Formation of the Solar SystemThe Solar system TodayWhen we make a perform of the features of the solar mechanism as we check out it today, we discover the complying with facts: The planet orbits have actually the following characteristics They all go approximately the sunlight in the very same direction (right hand rule). (The best hand ascendancy is this: allude your ignorance in the direction of the north pole, and also the thing rotates or revolves in the direction the your fingers curl.) The sunlight rotates in this same, right-hand-rule direction. every planetary orbits lie in virtually the exact same plane. every planetary orbits are practically circular (eccentricity close to zero). The planets rotate on axes that room tilted randomly indigenous this direction, but most obey appropriate hand rule. virtually all moons orbit their planet in the same, right-hand-rule sense, and also near the planet"s equatorial plane. The inner planets room "terrestrial" planets, favor Earth, through the following qualities They are small, and also made the rock and also metal Their density (mass/volume) is high (4000-5000 kg/m3) they have few moons None have rings The external planets space "jovian" planets, prefer Jupiter, through the following characteristics They space large, and also made the hydrogen, helium, and hydrogen link Their density is low (less 보다 2000 kg/m3) they have many moons lock all have rings Pluto is an exemption to numerous of these rules--it is an external planet the is small, orbits in one eccentric, skinny orbit, and also has a low density. The asteroids orbit mainly in the asteroid belt between Mars and also Jupiter. They obey most of the rules because that terrestrial planets. They space rocky or metallic objects. Comets orbit in every directions, with extremely inclined, eccentric orbits. They are icy objects, v hydrogen compounds. They show up to come native a spherical cloud dubbed the Oort Cloud. There space recently uncovered Kuiper Belt Objects (KBO"s) that are prefer Pluto (some are referred to as Plutinos), icy, small, and also apparently numerous! all orbit close to the ecliptic plane, beyond Neptune. Lecture concern #1

Explaining this CharacteristicsIf we want to understandhow the Earth and planets came about, we need a frame (a scientificmodel) that explains all of these characteristics. We questioned thedifference in between a hypothesis and a theory. What was as soon as calledthe Nebular hypothesis for the origin of the solar system has actually now reachedthe status of a theory, both by explaining well-known facts and also predictingother facts the have due to the fact that been confirmed by observations. We willdiscuss this verifying observations later. We deserve to now contact it theNebularTheory of Solar mechanism Formation. Freshly there room observationsof various other solar systems that execute not seem to be defined by the nebulartheory, for this reason the concept is in require of adjustment. We will discuss thislater, too.

