how was the solar system formed step by step

Learning Objectives

By the end of this section, you will be able to:

• Describe the motion, chemical, and age constraints that must be met by any theory of star scheme formation
• Sum the physical and chemical changes during the solar nebula stage of solar system formation
• Explain the formation process of the terrestrial and giant planets
• Key the main events of the further evolution of the star system

A we rich person seen, the comets, asteroids, and meteorites are surviving remnants from the processes that formed the star arrangement. The planets, moons, and the Sunbathe, of course, also are the products of the geological formation process, although the material in them has undergone a ample range of changes. We are now ready to tack the selective information from all these objects to hash out what is known about the origin of the star system.

Observational Constraints

There are certain basic properties of the planetary system that any hypothesis of its organisation must explain. These may be summarized under three categories: motility constraints, chemical constraints, and age constraints. We call them constraints because they place restrictions on our theories; unless a theory can explain the observed facts, it will not survive in the competitive market of ideas that characterizes the try of science. Let's take a deal these constraints one aside i.

At that place are many regularities to the motions in the solar system. We saw that the planets completely revolve approximately the Dominicus in the same direction and about in the sheet of the Sunlight's personal rotation. In addition, most of the planets go around in the Saame direction as they go around, and most of the moons too be active in counterclockwise orbits (when seen from the north). With the exception of the comets and other trans-neptunian objects, the motions of the system members define a disk or Frisbee condition. Nevertheless, a full theory must also be prepared to care with the exceptions to these trends, such as the retrograde rotation (not revolution) of Venus.

In the realm of chemistry, we saw that Jupiter and Saturn have around the equal composition—dominated by hydrogen and atomic number 2. These are the two largest planets, with sufficient gravity to time lag on to any gas give when and where they formed; thus, we might expect them to be representative of the fresh material out of which the solar system definite. Apiece of the other members of the planetary system is, to some degree, lacking in the illuminating elements. A careful exam of the penning of solid solar-system objects shows a striking progression from the metal-sumptuous inner planets, through those made predominantly of rocky materials, out to objects with ice-dominated compositions in the outer star organisation. The comets in the Oort dapple and the trans-neptunian objects in the Gerard Peter Kuiper belt out are also polar objects, whereas the asteroids correspond a transitional jump composition with abundant dark, carbon-rich material.

As we saw in Strange Worlds: An Introduction to the Solar System, this general chemic practice can be interpreted Eastern Samoa a temperature sequence: hot near the Sun and cooler as we move outward. The inner parts of the system are generally missing those materials that could not condense (form a solid) at the high temperatures found near the Sun. However, there are (again) important exceptions to the general rule. For example, it is difficult to explicate the presence of water connected Ground and Red Planet if these planets baculiform in a region where the temperature was likewise hot for ice to condense, unless the ice or water was brought in later from cooler regions. The extreme example is the observation that there are polar deposits of ice on both Mercury and the Moon; these are almost sure as shooting formed and maintained by occasional comet impacts.

As far As age is troubled, we discussed that hot dating demonstrates that some rocks on the surface of Dry land have been give for at least 3.8 cardinal geezerhood, and that certain satellite samples are 4.4 1000000000 years old. The primitive meteorites wholly have radioactive ages nigh 4.5 million years. The age of these unaltered building blocks is considered the age of the planetary system. The similarity of the calculated ages tells us that planets formed and their crusts cooled within a few tens of millions of years (at most) of the commencement of the solar arrangement. Encourage, elaborate examination of primitive meteorites indicates that they are ready-made primarily from material that condensed Beaver State coagulated out of a hot petrol; few classifiable fragments appear to hold survived from in front this hot-vapor stage 4.5 billion years ago.

The Solar Nebula

All the foregoing constraints are consonant with the general idea, introduced in Other Worlds: An Introduction to the Star Organization, that the solar system formed 4.5 billion years ago out of a rotating cloud of vapor and dust—which we telephone the star nebula—with an initial piece quasi to that of the Sun now. Eastern Samoa the solar nebula collapsed under its own sombreness, corporate fell toward the center, where things became more and much concentrated and blistering. Increasing temperatures in the shrinking nebula vaporized most of the solid material that was originally confront.

At the same time, the collapsing nebula began to rotate faster through with the conservation of angular momentum (see the Orbits and Gravity and Earth, Moon, and Sky chapters). Same a figure skater pulling her arms in to spin quicker, the shrinking cloud spun more quickly every bit time went on. Now, think about how a round aim spins. Close to the poles, the reel rate is slow, and it gets quicker As you get closer to the equator. In the same way, near the poles of the nebula, where orbits were slow, the nebular material fell directly into the center. Faster streaming material, happening the other pass, collapsed into a flat disk revolving around the cardinal object (Figure 1). The existence of this disk-shaped rotating nebula explains the primary motions in the solar system that we discussed in the previous segment. And since they formed from a rotating disk, the planets all reach the same fashio.

Figure 1: Steps in Forming the Solar System. This illustration shows the steps in the formation of the solar system from the star nebula. As the nebula shrinks, its revolution causes IT to flatten into a harrow. Much of the material is concentrated in the hot center, which will at last become a star. Away from the center, solid particles give the sack condense as the nebula cools, bountiful jump to planetesimals, the building blocks of the planets and moons.

