One of the major reasons why Mars is such a popular object to study in our Solar System is because scientists believe that it may have looked much different millions of years ago. There exists evidence that Mars may have once been similar to Earth, with oceans, lakes, and rivers galore. How then did Mars become this barren, dry wasteland? Global warming and climate change. If scientists can understand how the climate of Mars evolved and changed, then maybe they can prevent a similar future on Earth.
Scientists led by a team at the University of Houston are studying the traces of climate change that occurred on Mars long ago to help other scientists understand climate issues on Earth. The team presented a global picture of the climate of Mars in the Proceedings of the National Academy of Sciences.
Making use of observations from Martian satellites, landers, and rovers (e.g., NASA’s Mars Global Surveyor, Curiosity Rover, and InSight), the team estimated the emitted energy of Mars as a function of season. They found that the radiant energy budget – the measure of solar energy a planet takes in from the Sun and then releases as heat – is imbalanced, and varies diurnally and seasonally. The radiant energy budget is a fundamental metric of a planet and could play an important role in understanding the climate and atmosphere of Mars. Current climate models assume that Mars’ radiant energy is balanced between seasons, meaning that any conclusions derived from these models are incorrect.
The team found a strong energy imbalance – more energy is being absorbed by the planet than is being produced by the planet – of approximately 15.3% between seasons. This is much larger than the energy imbalance of other worlds (e.g., Earth – 0.4% or Titan – 2.9%). Our home, the Earth, has an almost circular orbit around the Sun, which means the Earth is almost exactly the same distance from the Sun at all times of the year. Unlike Earth, Mars has an extremely elliptical orbit, and also unlike Earth, Mars does not have much of an atmosphere. These two factors make Mars susceptible to extreme temperature variations. The “seasons” of Mars occur when it is closer and further from the Sun – meaning the reasons for the “seasons” on Mars are much different than the reasons for seasons on Earth. When Mars gets closer to the Sun, it absorbs extreme amounts of heat – or energy – from the Sun, and when Mars gets further from the Sun in its orbit, it absorbs less heat.
The times when Mars is closer to the Sun also happens to be when global dust storms occur on its surface. The team believes that the seasonal energy imbalances are the driving forces behind these global dust storms. During a global dust storm in 2001, the global-average emitted power decreased by 22% during the daytime, and increased 29% during the nighttime. Perhaps the energy went into generating the global dust storms that plague Mars!
These results, in combination with numerical global climate models, could help to improve our current understanding of the Martian climate and atmosphere. Additionally, understanding the driving forces behind Martian dust storms could help climate scientists understand what causes severe storms – a sign of climate change – on Earth. So, perhaps lessons from the history and evolution of the climate of Mars can help us solve our own climate troubles on Earth.