【明報專訊】On 2 March 2004, NASA announced that Opportunity (機會號), a Mars rover (火星探測車), had landed in an area of the planet "where liquid water once drenched (覆蓋) the surface", fascinating scientists worldwide.

1. Opportunity and its scientific findings

Also known as MER-B (Mars Exploration Rover - B) or MER-1, Opportunity is a robotic rover that has been active on Mars since 2004. Launched on 7 July 2003, it has amassed an enormous amount of scientific information related to the geology (地質學) and atmosphere (大氣) of Mars.

Opportunity was first directed to a site that had displayed large amounts of hematite (赤鐵礦), which often forms in the presence of water. When Opportunity landed, layered rocks and marble-like hematite concretions (結石) were easily visible. On 5 March 2004, NASA announced that Spirit (精神號), Opportunity's twin rover, had found hints of water history on Mars in a rock dubbed "Humphrey". In its years of continuous operation, Opportunity sent back much evidence that a wide area on Mars was soaked in liquid water.

Water on Mars exists today almost exclusively as ice, with a small amount present in the atmosphere as vapour.

2. Why are we so interested in Mars?

Humankind's fantasies about finding a habitat outside Earth are well demonstrated in such films like 2001: A Space Odyssey (《2001太空漫遊》, 1968), an all-time classic, and Interstellar (《星際啟示錄》, 2014), a recent blockbuster. Owing to its proximity and similarity to the planet we live on, Mars is one of the planetary bodies that continue to fuel our imagination of space colonisation. In 2014, Mars One, a Dutch company, launched a Mars migration programme, which drew over 100,000 applications. The company intends the journey to be a one-way trip, meaning that those chosen to join the programme will have to stay on Mars.

But is Mars habitable? So far there is no evidence of life on Mars. That said, there is a growing body of evidence that Mars once was habitable and it may harbour life forms now. NASA reported in January 2015 that Opportunity and Curiosity (好奇號), another Mars rover, will now be searching for evidence of ancient life.

3. Space exploration - is it worth the money?

In Interstellar former NASA pilot Cooper, played by Oscar-winning actor Matthew McConaughey, is dismayed when a teacher of his daughter tells him the 1969 moon landing of the US was a fake intended to "bankrupt the Soviet Union". This scene well captures many people's scepticism (懷疑態度) over space exploration. Opponents to space exploration argue that it gives mankind no direct benefit and our money should be spent to address problems on Earth. The Space Shuttle programme, for example, has long been cited as a colossal waste of the taxpayer's money. The programme was shut down in 2011. Since then NASA has increasingly relied on collaboration with companies such as Deep Space Industries and SpaceX for travel to space.

However, supporters argue that scientific findings from space exploration have important applications on Earth. In fact, NASA has revealed in its 2015 budget its proposal to work together with a mining company to carry out a project in which an asteroid (小行星) will be retrieved and its samples of resources will be sent back to Earth.