The radioactive dating of meteorites says that the Sun, planets, moons, and solar system fluff formed about 4. What was it like then? How did the solar system form? There are some observed characteristics that any model of the solar system formation must explain. Observables a.
The gravity of the planetesimals tended to divide the solar nebula into ring-shaped zones. Planetary orbits are slightly elliptical, very nearly circular. Thousands of exoplanets have been identified in the last twenty Solar nebula model. Retrieved Perhaps, one should not be surprised that that could happen.
Yeast rash on bottom. Key Concepts:
Main article: History of Solar System Solar nebula model and evolution hypotheses. The period required for the Solar System to complete one revolution around the Galactic Centre, the galactic yearis in the range of — million years. In this treatise, he argued that Throat spay clouds nebulae slowly rotate, gradually collapsing and Solar nebula model due to gravity and forming stars and planets. Other lines of evidence come Solar nebula model simulations of the process. The evolution of moon systems is driven by tidal forces. Another possible mechanism for the formation of planetesimals is the streaming instability in which the drag felt by particles orbiting movel gas jebula a feedback effect causing the growth of local concentrations. News at Princeton. Due to their higher boiling points, only metals and silicates could exist in solid form closer to the Sun, and these would eventually form the terrestrial planets of MercuryVenusEarthand Mars. The astronomy course I attended looked at the core collapse model of large planets. Astrobiology:Future Perspectives. The region of a planetary system adjacent to the giant planets will be influenced in a different way.
Since time immemorial, humans have been searching for the answer of how the Universe came to be.
- Since time immemorial, humans have been searching for the answer of how the Universe came to be.
- The nebular hypothesis is the leading hypothesis, amongst scientists, which states that the planets were formed out of a cloud of material associated with a youthful sun , which was slowly rotating.
- The standard model for formation of the Solar System is that it formed from a giant interstellar cloud.
Since time immemorial, humans have been searching for the answer of how the Universe came to be. However, it has only been within the past few centuries, with the Scientific Revolution, that the predominant theories have been empirical in nature. It was during this time, from the 16th to 18th centuries, that astronomers and physicists began to formulate evidence-based explanations of how our Sun, the planets, and the Universe began.
In essence, this theory states that the Sun, the planets, and all other objects in the Solar System formed from nebulous material billions of years ago. Originally proposed to explain the origin of the Solar System, this theory has gone on to become a widely accepted view of how all star systems came to be. According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust.
Then, about 4. This could have been the result of a passing star, or shock waves from a supernova, but the end result was a gravitational collapse at the center of the cloud. From this collapse, pockets of dust and gas began to collect into denser regions. While the ball at the center formed the Sun, the rest of the material would form into the protoplanetary disc.
The planets formed by accretion from this disc, in which dust and gas gravitated together and coalesced to form ever larger bodies. Due to their higher boiling points, only metals and silicates could exist in solid form closer to the Sun, and these would eventually form the terrestrial planets of Mercury , Venus , Earth , and Mars.
Because metallic elements only comprised a very small fraction of the solar nebula, the terrestrial planets could not grow very large. In contrast, the giant planets Jupiter , Saturn , Uranus , and Neptune formed beyond the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid i.
Leftover debris that never became planets congregated in regions such as the Asteroid Belt , Kuiper Belt , and Oort Cloud. Within 50 million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin thermonuclear fusion.
The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved. At this point, the Sun became a main-sequence star.
Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process. The idea that the Solar System originated from a nebula was first proposed in by Swedish scientist and theologian Emanual Swedenborg.
In this treatise, he argued that gaseous clouds nebulae slowly rotate, gradually collapsing and flattening due to gravity and forming stars and planets. The Laplacian nebular model was widely accepted during the 19th century, but it had some rather pronounced difficulties.
The main issue was angular momentum distribution between the Sun and planets, which the nebular model could not explain. In addition, Scottish scientist James Clerk Maxwell — asserted that different rotational velocities between the inner and outer parts of a ring could not allow for condensation of material. By the early 20th century, the Laplacian model had fallen out of favor, prompting scientists to seek out new theories. Credit for this goes to Soviet astronomer Victor Safronov and his book Evolution of the protoplanetary cloud and formation of the Earth and the planets For example, the SNDM model has been successful in explaining the appearance of accretion discs around young stellar objects.
Various simulations have also demonstrated that the accretion of material in these discs leads to the formation of a few Earth-sized bodies. While originally applied only to the Solar System, the SNDM was subsequently thought by theorists to be at work throughout the Universe, and has been used to explain the formation of many of the exoplanets that have been discovered throughout our galaxy.
Although the nebular theory is widely accepted, there are still problems with it that astronomers have not been able to resolve.
For example, there is the problem of tilted axes. According to the nebular theory, all planets around a star should be tilted the same way relative to the ecliptic.
