The formation and evolution of our solar system
Our solar system was born 4,6 billion years ago. Back then, the Sun and all the planets in our solar system were merely a giant cloud of gas and dust. Then, however, a small part of the gas-cloud collapsed and all the objects in our solar system were formed.
This hypothesis is known as the Nebular Hypothesis and is the most widely accepted theory about the origin of our solar system among scientists.
According to this theory, the Sun was formed when denser regions of the collapsed cloud pulled in more and more material, and as a consequence of conservation of momentum, the denser regions began rotating and the increasing pressure caused it to heat up. A ball of material gathered in the center and formed the Sun while the rest of the material flattened out into a protoplanetary disk surrounding the Sun. It is from this protoplanetary disk that all the planets, moons and other objects were formed.
The planets formed when gas and dust from the disk gravitated together and formed larger bodies. Near the center of the disk only the materials with high boiling points could exist in solid form. This meant that silicates and metals eventually formed the terrestrial planets (Mercury, Venus, Earth and Mars) while the larger Jovian planets (Jupiter, Saturn, Uranus and Neptune) formed beyond the point where material is cool enough to remain solid (so-called volatiles). Leftover material gathered in regions such as Kuiper Belt and Oort cloud.
Since then, our solar system has evolved considerably and it will continue to do so in years to come. Our Sun will burn through its current hydrogen fuel and in roughly 5 billion years the Sun will cool and expand to a massive red giant. By then, Mercury and possibly Venus and Earth will be swallowed by the Sun's massive gravitational attraction.
The following video from youtube illustrates the formation of solar system in greater detail:
This hypothesis is known as the Nebular Hypothesis and is the most widely accepted theory about the origin of our solar system among scientists.
According to this theory, the Sun was formed when denser regions of the collapsed cloud pulled in more and more material, and as a consequence of conservation of momentum, the denser regions began rotating and the increasing pressure caused it to heat up. A ball of material gathered in the center and formed the Sun while the rest of the material flattened out into a protoplanetary disk surrounding the Sun. It is from this protoplanetary disk that all the planets, moons and other objects were formed.
The planets formed when gas and dust from the disk gravitated together and formed larger bodies. Near the center of the disk only the materials with high boiling points could exist in solid form. This meant that silicates and metals eventually formed the terrestrial planets (Mercury, Venus, Earth and Mars) while the larger Jovian planets (Jupiter, Saturn, Uranus and Neptune) formed beyond the point where material is cool enough to remain solid (so-called volatiles). Leftover material gathered in regions such as Kuiper Belt and Oort cloud.
Since then, our solar system has evolved considerably and it will continue to do so in years to come. Our Sun will burn through its current hydrogen fuel and in roughly 5 billion years the Sun will cool and expand to a massive red giant. By then, Mercury and possibly Venus and Earth will be swallowed by the Sun's massive gravitational attraction.
The following video from youtube illustrates the formation of solar system in greater detail:
Illustration of how the solar system came to be
Understanding our Sun
Our Sun is a star at the center of our solar system. The gravity of the Sun holds the entire solar system together and keeps all of the planets and other objects in orbit around it. The energy from the Sun is crucial for all life on Earth, without the Sun the Earth would be cold and abandoned. Its size is enormous compared to Earth, with a diameter of around 109.000 (!) Earths and a mass of 1.989 x 10^30 kg, equivalent to 330.000 Earth-masses.
Contrary to what most people think, the Sun is not completely stationary in the center of our solar system. The gravitational pull from the planets, especially that of Jupiter, makes the Sun rotates around its center of mass with an orbital period equal to that of Jupiters orbital period of about 12 years. In addition, the Sun takes about 25 days to complete one solar rotation at the equator and 34 days at the poles.
The Sun can be divided into 6 regions with the core, the radiative zone, the convective zone in the interior. Then the photosphere, the chromosphere and the corona as the outermost layers. The temperature of the Sun varies a lot, depending on whether you are at its core or at its surface. The core reaches an astonishing temperature of no less than 1,57 x 10^7 Kelvin, while the surface temperature is 5778 Kelvin. The Sun consists, like other stars, of gasses, with around 70% of its mass being hydrogen and 27% helium. The staggering temperature at the core is enough for the hydrogen atoms to fuse to helium, a process that releases enormous amounts of energy that eventually powers all the heat and light the Sun emits.
