Global Storms Launch Dust Towers Into The Martian Sky
No other planet in our Solar System has inspired the human imagination more than Mars. This is because, historically, the Red Planet was considered the most likely world to be the distant home of life beyond Earth. While this viewpoint has certainly become greatly outdated, Mars still entices Earthlings with its rusty-red surface, etched with small valleys carved into slopes, that are eerily similar in shape to gullies formed by rushing water flowing on the surface of our own planet–and where liquid water exists, life as we know it may also exist. But, today, Mars is a frigid and dry wasteland, where violent dust storms are common–but, every ten years or so, something unpredictable happens, and a series of runaway storms break out that cover the entire planet in a dense shroud of swirling dust. In November, 2019, planetary scientists announced that a fleet of NASA spacecraft managed to get a good look at the life cycle of the enormous–and highly destructive–2018 global dust storm that prematurely ended the visiting rover Opportunity’s mission of exploration on the surface of the Red Planet.
At this time, planetary scientists are still in the process of studying the new and puzzling data. However, two papers have recently been published that shed new light on a phenomenon seen occurring within the enormous dust storm–dust towers, which are concentrated clouds of dust that become warm in sunlight and then rise rise high into the air. Planetary scientists have proposed that water vapor, imprisoned by the dense, swirling dust, may be riding them in a way that has been compared to an elevator into space, where radiation from our Sun rips their molecules apart. This suggestion might help explain how the Martian water vanished over the passage of billions of years.
Our Solar System is about 4.6 billion years old. Prior to approximately 3.8 billion years ago, Mars may have had a much denser atmosphere than it has today, as well as higher surface temperatures. These ancient conditions would have permitted vast quantities of liquid water to exist on the Martian surface, including a large ocean covering one-third of the planet.
Almost all of the water on Mars today is in the form of ice, although some of it also exists as water vapor in its atmosphere. The only place where water ice is visible on the Martian surface is at the north polar ice cap. However, a large amount of water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole, as well as in the shallow subsurface at more temperate conditions.
More than 21 million kilometers of ice have been discovered at or near the Martian surface. This amounts to enough water ice to cover the entire planet to a depth of 115 feet. It is even more likely that water ice is lurking in the deep Martian subsurface.
Large quantities of dust have formed on the surface of the Red Planet as a result of its currently dry conditions. Dust towers are churning, enormous clouds that climb considerably higher than the normal background dust in the thin Martian atmosphere. Even though dust towers have also been seen under more normal conditions, they appear to form in greater numbers as the result of global storms.
A tower first forms on a planet’s surface. It begins as a region of rapidly lifted dust that is approximately as wide as Rhode Island. By the time this dusty tower reaches the lofty height of 50 miles, as observed during the infamous 2018 global dust storm, it may be as wide as the state of Nevada. As the tower begins to lose strength, it can form a layer of dust 35 miles above the surface of a planet that can be wider than the entire continental United States.
The 2019 findings, pertaining to the exotic Martian dust towers, were derived courtesy of NASA’s Mars Reconnaissance Orbiter (MRO), which is led by the agency’s Jet Propulsion Laboratory (JPL) located in Pasadena, California. Even though dust storms blanket the Martian surface, MRO is able to use its heat-sensing Mars Climate Sounder instrument to penetrate the heavy haze. The instrument is designed specifically for measuring the levels of dust. Its data, along with pictures obtained from a camera aboard the orbiter called the Mars Context Imager (MARC), enabled planetary scientists to spot numerous expanding dust towers.
The Realm Of The Red Planet
Mars is the fourth planet from our Sun, as well as the second-smallest major planet in our Sun’s family after Mercury. In English, Mars is named for the Roman god of war because of its rusty-red hue. This reddish coloring comes courtesy of the large quantities of iron oxide on the Martian surface, and it is unique among the astronomical bodies visible to the unaided human eye. Mars is a solid, terrestrial planet, that displays only a thin atmosphere. It also possesses surface features reminiscent both of the impact craters of Earth’s Moon and the polar ice caps, valleys, and deserts of Earth.
The Martian days and seasons are also comparable to those of our own planet. This is because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar for both sister worlds. Mars also hosts Olympus Mons, the largest volcano and tallest known mountain in our entire Solar System. Another surface feature, named Valles Marineris, is one of the largest canyons in our Sun’s familiar family of planets, moons, and smaller objects. The smooth Borealis basin, located in the northern Martian hemisphere, covers 40% of the planet and is thought to be a gigantic impact scar left by a huge crashing object. Mars also is circled by a duo of tiny moons, Phobos and Deimos, which are irregularly shaped and resemble potatoes. The two little moons are considered to be captured asteroids.