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For a great interactive introductionto this theory, pick the Formationof the Solar mechanism tutorial ~ above Astronomy Place internet site and go throughit.When you are finished withthis tutorial, you should know thatthe solar system formed froma cloud, or nebulaas the cloud broke down due togravity itheated up by converting gravitationalpotential energy to heat (a type of kinetic energy)spun faster and also faster early toconservation of angular momentumflattened into a disk (alsodue to conservation of angular momentum)the disk was hotter in the centerand cooler in the external parts whichbeyond the "rock line" (1500K), permitted only rocky and metallic flakes to condense beyond about 0.3AUbeyond the "frost line" (150K), enabled rock, metal and also ice flakes to condense beyond about 3.5 AUthe flakes stuck with each other toform planetesimals, with the following characteristicsthe inner component had small, rockyplanetesimalsthe outer part had lot largersolid planetesimals as result of both rock and ice flakesthe planetesimals joined toform the planets, v the complying with characteristicsthe inner planets had only rockand metal, for this reason did not acquire very huge and can not save light gasesthe outer planets had rock,metal, and ice, and also grew so large that they could gravitationally keeplight gases bound to them. They might grow come be large planets, withrock, metal, ice, and also gaseseventually, the Sun ended up being astar and also the young stellar wind blew the gases away, preventing the planetformation process.Pluto never ever grew huge enoughto tempt gases, so it never ended up being a giant planet. It and otherKBO"s space left over remnants, together with asteroids and also comets--pieces thatnever became parts of planets.Evidence for the NebularTheoryWe can look outat other stars, v the incredible instruments easily accessible today, and seemany of the attributes of this concept in progress. We have the right to alsolook in ~ left-over piece of the solar mechanism that fall to planet (meteorites).Let"s look at a few: points that do Not quite Fit As lengthy as we had actually only one solar system to explain, us could adjust the nebular theory to be a great fit. But what happens once we find other solar systems. Execute they enhance the scenario? In simply the critical 5 or 6 years, new techniques have actually been arisen to detect planets around other stars. We mentioned them earlier, in the first lecture (see list). The an approach uses the "wobble" that a star as result of the gravitational influence of an orbiting planet, detect by a regular doppler shift of spectral lines. Choose the Detecting Extrasolar Planets accuse on Astronomy Place net site and also go with it. When you room finished, you should know that stars travel in small orbits (the "wobble") come balance the traction of one orbiting earth substantial and/or close-in planets are the simplest to finding at the very least one star is overshadowed by the world that causes the wobble tiny and also distant planets are hard to finding The planets so much detected space all bigger than Jupiter--some are much larger. Below is an older overview, (latest one) showing only about fifty percent of the planetary systems currently detected. Below is one artist"s conception the 51 Pegasi. We have detected numerous stars with planets, but the planets are gas large (jovian) form planets, some an extremely close come the star. In what methods does this hurt the nebular concept model? no one yet knows exactly how such planets might form, but here space a couple of possibilities-- If the nebula starts out with much more than one center, climate the larger one might end up together a star if a smaller one collapses in location to type a planet. The world would not have to kind from the bottom up, beginning with flakes. A planetary collision in between two very large "planetesimals" could cause one to move in close to the star if the various other is ejected native the newly forming solar system. One could expect these planets to have actually a very eccentric orbit. Why perform we check out so numerous of these solar equipment that space so various from ours. Is ours the odd-ball? maybe not. The method for finding planets deserve to (so far) only detect large, close-in planets, so it is not surprising that those room the sort we see. We could not recognize solar systems prefer ours with existing techniques. But we are experimenting ways to perform better, and we expect to detect Earth-like planets some day. One thing is certain--this is an interesting time to be alive, to discover more about how we became here, and what other possible solar system species there are.

Lecture question #2

Remnants that the Solar device Remnants of development

The little bodies that the solar system are the leftovers in the process of solar system formation. These space the asteroids, comets, and Kuiper Belt objects (KBOs). We saw that during the formation, small flakes that ices, rock, and also metal gradually linked to make planetesimals, i m sorry in turn an unified to form the planets. Several of these tiny planetesimals, the building blocks the planets, made it through in the kind of asteroids, comets, and also other bodies. They bring up number of questions, because that which we need to look at the complying with clues:

Why didn"t they end up as parts of planets? clue: orbit properties have they readjusted at all since they were developed 4.6 billion year ago? clue: their framework What can they phone call us about the early on formation of the solar system? clue: what they room made the

Orbital properties

These remnants of the solar mechanism come in several unique types, through the complying with properties:

How did this orbits come to be? Both asteroids and KBOs were created where they are now, however they proceed to experience collisions and also gravitational perturbations that can "scatter" few of them. This has the result of flinging them about the solar system, therefore that part pass nearby the Earth, and sometimes also hit us!

Comets indigenous the Oort Cloud have actually a various origin. Us think that they were initially created in the region between Jupiter and also Neptune (the gas gigantic planets), and were flung much out into space due come near-miss collisions through those planets. There may be as many as one sunshine comets in the Oort Cloud!