The followering video shows how the STEREO satelittes reveal the entire Sun-surface to us, and thus is able to detect coronal mass ejections and other sun phenomenas on the far side of the sun, which normally is obscured to our ground based telescopes.
The 4 Terrestrial Planets
MercuryMercury is regarded as the first planet closest to our Sun in our solar system and it is notoriously difficult to observe due to it never being more than 30 degress away from the Sun. Historically, it has been difficult to discover its true rotation, however came about radar astronomy and its properties were unraveled. Its specially slow rotation means that it takes 175.9 days to complete a full rotation. Mercury has a fairly eccentric orbit, meaning that it moves in as close as 47 million km to sun and as far away as 70 million km. It's also the fastest known planet with a travel speed of about 50 km/s.
When Mercury is at its perihelion, its surface temperatur can reach 430 degrees celsius. However its lack of atmosphere and thus the ability to retain the heat, means that during night it may fall below -180 degrees celsius. Mercury has an interesting natural phenomenae where its thin exosphere gets blasted off the surface by the intense solar wind. Due to solar radiation pressure, the atoms escape into space and form a tail of neutral particles. With the aid of Mercury's magnetic field, this creates episodically intense magnetic tornadoes that funnel fast, hot solar wind plasma down to the planets surface. Mercury's surface resembles that of our Moon, by being heavily scared by impact craters up to 1550 km in diameter. It is anticipated, based on having the second highest density after Earth, that the planet has a large metallic core with a radius of about 2000 km, which accounts for 80% of the planets radius. Ground based radars indicate that its core could be partially molten. NASA's spacecraft Messenger have been examining and mapping the planet extensively since it arrived in 2008. To this date almost the entire planet has been imaged, thus revealing a surfaced shaped by extensive volcanism and impacts. |
Source: http://solarsystem.nasa.gov/planets/mercury/indepth
Facts:
Aphelion: 0.466 AU Perihelion: 0.307 AU Semi-major-axis: 0.387 AU Eccentricity: 0.205 Avg. Orbital speed: 47 km/s Mean Radius: 0.3829 Earths Mass: 0.055 Earths Source:
https://en.wikipedia.org/wiki/Mercury_(planet) |
Source: http://solarsystem.nasa.gov/planets/venus/indepth
Facts:
Aphelion: 0.728 AU Perihelion: 0.718 AU Semi-major-axis: 0.723 AU Eccentricity: 0.0067 Avg. Orbital speed: 35 km/s Mean Radius: 0.9499 Earths Mass: 0.815 Earths Source:
https://en.wikipedia.org/wiki/Venus |
VenusVenus is the second planet from the Sun and our closest planetary neighbour and of similar size to Earth.
Venus' rotation and orbit is quite unusual in several aspects. Venus is one out of two planets that rotate from east to west. 1 rotation for Venus, takes 243 days, which is also the slowest planetary rotation known in our system. Due to the opposite rotation, the mechanics of the Sun "setting each venusian day", doesn't occur. A day-night cycle takes 117 Earth days as it rotates opposite of its orbital revolution. Its eccentricity is also the most "perfect" in our solar system, creating a near perfect circle. Venus is somewhat similar to Earth in its structure. It has an iron core of approximately 3200 km in radius. Followed by a mantle driven by an internal heat source, presumably by radioactive decay. This creates similar forces to that on Earth with volcanoes and tectonic activity. Its mean radius and mass is also somewhat similar to Earth. Venus is a good example of a planet with a rampant runaway greenhouse gas scenario. Its enormous amounts of carbon dioxide and clouds made of sulfuric acid droplets traps the Sun's heat, resulting in surface temperatures higher than 470 degrees celsius. The shear amount of gas creates such a heavy atmosphere, that it would be equal to being 1.6 km under water on Earth. However as you leave the surface and travel to higher levels, the amount of heat dissipates as it escapes into space. Man-made spacecrafts have landed on Venus, but due to the extreme conditions, nothing can last for long and there are serious, near impossible challenges to colonize this hot rock. Therefore potential for life in any form or shape as we know it on Earth, seems readily impossible except for in its top atmospheric layers. However it can be speculated whether the planet may have housed life at a earlier time in its history. Perhaps with a less developed Sun or a less developed greenhouse gas atmosphere. |
EarthYou know this one...
