Giant Planets Wreck Havoc
The giant planets formed closer to the Sun than where they are now. There wasnât enough materialin the solar disk for Uranus and Neptune to form where they currentlyorbit, 19 and 30 times farther from the Sun than Earth, respectively.The Kuiper belt also likely formed closer in, roughly spanning thecurrent orbital distances of Uranus and Neptune.
Simulations suggest that the orbits of the giant planets shiftedabout 4.1 billion years ago. Gravity from the numerous Kuiper beltobjects nudged Jupiter and Saturn into a 2:1 resonance, meaning Jupiterorbited the Sun twice for every Saturn orbit. This periodically broughtthe two planets close together, causing wide-ranging gravitationaleffects.
Uranus and Neptune got pushed further away from the Sun, ploughingthrough the Kuiper belt, scattering most of its objects either inward oroutward over the next millions of years. Any additional ice giants thathad formed were kicked out of the solar system entirely. The outwardlyscattered worlds formed todayâs sparsely populated Kuiper belt and thefarther-away sphere of icy bodies we call the Oort cloud. This is wheremost comets come from.
The inwardly scattered worlds raced through the inner solar system,smashing into the worlds there and creating basins as large as athousand kilometers or more on Mercury, Venus, Earth, the Moon, andMars. Scientists call this event the Late Heavy Bombardment.
Image: Mark Booth / Wikipedia
Searching For Other Planets
For as long as weve been able to, humankind has searched for another Earth. In February 2017, scientists announced the discovery of the TRAPPIST-1 system, which has a record-breaking seven planets, three of which are in the Goldilocks zone the area around a star where the temperature is not too hot and not too cold. Planets that are in this area are thought to be good contenders for having liquid surface water and, potentially, life. A system like this has never been seen before, and scientists say its the best bet today for finding a planet that could support life.
Look up at the stars and not down at your feet. Try to make sense of what you see, and wonder about what makes the universe exist. Be curious.
Formation Of The Terrestrial Planets
The grains that condensed in the solar nebula rather quickly joined into larger and larger chunks, until most of the solid material was in the form of planetesimals, chunks a few kilometers to a few tens of kilometers in diameter. Some planetesimals still survive today as comets and asteroids. Others have left their imprint on the cratered surfaces of many of the worlds we studied in earlier chapters. A substantial step up in size is required, however, to go from planetesimal to planet.
Some planetesimals were large enough to attract their neighbors gravitationally and thus to grow by the process called accretion. While the intermediate steps are not well understood, ultimately several dozen centers of accretion seem to have grown in the inner solar system. Each of these attracted surrounding planetesimals until it had acquired a mass similar to that of Mercury or Mars. At this stage, we may think of these objects as protoplanetsnot quite ready for prime time planets.
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Faq: Which Spacecraft Are Headed To Interstellar Space
Five spacecraft have achieved enough velocity to eventually travel beyond the boundaries of our solar system. Two of them reached the unexplored space between the stars after several decades in space.
- Voyager 1 went interstellar in 2012 and Voyager 2 joined it in 2018. Both spacecraft are still in communication with Earth. Both spacecraft launched in 1977.
- NASA’s New Horizons spacecraft is currently exploring an icy region beyond Neptune called the Kuiper Belt. It eventually will leave our solar system.
- Pioneer 10 and Pioneer 11 also will ultimately travel silently among the stars. The spacecraft used up their power supplies decades ago.
Example : Rotation Of The Solar Nebula
We can use the concept of angular momentum to trace the evolution of the collapsing solar nebula. The angular momentum of an object is proportional to the square of its size times its period of rotation . If angular momentum is conserved, then any change in the size of a nebula must be compensated for by a proportional change in period, in order to keep D2/P constant. Suppose the solar nebula began with a diameter of 10,000 AU and a rotation period of 1 million years. What is its rotation period when it has shrunk to the size of Plutos orbit, which Appendix F tells us has a radius of about 40 AU?
We are given that the final diameter of the solar nebula is about 80 AU. Noting the initial state before the collapse and the final state at Plutos orbit, then
With Pinitial equal to 1,000,000 years, Pfinal, the new rotation period, is 64 years. This is a lot shorter than the actual time Pluto takes to go around the Sun, but it gives you a sense of the kind of speeding up the conservation of angular momentum can produce. As we noted earlier, other mechanisms helped the material in the disk lose angular momentum before the planets fully formed.
Check Your Learning
What would the rotation period of the nebula in our example be when it had shrunk to the size of Jupiters orbit?
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How The Solar System Formed
Our solar system evolved from a dense cloud of interstellar gas and dust about 4.5 billion years ago. The cloud imploded, possibly as a result of a nearby asteroid or comet known as a supernova. When this dust cloud disintegrated, it created a solar nebula, which is a spinning, swirling disc of material.
