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I think we were all inspired by the Japanese adventure in bringing samples of asteroid back to Earth. The capsule which is now safely installed in the Sagamihara curation facility in Kanagawa.

We await news of the opening of the canister and confirmation that asteroid dust is inside.

Of course, the really big prize would be to , a planet where microbial life may once have thrived (and may still in some corner).

And I've had an opportunity in recent days to discuss the topic with top Nasa officials who've been on a tour of Europe to review progress on the European Space Agency's (Esa) .

As previously mentioned in this blog, all US and European activity at the Red Planet will become a combined effort from mid-decade onwards.

This joint initiative will start in 2016 with an orbiting spacecraft that will investigate trace gases such as methane in the Martian atmosphere, and then progress on to a double rover mission that will launch in 2018.

The Americans plan on using a "" to land both the ExoMars vehicle and a robotic rover of their own design.

This will be an extraordinary sight - if only you could be on Mars to see it!

The skycrane is a kind of rocket-powered cradle. The crane will lower a pallet containing the two rovers on to the surface before moving itself clear and dropping to the ground at a safe distance.

We'll be able to assess how well this technology works in 2012 because the exact same system is being used to land the next US rover, .

The one big difference is that MSL will be put down directly on to its wheels; there will be no pallet involved.

The crane should be capable of landing a tonne or so, which means ExoMars and its co-passenger American vehicle will be allocated 300kg each.

But what will the US robot actually do? and how it will drill below the surface looking for extinct or extant life, but I must confess I've been a little vague on the American side of things.

Their vehicle will be what's termed a caching rover. Its working name is Max-C (Mars Astrobiology Explorer-Cacher [PDF]). It will seek out interesting rocks on the surface of the planet, study them with a suite of instruments and then bag samples. Charles Whetsel, a spacecraft systems engineer at Nasa's Jet Propulsion Laboratory, described the US rover's mission to me this way:

"The concept right now is that it will have a coring tool able to go about five centimetres in, about a centimetre in diameter. It will be able to go up to the rocks we find most interesting and take a 'biopsy', if you will, to lift the core out and start building up a library onboard the rover. If we can do one of those every week or so, and we plan on being there for the better part of a year, at the end of that year we could have a little 'backpack' of about 30 samples."

Nasa now says these cores gathered by Max-C will be the same ones that a later mission, perhaps in the 2020s, will attempt to retrieve and bring back to Earth. Doug McCuistion, the director of the Mars Exploration Program at Nasa Headquarters in Washington DC, told me:

"Our expectation is that these samples will be acquired with the intention to go get them, unless something significant occurs that prevents us from doing that."

So, the Mars sample return project starts in earnest with the launch of ExoMars and Max-C in 2018. This makes it a hugely significant venture.

It raises some interesting questions, too, which Nasa and Esa planners have really only .

Can a landing location be identified that is optimal for both drilling into the sub-surface and for finding the right type of rocks you might want to bring back to Earth?

Also, when the two rovers drive off their pallet, do they go in the same direction or do they stick close together? Charles Whetsel:

"We're still talking about that. For us, getting those 30 cores is going to involve some hoping about on our part, whereas ExoMars's theme will be about getting below the surface and exploring Mars with vertical mobility instead of horizontal mobility. That means ExoMars will tend to go to a relatively small number of sites and camp out. The science community has started thinking about how you might reconcile those different modes of operation. One possibility is that you could use the rock-hopping approach of the American rover to scout out locations for ExoMars."

One question that comes into my mind: is there any possibility that ExoMars could pass some of the material it has drilled from two metres below the surface over to Max-C? After all, we know the ultraviolet conditions on the surface today would make it a tough environment for any Martian microbes. There's more chance of them existing deeper in the dirt.

Well, the engineers are apparently considering this one, too.

Max-C's backpack will need to be easily accessible to the later retrieval mission. One idea is that the rover simply dumps a canister on the ground that can be picked up and then blasted into orbit for capture and boosting back to Earth.

But we're getting a little bit ahead of ourselves here. First, ExoMars and Max-C have got to be made to work before we can start dreaming of what might be in the 2020s.

I tell you what I am looking forward to, though - seeing the pictures the rovers take of each other.

The static lander imaged the little Sojourner rover on the Red Planet in 1997, but this would be something different altogether - an album of snaps from a fly-drive excursion on another planet.

Watch this space.

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