Europe's BepiColombo mission has returned its first pictures of Mercury, the Solar System's innermost planet.

The probe took the images shortly after it zipped over the little world yesterday at an altitude of just 125 miles.

We will soon know a lot more about the smallest planet in our solar system.

Catching a planet is not easy. Mercury is named after the swift-footed Roman god of messengers and it zips along at over 100,000 mph. Bepi will make five more passes, each time slowing down a little, before entering the planet's orbit.

In 2025, at the end of its voyage, it will jettisonAbandon or throw away. powerful ion thrustersA method of propelling objects through space across huge distances. BepiColombo has the most powerful ion engine ever sent into space. and release two satellites. A Japanese orbiter will study Mercury's magnetic field. Its European counterpart will gather data on the planet's mysterious surface.

And Mercury is a weird place. A day lasts 55 days on Earth. With virtually no atmosphere, temperatures jump between 450C and -180C. The moon-like surface is pockmarked with huge craters called impact basins. The largest, Caloris1,550 km in diameter, Caloris is one of the largest impact basins in the solar system. Photographed for the first time in 2008, scientists discovered a mysterious unexplained "spider scar" at its centre., is as big as Western Europe.

We once thought this was an "ancient world" with nothing going on, says scientist Tom Watters. But the last probe to visit Mercury made discoveries that surprised everyone. MessengerThe groundbreaking mission between 2008 and 2015 discovered water ice and organic compounds at the north pole and took a "family portrait" photo of our solar system. detected a magnetic field and evidence of huge volcanic activity.

These included "big fire fountains of magma", says planetary geologist Brett Denevi. It suggests Mercury is rich in volatilesElements and compounds such as hydrogen, nitrogen and carbon dioxide are necessary for creating a breathable atmosphere and the building blocks of life., the essential ingredients for life. Space physicist Suzie Imber says the planet's formation is an "anomalyIn science, something that does not fit a pattern or behave as expected." that our current theories "can't explain".

Mercury is "much too extreme for any kind of life", Dr Imber says. But some wonder whether it could be a future home for humans. Current plans to colonise space focus on Mars and the moon. China plans a permanent colony on Earth's natural satellite by 2030 and Elon Musk's SpaceX aims for a Martian settlement by 2050.

But they face huge challenges. With no atmosphere, moonwalkers are exposed to radiation 200 times the level on Earth. Cosmic rays snap DNA in two and meteorites rip through spacesuits. Lunar dustA fine dust on the surface of the moon, formed by the debris from asteroid collisions. Because it is quite abrasive, Nasa is concerned that it could damage equipment and harm astronauts who spend prolonged periods on the moon., sharp as glass, damages everything it touches.

Alternatively, the atmosphere on Mars is mostly poisonous carbon dioxide. And its low atmospheric pressure literally boils blood. As planetary scientist Pascal Lee puts it, on Mars "you would fizz to death."

Water once flowed on Mars, with evidence of river valleys, flood channels and an ocean as big as the Atlantic. But a new study of Martian meteorites suggests it lost its water early in its history.

Mars was doomed to become a desert planet because of its size, says researcher Kun Wang. Small planets are unable to hold their magnetic field, so their atmosphere thins and volatiles vaporise into space.

Mercury does have a magnetic field. And there is water in its exosphereInstead of an atmosphere, Mercury has a thin layer of molecules blasted from the surface by solar winds and meteor strikes. and at the north pole. Below the surface, in lava tubesCaves opened up by lava flows and accessed by collapsed "skylights". They could also shield a colony from meteorites and cosmic radiation., there may be stable temperatures and mineral deposits. Planetary scientist Jeffrey Kargel says life on Mercury "might be nuts, but it's not completely nuts".

Some say no, Mercury is a dangerous wildcard. It has extreme deadly weather caused by its proximity to the sun and weak atmosphere. On Earth, solar winds create the Northern Lights and disrupt satellites. On Mercury, they cause colossal magnetic tornadoes that vaporise everything in their path.

Others say yes, Mercury's mysteries should give us hope. Its mineral wealth, low gravity and limitless solar energy make it the perfect mining colony and spaceship factory to begin our colonisation of space. The challenges we will overcome there will help us live in much less hospitable parts of the galaxy.