Gravity drew too much material into the center. The pressure in the core eventually reached such a high level that hydrogen atoms started to merge and form helium, releasing massive amounts of energy. As a result, our Sun was born, and it ultimately accumulated more than 99% of total matter.
Further out in the disc, the matter was also clumping together. These clumps collided and merged, forming larger and larger objects. Some of them grew large enough for gravity to shape them into spheres, giving rise to planets, dwarf planets, and large moons.
Planets did not form in other cases: the asteroid belt is made up of bits and pieces of the early solar system that could never quite come together to form a planet. Other smaller fragments evolved into asteroids, comets, meteoroids, and small, irregular moons.
Test Your Space Knowledge
Test your knowledge of all aspects of space, including a few things about life here on Earth, by taking these quizzes.
Laplaces model begins with the Sun already formed and rotating and its atmosphere extending beyond the distance at which the farthest planet would be created. Knowing nothing about the source of energy in stars, Laplace assumed that the Sun would start to cool as it radiated away its heat. In response to this cooling, as the pressure exerted by its gases declined, the Sun would contract. According to the law of conservation of angular momentum, the decrease in size would be accompanied by an increase in the Suns rotational velocity. Centrifugal acceleration would push the material in the atmosphere outward, while gravitational attraction would pull it toward the central mass when these forces just balanced, a ring of material would be left behind in the plane of the Suns equator. This process would have continued through the formation of several concentric rings, each of which then would have coalesced to form a planet. Similarly, a planets moons would have originated from rings produced by the forming planets.
See related solar system articles:
SOlar SystemASteroids and Comets
Composition of the Solar System
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Planets & Their Moons
The four inner, or terrestrial, planets are Mercury, Venus, Earth, and Mars
The four outer planets Jupiter, Saturn, Uranus, and Neptune are known as the Jovian, or giant, planets.
Pluto is a one-of-a-kind icy, low-density body smaller than Earths Moon, more resembling comets or the large icy moons of the outer planets than any of the planets themselves.
The smaller inner planets have solid surfaces, no ring systems, and few or no moons.
Whereas, the four massive outer planets are much larger than the terrestrial planets. They do not have solid surfaces, but they do have a magnetic field and a ring system, and numerous known moons, with more likely to be identified.
Pluto is known to have no rings and only five moons.
Several other Kuiper belt objects and asteroids have moons as well.
The majority of known moons orbit their planets in the very same direction that the planets orbit the Sun. They are extremely varied and represent a wide range of environments.
Jupiter is orbited by Io, a body gripped by intense volcanism.
Titan, Saturns largest moon a body larger than the terrestrial planet Mercury has a primitive atmosphere denser than Earths.
Triton orbits Neptune in a retrograde orbit that is, in the opposite direction of the planets orbit around the Sun and has plumes of material soaring through its tenuous atmosphere from a surface with a temperature of only 37 kelvins .
Comets And How The Solar System Formed
The Solar System formed about 4.6 billion years ago when a cloud of gas and dust started to collapse. A disc of material formed around the early Sun, the particles of which collided and joined together, growing increasingly larger and larger, until they formed planets, their moons and millions of asteroids and comets.
Over billions of years the planets have undergone large internal changes due to their own gravity. Comets, however, are so small that they have remained almost unchanged. As they spend most of their time far from the Sun in a ‘deep freeze’ their matter preserves the original material of the primitive nebula, helping us look back to the very infancy of the Solar System.
In 1986, ESA’s Giotto mission achieved the first close encounter of a comet, passing within 600 km of Comet Halley. Giotto, a pioneer in comet science, provided us with the first ever images of a comet’s nucleus.
Ground-based observatories and Giotto have shown that comets contain complex organic molecules rich in carbon, hydrogen, oxygen and nitrogen – essential ingredients for life. With Rosetta, scientists expect to be able to answer whether cometary impacts, very common in the early Solar System, brought large quantities of water to Earth, creating the conditions for life to form and evolve.
This panel is available in a print-ready version for the format 70 × 100 cm, which can be downloaded here as a PDF.
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How Did The Planets Form
The planets, moons, asteroids and everything else in the solar system formed from the small fraction of material in the region that wasn’t incorporated in the young sun. This material formed a massive disk around the baby star, which surrounded it for about 100 million years an eyeblink in astronomical terms.
During that time, planets and moons formed out of the disk. Among the planets, Jupiter likely formed first, perhaps as soon as a million years into the solar system’s life, scientists have argued .
Scientists have developed three different models to explain how planets in and out of the solar system may have formed. The first and most widely accepted model, core accretion, works well with the formation of the rocky terrestrial planets but has problems with giant planets. The second, pebble accretion, could allow planets to quickly form from the tiniest materials. The third, the disk instability method, may account for the creation of giant planets.
