Link to newsround

Mission to solve Mars moon mysteries

An artist's impression of the MMX spacecraft - which is a gold and black spacecraft with large solar panels, thrusters and antenna - flies above the red surface of Mars, which looms large in the background. It is heading towards the small, dark and irregularly shaped moon called Phobos. JAXA

The spacecraft will head to Mars's larger moon, Phobos

Earth and Mars don't have a huge amount in common, but one thing they both share are moons.

Earth has one but did you know that Mars has two - Deimos and Phobos.

Scientists have puzzled for years about where Mars's two moons came from.

And now a Japanese-led mission launching on Monday is hoping to find the answer.

More stories from the red planet

What is the Mars Moons Exploration mission?

Mars fills most of the scene - it is orange and its surface is pitted with craters and canyons. Next to Mars, and against the blackness of space, there are its two small, irregularly shaped moons. In the foreground, the larger moon Phobos is pale red and covered in craters. In the distance, the smaller moon, Deimos, is grey and orange with an irregular shape.NASA

Mars got its moons about 4.5bn years ago - but no one knows how they formed

Japan's space agency, Jaxa, have called this the Mars Moons Exploration mission, or MMX.

Following blast-off on Monday 19 October, a spacecraft will begin the journey from Earth to Phobos - the larger of Mars's two moons.

Jaxa say the plan is for the MMX rover to land on Phobos in August 2027, and collect a sample of rock from the moon's surface.

This has never been done before in the history of space exploration.

Scientists want to know if the Mars moons were created from the debris of smashed Martian rock, or if they are in fact made up of asteroids from the outer Solar System.

Prof Sara Russell, from the Natural History Museum in London, will help analyse a sample of the Mars moon Phobos when it is returned to Earth.

"I think this is an incredibly ambitious and fun mission," she said.

An artist's impression of the MMX spacecraft on the dark, rocky surface of Phobos. The spacecraft is gold and black and has four triangular legs and dark solar panels. The red disc of Mars is in the background.JAXA

The spacecraft will collect 10 grams of moon dust from the surface of Phobos

Both of Mars' moons are very small in comparison to our Moon.

Phobos is 20 kilometres wide (12 miles) and Deimos is 10 kilometres (6 miles).

They are also not ball-shaped like our Moon, instead they have been described as shaped like potatoes!

Once the MMX rover has collected its sample, it will send them back to Earth in 2031.

It's hoped the sample will land in a desert in South Australia.

And the amount that is being returned is very small - just 10 grams. That's the same weight as a dry tea bag!

But despite the small size, there's a lot you can do with it said Dr Chrysa Avdellidou from Leicester University.

"You don't need to have kilos back from a surface in order to do science. So it's worth every gram," she told BBC News.