ES DLA Solar System.pdf

Earth Science DYCIan Learning Account No. 2 THE SOLAR SYSTEM During you fifth grade Science came your aware...

Earth Science DYCIan Learning Account No. 2 THE SOLAR SYSTEM During you fifth grade Science came your awareness and curiosity of the solar system where our planet belongs because those were the times the basics of astronomy were introduced to you. As you go further in your academic years, your knowledge and understanding about this topic will come to new depths and heights as you digest this learning account. At the end of this learning account, you are expected to: 1. Identify the large scale and small scale properties of the solar system 2. Discuss the different hypotheses explaining the origin of the solar system and the story of planet building. After discussing the formation of the universe in the previous learning account, you will now be acquainted where we are located in the great scheme of things. Well, we are also talking about of something big here when we are pertaining to the solar system and the galaxy where the Earth is located, but understanding and knowing the origin of the planetary system* where the Earth is located will give us a better view of the origin and mechanisms of our planet. [*A planetary system is a generic term used for a group of planets and other bodies circling a star. Our solar system is called as such because the sun is sometimes termed as Sol, hence the term it came from (Fraknoi et al., 2016)] According to NASA, the solar system is located in the outer spiral arm of the Milky Way galaxy. In this huge disc and spiral shaped aggregation, our planetary system Figure 2.1 shows the location of solar system in the Milky Way galaxy lies among with 100 billion stars and other Photo credit: basicknowledge101.com bodies, at the center of which lies a super massive black hole. Features of the solar system The solar system comprises the Sun, the planets, their moons and rings, and such “debris” as asteroids and comets (Fraknoi et al., 2016). Other minor bodies such as the Kuiper belt and interplanetary dusts are included. All of this is gravitationally-bounded to each other. 1 Earth Science Figure 2.2 A view of the solar system ( Photo credit: Getty images, 2017) Before proceeding to the origin of the solar system and the planet formation, you must first know the large and small scale properties of the solar system because it will bring you to the next part which is the different theories supporting the origin of the solar system. This large and small scale properties must be consistent and have a set of explanations with any acceptable scientific thought on the origin of the solar system. Large scale features of the solar system: Mass Much of the mass of the solar system is concentrated at the center which is the sun. The sun holds together the gravitational field of the solar system because it contains 99.85% of the solar system’s mass (Canright, 2009) The remaining 0.135% of the mass is distributed among the planets, comets, and satellites and the 0.015% is distributed to the minor planets, meteoroid and interplanetary medium. On the other hand, the angular momentum of the solar Figure 2.3 shows a visual size system is transferred to the outer planets. Angular momentum is the comparison of the sun and measure of the rotation of a body as it revolves around some fixed the planets (not to scale) point (Fraknoi et al., 2016).It is the product of the mass, velocity, Photo credit: Graham Foster and distance. Most of the angular momentum of the solar system is held by Jupiter (60%). The other gas giants, Saturn, Neptune, and Uranus have about 24%, 7%, and 5% respectively. The sun eventhough has most of the mass of solar system has only 4% of the angular momentum of it. 2  Earth Science Figure 2.4 Orbits of the planet are elliptical and on the same plane Photo credit: Openstax astronomy, 2016 Orbits of the planet The path of an object through space is called as its orbit (Fraknoi et al., 2016) Johannes Kepler’s Law of planetary motion gave a great leap to astronomy when it debunked the Greek’s belief that planets move in perfect circular shape. According to Kepler’s first Law of Planetary motion, the law of Ellipses, the orbits of the planets are ellipses, with the sun at one focus of the ellipse. The solar system is a very organized place where the planets’ orbit lies on the same plane. Planets are located at regular intervals from the sun. The location is ideal for each other that planets can’t be influenced by another planet’s gravity and collide. The sun’s gravity holds everything in the solar system in place. You must be thinking that, why are the planets’ orbit not randomly arranged? Astronomers observed other planetary system and concluded that planets from those systems also lies on the same plane. The difference of the orientation of their plane of orbit and our solar system’s plane of orbit is minimal. The reason for this is the protoplanetary disk where these planets originate, have the same orientation. Revolution Kepler’s third law of planetary motion, the Law of Harmonies present the relationship between the period of the orbit of the planets and their average distances from the sun. The revolution or the planet’s orbital period is referred as the time it takes for the planet to complete its travel around the sun (Fraknoi et al., 2016) It just implies that the period of the revolution Figure 2.5 approximate distance of of the planet increases as its distance increases from planets from the sun the sun. The inner planets being the nearest to the sun Photo credit: completes its revolution the fastest, contrary to the https://www.universetoday.com/55423/kepl ers-law/, 2010 outer planets which revolves the slowest. 