The Classification Of Planets
You may recall that Pluto was reclassified as a dwarf planet in 2006, changing its classification to dwarf planet and changing our Solar System planet count to eight. One of the reasons this occurred was because of the discovery of other small, rocky objects like Pluto. The International Astronomical Union is an organisation that, among other things, is responsible for naming planets and stars and setting the classification requirements for a planet. The IAU definition for a planet in our Solar System is a celestial body that:
- is in orbit around the Sun
- has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes hydrostatic equilibrium
- has cleared the neighbourhood around its orbit.
It is the last point that Pluto fails, along with other similar-sized planets like Ceres , Eris, Haumea and Makemake . The gravitational pull of the object isnt strong enough to clear its neighbourhood. Pluto is in the Kuiper belt, an area filled with frozen asteroids and other dwarf planets leftovers from the formation of our Solar System. If the IAU definition was changed to include Pluto, other planets would need to be included in our Solar System as well, making for a large family of planets.
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The Modern Nebular Theory
The planets originate in a dense disk formed from material in the gas and dust cloud that collapses to give us the Sun. The density of this disk had to be sufficient to allow the formation of the planets and yet be thin enough for the residual matter to be blown away by the Sun as its energy output increased.
In 1992 the Hubble Space Telescope obtained the first images of proto-planetary disks in the Orion nebula. They are roughly on the same scale as the Solar System and lend strong support to this theory.
But Exactly How Did This Proceed
New observations of young solar systems, complete with still-forming material around just-born planets, may give us a clue. And that clue has one name: dust.
According to new research, the material around the young Jupiter acted as a dust trap, collecting any wayward material drifting through the baby solar system. This allowed proto-moons to form one by one and then migrate inwards to find a home orbit around their parent planet. Without the dust, it’s a little unclear how exactly the moons of the gas giants could form in a short enough amount of time .
This new model is bolstered by the observation of a lot more dust than expected around young alien exoplanets if it is happening over there, right now, it might have happened here, long ago.
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Nebular Hypothesis Or Laplacian Hypothesis
Pierre-Simon Laplace of France took a significant step forward 40 years later. Laplace was a brilliant mathematician who excelled in the field of celestial mechanics.
In addition to a monumental treatise on the subject, he wrote a popular book on astronomy, which included an appendix in which he proposed some theories about the origin of the solar system.
1. The Sun is already formed and rotating in Laplaces model, and its atmosphere extends beyond the distance at which the farthest planet would be created.
2. Knowing nothing about the true source of energy in stars, Laplace assumed that as the Sun radiated away from its heat, it would begin to cool.
3. According to the law of conservation of angular momentum, the Suns rotational velocity would increase as its size decreased.
4. This process would have continued until several concentric rings formed, each of which would have coalesced to form a planet.
5. Similarly, the moons of a planet would have been created from the rings shaped by the planets as they formed.
Laplaces model naturally resulted in planets revolving around the Sun in the same plane and direction as the Sun rotates.
Because Laplaces theory included Kants idea of planets converging from dispersed material, their two approaches are frequently combined in a single model known as the Kant-Laplace nebular hypothesis.
For the solar system to conform to this theory, either the Sun should rotate faster or the planets should revolve around it more slowly.
Natural Resources And Land Use
Earth has resources that have been exploited by humans. Those termed non-renewable resources, such as fossil fuels, are only replenished over geological timescales.Large deposits of fossil fuels are obtained from Earth’s crust, consisting of coal, petroleum, and natural gas. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed within the crust through a process of ore genesis, resulting from actions of magmatism, erosion, and plate tectonics. These metals and other elements are extracted by mining, a process which often brings environmental and health damage.
Earth’s biosphere produces many useful biological products for humans, including food, wood, pharmaceuticals, oxygen, and the recycling of organic waste. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends on dissolved nutrients washed down from the land. In 2019, 39 million km2 of Earth’s land surface consisted of forest and woodlands, 12 million km2 was shrub and grassland, 40 million km2 were used for animal feed production and grazing, and 11 million km2 were cultivated as croplands. Of the 12â14% of ice-free land that is used for croplands, 2 percentage points were irrigated in 2015. Humans use building materials to construct shelters.
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The Disk Instability Model
Other models struggle to explain the formation of the gas giants. According to core accretion models, the process would take several million years, longer than the light gases were available in the early solar system.
“Giant planets form really fast, in a few million years,” Kevin Walsh, a researcher at the Southwest Research Institute in Boulder, Colorado, told Space.com. “That creates a time limit because the gas disk around the sun only lasts 4 to 5 million years.”
A relatively new theory called disk instability addresses this challenge. In the disk instability model of planet formation, clumps of dust and gas are bound together early in the life of the solar system. Over time, these clumps slowly compact into a giant planet.
Planets can form in this way in as little as 1,000 years, the models suggest, allowing them to trap the rapidly vanishing lighter gases. They also quickly reach an orbit-stabilizing mass that keeps them from death-marching into the sun.
As scientists continue to study planets inside of the solar system, as well as around other stars, they will better understand how gas giants formed.