With a rover trundling over red soil, a spacecraft diving through the atmosphere and teams at work all around the Earth, Mars has given up a string of secrets to Nasa in the last year. Here are some of the major discoveries of 2015.
Liquid water on Mars
Sought after for decades, evidence of liquid water on Mars literally emerged from the planet in July, running down canyons and crater walls over the summer season. A Nasa team found hydrated salts, a smoking gun for liquid water, at four sites where dark stains trickled down the Martian terrain.
Nasa does not yet know the source of the briny downhill flow, which might rise up from underground ice or aquifers, or condense out of the atmosphere. Past missions have found hints of water, including images of what appeared to be small streams and even water pouring down gullies, but the summer discovery was hailed as the first confirmed evidence of the liquid most associated with life.
Researchers have long held that liquid water is a primary ingredient for life – Nasa’s mantra in the quest is “follow the water” – but the scientists now face a dilemma over how to investigate the streams. The Curiosity rover that has explored Mars for three years is not sterile, 和 could contaminate the wet areas with terrestrial bugs that clung onto the spacecraft through the cosmos. The rover could investigate from a distance, with a laser that would measure the streaks, or it could risk approaching to scoop up some mud.
An atmosphere stripped by wind from the sun
On Thursday, Nasa announced a series of findings about Mars’ atmosphere that could help solve the mystery of what happened to Mars, which billions of years ago was a wet, warm world with an atmosphere 100 times thicker. Today Mars is dry, frigid and bombarded by radiation – a world without the strong magnetic field that surrounds the Earth and protects it from explosions on the sun.
Findings from Nasa’s Maven spacecraft, which reached Mars last fall to investigate its thin atmosphere, are helping to solve that mystery. Mission scientists found that solar storms, which blast energy and magnetism outward, strip away particles from the atmosphere of Mars at an incredible rate.
“Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” said Bruce Jakosky, Maven’s principal investigator. Solar storms were more common and intense earlier in the solar system’s history, meaning that events on the sun may have had major repercussions for the water and atmosphere of Mars.
The mission also measured the composition of Mars’ atmosphere for the first time since the Viking missions 40 years ago, and found a mysterious amount of dust hovering above the planet. The researchers suggested it could be interplanetary dust – the cosmic grains left behind by comets and asteroids traversing the solar system.
In October, Nasa scientists found evidence of lakes that could have lasted up to 10,000 years – possibly long enough for life to develop in a marshy landscape of shallow streams and deltas. Analysis of sediment showed scientists that water flowed, carrying gravel and sand down into the gigantic Gale crater. In the center of the crater stands a towering mountain called Mount Sharp, itself the accumulation of three-miles of sediment layers.
In April, the Curiosity rover found evidence of liquid water below the surface of Mars, and recorded temperatures in the Gale crater that were just right for liquid brine. The findings suggested that Martian soil is damp with water that can stay liquid thanks to a salt, calcium perchlorate, which keeps it fluid down to about -70C.
Maven scientists also found that solar wind creates the equivalent of northern lights across vast swaths of Mars, caused by the high-energy particles exciting an atmosphere unguarded by a magnetic field. Humans could theoretically see the Martian auroras as red, blue and green colors on the visible spectrum, but Nasa does not yet know what the lights might look like, since its rovers lack the equipment to see them.
The auroras also suggest that most of Mars is buffeted by solar winds, lending evidence to the idea that solar events contributed to the loss of atmosphere all around the planet. Some magnetic fields remain in sections of crust scattered around the planet, but the planet lacks the global shield that it once had.
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