Friday, January 17, 2025
Top three images from BepiColombo’s sixth Mercury flyby - UNIVERSE
On 8 January 2025, the
ESA/JAXA BepiColombo mission flew past Mercury for the sixth time, successfully
completing the final ‘gravity assist manoeuvre’ needed to steer it into orbit
around the planet in late 2026. The spacecraft flew just a few hundred kilometres
above the planet’s north pole. Close-up images expose possibly icy craters
whose floors are in permanent shadow, and the vast sunlit northern plains.
At 06:59 CET, BepiColombo flew just 295
km above Mercury’s surface on the planet’s cold, dark night side. Around seven
minutes later, it passed directly over the Mercury’s north pole before getting
clear views of the planet’s sunlit north.
European Space Agency (ESA) Director
General Josef Aschbacher revealed the first image during his Annual Press
Briefing on 9 January. As during BepiColombo’s previous flybys, the
spacecraft’s monitoring cameras (M-CAMs) did not disappoint.
This flyby also marks the last time that
the mission’s M-CAMs get up-close views of Mercury, as the spacecraft module
they are attached to will separate from the mission’s two orbiters – ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter – before they enter orbit around Mercury in late
2026.
Celebrating the M-CAMs’ final hurrah,
let’s explore the best three images from BepiColombo’s sixth close encounter
with the little planet, and what they reveal about mysterious Mercury.
Mercury’s shadowy
north pole revealed by M-CAM 1
Open Image
Peering into Mercury’s darkest craters
After flying through Mercury’s shadow, BepiColombo’s monitoring camera 1
(M-CAM 1) got the first close views of Mercury’s surface. Flying over the
‘terminator’ – the boundary between day and night – the spacecraft got a unique
opportunity to peer directly down into the forever-shadowed craters at planet’s
north pole.
The rims of craters Prokofiev, Kandinsky, Tolkien and Gordimer cast
permanent shadows on their floors. This makes these unlit craters some of the
coldest places in the Solar System, despite Mercury being the closest planet to
the Sun!
Excitingly, there is existing evidence that these dark craters contain frozen water. Whether there is really water on Mercury is one of the key Mercury mysteries that BepiColombo will investigate once it is in orbit around the planet.
A surface shaped by impacts and lava
To the left of Mercury’s north pole in M-CAM 1’s view lie the vast volcanic
plains known as Borealis Planitia. These are Mercury’s largest expanse of
‘smooth plains’ and were formed by the widespread eruption of runny lava 3.7
billion years ago.
This lava flooded existing craters, such as the Henri and Lismer craters
highlighted in the image. The wrinkles in the surface were formed over billions
of years following the solidification of the lava, probably in response to the
planet contracting as its interior cooled down.
Mercury’s sunlit north
viewed by M-CAM 1
Open Image
Another M-CAM 1 image, taken just five minutes after the first, shows that
these plains extend over a large part of Mercury’s surface. Prominently visible
is the Mendelssohn crater, whose outer rim is barely visible above its flooded
interior. Just a handful of smaller, more recent impact craters dent the smooth
surface.
Further out, but still within the Borealis Planitia, the Rustaveli crater
suffered a similar fate.
On the bottom left of the image lies the massive Caloris basin, Mercury’s
largest impact crater, which spans more than 1500 km. The impact that created
this basin scarred Mercury’s surface up to thousands of kilometres away, as
evidenced by the linear troughs radiating out from it.
Above a particularly large trough, a boomerang-shaped curve brightens the
surface. This bright lava flow appears to connect to a deep trough below it. It
appears similar in colour to both the lava on the floor of the Caloris basin
and the lava of Borealis Planitia further north. Yet another mystery that
BepiColombo hopes to solve is which way this lava moved: into the Caloris
basin, or out of it?
Lava and debris
brighten Mercury’s surface
Open Image
On Mercury, a bright surface is a young surface
While M-CAM’s images might not always make it appear so, Mercury is a
remarkably dark planet. At a first glance the cratered planet may resemble the
Moon, but its cratered surface only reflects about two-thirds as much light.
On this dark planet, younger features on the surface tend to appear
brighter. Scientists don’t yet know what exactly Mercury is made of, but it is
clear that material brought up from beneath the outer surface gradually becomes
darker with age.
BepiColombo’s third image selected from this flyby, taken by M-CAM 2, shows
spectacular examples of the two things that bring bright material to the
surface: volcanic activity and large impacts.
The bright patch near the planet’s upper edge in this image is the Nathair
Facula, the aftermath of the largest volcanic explosion on Mercury. At its
centre is a volcanic vent of around 40 km across that has been the site of at
least three major eruptions. The explosive volcanic deposit is at least 300 km
in diameter.
And to the left lies the relatively young Fonteyn crater, which formed a
‘mere’ 300 million years ago. Its youth is apparent from the brightness of the
impact debris that radiates out from it.
Throughout its mission, several BepiColombo instruments will measure the composition of both old and new parts of the planet’s surface. This will teach us about what Mercury is made of, and how the planet formed.
Finishing in style
“This is the first time that we performed two flyby campaigns back-to-back.
This flyby happens a bit more than a month after the previous one,” says Frank
Budnik, BepiColombo Flight Dynamics Manager. “Based on our preliminary
assessment, everything proceeded smoothly and flawlessly.”
“BepiColombo’s main mission phase may only start two years from now, but
all six of its flybys of Mercury have given us invaluable new information about
the little-explored planet. In the next few weeks, the BepiColombo team will
work hard to unravel as many of Mercury’s mysteries with the data from this
flyby as we can,” concludes Geraint Jones, BepiColombo’s Project Scientist at
ESA.
Source: Top three images from BepiColombo’s sixth Mercury flyby – Scents of Science
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