angles.

BepiColombo approached the planet from the “nightside,” where the surface of Mercury gradually became illuminated by the Sun as the flyby continued.

M-CAM 2 delivered the clearest views of the planet, while M-CAM 3 also captured an impressive image of a newly named impact crater.

M-CAMs 2 and 3 have now been powered down, but M-CAM 1 will continue photographing Mercury until about midnight, giving one last view of the planet as it recedes.

Dramatic images of Mercury’s craters

A few minutes after its closest approach, BepiColombo spotted a large “peak ring basin” – a crater formed by the impact of an asteroid or comet.

These craters, ranging from 130 to 330 kilometers across, are defined by their inner ring of peaks.

One such crater is Vivaldi, named after the renowned Italian composer Antonio Vivaldi.

The crater spans 210 kilometers, and because BepiColombo observed it near the planet’s sunrise line, shadows dramatically highlighted its features.

A visible break in the peak ring shows where lava flows have recently entered and filled the crater.

Shortly after, another notable peak ring basin came into view. This one, 155 kilometers in diameter, was recently named Stoddart after New Zealand artist Margaret Olrog Stoddart.

“When we were planning for this flyby, we saw that this crater would be visible and decided it would be worth naming due to its potential interest for BepiColombo scientists in the future,” said David Rothery, member of the BepiColombo M-CAM imaging team.

Mercury’s peak ring basins

Mercury’s peak ring basins remain a subject of curiosity, with many questions still unanswered about their formation.

The peaks within the craters are believed to have been created by a rebound process during the impact, but scientists are still unclear about how deep these materials originated.

Additionally, many of Mercury’s basins, including Vivaldi and Stoddart, have been partially filled by lava flows long after the impacts. Stoddart’s crater, for instance, shows traces of a smaller 16-kilometer crater beneath the newer lava layer.

These peak ring basins are a top priority for further study once BepiColombo begins its detailed survey of Mercury with its full array of scientific instruments.

Observing the scars of billions of years

The images taken during this flyby, from BepiColombo’s closest pass to date, provide a fascinating look at Mercury’s surface.

These shots reveal the scars of billions of years of impacts by asteroids and comets, offering clues about the planet’s history and its role in the broader evolution of the Solar System.

It’s important to remember, however, that these photos were an added bonus. The M-CAMs are not intended for studying Mercury but were designed to monitor the spacecraft during critical phases, such as after launch. 

They produce black-and-white images at a resolution of 1024×1024 pixels. BepiColombo’s main science camera is protected during its journey to Mercury and will capture much higher-resolution images once the spacecraft enters orbit.

Future of the BepiColombo mission 

By 2027, BepiColombo’s primary science mission will begin. The mission’s full suite of instruments will then reveal much more about Mercury, uncovering details that are currently invisible to us, and helping scientists better understand the planet’s origin and its proximity to the Sun.

Meanwhile, science is already underway. Most of BepiColombo’s instruments were activated during the flyby to measure Mercury’s magnetic field, plasma, and particle environment.

These data are crucial, as they come from regions that the spacecraft won’t be able to access once it is in orbit.

BepiColombo comprises two scientific orbiters: ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter. These orbiters are being transported to Mercury by the Mercury Transfer Module. 

Even though the spacecraft is in a “stacked” configuration during this cruise phase, preventing full operation of many instruments, scientists can still gather valuable data and prepare the instruments for the mission’s main phase.

Solving the mysteries of Mercury 

“BepiColombo is only the third space mission to visit Mercury, making it the least-explored planet in the inner Solar System, partly because it is so difficult to get to,” said Jack Wright, an ESA research fellow, planetary scientist, and M-CAM imaging team coordinator.

“It is a world of extremes and contradictions, so I dubbed it the ‘Problem Child of the Solar System’ in the past. The images and science data collected during the flybys offer a tantalizing prelude to BepiColombo’s orbital phase, where it will help to solve Mercury’s outstanding mysteries.”

The fourth flyby is just one step in BepiColombo’s journey. The spacecraft is now on course for its fifth and sixth flybys of Mercury, scheduled for December 1, 2024, and January 8, 2025.

Each flyby brings BepiColombo closer to Mercury’s orbit around the Sun.

After the sixth flyby, the BepiColombo flight control team will return to a regular cruise phase until the spacecraft finally enters orbit around Mercury in November 2026.

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