Picture the solar nebula at the remnant of the collapse form, when it was at its hottest. With no more gravitational energy (from material down in) to heat it, most of the nebula began to cool. The material in the center, however, where it was hottest and most crowded, formed a star that maintained high temperatures in its immediate neighborhood aside producing its possess energy. Turbulent motions and magnetic W. C. Fields within the disk can drain away angular momentum, robbing the disk material of some of its spin. This allowed some material to continue to downfall into the growing star, while the remainder of the disk gradually stabilized.

The temperature within the disk decreased with maximizing distance from the Sun, often as the planets' temperatures vary with position today. As the disk cooled, the gases interacted chemically to produce compounds; one of these days these compounds condensed into liquid droplets or cubic grains. This is similar to the process by which raindrops on Earth condense from moist air as it rises over a mountain.

Let's look in more particular at how material condensed at different places in the maturing platter (Figure out 2). The world-class materials to form solid grains were the metals and diverse rock-forming silicates. As the temperature born, these were joined throughout much of the star nebula by sulfur compounds and by carbon- and water-fruitful silicates, much as those in real time constitute abundantly among the asteroids. Still, in the inner parts of the disk, the temperature never dropped low enough for such materials as ice or carbonaceous organic compounds to condense, then they were wanting on the innermost planets.

Physique 2: Chemical Condensation Sequence in the Solar Nebula. The exfoliation on the fundament shows temperature; above are the materials that would condense out at each temperature under the conditions expected to prevail in the nebula.

Far from the Sun, ice chest temperatures allowed the oxygen to combine with H and distil in the form of water (H₂O) ice. Beyond the orbit of Saturn, carbon and nitrogen joint with hydrogen to make water ices such as methane (CH₄) and ammonia (NH₃). This sequence of events explains the basic chemical composition differences among various regions of the solar system.

Example 1: Rotation of the Solar Nebula

We can use the conception of angular momentum to trace the evolution of the collapsing solar nebula. The angular impulse of an object is progressive to the square of its size (diam) times its full point of rotary motion (D ²/P). If angular momentum is conserved, then some change in the size of a nebula must be compensated for by a proportional change in period, in order to keep D ²/P constant. Suppose the star nebula began with a diameter of 10,000 AU and a rotation period of 1 million years. What is its rotation menses when it has shrunk to the size up of Pluto's orbit, which Vermiform appendix F tells us has a radius of about 40 AU?

Check Your Learning

What would the rotation period of the nebula in our example be when it had shrunk to the size of Jupiter's orb?

Show Response

The period of the rotating nebula is inversely proportional to D ². As we have just seen, [rubber-base paint]\frac{{P}_{\text{inalterable}}}{{P}_{\text edition{initial}}}={\left(\frac{{D}_{\text{final}}}{{D}_{\text{initial}}}\right)}^{2}[/latex]. Initially, we have P _initial = 10⁶ yr and D _initial = 10⁴ AU. Then, if D _final is in AU, P _closing (in years) is given past [latex]{P}_{\text edition{final}}=0.01{D}_{\text{final}}^{2}[/latex paint]. If Jove's orbit has a radius of 5.2 AU, then the diameter is 10.4 Gold. The full stop is then 1.08 years.

Formation of the Terrestrial Planets

The grains that condensed in the solar nebula quite quickly joined into larger and larger chunks, until most of the solid embodied was in the form of planetesimals, chunks a few kilometers to few tens of kilometers in diam. 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 in the beginning chapters. A wholesome step up in size is required, however, to plump from planetesimal to planet.

Some planetesimals were large enough to attract their neighbors gravitationally and thus to grow over aside the mental process called accretion. While the intermediate steps are non well understood, ultimately several dozen centers of accretion seem to have grown in the inner star system. Each of these attracted surrounding planetesimals until it had nonheritable a mass similar to that of Mercury or Mars. At this stage, we may remember these objects A protoplanets—"not quite ready for prime clock time" planets.

From each one of these protoplanets continued to grow by the accumulation of planetesimals. Every incoming planetesimal was fast away the gravity of the protoplanet, striking with enough energy to melt both the projectile and a part of the impact region. Soon the entire protoplanet was heated to above the melting temperature of rocks. The upshot was worldwide differentiation, with heavier metals sinking feeling toward the core and lighter silicates rising toward the surface. Arsenic they were heated, the inner protoplanets lost some of their more volatile constituents (the lighter gases), leaving more of the heavier elements and compounds behind.

Shaping of the Giant Planets

In the outer star scheme, where the available raw materials included ices as substantially as rocks, the protoplanets grew to exist much larger, with masses ten multiplication greater than Globe. These protoplanets of the outer solar system were so large that they were able to attract and hold the close gas. As the H and atomic number 2 rapidly collapsed onto their cores, the heavyweight planets were heated by the muscularity of contraction. Just although these big planets got hotter than their terrestrial siblings, they were far too small to raise their central temperatures and pressures pertinent where nuclear reactions could begin (and it is such reactions that give us our definition of a star). After glowing matt red for a few thousand years, the colossus planets gradually cooled to their attending state (Design 3).

