Click here for images from the launch of Japan's lunar probe

Google is offering $20 million to any company which can land a robotic rover on the moon and beam images of the lunar surface back to earth.

To be eligible, the winning craft will have to land on the moon, roam for a minimum of 500m and take a series of panoramic images as well as videos to be streamed on Google's website.

Participants have until the end of 2012 to complete the challenge.

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There is a $5 million second place prize, as well as $5 million in bonus cash if the winner exceeds the minimum requirements.

If no successful entry emerges by 2012, the winning prize will be lowered to $15 million, and the competition extended until 2014.

"I hope that a very ambitious team of people will allow us all to virtually go back ot the moon very soon - I couldn't be more excited about that," Larry Page, one of Google's co-founders, said launching the competition at a Wired magazine technology show in Los Angeles.

The search company is running the competition in conjunction with the X Prize Foundation - a not-for-profit group best known for awarding $10 million to the company which made the first private, sub-orbital space flight in 2004.

SpaceShipOne, the craft designed by the aerospace engineer Burt Rutan, is being developed by Sir Richard Branson's space tourism company Virgin Galactic, which has said it wants to offer $200,000 (£99,000) trips to space by 2009.

The Google-sponsored contest aimed to meet "one of the grand challenges of our time," Dr Peter H. Diamandis, the chairman and chief executive of X Prize Foundation, said at the launch.

Dr Diamandis added that while the technologies involved "weren 't easy," there was no reason, given the advancements in robot and sensor devices, why a team couldn't put together a machine that would meet the cometition requirements.

The 'Google Lunar X Prize' is offered at a time of renewed interest in lunar exploration.

Japan's space agency, Jaxa, today launched its first lunar orbiter, called Selene, from an island in southern Japan, and Nasa also plans send a probe into lunar orbit next year.

In a separate development, Google today called for the development of new privacy laws to protect personal information that is stored online.

Peter Fleischer, a privacy lawyer at Google, said that an international body, such as the United Nations or the Organisation for Economic Co-operation and Development (OECD), should draft new laws to replace existing guidelines which were out of date.

The OECD's guidelines on personal data were set up more than 20 years ago, and the European Commission's directive on privacy dated to 1995, when the internet was in its early stages.

Neither took account of the changes that had occurred in the internet and the shift towards storing large amounts of data online, Mr Fleischer said.

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