However as used to it as we are, it's one of the most spectacular planets in the solar system. 3rd planet from the Sun. Only confirmed location of life so far, liquid H2O at the surface, breathable atmosphere, magnetic field strong enough to protect biological life and a slight greenhouse effect keeping our planet out of the freezer. In fact if it wasn't for greenhouse gasses at all, the Earth's average temperature would be about -20 degrees celsius. The atmosphere also shields us from most meteors as they burn up upon collision with the atmosphere. The Earth is composed of an inner core, outer core, mantle and crust. The inner core consists of iron and nickel metals presumeably due to geochemical differentiation. These dense minerals make up the core and is the main constituent in producing the Earth's strong magnetic field. This inner core is about 1221 kilometers in radius and nearly the same temperatur as the Sun's surface, at a blistering 5400 degrees celsius. The surrounding layer is the outer core. S-wave limitation discovered in this shadow zone by seismic investigation conveys the idea that this part of the core is liquid and consisting of iron and nickel fluids since S-waves cannot travel in fluids. S-waves are a secondary type of shockwaves that travel through the Earth's interior together with P-waves. S-waves(Shear waves) do not travel through fluids (See more information on S-waves here) The mantle is the thickest layer and is made up of hot viscious mixture of rock compareable to the consistency of caramel. This is due to massive pressure and temperature. The outermost layer is the crust and its depth vary greatly. The crust is thickest and oldest on land and shallow and relatively young in the ocean. This is due to the fact that the oceanic crust is constantly undergoing tectonic forces and thus being subducted back into the mantle every couple of hundreds of millions of year. The total radius of Earth is 6378 km and this makes it the largest terrestrial planet in our system. The surface of the planet is 70% covered by saline oceans and with an average depth of 4 km. 97% of the Earths water resides in these oceans. The remainder is freshwater locked up in glacial settings, lakes and rivers or locked up as groundwater. The highest mountain on land is Mt. Everest at about 8 km, however the largest surface protruding element is the Hawaii's Mauna Kea volcano from the bottom of the ocean towering a total of 10 km from its oceanic subsurface base. The shallowest part is the subduction zone known as the Mariana trench reaching nearly 11 km depth. Our Moon is tidally locked with the Earth, meaning the same side always faces the planet as the Moon rotates around us. We're the only planet in the solar system to have only 1 Moon, although we do temporarily give host to asteroids being caught into orbit. Our Moon has a particular interesting genesis as it's postulated that it's the product of a large and early collision between two planetary objects. The Moon contributes greatly to the tidal forces on our planet and also have a miniscule effect on slowing the rotation of our planet. |
Source:
http://solarsystem.nasa.gov/planets/earth/indepth Facts:
Aphelion: 1.016 AU Perihelion: 0.983 AU Semi-major-axis: 1 AU ( 149.6 million km ) Eccentricity: 0.016 Avg. Orbital speed: 29.8 km/s Mean Radius: 1 Earths Mass: 1 Earths Source:
https://en.wikipedia.org/wiki/Earth |
Source:
http://solarsystem.nasa.gov/planets/mars/indepth Facts:
Aphelion: 1.666 AU Perihelion: 1.381 AU Semi-major-axis: 1.523 AU Eccentricity: 0.093 Avg. Orbital speed: 24 km/s Mean Radius: 0.54 Earths Mass: 0.107 Earths Source:
https://en.wikipedia.org/wiki/Mars |
MarsMars is the 4th planet from the Sun and the last of the terrestrial planets. It's also currently the most examined and hyped planet by humans. The next big one up for human exploration and possibly, in the future, our first attempt at colonizing another planet. The planet is fairly interesting to humans due to it's closeness and hospitalitywise - similarity to earth. It has relatively mild temperatures with an avg of -63 degrees celsius. It doesnt appear to be a host of crazy weather phenomena's other than dust storms and it has a presence of water in form of ice. The gravity is relatively low, but neither to strong or to weak for short-term human health. However long-term effect on Earth-originated biology is yet unknown, although the perils of zero gravity in space is well understood in the detoriation of bones and muscles.
