Climate System and Aeaolian Erosion in Terrestrial Planets (2020)
Climate System and Aeolian Erosion in Terrestrial Planets
Preface
At present eight plants orbiting sun. The inner, rocky planets are Mercury, Venus, Earth and Mars. Mercury is the smallest planet in our solar system and nearest to the Sun. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system.
Venus is a terrestrial plant and it is shrouded by an opaque layer of highly reflective clouds of sulfuric acid. Much of the Venus surface has been shaped by volcanic activity. About thousand impact craters on Venus are distributed. Venus has an extremely dense CO2/N2 atmosphere, and it is characterized as having an atmosphere 92 times more massive than that of the Earth. High winds circle the planet from east to west, at speeds 60 times faster than rotation of the solid planet. All winds on the planet are ultimately driven by convection. Venus’s clouds as well as its CO2 concentration further increase its opacity. The atmosphere is divided into a number of sections depending on altitude. The densest part of Venusian atmosphere is the troposphere. The troposphere contains 99% of the atmosphere’s mass. Venus is Earth's twin in many ways, but without lack of liquid water.
In the absence of fluvial processes (or glacial abrasion, or freeze–thaw), it is hard to imagine how to make much sand. The observed aeolian features are dark mantles, wind streaks, yardangs and dunes. Dark mantles and wind streaks are rather common features on Venus, while yardangs and dunes large are observed in only a few localities. The prominent aeolian process on Venus is known as saltation in which grains hop along the surface in low angle trajectories. Formation of aeolian ripples is strongly influenced by size sorting of sand. Sand on Venus is scarce. It has attributed to the fact that erosion by water does not operate on Venus, and chemical weathering doesn’t produce sand. Wind streaks are the most abundant aeolian features on Venus. A field of possible yardangs is observed in the vicinity of the crater Mead, the largest impact crater on the planet.
Earth “our home planet” is the third planet from the Sun, and the only place that is inhabited by living things. Earth is the only world in our solar system with liquid water on the surface. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago. Of the Earth surface area, 70.8%, is below sea level and covered by ocean water. The remaining 29.2% has terrain that varies greatly from place to place and consists of mountains, deserts, plains, plateaus, and other landforms. The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from other planets in the Solar System.
Aeolian processes, involving erosion, transportation, and deposition of sediment by the wind, occur in a variety of environments, including the coastal zone, deserts, and
agricultural fields. The landforms that result from aeolian erosion include ventifacts, ridge and swale systems, yardangs, desert depressions, and inverted relief. On Earth surface, three main factors influence the piling of sand into dunes with particular shapes: (1) wind magnitude (above the threshold velocity), direction, and frequency; (2) vegetation covers and (3) grain size.
Many attempts have been made to classify dunes based on a combination of shape, number and orientation relative to the prevailing wind and degree of form mobility. Based on these factors descriptive terms such as ‘longitudinal’ and ‘transverse’, have been used. For instance, the term the term longitudinal dune should be applied only where the orientation of the long axis of the dune deviates by less than 15° from the resultant sand transport direction, while a transverse dune should have long axes which are within 15° of being normal to the resultant sand transport direction. In another attempt Earth dunes were classified in self-accumulated dunes include barchans, transverse (barchanoid) ridges, unvegetated linear dunes (seif dunes), dome dunes, and star dunes, and dunes formed by the presence of vegetation include parabolic dunes, vegetated linear dunes, and coppice or hummock dunes.
Mars is a dusty, cold, desert world with a very thin atmosphere. The robotic explorers have found lots of evidence that Mars was much wetter and warmer, with a thicker atmosphere, billions of years ago. The days and seasons are likewise comparable to those of Earth. Liquid water cannot exist on the surface of Mars due to low atmospheric pressure. Data show Martian soil to be slightly alkaline and containing elements such as magnesium, sodium, potassium and chlorine. These nutrients are found in soils on Earth, and they are necessary for growth of plants. Mars is scarred by a number of impact craters. The largest confirmed of these is the Hellass impact basin which is visible from Earth. Due to the smaller mass of Mars, the probability of an object colliding with the planet is about half that of Earth. Mars has two relatively small moons, Phobos and Deimos. Wind erosion and deposition are powerful agents of surface change on Mars. The topography on Mars shows a large scale asymmetry between the northern lowlands and the southern highlands. Mars exhibits many of the same dune forms as seen on the Earth, including barchan, transverse, yardangs, as well as star and climbing dunes. Many dunes are located in the floors of impact craters where sediment could accumulate. Mars is a very dusty planet. Dust storms on Mars are full of water. In 2018, the largest recorded dust storm circled the entire Martian globe, so thick that it hid the surface from the sun and killed the Opportunity rover. Most of the time the lofting and rearranging of dust is done by the dust devils that spin across the planetary surface. Dust on Mars is the most important driver of weather. The static electricity from rains rubbing against one another in these dry, sandy whirlwinds could be a problem. “It’s possible that all of the dust grains clattering together in these storms could produce a lot of electricity and disable electronics. The electric fields associated with dust devils on Mars are so much drier and dustier than in devils on Earth. Mechanical weathering is the primary mode for the generation of sand-sized particles on Mars, mainly because of the dearth of water under present Martian conditions. Impact craters also provide an intense but much localized means to break up near-surface rocks into smaller constituent pieces. The sand dunes are widespread around Mars, but not in a systematic manner.
A ring of sand called the North Polar Erg (NPE) surrounds the north polar cap on Mars. The dune field on the floor of Proctor crater was the first to be identified on Mars which covers an area approximately 2275 km2 in area. A variety of dune types have been recognized on Mars over the years, including barchan, barchanoid ridge, transverse, star, linear, dome, and complex dunes. Cater-related permanent wind streaks are observed around some craters on Mars.
Titan is the largest Saturn's moon. Titan is an icy world whose surface is completely obscured by a golden hazy atmosphere. The surface of Titan is one of the most Earthlike places in the solar system, albeit at vastly colder temperatures and with different chemistry. Here it is so cold (-179 degrees Celsius) that water ice plays the role of rock. Titan may have volcanic activity as well, but with liquid water “lava” instead of molten rock. At the surface of Titan, the atmospheric pressure is about 60 percent greater than on Earth—roughly the same pressure a person would feel swimming about 15 meters below the surface in the ocean on Earth. Titan's atmosphere is mostly nitrogen (about 95 percent) and methane (about 5 percent), with small amounts of other carbon-rich compounds. The low gravity and dense atmosphere on Titan make it a favorable environment for aeolian transportation of material in the sense that the wind speeds needed to saltate surface particles are rather low.
Our knowledge about erosional mechanisms on terrestrial planets is not even complete on Earth. We may gain further new insight in the future through space missions as well as by more observational, experimental and theoretical studies. However, in this book the reader finds base information as well as a discussion on what potential new results can tell us about the history of erosional mechanisms on sun terrestrial planets. I hope that this book can serve as guide for all those who are interested in aeolian processes on terrestrial planets with emphasize on Mercury, Venus, Earth, Mars and Earth’s Moon. Because on these planets, the principal causes of erosion (e.g., running water, glacial abrasion and freeze thaw) are absent.
I would like to express my thanks to the authorities of University of Kashan.
Kashan, July 2020 Abolfazl Ranjbar-Fordoei