Perched on a rock, she could be waiting for a bus.

But if so, she could be in for an awfully long wait.

A photo of what looks remarkably like a female figure with her arm outstretched was among several taken on Mars and sent back to Earth by NASA's Mars explorer Spirit, Britain's Daily Mail reported yesterday.

Though no official confirmation has come from NASA on whether the figure is an alien or an optical illusion caused by landscape on Mars, it has set the Internet abuzz that whether there really is life on Mars.

As one enthusiast put it on the newspaper's website: "These pictures are amazing. I couldn't believe my eyes when I saw what appears to be a naked alien running around on Mars."

Another wrote: "If you show me another rock in another photo from Mars, that naturally looks like that, I will reconsider."

A third contributor, who came closer to the majority view, said: "Ah, the human eye can be tricked so easily."

The news of the mystery woman on Mars came just days after a team of French scientists claimed to have discovered proof that Mars has high dense clouds of dry ice, which scud across its orange sky, Indian newspaper Hindustan Times reported.

Using data obtained by the OMEGA spectrometer on board European Space Agency's Mars Express, the team found the existence of ice clouds which sometimes become so dense that they throw quite dark shadows on the dusty surface of the planet.