But as we have learned, the inner planets and outer planets have radically different axial tilts. Also, the study of extrasolar planets have allowed scientists to notice irregularities that cast doubt on the nebular hypothesis. Astronomers have adjusted the nebular hypothesis to account for some of these problems, but have yet to address all outlying questions.
Alas, it seems that it questions that have to do with origins that are the toughest to answer. However, between our current models of star and planet formation, and the birth of our Universe, we have come a long way. We have written many articles about the Solar System here at Universe Today. Now maybe the Grand Tack with the assumption of mantle breaking impacts in the early days — those first 10 millions years were heady times! Nice overview, and I learned a lot.
However, there are some salient points that I think I have picked up earlier:. The study of star forming molecular clouds shows that same early, large stars form that way.
That blows a 1st geeration of large bubbles with massive, compressed shells that are seeded with supernova elements, as we see Earth started out with.
These stars have powerful solar winds. The astronomy course I attended looked at the core collapse model of large planets. ASs well as the direct collapse scenario. The terrestrial planets grow by slower accretion, and the material may have started to be cleared from the disk.
It was considered hard to grow grains above a cm, and when they grow they rapidly brake and fall onto the star. Now scientists have come up with grain collapse scenarios, where grains start to follow each other for reasons of gravity and viscous properties of the disk, I think. All sorts of bodies up to protoplanets can be grown quickly and, when over the problematic size, will start to clear the disk rather than being braked by it. Jupiter can be considered a clue, too massive to tilt by outside forces.
The general explanation tend to be the accretion process, where the tilt would be randomized. Venus may be an exception, since some claim it is becoming tidally locked to the Sun — Mercury is instead locked in a resonance — and it is in fact now retrograde with a putative near axis lock.
Possible Mercury bit at least Earth and Mars and Moon show late great impacts. A recent paper show that terrestrial planets would suffer impacts on the great impact scale, between 1 to 8 as norm with an average of 3. Skip to content. Nebular Hypothesis: According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. Like this: Like Loading
Bibcode : AJ Water delivered to Earth. Momose; Y. Publications of the Astronomical Society of the Pacific. Lunine This concept had developed for millennia Aristarchus of Samos had suggested it as early as BC , but was not widely accepted until the end of the 17th century. Also, the study of extrasolar planets have allowed scientists to notice irregularities that cast doubt on the nebular hypothesis.
Solar nebula model. Nebular Hypothesis:
How Was the Solar System Formed? - The Nebular Hypothesis - Universe Today
The radioactive dating of meteorites says that the Sun, planets, moons, and solar system fluff formed about 4. What was it like then? How did the solar system form? There are some observed characteristics that any model of the solar system formation must explain.
Observables a. All the planets' orbits lie roughly in the same plane. The Sun's rotational equator lies nearly in this plane. Planetary orbits are slightly elliptical, very nearly circular. The planets revolve in a west-to-east direction. The Sun rotates in the same west-to-east direction. The planets differ in composition. Their composition varies roughly with distance from the Sun: dense, metal-rich planets are in the inner part and giant, hydrogen-rich planets are in the outer part.
Meteorites differ in chemical and geologic properties from the planets and the Moon. Their obliquity the tilt of their rotation axes with respect to their orbits are small. Uranus and Venus are exceptions. The rotation rates of the planets and asteroids are similar to 15 hours, unless tides slow them down. The planet distances from the Sun obey Bode's lawa descriptive law that has no theoretical justification.
However, Neptune is a significant exception to Bode's "law". Planet-satellite systems resemble the solar system. The Oort Cloud and Kuiper Belt of comets. Condensation Model The model that best explains the observed characteristics of the present-day solar system is called the Condensation Model.
The solar system formed from a large gas nebula that had some dust grains in it. The nebula collapsed under its own gravity to form the Sun and planets. What triggered the initial collapse is not known. Two of the best candidates are a shock wave from a nearby supernova or from the passage through a spiral arm. The gas cloud that made our solar system was probably part of a large star formation cloud complex.
The stars that formed in the vicinity of the Sun have long since scattered to other parts of the galactic disk. Other stars and planets in our galaxy form in the same basic way as will be described here.
The figure below summarizes the basic features of the Condensation Model. After the figure is further explanation of the model and how it explains the observable items in the previous section.
A piece of a large cloud complex started to collapse about five billion years ago. The cloud complex had already been "polluted" with dust grains from previous generations of stars, so it was possible to form the rocky terrestrial planets.
As the piece, called the solar nebula collapsed, its slight rotation increased. This is because of the conservation of angular momentum. Centrifugal effects caused the outer parts of the nebula to flatten into a disk, while the core of the solar nebula formed the Sun. The planets formed from material in the disk and the Sun was at the center of the disk. This explains items a and b of the observables above.
Those on noncircular orbits collided with other particles, so eventually the noncircular motions were dampened out. The large scale motion in the disk material was parallel, circular orbits. This explains items c and d of the observables above. As the solar nebula collapsed, the gas and dust heated up through collisions among the particles. The solar nebula heated up to around K so everything was in a gaseous form.
