A high-resolution image captured by Mars exploration rover Opportunity’s panoramic camera, of a puzzling rock outcrop, seen on Nasa’s screen. (AFP)

An image released by Nasa of a portion of the same outcrop. Data from the camera’s near-infrared, blue and green filters were combined to create this image, it said. (AFP)

American space agency Nasa has been accused of doctoring its pictures of Mars to make the Martian surface conform to our impression of the red planet. Nasa has been accused of digitally “tweaking” drab brown scenery to make it redder. It has even been suggested that Nasa removed green patches to hide evidence of life. The theories gained credence after Nasa told New Scientist that “getting the colours right is a surprisingly difficult and subjective job”, the magazine reported today. Most of the pictures have been taken through green, blue and infrared filters — instead of green, blue and standard red filters, which would have produced more accurate colours. Jim Bell, who worked with Nasa on the Mars rovers’ cameras, said infrared filters were used because they helped geologists distinguish rock types. In reality, Mars appears red largely because of the dust in its atmosphere.