Like Earth, Mars is a rocky planet and with half the size of Earth. The features present on other terrestrial planets are also found here. Volcanoes, impact craters, evidence of past crustal movement and dust storms. However it seems that tectonic activity has disappeared as well as its atmosphere. The planet is nearly devoid of a magnetic field, which in geological terms could indicate a core standstil. The core is believed to have a geochemically differentiated dense metallic core, overlaid by a less dense material. Current models indicate it has a radius of 1794 km and consisting mainly of iron, nickel and sulfur. This core is thought to be twice as rich in lighter elements than Earth's core. The tectonics of the planet seem to have been dormant for millions of years. This could portray Mars as the future of Earth in billions of years when Earth's core is expected to cool down and come to a standstill and therefore will seize all tectonic movement. The red color that has come to represent Mars, is due to oxidised iron in the soil. So what happened to Mars is of great interest to many scientists as it could help us understand what events can possibly occur to our own. But it's also of interest to scientists to attempt to generate a greenhouse gas effect on Mars. Such a terraforming event is yet not possible, but neither unimaginable. Potential for life on Mars seems slim. Ground analyses have revealed no biology present as of yet. However it's not impossible to rule out yet, whether the planet may have played host to life at an earlier stage of its lifetime. |
The 4 Jovian Planets
JupiterJupiter is the 5th planet in our solar system and the first gas giant. Giant is an appropriate name, since this behemoth is the largest object in our solar system next to our star. Its diameter is eleven times that of the Earth.
Jupiter is a gaseous construct with enormous pressure and what we can observe on the surface is a cloud layer and therefore not a true "surface". These clouds can be seen swirling around the planet in turbulent streams blowing up around to 480 km/h. The trademark of Jupiter, is the large red spot below its equator. This spot is a great storm thats been going on for more than 186 years and possibly for as long as 351 years. These powerful winds on Jupiter consist of ammonia, hydrogen, sulfide and water. There are traces of other elements such as carbon, neon, oxygen and much more, but hydrogen is found in largest abundance. Jupiter's interior is well hidden due to its cloudy layer, however it is thought to consist of a dense core with a mixture of elements, then followed by a surrounding layer of liquid metallic hydrogen and helium. The outer layer is predominantly made of molecular hydrogen. Jupiter's massive gravitational pull is keeping 67 possible moons in check around its orbit, as well as affecting the Sun's center of mass. Interesting note is, that had Jupiter been 75 times more massive, it would theoretically be able to fuse hydrogen and thus become a star. Jupiter is also known to produce a massive magnetic field and thus is the host of some of the solar system's most magnificent auroras at the planet's poles. Potential for life on Jupiter is very unlikely as we know it. The temperatures, pressures and materials that make up this planet are most likely too extreme and volatile for any currently known organisms to adapt to. |
Source:
http://solarsystem.nasa.gov/planets/jupiter/indepth Facts:
Aphelion: 5.454 AU Perihelion: 4.950 AU Semi-major-axis: 5.202 AU Eccentricity: 0.048 Avg. Orbital speed:13 km/s Mean Radius: 11.2 Earths Mass: 317 Earths Source:
https://en.wikipedia.org/wiki/Jupiter |
Source:
http://solarsystem.nasa.gov/planets/saturn/indepth Facts:
Aphelion: 10.086 AU Perihelion: 9.024 AU Semi-major-axis: 9.554 AU Eccentricity: 0.055 Avg. Orbital speed: 9.69 km/s Mean Radius: 9.449 Earths Mass: 95.16 Earths Source:
https://en.wikipedia.org/wiki/Saturn |
SaturnSaturn is the 6th planet and the 2nd of the Jovian planets. Saturn shares some similarities with Jupiter. For one its massive size being 755 times bigger than Earth, and that it is primarily made of hydrogen and helium.