Lecture concern #3


Asteroids several spacecraft have flown previous asteroids on the method to the external solar system, and also one (the close to spacecraft) in reality orbited one for over 1 year, and also eventually came down on it! below are part close-up images of a couple of asteroids:

Not all asteroids look favor this, however. The bigger ones room so big that their gravity forces them right into a spherical shape. Any object v a radius of an ext than 500 km will be spherical. Near planet Asteroids, potentially Hazardous Asteroids and also Collision Probability


Comets Comets can finest be explained as "dirty snowballs" typically of a couple of km in size, although lock can range in size all the method up to Pluto. Comets spend most of your time far from the sunlight (recall that objects move slowest as soon as at aphelion) where they stay inert icy snowballs. Together they strategy the Sun, castle move ever before faster, and also spend only a couple of weeks in the hotter part of the solar system. There, the ices of volatile compounds (water ice, methane ice, frozen carbon dioxide, frozen ammonia, etc.) begin to sublimate into gases. This gases jet the end from the interior, and sometimes break turn off chunks that the rocky parts. Comets space fragile! Several have been seen to break up, and also some have actually disappeared completely, together we will see below.

Two Tails Comets have two tails, as shown in the image below -- a ionized gas tail (the blue, directly tail) and a dust tail (the white, bent tail). They begin out an extremely small, and also grow larger and longer as the comet nears the Sun.


The ionized gas tail is pulled far from the sun by the solar wind. The dust tail is pushed away native the sunlight by irradiate pressure. Both tails allude away from the Sun, but the ionized gas is lot lighter and also faster, and also so points straight away indigenous the Sun. The heavier, slower relocating dust curves much more along the direction the the comet"s orbit.

Comets and Meteor Showers The dust from a comet stretches all follow me its orbit, for this reason when planet crosses the orbit the a comet, these dust and also fine grained particles hit the Earth"s atmosphere and also burn up as meteors. This is what reasons meteor showers. The earth crosses the orbits of number of comets each year, at the same time the year each year. That is just how we recognize when meteor showers will certainly occur.

Images that some famous comets

KBOs We currently talked about Kuiper Belt objects, and what they look like. We have uncovered a variety of larger objects, which space spherical in shape. Smaller objects, comparable to the asteroids, additionally no doubt exist however are too small and dim to watch from Earth.

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We have numerous ways to discover what these objects space made of. We deserve to look at the reflected light from them, which have the right to be matched approximately to rock, metal, and also ices. We can likewise measure the IR radiation that they radiate. Yet the best method to know what asteroids space made of is to uncover pieces of them that loss to earth as meteorites. We discover that some space made of regardless of rock and also metal flakes, and also were never part of a bigger object. Others are distinguished (separated right into pure rocks and pure metals), and also so were component of the larger, spherical asteroids such as Vesta. Right here is one idea that the background of Vesta:


Broken chunks the the interiors that asteroids might be a resource of an useful metals and also minerals, perhaps making mining of asteroids economically in the future. Were the asteroids all part of a solitary planet that broke up? We do not think so, since even if every one of the asteroids were gathered right into a solitary "planet," it would still just be 1/10th the mass of ours Moon, which chin is smaller sized than the smallest planet. In addition, we perform not know just how such a body can break increase entirely. Also a collision between two large objects would not scatter the piece in the means we see them, yet would leaving the pieces in a similar orbit that eventually would recombine. Instead, we believe that the asteroids space a earth that walk not finish forming prior to the young Sun"s wind go out the continuing to be solar nebula out right into interstellar space.

It is even easier to determine what comets are made of, because we deserve to see the volatile gases that come native them when they heat up as they close to the Sun. We can likewise study the irradiate reflected indigenous the dust of comets. We currently mentioned the comets are made the the ices the volatile compounds (water ice, methane ice, frozen carbon dioxide, frozen ammonia), points that we mean to be current in the solar nebula indigenous which the solar system formed.

So we check out that we can define the orbital dynamics, structure, and also chemical makeup of the little bodies that the solar system in terms of the Nebular theory of the development of the Solar System. Yet if so, there are a lot of of clues out over there that need to fit ours understanding. So astronomers and space scientists are an extremely interested in studying these primordial piece of the solar nebula up close. Goals to collection comet dust, or return samples of comets and asteroids, are now being planned.