3 Earth Science Small scale features of the solar system Composition Planet /Structure Rotation Atmosphere Density Volatile contents made of Terrestrial or materials with Rotate Have thin or Higher Lower inner planets high melting slower no density contents of (Mercury, points such as atmosphere volatile Venus, Earth silicates, Iron, Mars) Nickel dominance of Rotate Have thick Lower Fluid interiors Jovian or outer gases and faster atmosphere density rich in planets has large size Hydrogen, (Jupiter, Helium, and Saturn, Uranus, ices Neptune) Table 1 summary of the small scale features of the solar system Composition/ structure Terrestrial planets are smaller compared to the Jovian planets and are composed primarily of rocks and metals. The internal structure of the inner planets are less dense silicates that can be found near the surface and the denser metals at the core. The Jovian planets on the other hand comprises the massive planets in the solar system, hence the term “gas giants” (Jupiter, Saturn) and “ice giants” (Uranus, Neptune). Hydrogen and Helium mostly comprises the gas giants while the ice giants have higher concentrations of methane and heavier elements. The core of the Jovian planets are probably molten and of Figure 2.6 Interior models of the giant rocky composition. The composition of the planets, showing rocky cores overlaid terrestrial and Jovian planets lead the scientists by solid and gaseous envelopes. to conclude that they are formed under Photo credit: NASA/JPL, 2016 different conditions (Fraknoi et al., 2016) (https://www.universetoday.com/33061/what-are-the- jovian-planets/) 4  Earth Science Rotation According to National Geographic, rotation is described as the circular motion of an object to its center which is termed as the axis. Planets rotate on its own axis, but they revolve around the sun. In terms of the rate of motion between the terrestrial and jovian planets, terrestrial planets rotate slower. The reason for the rapid rotation of the jovian planets is caused by the way it was formed and the conservation of angular momentum. Most of the planets rotate prograde, meaning in a counterclockwise direction. The exceptions are Venus and Uranus which rotate retrograde or in clockwise motion. Why Figure 2.7 Degree of rotation of the is that so? The rate of rotation of the inner and planets Photo credit: outer planets and the direction of rotation of https://technologyonscience.blogspot.com/20 Venus and Uranus will further be tackled on 19/10/why-does-planet-venus-rotate- the later part of this learning account. clockwise.html Atmosphere The two planet classifications differ greatly in terms of the atmosphere. Terrestrial planets have thin atmosphere compose mostly of nitrogen and carbon dioxide. Of all the terrestrial planets, Venus has a massive atmosphere composed of almost 96% carbon dioxide and has sulfuric clouds (Fraknoi et al., 2016). This atmospheric composition of Venus causes high surface temperature brought by greenhouse effect in the planet. Jovian planets on the other hand have no solid surface and have thick atmosphere dominated by Hydrogen Figure 2.8 Vibrant colors of and Helium. These planets develop dramatic weather Jupiter’s atmosphere Photo credit: modification of patterns and storms much larger than our planet. work by Voyager Project, JPL, and NASA) Figure 2.9 Shows the relationship between the temperature and altitude of the jovian planets and the atmospheric composition Photo credit: Open stax Astronomy 5 Earth Science Density Considering the composition of the planets, you can conclude that terrestrial planets are less dense than jovian planets. Terrestrial planets are composed mainly of metals and silicates from its surface down to the core, meaning they are of solid composition. Jovian planets are less dense because it is composed mainly of gas, liquid materials, and ices. Their density varies between the outer and inner layers, ranging from a liquid state to materials that become denser at the core which become solid (Williams, 2016) Note that of all the planets, the densest is the Earth which is a terrestrial planet and the least dense is Saturn which could float in water (water Figure 2.10 Graph shows the density density: 1 g/cm3), which in turn is a jovian planet. of each planet The density of the planets guide the scientists in Photo credit: https://www.enchantedlearning.com/su knowing the formation of these two classification of bjects/astronomy/planets/ planets as they originated from one solar nebula which will be discussed later on. Volatile contents Volatiles are substances with low boiling points and one of the main factors in determining the atmosphere and habitability of a planet. Examples of volatiles existing in a planet is Nitrogen, Ammonia, Water, Carbon dioxide, Methane, and Sulfur. Jovian planets is composed mostly of these volatiles either in gas or liquid form while terrestrial planets only contain less amounts of volatiles. The volatile Figure 2.11 Depiction of early Earth contents of the planets were influenced as Photo credit: NASA they evolve in the early solar system. (http://astrobiology.com/2020/03/delivery-of- water-and-volatiles-to-the-terrestrial-planets- and-the-moon.html) Why do you think we need to discuss first the small scale and large scale features of the solar system before proceeding to the origin of the solar system and formation of the planets? This features will serve as a prerequisite in understanding deeply and connecting the happenings in the formation of the solar system to what our solar system is today. These patterns lead the scientists to the hypotheses and theories that our planetary system arise from the same cloud of gas and dust. The large and small scale feature of the solar system serves as evidences to find out where the solar system originated and how it is formed. 