Saturns greatest known feature is its famous ring system. This ring system extends hundreds of thousands of kilometers from the planet, yet the vertical height of the rings only extend 10 meters in the main rings. Its ring system consists of 9 continous main rings and 3 discontinous arcs which is composed mostly of ice particles and small amounts of rocky debris and dust. Just as with Jupiter, Saturn plays host to a lot of moons. A total possible of 62 moons, yet only 53 confirmed. At Saturn's center is believed to be a dense core of rock, iron-nickel, ice, water and other compounds made solid by intense pressure and heat. This core is enveloped by liquid metallic hydrogen, similar to Jupiter, but considerably smaller. |
UranusUranus is the 7th planet and the 3rd of the Jovian planets. It's also the planet with the third largest diameter in our system. This ice giant is very cold, windy and surrounded by 13 faint rings such as those of Saturn. It's also the keeper of 27 small moons. Due to Uranus great distance from the Sun, 1 Uranian year is the equivilant of 84 Earth years.
Where Uranus is truly unique, is in its rotationel axis. The planet has a tilt of 97.77 degrees and is therefore on "its side" relative to the orbital plane. It's speculated that this unique and peciluar rotational axis could be due to a collision with an Earth-sized object. This extreme tilt creates some of the most extreme seasons in the solar system. For a quarter of a Uranian year the Sun shines directly over its pole, plunging the other half of the planet into a 21-year long dark winter. The oddity doesn't stop here, Uranus is like Venus in terms of its rotation. They both rotate in the opposite direction than all other planets - east to the west. Uranus is unlike the 2 first Jovian planets, whose main constitutents are gasseous. Uranus is an ice giant, where about 80 % of the planets mass is made up of a hot dense fluid of "icy" materials. This sits on top of a small presumably rocky core. Near the core it heats up to nearly 5000 degrees celsius. Uranus' unique blue-green color is a product of the methane gas in its atmosphere. The incoming sunlight passes through its atmosphere and is then reflected back through the cloudy layer. Since methane gas retains the red part of the light spectrum, the blue-green parts of the light spectrum escapes the planet. However the atmosphere does primarily consist of hydrogen and helium. The planet experience a minimum temperature of -224.2 degrees celsius, making it an extremely cold planet. Potential for life on Uranus looks to be a far fetched idea! The temperatures, pressures and materials of this planet are most likely too extreme and volatile for organisms as we know it to exist. |
Source:
http://solarsystem.nasa.gov/planets/uranus/indepth Facts:
Aphelion: 20.11 AU Perihelion: 18.33 AU Semi-major-axis: 12.21 AU Eccentricity: 0.046 Avg. Orbital speed: 6.80 km/s Mean Radius: 4 Earths Mass: 14.53 Earths Source:
https://en.wikipedia.org/wiki/Uranus |
Source:
http://solarsystem.nasa.gov/planets/neptune/indepth Facts:
Aphelion: 30.33 AU Perihelion: 29.81 AU Semi-major-axis: 30.11 AU Eccentricity: 0.009 Avg. Orbital speed: 5.43 km/s Mean Radius: 3.88 Earths Mass: 17.14 Earths Source:
https://en.wikipedia.org/wiki/Neptune |
NeptuneNeptune is the 8th and last of the 4 Jovian planets. Like Uranus it's an ice giant. Noteworthy to its discovery, is the fact that its presence was mathematically predicted rather than directly observed. Another interesting fact is related to the once-beloved planet Pluto's highly eccentric orbit. These two objects cross each others paths, yet they never crash into each other. This means that for a 20-year-long period, out of 248 Earth years, Pluto is within Neptune's orbit.
Neptune's magnetic field axis is tipped over by about 47 degrees compared to the planets rotation axis. This creates wild variations in its magnetosphere due to this misalignment. Neptune's atmosphere is known to extend to great depths, hence merging into water and melted ice, over a heavier and presumably Earth-sized solid core. The blue color of its atmosphere is, like Uranus, the result of methane in the atmosphere. Though Neptune has a more intense blue color than its neighbour Uranus. It's speculated that Neptune's atmosphere must contain unknown constituents that causes its blue color to be more distinct. Neptune have a lot of strong winds, up to three times stronger than on Jupiter, even though it's so far away from the Sun and receives very little energy input. Large dark spots have been seen in its atmosphere moving at more than 1200 km/h. There have currently been observed 6 rings around the planet. These are not as uniform and perfect as Saturn's rings are. The Neptunian rings are thought to be young and short-lived. |
Asteroids and other objects
Humankind's interest in asteroids is not only based on their potential danger to life on Earth,
but also because they hold information about the early stages of our solar system.
