Just 50 years ago, astronomers thought Mars was a dead, icy stone desert with almost no chance of life ever thriving there.
That view changed completely when the American space probes Viking 1 and Viking 2 went to the planet in 1976 and sent pictures back to Earth. The images showed clear outlines of dried up lakes, rivers and oceans on the surface.
Where there is liquid water, there can possibly be life, and Mars is therefore an obvious place when scientists try to answer one of the biggest questions in science: Did life start somewhere other than on Earth or are we alone in the universe?
Since the Viking probes landed on Mars, we have sent many probes and satellites to get answers. More and more research indicates that some form of life may have thrived on the red planet and may even still thrive. Here are the five biggest milestones in scientists’ quest for definitive proof.
1996: Pictures of microbes
The ALH 84001 meteorite is found in Antarctica. It contains shapes that look like petrified bacteria.
Meteorites contain possible fossils
Who made the discovery?
NASA scientists made headlines in 1996 when they announced that the Martian meteorite ALH 84001 contained definite evidence of life on Mars.
What was the discovery?
Studies of the rock showed that it formed in a watery environment on Mars four billion years ago. Inside the rock, scientists found forms that looked like fossilized bacteria. In addition, the meteorite contained small spherical carbon particles and crystals that may have formed from bacteria on Mars.
How secure is the evidence?
Today, the vast majority of scientists believe that the possible signs of life in ALH 84001 are either due to contamination of samples from Earth or of an inorganic origin.
2008: Food sources for bacteria
In 2008, the Phoenix spacecraft found special salts that could be the basis for the existence of bacteria.
The spacecraft looks for possible food that bacteria took advantage of.
Who made the discovery?
NASA’s Phoenix Mars Lander was a vehicle that operated in the red planet’s northern reaches known as the Vastitas Borealis. The goal was to investigate whether ice was hidden beneath the surface of Mars.
What was the discovery?
Phoenix found not only ice, but also perchlorate salts that can be food for bacteria. The salts also have the ability to keep water liquid at -72 °C. With both that nutrition and water, bacteria can thrive.
How secure is the evidence?
Experiments have shown that the salts cannot sustain life in terrestrial bacteria under conditions similar to those on Mars. However, it cannot be ruled out that Martian bacteria are much more hardy than those from Earth.
2012: Possible remnant cells
The Curiosity rover is still traveling through Gale Crater, which billions of years ago contained a large lake.
Craters contain the building blocks of life
Who made the discovery?
NASA’s Curiosity rover, which landed in Gale Crater in 2012, has found more signs of life on Mars recently.
What was the discovery?
There is a large lake in the crater, and in drill samples, the probe has identified organic molecules that resemble fatty acids in the cell walls of bacteria. In addition, the samples contain materials similar to the building blocks of oil and natural gas. Here on Earth, oil and natural gas are formed mainly from plankton that has sunk to the bottom of shallow oceans.
How secure is the evidence?
The results are strong evidence that there was life on Mars when the planet was young, but scientists are still unsure.
2015: Strange methane release
The Trace Gas Orbiter satellite searches for methane in the Martian atmosphere. The gas could be a sign of life today.
Mysterious methane may be coming from living organisms
Who made the discovery?
The space probe Curiosity has detected traces of methane gas, which are now being studied in more detail by the ESA Trace Gas Orbiter satellite.
What was the discovery?
The mysterious release of methane measured by the probe in Gale Crater could be coming from below the surface, but it could also be caused by living methane bacteria that are especially active in the summer. Although the satellite has not yet spotted methane above Mars, it may be because the gas breaks down and dissipates on its way up through the atmosphere.
How secure is the evidence?
The evidence is not enough. The concentration of the methane gas must be higher to determine if it is of biological origin.
2033: Borkjarnar promises good things
The drill core in the middle of the image may contain evidence of life on Mars. It will be revealed when he returns to Earth in 2033.
Drilling tests can provide a definitive answer
Who made the discovery?
NASA’s Perseverance spacecraft is currently operating in the water crater, which was covered by a lake and river system 3.5 billion years ago. The goal is to drill and collect 43 drill cores.
What will be the possible discovery?
At the edge of the river system, Perseverance has drilled cores in shale containing large amounts of organic molecules of possible biological origin. Now the space probe is drilling in the riverbed itself. Here on Earth, river systems are teeming with life, so the hope is that the Jezero Crater samples will contain fossilized microbes.
When will we get bullet proof evidence?
The plan of NASA and ESA is to organize a mission that in 2033 will bring 30 drill cores from Mars for research on Earth.