6  Earth Science Origin of the solar system Three main hypotheses on the origin of the solar system supported the features mentioned earlier and is consistent with the idea that the planets were formed from the same interstellar gas simultaneously 4.5 billion years ago. Comparison against other existing hypotheses or theories and modifications were applied to strengthen these hypotheses. The concepts and drawbacks of the hypotheses regarding the origin of the solar system are as follow: Encounter hypothesis This hypothesis is one of the early attempt in explaining the origin of the planets. It all started when a rogue star passes close to the sun. Rogue stars are also termed as intergalactic stars, they are independent, hyper-velocity stars which is free from the gravitational hold of its home galaxy (Starr, 2018) The materials (in the form of hot gas) which will later be essential for planet formation is removed tidally from the sun and the rogue star. These materials break apart into smaller lumps that form the planets. ADVANTAGE: Explains why the planets revolve in the same direction and why inner worlds are denser than the outer worlds DRAWBACKS: Hot gas expands and not contract, lumps of hot gas would not form planets : encounters between stars are extremely rare Figure 2.12 shows the events in the encounter of the sun and the rogue star Photo credit: http://abyss.uoregon.edu/~j s/ast121/lectures/lec23.html #:~:text=A%20second%20th eory%20is%20called,that%20 contracts%20under%20self% 2Dgravity.&text=Protoplanet %20Hypothesis%3A,is%20call ed%20the%20protoplanet%2 0hypothesis. 7 Earth Science Nebular hypothesis The widely known hypothesis that our planetary system came from a gaseous cloud that collapse at the center under self-gravity (Williams, 2016). No one can figure out why the cloud collapse but this hypothesis contributed to the view how all the planetary systems originate. After the collapse, the denser regions in the cloud attract more matter. Conservation of angular momentum caused it to rotate and pressure caused it to heat up. The spin of the cloud transform it into a disc, it is flattened at the poles and bulging at the center. The concentrated mass at the center forms the sun, while the rest became a protoplanetary disk. DRAWBACKS: It failed to take account of the distribution of angular momentum of the solar system. It did not explain how the outer planets held most of the solar system’s angular momentum but the sun holds most of the mass : It did not explain how the disk turned into individual planets Figure 2.13 shows the events that took place in the nebular hypothesis Photo credit: http://abyss.uoregon.edu/~js/a st121/lectures/lec23.html#:~:tex t=A%20second%20theory%20is% 20called,that%20contracts%20u nder%20self%2Dgravity.&text=Pr otoplanet%20Hypothesis%3A,is %20called%20the%20protoplan et%20hypothesis. 8  Earth Science Protoplanet hypothesis Protoplanet hypothesis is the leading and most accepted hypothesis in the origin of the solar system. This hypothesis modified the nebular hypothesis but incorporated concepts that the slowly-rotating cloud dominated by dust and Hydrogen and Helium gas starts to contract because of its own gravity. The mass is also concentrated to the center which became the proto-sun, the remaining materials form a disk that eventually became the planets. The momentum is transferred outwards, but one thing that let this hypothesis edge among the rest is that it explains the mechanism of planet formation. The following discussion will focus on the story of planet building supported by protoplanet hypothesis. Figure 2.14 shows the main events that happened in the protoplanet hypothesis Photo credit: https://puserscontentstorage.blo b.core.windows.net/userimages/ 52dd5b0a-2db6-4a81- bca7-5ee3a4c3c05c/aa8d4f1a- b99d-42ed-8c70- a104ca40ec3eimage6.jpeg) The story of planet building The patterns and hypotheses mentioned on the early parts of this learning account will lead you to further understand the complexity of how planets were formed. These patterns or features were used to describe the processes involved on how the formation of the outer planets were quite different from the inner planets. 1. Condensation This process explains the formation of solid grains or liquid droplets from the disk that was formed in the nebula as it cools down. (Fraknoi et al., 2016) Different materials form depending on the region of the disk and its distance from the sun. In that case, the kind of material that condense varies depending on the temperature of that region in the disk. The main factor that gives way in the condensation of materials is the temperature. 