A few words regarding the Earth:
The Earth is composed mainly of O, Si, Mg, Fe and other lesser abundant elements such as S, Ni, Al, Ca, K, along with trace-elements. Throughout the early stages of Earth’s evolution, heavy elements gathered in the middle of the planet and lighter elements in the outer layers. The mean density of the Earth is about 5.51g/cm^3, this is very different from the normal weight of a rock you pick up on the beach, which is about 2-3g/cm^3. This high mean density is due to internal heating and geochemical differentiation of the molten rock over a long period of time. By seismics and other studies, we’ve concluded that the Earth's core is a solid sphere primarily made of iron.
There are many objects between the planets in our solar system, such as comets, asteroids, meteroids and dust.
Comets are objects made of ice and rock that originated from somewhere possibly outside our solar system or in unknown areas beyond the furthest planet that we currently know of - Neptune. One of the most well-known comets, named Hale-Bopp, last passed the Sun in the 1990's. It was thoroughly studied at that time, as it was easily seen by eyesight, but will not return for some millennia.
but also because they hold information about the early stages of our solar system.
A few words regarding the Earth:
The Earth is composed mainly of O, Si, Mg, Fe and other lesser abundant elements such as S, Ni, Al, Ca, K, along with trace-elements. Throughout the early stages of Earth’s evolution, heavy elements gathered in the middle of the planet and lighter elements in the outer layers. The mean density of the Earth is about 5.51g/cm^3, this is very different from the normal weight of a rock you pick up on the beach, which is about 2-3g/cm^3. This high mean density is due to internal heating and geochemical differentiation of the molten rock over a long period of time. By seismics and other studies, we’ve concluded that the Earth's core is a solid sphere primarily made of iron.
There are many objects between the planets in our solar system, such as comets, asteroids, meteroids and dust.
Comets are objects made of ice and rock that originated from somewhere possibly outside our solar system or in unknown areas beyond the furthest planet that we currently know of - Neptune. One of the most well-known comets, named Hale-Bopp, last passed the Sun in the 1990's. It was thoroughly studied at that time, as it was easily seen by eyesight, but will not return for some millennia.
Asteroids originated from a region between Mars and Jupiter called the asteroid belt. They are believed to contain the original chemical composition of the solar system in the early stages of the solar system’s evolution. Asteroids are not dangerous for life on Earth directly, but occasionally, they are flung out of the asteroid belt because of gravitational interactions between planets or due to internal collisions. Their mass is not big enough to form their own atmosphere, neither enough to form a round shape, which is why they are boulder-like and irregular shaped. Theories about the origin of asteroids suggested that there once was a planet between Mars and Jupiter, which was destroyed and much of the material was then “sucked in” by Jupiter’s gravitational field. This idea, although, was rejected for several reasons. The other theory assumes that material in the asteroid belt dates back to the early stages of the solar system, where material was distributed in a disk around the Sun, which then formed the inner solid and terrestrial planets; Mercury, Venus, Earth and Mars.
Jupiter, Saturn, Uranus, and Neptune consist of gas and ice and are called Jovian planets.
Meteoroids are smaller asteroids in the sense that they are products of collision between asteroids in the asteroid belt. Meteoroids are defined to be objects bigger than dust grains but smaller than asteroids ranging from a few millimeters to several tens of kilometers. Their velocity is based on the conditions of impact, ranging from no velocity to 20 kilometers per second. The figure above (Figure 1) shows the differences between comets, asteroids, meteoroids, meteors, and meteorites.
If a meteoroid enters Earth’s atmosphere it accelerates and starts to melt, if it survives the descent and reaches the surface it is called a meteorite.
Litterature:
https://en.wikipedia.org/wiki/ - Individual planetary facts
http://solarsystem.nasa.gov/planets/comets
https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html
http://solarsystem.nasa.gov/planets/earth/indepth
http://solarsystem.nasa.gov/planets/meteors/basic
https://en.wikipedia.org/wiki/ - Individual planetary facts
http://solarsystem.nasa.gov/planets/comets
https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html
http://solarsystem.nasa.gov/planets/earth/indepth
http://solarsystem.nasa.gov/planets/meteors/basic