MERCURY, the tiny planet closest to the sun, has long remained a mystery.
But it’s hoped a new British-built spacecraft will change all of that, as it prepares to blast off later this month seeking answers of the solar system’s most volatile planet.
The famously dark planet, which is largely made from iron, has been awash with conspiracy theories, including an ‘alien door’ and 17 ‘alien domes’ that were spotted on its surface.
The mission, BepiColombo, one of the most ambitious ever undertaken by the European Space Agency, hopes to set the record straight and unravel many unanswered questions about Mercury.
Costing £1.4bn, it will take seven years for two orbiters to explore the planet where temperatures can reach a fiery 500C.
It is only the third ever mission to Mercury, following Mariner 10 in 1973 and MESSENGER – which stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging – in 2004.
The scientists working on the new spacecraft hope to “piece together a bigger picture of the Solar System and our place in it”.
An artists’ impression of the BepiColombo spacecraft
A tale of two extreme temperatures
Mercury is the smallest planet in our Solar System, taking the accolade from Pluto in 2006 after it was downgraded to a ‘dwarf planet’.
It is the closest planet to the sun, and has a radius of just 1516 miles – slightly less than the distance between London and Moscow.
Scientists describe it as a “place of extremes”: on the half facing the sun, it has a scorching temperature of 510°C, while the night side freezes at –210°C – because of this, it is believed to be unable to support life.
Its axis has very little tilt so its polar regions don’t receive much direct sunlight – in fact some of the craters in this area are kept forever dark.
Due to these quirks, the planet has long baffled scientists.
The MESSENGER mission showed that Mercury was shrinking, and that its core has more iron in it than any other planet in the solar system.
What scientists do know is planets that form near each other have similar interior structures.
Venus, Earth and Mars all have small, dense metallic cores at their centres which are surrounded by a thick blanket of rock.
However, Mercury is missing most of its rocky sheath – and scientists don’t know why this is.
Theories include Mercury forming elsewhere then migrating towards the centre of our solar system, that it had a collision with another planet or asteroid that scraped its skin of lighter material.
Essentially, there is a secret in Mercury’s past to explain why it’s mostly metal – and it’s something this latest mission could potentially uncover.
Alien doors and second suns
As it has such an unusual structure, it’s little surprise Mercury has been the focus of conspiracy theories.
Two years ago, self-described alien fanatic Scott C. Waring was looking over some photos of the planet when he spotted what he believed to be a “black doorway” he estimated to measure 3.4 miles long on its surface.
“It is long and rectangle in shape with four almost perfect right-angled corners,” he said at the time.
“Unless meteor cubes are pummelling planets, this seems to be made by ancient aliens.
“That is a giant doorway for giant ships to travel through.”
That same year, Waring also wrote on this blog that he could see 17 “domes” on the edge of craters on Mercury, after looking at close-up images taken by NASA.
Again, he believed these were structures created by ancient aliens.
While Paul Cox, an astronomer, claimed in 2016 that there is a “second sun” in our solar system, that NASA has been deliberately keeping secret.
During an eight-hour live broadcast, he showed a live feed of his telescope examining the planets.
Pointing to a black dot – Mercury – he said it wasn’t the planet but in fact another sun.
“I don’t know if you knew that we had a second sun,” he said. “But there it is. It is normally hidden from view. NASA and other organisations usually hide that stuff away from us.”
During his ‘Transit of Mercury’ video, Cox also alluded to the Planet X theory, which says that a broken planet will come from behind this sun, eventually crashing into Earth and wiping out humanity.
And keen astrologers will be familiar with the ‘Mercury Retrograde’ theory – an illusion where the planet appears to travels backwards three to four times a year.
When this happens, it’s believed to cause chaos on Earth and meddle with technology, travel and communication.
Years that are shorter than a day
Strangely, one day on Mercury (sunrise to sunrise) is longer than one year on Mercury (one orbit around the Sun).
This is because while it orbits the Sun quickly, it rotates more slowly on its axis. It can travel around the Sun in 88 Earth days, but takes double that – 176 Earth days – to spin round on its own axis.
And its unusual year isn’t the only odd thing: the surface of the planet is a mix of giant plains, impact craters and imposing ridges, some of which are hundreds of miles long and more than a mile high.
One astronomer at the Royal Observatory in Greenwich, Jim O’Donnell described these as “geological features we don’t see on other planets”, and adds that “no one knows how they formed”.
Scientist Professor Emma Bunce, who is working on the BepiColombo project which will map every part of the planet’s surface – says the MESSENGER mission supplied some answers, but “also raised more questions”.
“However, one thing Messenger taught us is that there are many volatile substances on Mercury’s surface,” she says. “This is a puzzle because the heat of a major impact should have burned these volatiles (substances such as sodium, potassium and chlorine) away.”
Another mystery is the fact that there is X-ray florescence – a bit like the Northern Lights – on the planet’s ‘dark side’, despite there being no sun there.
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This, Professor Bunce says, is another unusual scenario in the solar system that we can study to learn more about Earth and how the Universe formed.
“We want to understand how the solar system works and how it was formed,” says Professor Bunce.
“Knowing how Mercury has survived will help us piece together a bigger picture of the solar system and our place in it.”