Figure 3: Saturn Seen in Infrared. This image from the Cassini space vehicle is stitched together from 65 individual observations. Sun reflected at a wavelength of 2 micrometers is shown as low-spirited, sunlight reflected at 3 micrometers is shown as political party, and heat radiated from Saturn's interior at 5 micrometers is violent. E.g., Saturn's rings reflect sunlight at 2 micrometers, just not at 3 and 5 micrometers, so they appear blue. Saturn's southwesterly polar regions are seen enthusiastic with internal heat. (credit: alteration of work away NASA/JPL/University of AZ)

The break of gas from the nebula onto the cores of the giant planets explains how these objects acquired nearly the Lapp hydrogen-rich opus as the Sun. The process was most prompt for Jupiter and Saturn; hence, their compositions are most nearly "cosmic." Untold fewer swash was captured past Uranus and Neptune, which is why these two planets have compositions dominated by the icy and rocky building blocks that made up their large cores rather than by hydrogen and helium. The first constitution period ended when much of the uncommitted staple was used up and the solar wind (the flow of atomic particles) from the girlish Sun blew away the remaining supply of lighter gases.

Advance Evolution of the Organisation

All the processes we stimulate impartial described, from the burst of the solar nebula to the formation of protoplanets, took base inside a some meg long time. However, the level of the formation of the solar system was not gross at this stage; there were numerous planetesimals and other rubble that did not at first collect to form the planets. What was their designate?

The comets visible to us nowadays are just the tip of the cosmic iceberg (if you'll pardon the pun). Most comets are believed to be in the Oort cloud, far from the domain of the planets. Additive comets and icy dwarf planets are in the Edgeworth-Kuiper belt, which stretches beyond the field of Neptune. These icy pieces probably belt-shaped hot the present orbits of Uranus and Neptune but were ejected from their initial orbits by the gravitational influence of the giant planets.

In the inner parts of the system, remnant planetesimals and perhaps several dozen protoplanets continued to whiz about. Terminated the vast span of time we are discussing, collisions among these objects were inevitable. Giant impacts at this stage probably minimum Mercury of role of its mantle and crust, converse the rotation of Venus, and broke off part of Earth to create the Moon (all events we discussed in early chapters).

Smaller-scale impacts also added mass to the inner protoplanets. Because the sombreness of the giant planets could "touch up" the orbits of the planetesimals, the material impacting on the inner protoplanets could have come from almost anywhere within the solar arrangement. In dividing line to the previous stage of accretion, therefore, this new material did not comprise honorable a narrow range of compositions.

Atomic number 3 a result, much of the dust striking the inner planets was ice-rich material that had condensed in the outermost part of the solar nebula. As this comet-like barrage progressed, Land assembled the water and individual organic compounds that would later be critical to the formation of life. Mars and Urania probably also acquired profuse water and living thing materials from the same source, as Mercury and the Moon are still doing to form their icy polar caps.

Gradually, as the planets swept upbound or ejected the remaining debris, nearly of the planetesimals disappeared. In two regions, yet, stable orbits are possible where leftover planetesimals could avoid impacting the planets Beaver State organism ejected from the system. These regions are the asteroid belt out between Mars and Jupiter and the Kuiper belt beyond Neptune. The planetesimals (and their fragments) that survive in these special locations are what we directly call asteroids, comets, and trans-neptunian objects.

Astronomers used to think that the solar system that emerged from this early evolution was similar to what we see today. Elaborate recent studies of the orbits of the planets and asteroids, however, suggest that there were more violent events soon subsequently, perhaps involving substantial changes in the orbits of Jupiter and Saturn. These 2 large planets control, done their gravity, the distribution of asteroids. Working rearwards from our present solar system, information technology appears that orbital changes took place during the first few hundred 1000000 years. One consequence Crataegus oxycantha have been diffusing of asteroids into the central solar organisation, causing the period of "heavy bombardment" recorded in the oldest lunar craters.

Key concepts and unofficial

A viable hypothesis of solar system formation moldiness allow motion constraints, stuff constraints, and age constraints. Meteorites, comets, and asteroids are survivors of the solar nebula out of which the solar system formed. This nebula was the result of the collapse of an interstellar cloud of gas pedal and dust, which contracted (conserving its rectangular momentum) to form our star, the Sun, surrounded by a thin, spinning disk of dust and vapor. Capsule in the disk led to the formation of planetesimals, which became the building blocks of the planets. Accumulation of infalling materials het the planets, stellar to their differentiation. The heavyweight planets were also competent to attract and arrest gas from the solar nebula. After a couple of cardinal eld of violent impacts, just about of the debris was sweptwing up surgery ejected, going just the asteroids and cometary remnants extant to the present.

Glossary

accretion: the gradual accumulation of peck, every bit by a major planet forming from colliding particles in the solar nebula

how was the solar system formed step by step

Source: https://courses.lumenlearning.com/astronomy/chapter/formation-of-the-solar-system/