NASA researchers say the bumpy surface of this chip of Martian meteorite ALH84001, seen with a scanning electron microscope, resembles fossilized bacteria colonies seen on Earth. (NASA)

A new NASA study of a Martian meteorite that made headlines 13 years ago strengthens the original claim that the rock contains evidence of life on ancient Mars.

Researchers at the Johnson Space Center used advanced electron microscopes that weren't available in 1996 to re-examine the magnetite crystals on the meteorite.

The meteorite, called ALH84001, was blasted from the surface of Mars 16 million years ago, scientists say, and is thought to have landed on Earth 13,000 years ago. An American scientist found it in Antarctica in 1984.

The original study, published in the journal Science in 1996, grabbed headlines and sparked a debate among scientists as to the origin of the crystals of magnetite, an iron-bearing, magnetic mineral, found in the meteorite.

The study suggested that some of the crystals were likely the result of biological processes because they looked so similar to those created by bacteria on Earth.

Other scientists argued that the magnetite crystals could be produced by chemical and physical processes, and even created similar crystals in the lab by heating carbonates.

In a new study, the Johnson Space Center researchers examined the magnetite crystals from the meteorite, known microfossil samples from Earth and other crystals created artificially in the lab using high-resolution scanning electron microscopes.

'Biogenic hypothesis is stronger now'

They found that the Martian crystals didn't resemble the ones created in the lab, and concluded that biology is still the best explanation for the Martian crystals.

"We believe that the biogenic hypothesis is stronger now than when we first proposed it 13 years ago," said Everett Gibson, NASA senior scientist.

"The evidence supporting the possibility of past life on Mars has been slowly building up during the past decade," said David McKay, NASA chief scientist for exploration and astrobiology.

"This evidence includes signs of past surface water … signs of current water near or at the surface, water-derived deposits of clay minerals and carbonates in old terrain, and the recent release of methane into the Martian atmosphere, a finding that may have several explanations, including the presence of microbial life, the main source of methane on Earth," McKay said.

The NASA team published their research in the journal Geochimica et Cosmochimica Acta of The Geochemical Society and The Meteoritical Society.