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NASA’s Perseverance rover successfully landed on Mars last month and began transmitting images.
But people might be surprised to learn that there have been 48 other missions to the red planet so far. Of these, more than half failed the stages from lift-off to deployment, including the 1999 Mars Climate Orbiter, destroyed at the entrance to Mars after someone failed to convert imperial measurements to metrics.
Successful missions include Mars Insight, which is studying the interior by measuring “marsquakes,” and the Curiosity rover, which landed in 2012 and has been examining the geology of Mt. Sharp.
Although there have been no return missions, there is much we can learn without traveling to Mars from the more than 260 Martian meteorites that have fallen to Earth.
Images taken by orbiters reveal that Mars has more than 40,000 craters, each formed by an asteroid colliding with the surface. You can explore these craters yourself by going to Google Earth, activating Google Mars mode, and zooming in.
If some of the debris from large impacts reached escape velocity (about 5 km / s on Mars), it could leave the gravitational field of the planet. Eventually, some of the ejected Martian material has intercepted Earth’s path, traversing the atmosphere until it burned or came to rest on the surface.
Although Martian meteorites have been found on Earth, most have been collected in Antarctica or the deserts of northwestern Africa. In both cases, the black crust that forms when the meteor partially burns through Earth’s atmosphere stands out clearly against ice or sand.
This interplanetary mode of travel is important because it raises the possibility that life may inadvertently travel from one planet to another. In 1996, a Martian meteorite, ALH84001, was controversially thought to contain fossilized bacteria.
Some of the oldest landers have almost certainly carried bacteria from Earth to Mars, as they were not purified before launch.
A bubble of Martian atmosphere
Small planets cool rapidly, and the core of Mars has long been suspected to have largely, but not fully, crystallized. This means that Mars has mainly lost the protective magnetic field that deflects cosmic radiation.
But we are sure that Mars once had an ocean, which contained water as we know it. The temperature was above freezing and the conditions were right for life. The removal of the magnetic field early in the history of Mars means that this ocean is long gone and the average temperature is now -65 ℃, but frost, clouds and polar ice caps remain.
Not having the luck to wander the deserts of Africa or the icy plateaus of Antarctica, I found my first Martian meteorite in a closet at a gem store in the small town of Akaroa in New Zealand.
Using a scanning electron microscope, my examination revealed that it was a shergottite, one of the most common Martian meteorites, equivalent to what we know on Earth as basalt. However, if it is basalt, how do we know it is from Mars?
There are several ways to recognize a Martian meteorite. One is for its gas content. When a meteor hits the surface of Mars, the “target” rocks are subjected to such great pressure that they partially melt and trap the Martian atmosphere within gas bubbles. Some of these rocks are ejected from the planet and become meteorites.
The gases from these meteorites can be measured on Earth and compared to the known Martian atmosphere, which comprises 95% carbon dioxide and different concentrations of noble gases.
The thousands of craters that mark the surface of Mars mean that it is ancient. This was confirmed when a meteorite was dated to be 4.4 billion years old. The properties of some other Martian meteorites show that Mars formed within 13 million years after the formation of the Solar System. This, in turn, means that part of the first planetary crust that formed on Mars likely still exists on the surface.
Old and cold, but not dead
This inference, along with some mineral and isotopic properties of meteorites, implies that Mars has not been shaped by plate tectonics, the global process that formed Earth’s continents, mountain ranges, and ocean basins.
And, since most dated Martian meteorites are less than 1.5 billion years old, volcanism has continued throughout its history. Mars may be cold but not dead.
Martian meteorites also hold clues to how people will one day be able to survive on the planet.
While living in lava tubes hollowed out in Martian basalt may attract some hopeful interplanetary settlers, we will ultimately need to build shelters to protect ourselves from cosmic radiation and the vast dust storms that engulf the planet.
Martian meteorites show that olivine, a magnesium silicate mineral, is common. Experiments are underway to evaluate the use of a decomposition component, magnesium carbonate, to form a concrete binder from which we could make buildings.
Martian meteorites show that great insights can be gained from small rocks and reveal what Mars is made of.
This article was originally published on The conversation for James scott at UCL. Read the original article here.
