HAVING helped spread the internet's tentacles across the globe, boffins are now thinking of extending them further. Assorted space agencies believe it would be rather nifty if the world wide web encompassed more of the world than just one planet. Those at the European Space Agency (ESA) are therefore designing an interplanetary network, which might help space stations, planetary rovers, astronauts and ground stations communicate more effectively.

In October they are planning to test just such a network by getting an astronaut in the International Space Station (ISS) to control a rover on Earth. This will be a test of the technology for use on future Mars missions. They are also exploring the possibility of creating a universal information-exchange system, allowing many of the different space agencies to share data quickly.

Nestor Peccia, who heads ground-software development at the ESA, says that the main challenges are more political than technological. An interplanetary web's assets, like Earth ground stations, relay satellites, rovers, moon stations, etc, will probably belong to national space agencies. Government agencies may be reluctant to share them with others and it may be a while before enough space entrepreneurs like Elon Musk stump up the amounts of money need in to mimic Earth-bound internet's decentralised charm in orbit.

These would be considerable. It tends to cost around $50m just to launch a single satellite, not counting design and construction, though Mr Musk's company, SpaceX, may yet bring that down. And a fully fledged interplanetary web would need a sizeable flotilla.