For the first time in history, astronomers can document the global wind circulation patterns of Mars. Their findings are mostly based on local observations, and all the data were collected by a spacecraft that is not explicitly designed to collect wind measurements.
HOW WAS THE MAVEN SPACECRAFT ABLE TO MEASURE MARTIAN WIND?
The National Aeronautics and Space Administration launched the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft last November 18, 2013, designed to determine how the Martian atmosphere and water disappeared over time. The spacecraft reached the Martian orbit in September 2014 and delivered back information on how the surface of the Red Planet deteriorated over time due to solar storms.
By 2016, planetary scientist Mehdi Benna and colleagues proposed to the MAVEN team to do an experiment with the spacecraft and the Natural Gas and Ion Mass Spectrometer (NGIMS). Benna and the team wanted to see if the spectrometer is able to swing back and forth, kind of like a windshield. It seems like a childish query, but it has proven to help gather data. Understandably, the MAVEN team was reluctant, and since the spacecraft and its spectrometer have been working well, they can't afford the risk.
However, Benna and his team were persistent. According to them, the experiment will be able to collect new kinds of data that will help them understand the structure of Mars' upper atmosphere and planetary climate. The team came up with the windshield-wiper idea while figuring out how to make an instrument that can collect information about Earth's circulation patterns in the upper atmosphere. Benna had a eureka moment when it occurred to him that, together with the MAVEN spacecraft, the NGIMS will be able to collect information about the global circulation pattern on Mars.
After preliminary analyses and backup from spacecraft manufacturer Lockheed Martin, the team was able to convince the people behind the MAVEN mission to give their idea a try. He says, "It's a clever reengineering in the flight of how to operate the spacecraft and the instrument, and by doing both—the spacecraft doing something it was not designed to and the instrument doing something it was not designed to do -- we made the wind measurements possible."
WHAT DID THE MODIFICATIONS ON THE MAVEN SPACECRAFT BRING?
The journal on the findings of the modified MAVEN spacecraft, published in Science, was completed in collaboration with Yuni Lee from the Center for Space Sciences and Technology at the University of Maryland, Baltimore County and with the help of Benna's colleagues from the University of Michigan, George Mason University, and NASA.
The journal details the findings that were collected by the modified MAVEN spacecraft from 2016 to 2018, and there were a lot of surprises for the astronomers. Benna explains that most of the patterns observed on Mars were predicted by the models they developed. The circulation patterns on Mars are stable despite the changing seasons. However, when the team analyzed the shorter-term variability of winds in the planet's upper atmosphere, it was greater than they have anticipated. Benna explains, "on Mars, the average circulation is steady, but if you take a snapshot at any given time, the winds are highly variable."
Another surprise that the astronomers discovered is that the winds that occur on the upper atmosphere (which more or less measure up to a hundred kilometers above the surface) can still contain information about the land formations below. It is because of the planet's airflow when passing by mountains and canyons, creating a ripple effect that flows up to the upper atmosphere, which will then be detected by the modified MAVEN spacecraft and NGIMS. Benna explains that the same kinds of waves occur on Earth but not at such high altitudes.
Benna and his colleagues called the airflow "orthographic waves," and they think it occurs because the atmosphere on the planet is thinner compared to Earth, so that enables waves to travel further. They also hypothesized that the average difference between geographic peaks and valleys is much greater on Mars than it is on Earth. For instance, a mountain on Mars can stand up to 20 kilometers high, whereas Mt. Everest on Earth is barely 9 kilometers tall, so the topography of the planet is related to the circulation patterns somehow.