This 1999 Hubble telescope image shows Mars when Mars was 54 million miles (87 million kilometers) from Earth. A NASA spacecraft designed to investigate how Mars lost its water is expected to put itself into orbit around the Red Planet on Sunday after a 10-month journey. After traveling 442 million miles (711 million km) from Earth, the Mars Atmosphere and Volatile Evolution, or MAVEN, probe faces a do-or-die burn of its six braking rockets beginning at 9:37 p.m. EDT/0137 GMT. REUTERS/NASA/Handout

Conspiracy theorists and alien hunters are ever more convinced that life once existed on Mars as shown by a picture taken and transmitted back by NASA's Curiosity Rover in which a concrete coffin was allegedly visible.

First raised by blog site UFO Sightings Daily and picked up by The Daily Mail, the reported stone-carved alien coffin is thought to have the following dimension - 3.2 feet long and 1.5 feet both width and depth.

A YouTube clip is viewable here.

Traces of past alien activities

The same blog report is claiming that with the observed built and measurement, the mysterious coffin is able to hold extra-terrestrial life form that UFO enthusiasts refer to as "greys," generally characterised as short aliens.

Greys are rendered too as unusual life forms - "with an oval shaped head and large eyes," in numerous Hollywood-made films, The Daily Mail noted on its report.

Accompanying the observed discovery are stoneworks that lie near where the coffin rests, which the blog report said indicate of "some old civilisation constructions."

Whether these claims will get confirmation is the big question as the report conceded that authorities will routinely dismiss the latest sighting.

The blog report asked: "What would it take to get NASA to turn the rover around and examine the contents of this box?"

Fertile minds

Scientists, however, are not buying that a concrete coffin was once used and is now abandoned on Mars, The Daily Mail said.

Sightings such as the coffin on Mars fall on what experts termed as Pareidolia or the natural ability of the human mind to conjure up wild imaginations that lead to the recognition of known shapes and forms when focused on a particular object.

This psychological phenomenon, the UK-based publication added, is especially helpful in spotting familiar faces in a sea of crowd.

Objects are also made out by some individuals "even when they're not there," and it's all because of Pareidolia, the report added.

The Daily Mail cited previous cases of apparitions in which persons saw the mirage of religious icons such as the Virgin Mary, Jesus Christ and the Pope as solid instances of Pareidolia.

And the same applies when alien hunters put out reports of fossilised lizard and even the face of U.S. President Barack Obama being observed on images taken of the Martian surface.

In recent months though, fantastic claims have surfaced that intelligent life forms once walked, flourished and established a civilisation on the Red Planet when it was Earth-like but was eventually obliterated when Mars came under nuclear attack from a rival alien group millions of years ago.