9  Earth Science The region that is close to the sun, the inner solar system which will later produce the inner planets, produce materials of high melting points such as metals and metal oxides. Metals and metal oxides has high density. The region that is far from the sun, the outer solar system, which obviously has lower temperature produced ices with little silicates that came from water vapor, methane, and ammonia that condensed on that region. These ices are low-density materials. You have learned on the feature of the solar system that the inner planets are composed of materials with high melting points, and the outer solar system is composed of materials with low melting point. The composition and the density of the planets fit to the condensation process that happened on the formation of the planets. Figure 2.15 Shows the Chemical Condensation Sequence in the disk of the nebula Photo credit: Openstax Astronomy The condensation sequence is the order which various materials condense from the gas as the distance increase from the sun to the region of low temperature. The inner portion of the disk is hot so that materials of high melting point and density could form there. The outer portion on the other hand is colder so that materials of low melting point and density could form there. That’s how the composition of inner and outer planets came to be. 2. Accretion After the condensation of the materials in the disk, the grains were combined together to form large chunks that form larger bodies called the planetesimals which will later be made as planets. Some planetesimals still exists today as comets and asteroids (Fraknoi et al., 2016) This is where the second process of planet formation takes place which is accretion. Accretion is the process wherein planetesimals grow in size as they attract neighboring planetesimals due to the force of gravity.. It is stated on the last DLA 10  Earth Science that even gravity is the weakest of all the fundamental forces, it is the reason things in the universe is bounded together. Everything which has mass is governed by the gravitational force that’s why stars are made and now the planets through accretion. These planetesimals as they consume or attract other planetesimals coalesce together and form the protoplanets. Protoplanets are massive objects that soon will become planets when they achieve the size and conditions of being a planet. 3. Gravitational collapse Gravity is a vital force in planet building. The more massive a planetesimal becomes, the greater gravitational force it has allowing it to capture greater chunks of solid for it to become a protoplanet. Once a protoplanet achieved a specific size, it will grow by gravitational collapse. Gravitational collapse is the process wherein a protoplanet gather large amounts of in falling gas from the nebula by gravitational force. The turbulence caused by these in falling particles released energy called heat of formation. Heat of formation and the decay of radioactive elements will heat the planet allowing it to differentiate, the next step in planet bulding. 4. Differentiation Planetary differentiation is the result of heating the planet because of heat of formation and the decay of radioactive elements during gravitational collapse. Differentiation is the separation of materials or metal in the planet according to its density. Due to the heat present, the planet is melted and its components were separated according to density. The denser materials, this time it is the heavy metals such as Iron and Nickel would sink or settle at the core while the less dense materials, some lighter silicates for example would arise or float to the surface. You know that our planet’s geosphere has three layers which are the crust, mantle, and the core. Differentiation allows the build up of this three layers. 5. Outgassing The atmosphere is the layer of gas that envelopes the planet. So where do all these gases came from? In the context of planetary science, outgassing is the formation of planetary atmosphere that is vented out from the planet’s interior. Gases released from the planet’s interior during differentiation and gases brought by planetesimals’ impact are the reason of the existence of planetary atmosphere. Jovian problem The outer planets’ formation is a puzzle for astronomers because these planets grew in their present size before the sun become hot enough to blow away the materials that composed them. According to the reference book, planets were possibly formed by direct gravitational collapse, skipping the condensation and accretion process. The Jovian planets grew large and quick enough before the sun evaporated the raw material that composes them. Their large size allows them to capture massive amount of Hydrogen by gravitational force, that’s why the term is direct gravitational collapse. The composition of Jovian planets is influenced by their region in the protoplanetary disk which is in the frost line. The temperature in the disk is not uniform that as you go farther from the sun, materials of low melting point were formed. 