When the solar nebula stopped collapsing it began cooling, though the core forming the Sun remained hot. Only metal and rock materials could condense solidify at the high temperatures close to the proto-Sun.
Therefore, the metal and rock materials could condense in all the places where the planets were forming. Volatile materials like water, methane and ammonia could only condense in the outer parts of the solar nebula. This explains item e of the observables above.
Around Jupiter's distance from the proto-Sun the temperature was cool enough to freeze water the so-called "snow line" or "frost line". Further out from the proto-Sun, ammonia and methane were able to condense.
There was a significant amount of water in the solar nebula. The greater amount of water ice at Jupiter's distance from the proto-Sun helped it grow larger than the other planets. Material with the highest freezing temperatures condensed to form the chondrules that were then incorporated in lower freezing temperature material. Any material that later became part of a planet underwent further heating and processing when the planet differentiated so the heavy metals sunk to the planet's core and lighter metals floated up to nearer the surface.
The first part of observables item f is explained. The inner planets were not totally devoid of volatile material, though.
Water could still be incorporated into the minerals to form hydrated minerals that could survive the extreme heat of the inner part of the solar system without all being vaporized away, even during the phase of numerous, large impacts in the early solar system. The three comets sampled up close by spacecraft, Tempel 1, Wild 2 and Churyumov-Gerasimenko , are made of a mixture of materials with high and low melting temperatures second part of observables item f.
The still-forming proto-Sun probably produced strong winds as seen in young, protostars today and those winds could be responsible for at least part of the mixing of solar nebula materials.
The coalescing particles tended to form bodies rotating in the same direction as the disk revolved. The forming planet eddies had similar rotation rates. This explains items g and h above.
The gravity of the planetesimals tended to divide the solar nebula into ring-shaped zones. This process explains item i above. Some planetesimals formed mini-solar nebulae around them which would later form the moons.
This explains item j above. The Jupiter and Saturn planetesimals had a lot of water ice mass, so they swept up a lot of hydrogen and helium. The Uranus and Neptune planetesimals were smaller so they swept up less hydrogen and helium there was also less to sweep up so far out. The inner planetesimals were too small to attract the abundant hydrogen and helium. The small icy planetesimals near the forming Jupiter and perhaps Saturn were flung out of the solar system. Those near Uranus and Neptune were flung to very large orbits.
This explains the Oort Cloud of item k above, though some of the gravitational flinging by Uranus and Neptune would have been weaker to form the closer scattered disk. There was not enough material to form a large planet beyond Neptune. The icy planetesimals beyond Neptune formed the Kuiper Belt. The large planets were able to stir things up enough to send some of the icy material near them careening toward the terrestrial planets.
The icy bodies gave water to the terrestrial planets. Recent sophisticated computer simulations have shown that gravity interactions between the giant planets themselves could have changed their orbits from the ones they originally had. Jupiter would have slowly spiraled inward while Saturn, Neptune, and Uranus would have slowly spiraled outward until Saturn reached the point where it took twice as long to orbit the Sun as Jupiter.
This resonance would have greatly changed the orbits of Neptune and Uranus, even to the point of shifting Neptune's closer orbit to a much larger one outside of Uranus' orbit. Older versions of the Condensation Model had difficulty explaining the formation of a planet the size of Neptune at Neptune's current distance from the Sun because of the amount of available material in the solar disk would have been too small at that distance from the forming Sun.
If Neptune had formed much closer in than it is now and later moved to its present position, then the problem goes away.
In addition, the onset of the Jupiter-Saturn resonance would have led to a sudden scattering of planetesimals which would explain the possible spike in the number of giant impacts throughout the solar system about 3. After forming the disk, the disk would have cooled as the heat was radiated to space.
If the nebula was warmer, then the "frost line" would have been further out, so Jupiter would have been a terrestrial planet. The ice cores forming beyond about Neptune's current distance never got big enough to capture the surrounding hydrogen and helium gasthey stayed small to become the dwarf planets such as Pluto, Eris, Makemake, Haumea, etc. Although the Condensation Model explains a number of observed facts of the properties of the present-day solar system, we have been looking at a sample size of just one: our solar system.
It has been only relatively recently that we have been able to test the theory with other forming and fully-developed planetary systems with the placement of powerful telescopes above the Earth's atmosphere and the development of very sensitive instruments for ground-based telescopes and analysis techniques. Observations in the infrared and sub-millimeter wavelengths have enabled us to peer through the thick dust that shields forming stars and their planetary disks.
We have used those observations to modify and improve the Condensation Model. In particular our observations of other planetary systems has forced us to seriously explore how planets can migrate inward from where they first started forming. Perhaps, one should not be surprised that that could happen. As described in item G above, gravitational interactions flung chunks of material all about.
As described in the next section, the observations show that gravitational interactions can shift things as big as planets as well as small planetesimals.