The first observations of Mars were made by ancient Egyptian sky-watchers. By 1534 BCE, these very early astronomers were already familiar with the retrograde motion of the Red Planet. By the time of the Neo-Babylonian Empire, the Babylonian sky-watchers were making regular records of the positions of planets, as well as systematic studies of their behavior. In the case of the Red Planet, the ancient astronomers discovered that it made 42 circuits of the zodiac every 79 years. These ancient astronomers even devised mathematical methods in order to make minor corrections in regard to the predicted positions of the planets in our Solar System. The ancient sky-watchers called the planets “wandering stars.”
In the fourth century BCE, the ancient Greek philosopher Aristotle noted that Mars disappeared behind Earth’s Moon during an occultation. This indicated that the Red Planet was farther away from Earth than our Moon. The Greek astronomer, Ptolemy–who lived in Alexandria, Egypt–tried to determine the orbital motion of Mars, and his collective works and model on astronomy were presented in his multi-volume collection, under the title Almagest. The Almagest was the authoritative work on Western astronomy for the next four centuries.
Ancient Chinese astronomers were also familiar with Mars no later than the fourth century BCE. In the fifth century CE, the Indian astronomical work titled Surya Siddhanta presented a measurement of the estimated diameter of the Red Planet. In East Asian cultures, Mars is usually called the “fire star”–based on the Five Elements: wood, water, earth, metal, and fire.
In the 17th century, the astronomer Tycho Brahe measured the diurnal parallax of Mars that Johannes Kepler had used to make early calculations of the distance of Mars from Earth. When the earliest telescopes, used for astronomical purposes became available, the diurnal parallax of Mars was determined to make this measurement in 1692. However, these early measurements were flawed because of the poor quality of the telescopes.
Mars hasn’t always looked the way we see it today. The Red Planet suffered a catastrophic tilt billions of years ago. Before this tilt occurred, the Martian poles were not situated where they are now.
There are current investigations assessing the past habitability potential of the Red Planet, as well as the possibility of extant life. Future astrobiology missions are currently being planned. These missions include the Mars 2020 and Rosalind Franklin rovers. Liquid water cannot pool on the Martian surface today–except at the lowest elevations for brief periods–because of the low atmospheric pressure, which amounts to less than 1% of Earth’s.
Dozens of crewless spacecraft, including rovers, orbiters, and landers, have been sent to Mars by the United States, Europe, India, and the Soviet Union. These missions observed the Red Planet’s surface, climate, and geology. For the past twenty years, cameras in orbit around Mars have dispatched back to our planet a cornucopia of revealing pictures of the “fire star”.
Dust Towers In The Martian Sky
Even though dust towers form throughout the entire Martian year, MRO observed something unusual about the catastrophic 2018 global dust storm. “Normally the dust would fall down in a day or so. But during a global storm, dust towers are renewed continuously for weeks,” commented the paper’s lead author, Dr. Nicholas Heavens, in a November 26, 2019 JPL Press Release. Dr. Heavens is of Hampton University in Hampton, Virginia.
In some cases, multiple towers have been observed for almost 4 weeks.
The rate of dust activity surprised Dr. Heavens and his colleagues. But what they found to be particularly intriguing was the possibility that dust towers function as “space elevators” for other material. If this proves to be the case, then dust towers may play the important role of transporting other materials through the Martian atmosphere. When airborne dust heats up, it forms updrafts that carry gases along for the ride–including small amounts of water vapor that are sometimes observed in the form of wispy clouds on Mars.
In an earlier paper, Dr. Heavens had demonstrated that during a 2007 global Martian dust storm, water molecules were launched high into the upper atmosphere, where radiation from our Sun could break them down into particles that escape screaming into interplanetary space. That mechanism could provide an important clue about how the Red Planet lost its lakes and rivers billions of years ago, thus becoming the frigid and desolate wasteland that it is today.
Planetary scientists are not sure about how global dust storms form. This is because they have only managed to study less than a dozen of these storms so far. But with more time to collect additional data, the MRO team will seek a new understanding about the way dust towers form within global storms and what role they may play in removing water from the Martian atmosphere.
Dr. David Kass, a Climate Sounder scientist at JPL, commented to the press that “Global dust storms are really unusual. We really don’t have anything like this on the Earth, where the entire planet’s weather changes for several months.”
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