SESSION 8 LIFE ON MARS?

The planet has long fascinated people because of the possibility that it harbours life In the 1890’s Percival Lowell suggested either past or present intelligent life on Mars to account for the presence of canals and seasonal colour changes His beliefs had a big following for some fifty years and imagination ran riot

Shaking hands with a martian soon after arrival

Flash Gordon meets with a local Martian in 1938

Martian invader meets the congregation in the 1996 Warner Brothers movie Mars Attacks!

CATCHING UP WITH FICTION In 1965 Mariner 4 took the first close-up images of Mars and found a heavily cratered landscape but no channels. In 1976 the twin Viking missions were dispatched to Mars specifically to look for life. They found no such evidence but discovered that the planet had very low temperatures, high radiation levels and a thin atmosphere lacking in oxygen

HUBBY’S SURPRISE In 1996 NASA scientist Everett Gibson brought home electron micrographs of a rock taken under high magnification His wife Morgan who was a biologist took one look at the image and asked “Why have you brought home images of bacteria?’ He told her that the rock in question had come from Mars and had the label ALH84001

What Morgan saw – a fossil from Mars?

STRANGER FROM MARS Gibson had many years experience in planetary geology having directed a programme of rock collecting on the Moon during the lifetime of the Apollo project How could NASA possess a rock from Mars when there have not yet been any missions to bring rock specimens back from the surface of the red planet?

METEORITES About 40,000 tonnes of space debris reaches earth every year and most of this has come from the asteroid belt They date at approximately 4550 million years, the age of formation of the solar system Occasionally meteorites are found that have younger ages and they are believed to have come from one of the rocky planets, especially Mars, our nearest neighbour

IMPACTS ON MARS To eject Martian rock fragments into space would require the impact of a large meteorite powerful enough to leave a crater at least 10 km in diameter. Quite a few are known Rock types involved would have to be massive igneous rocks such as basalts or granites in order to survive the impact without being pulverized

METEORITE COLLECTING More than 7,500 meteorites have been collected from around the world but only the larger ones survive passing through the atmosphere without burning up A favourite collecting place is Antarctica where dark-coloured meteorites are readily visible against a white background of ice and snow

SPECIMEN ALH84001 The catalogue number indicates that it was the first specimen to be collected in the Alan Hills of Antarctica in 1984 Specimens from Mars can be identified because compared with other meteorites they have a high water content, an abundance of oxygen bearing minerals and a distinctive oxygen isotope composition

Meteorite from Mars

METEORITES FROM MARS Twelve of the meteorites studied so far are believed to have come from Mars They are called SNC meteorites after the three principal discovery sites of Shergotty, Nakhla and Chessigny The Nakhla meteorite from Egypt is reputed to have killed a dog on impact Total weight of the many fragments was about 10 kg

SPECIMEN ALH84001 When found it weighed 1.9 kg and was about the size of a large potato Its age was determined as 4,500 MY indicating that it was probably part of the original crust of Mars AT 3,900 MY the rock became cracked and the fissures were filled with carbonate, sulphide and oxide minerals It contained tiny pockets of trapped air similar in composition to Mars’s atmosphere

NASA STUDIES The meteorite was studied by McKay and co-workers and they came up with five lines of evidence of life on Mars at the time: Carbonate minerals present as globules look similar to crystal aggregates produced by bacteria on Earth Structures within globules resemble bacterial remains found on Earth

NASA STUDIES Iron sulphide and oxide minerals present in forms known to be produced by bacteria (see next slide) Co-existence of minerals in cracks may indicate non-equilibrium conditions characteristic of life Organic compounds present may have been produced by living organisms

Magnetic crystals from the Martian meteorite magnified a half million times appear to be dead-ringers of crystals produced by bacteria on Earth

NASA CONFERENCE A press conference was held in Washington on 6 August, 1996 to announce probable evidence of former life on Mars The media had a field day but much of the evidence has since been labeled as inconclusive by other scientists

A field day for the media!

Some examples of front page news in American newspapers

NAKHLA METEORITE It fell to Earth in Egypt 28 June, 1911 and is of basaltic composition. It broke into many pieces together weighing about 10kg Its age is approximately 1300MY and it shows evidence of having been altered by the presence of water at about 1100MY. It was blasted from Mars into space about 11MY

Fragment of Nakhla meteorite

SIGNS OF LIFE? US geologist Fisk found tubular holes in the meteorite that appear similar to ones found in volcanic rocks on Earth They are 1 to 3 micrometers in diameter and up to 10 micrometers long Norwegian geologists found similar holes in 3500 MY old basalts and claimed that they were the earliest evidence for life on Earth

Tubular holes in Earth rock compared with similar evidence from the Nakhla meteorite

METHANE – SIGN OF LIFE? In 2004 a German scientist using a very sensitive spectrometer on board Mars Express detected very low concentrations of methane in the Martian atmosphere Strong UV radiation on Mars causes rapid breakdown of methane so there has to be a source producing enough gas to maintain its concentration

METHANE – SIGN OF LIFE? On Earth most methane found in the atmosphere is produced by microbes Such microbes survive even in the Greenland Icecap despite the frozen state of the medium Geologists claim that weathering of the mineral olivine, common in basaltic rocks, could be responsible for producing the levels of methane found on Mars