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Mars 3 lander, 1971 - The first successfully landed spacecraft on Mars was the Soviet Mars 3 lander, but its success was short-lived.

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Transmission lost - The Mars 3 lander sent back one photo, which is too blurry to be of any use, before losing transmission with Earth forever during the dust storm it landed in.

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20 seconds - The Mars 3 lander started transmitting back to Earth 90 seconds after landing, but stopped again after 20 seconds. Though a dust storm is believed to be the cause, no one is certain.

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Viking 1 lander, 1975 -

For NASA's first successful landing on Mars, NASA prepared two identical spacecrafts called the Viking 1 and the Viking 2. 

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Six years - The Viking 1 lander was the first spacecraft to succeed in its mission to Mars, spending over six years on the Martian surface, relaying a plethora of photos and data back to Earth.

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Search for life - Viking 1's mission was to search for life on Mars, and to test the conditions on the planet. Whether or not what the Viking 1 found was organic matter is the subject of some debate.

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Viking 2 lander, 1976 -

The Viking 2 landed on the Martian surface in 1976 and lasted four years until its batteries died.

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16,000 images - The Viking 2 lander studied the soil and rocks, and relayed 16,000 images back to Earth. The Viking 2 also claimed to have found organic material on Mars, though some argue they were reactions between non-organic materials.

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Water - The biggest discovery the Viking landers made was the dried up, former waterways on the surface of Mars.

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Mars Pathfinder and Sojourner, 1997 - The Pathfinder and Sojourner mission was the first where a rover would explore the Martian surface, ushering in a new era of planetary exploration.  

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Three months - The Sojourner lasted three months and traveled 100 m (328 ft), though it was only expected to last seven days.

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Cheaper and faster - Though the Pathfinder and Sojourner both performed environmental experiments, much of their mission was to prove that sending a lander and a rover to Mars could be done with only three years preparation time and at a low cost.  

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Rover - The Sojourner rover had three cameras, tested rocks for their composition, and was only solar-powered, meaning it couldn't travel at night.

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Volcanic activity - The mission confirmed former volcanic activity on Mars through analyzing rocks, where they found minerals similar to those found on Earth.

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Exploring - The mission was the first to explore the surface of another planet and paved the way for rovers to come.

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Spirit, 2004 - The Spirit rover landed on the Martian surface in 2004 and explored the surface of the red planet until 2010, lasting 20 times longer than expected.

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7.3 kilometers - Spirit traveled 7.3 km (4.5 mi) in its time on Mars, before getting stuck in late 2009 and losing contact with Earth in 2010. It was only designed to travel 600 m (.37 mi).

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Magnetic dust - The Spirit discovered that many of the minerals and hills on Mars were eroded by water, and that all the dust on Mars is magnetic.

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Opportunity, 2004 - Seen here with NASA Senior Engineer Dr. Edward W. Tunstel Jr., the Opportunity rover landed on Mars in 2004 and went into hibernation in June 2018 due to a dust storm.

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45 kilometers - The Opportunity traveled 45 km (28 mi) in its 14 years, finding numerous meteors that had struck the planet. The Opportunity explored a different part of Mars than the Spirit, though they operated for much of the same time.

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Advancing theories - Opportunity has allowed scientists on Earth to identify and categorize the soil and atmospheric chemicals of Mars, and provide further evidence that water once existed on the surface. 

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Phoenix, 2008 - The Phoenix lander touched down on the Martian surface in November 2008 and was operational for six months before it lost transmission with Earth. 

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Ice discovered - The Phoenix lander scooped up Martian soil and found watery ice just below Mars' surface for the first time. 

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Bigger - The Phoenix was the first in a line of bigger landers and rovers on Mars, giving it the ability to do more advanced tests.

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Curiosity, 2012 - Known as a space laboratory, the Curiosity rover can both explore and perform experiments. Curiosity landed in 2012 and is still functional.  

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Mission - The size of a car, Curiosity is attempting to determine the role of water on Mars, define the radiation levels for possible human missions, and assess the alien environment on the red planet.

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Microbes - Curiosity has already determined that life on a microbe level would have been possible on Mars in ancient times. Its new focus is to find fossils.

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InSight, 2018 - The InSight lander touched down on the Martian surface on November 26, 2018. 

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Objective - InSight is attempting to understand the history of Mars by studying the interior of the planet, scanning the planet's crust, mantle, and core.

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Major discoveries lie ahead -

The interior of Mars has never been mapped, and Mars is thought to be the best planet to help in understanding planetary formations due to its size and age.

In 2020, scientists were able to prove volcano activity on Mars. "This is the first study that proves activity in the Mars interior from a purely chemical point of view, on real Martian samples," explained planetary geologist Nicola Mari of the University of Glasgow to the website ScienceAlert.

See also: What would happen if we didn't have the moon?

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