11  Earth Science Other regions in the solar system Asteroid belt Broad region in space between Mars and Jupiter where most asteroids are found (Fraknoi et al., 2016). Early in the solar system, the disturbance of Jupiter’s gravity, is preventing any planet from forming but only colliding that’s why the asteroid belt was formed. The size of objects in the asteroid belt range from a dust particle to a dwarf planet. Ceres is the only dwarf planet found in the asteroid belt. Figure 2.16 Main asteroid belt that lies between the orbit of Mars and Jupiter Photo credit: https://nineplanets.org/asteroid-belt/ Figure 2.17 Illustration showing the two main reservoir of comets in the solar system Photo credit: https://www.esa.int/ESA_Multimedia/Images/2014/12/Kuiper_Belt_and_Oort_Cloud_in_context Kuiper belt A cold dark realm that lies beyond Neptune and comprises trans-Neptunian objects (TNO), numerous rock or icy bodies a few meters to hundred kilometers in size (Fraknoi et al., 2016) Kuiper belt is also the source of short-period comets. These comets have an orbital period of less than 200 years. The famous Halley’s comet thought to originate from the Kuiper belt. Oort cloud It marks the outer boundary of the solar system and serves as reservoir for long-period comets. They are comets that have an orbital period longer than 200 years, thousand years, if they return at all. 12  Earth Science Cosmic debris Not only the planets and the sun serve as evidence how the solar system evolve. The asteroids, comets, and meteoroids also exist to tell the tale of our planetary system. Asteroids Rocky worlds that lies in the asteroid belt which are also termed as minor planets or planetoids. They as termed as such because they are too small to be called a planet (Choi, 2017).Like the planets, they also revolve around the sun. And together with comets, asteroids can Figure 2.18 Asteroid vesta and Ceres tell the age of the solar system and essentially can Photo credit: modification of work by be identified as building blocks of planets. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA Comets Chunk of icy material that develops a temporary atmosphere as it approaches the sun (Fraknoi et al., 2016). These cosmic debris originate from the Kuiper belt and Oort cloud and develops a nebulous tail from its atmosphere as it approaches the sun. Water vapor and volatiles that was released from the nucleus once it enters the sun is detected in the head and tail of the comet. Comets are left over as the planets evolve, proving the disk had great amounts of icy materials. Figure 2.19 Comet Halley as it moved It is different from a meteor in a way among the stars that meteors are only streak of light that is Photo credit: modification of work by ESO seen in the sky while comets may be visible for weeks as it sweeps the sky. Meteorites Any fragment dust or rock particles that survives its fiery passage on the Earth’s atmosphere is termed as meteorites (Fraknoi et al., 2016) Where do you think these fragments came from? When ice in the comets evaporate, they leave abundant amounts of dust and rocks in the inner solar system, same as the dust that came from asteroids that collided and broken up. These are the sources of space rocks that literally fall from the sky. Before the fiery plunge, the debris exists in the space as meteoroid. Once it enters the Earth’s atmosphere and creates a brief fiery trail seen as streak of light, it is called as meteor, or commonly shooting star. 13  Earth Science Figure 2.20 This time-lapse meteor image was captured in April 2014 at the Atacama Large Millimeter/Submillimeter Array (ALMA) Photo credit: modification of work by ESO/C Malin According to NASA, meteorites serves as evidence in revealing the age of the solar system. It comprises the variety of materials that formed the planets as the solar system is evolving. Meteorites are oldest materials accessible to our planet that represents the processes involved in planet building. The craters or impacts imprinted on it reveals us the nature of the solar system our planet is existing. Scientists determine the age of meteorite by radioactive dating. They are using the decay of radioactive substances in the Figure 2.21 Martian meteorite named “Black space rock and trace it way back to the time since the material in Beauty” that rock was last melted. The oldest meteorite samples are 4.56 Photo credit billion years old, but radioactive dating reveals that age of https://solarsystem.nasa.gov/a meteorites varies. The age of the solar system is based on the age steroids-comets-and- of the oldest meteorite. meteors/meteors-and- meteorites/in-depth/ Odd rotation of Venus and Uranus After knowing the features of the solar system and the planet building, do you have any idea why these two planets spin the opposite way? As mentioned earlier on this learning account, Venus rotate the opposite way causing the sun to rise on the West and set on the East. Another wonder is that a day on Venus lasts longer than a year. It takes 243 Earth days to rotate on its axis and 225 Earth days for it to complete its orbit around the sun. Scientists suggested that these two originally rotated like the rest of the planets. Collisions from massive objects brought these planets spinning into opposite directions. There came a time Venus almost stop rotating then spin the way it is now, so the explanation that it has longer days than a year. Some studies stated that instead of one violent impact, small collisions knocked the Uranus into spinning almost on its side. While other explanations suggested that Uranus once has a large moon causing the planet to fall down on its side. Then that moon is eventually knocked out by other larger celestial body and stayed out of its orbit. Knowing all these basic things will point you to one thing- that all the processes involved in the evolution of the solar system leads in further understanding our home which is the Earth. We will focus the discussion on our planet on the succeeding learning accounts. 14