Chapter 8 Survey of Solar Systems

The solar system formed from a cloud of cold gas and dust called the solar nebula about 4.6 billion years ago Astronomers believe that the solar system formed from a vast cloud of interstellar gas and dust called the solar nebula. This cloud condensed 4.6 billion years ago under the influence of its own gravitational force to form our Sun, the planets, and the other bodies in the solar system. This is an image of one of these clouds (the Orion nebula) The stars in this cloud as formed from the gas in the cloud. Many Astronomers believe that the univers3e formed between 14-15 billion years ago in a violent event called the “Big Bang”. But during this event, only the lightest elements existed such as hydrogen, helium, and lithium. So the first stars that were formed only contained these light elements. But we know that there are elements much heavier than these that exist on Earth such as oxygen, silicon, aluminum, carbon, iron, etc. So when we come up with a theory for how our solar system was formed, we must take into consideration the existence of these heavy elements. Remember, the creation of our solar system is an entirely different event from the big bang. The big bang brought about the existence of our Universe, but the solar system was formed billions of years later. We now know that it was born in gas and dust that contained heavy elements. These elements were created from the birth and deaths of several generations of stars. We will later find out that stars live because they undergo nuclear reactions in their centers. The end states of these nuclear reactions are heavier elements. Which get ejected outwards when some stars explode as supernovae. Then eventually new stars are created out of the gas ejected from the stars that are exploded. And that is why we know that we were not created from the first generation of stars. Because of the existence of these heavier elements. Planets like the Earth, cannot exist until several billions of years after the Big Bang. This would give it enough time for stars to be born and die and new stars to be born and die and have planets with heavy elements. Sometimes the explosive force of a supernova compresses fragments of interstellar gas and dust clouds that had been ejected from earlier generations of stars. These fragments are pulled inward on themselves by mutual gravitation attraction of their gas and dust particles thereby creating new star and planetary systems. The collapsing matter is primarily hydrogen and helium, but the stars that ejected it had converted some of it into heavier elements. These include the building blocks of life and this is believed to be how the solar system formed- the debris leftover from a previous generation of stars. Shakespare line: we are the stuff that stars are made of.

Redshift 2: History of the solar system A huge cloud of gas and dust in pace collapsed, pulled together by the force of gravity. What triggered the collapse isn’t known. It might have been gravity pulling together a random cloud, or it might have been a shock wave from a nearby supernova. The solar system began to spin faster as it collapsed; this is the same phenomenon that happens if you watch an ice skater as they spin faster when they pull their arms in. Objects that are spinning around tend to fly off and this force eventually became strong enough to counteract the force of gravity pulling inwards. Thus, the solar system started to collapse into a plane. The central region became hot and dense, eventually becoming hot enough for the gas to shine, forming our Sun. In the disk of gas and dust, the material began to clump and smaller clumps joined together to make larger ones and eventually planetesimals, bodies that range from millimeter size up to a few hundred kilometers across were formed. Gravity pulled many planetesimals together to make protoplanets orbiting a protosun. The protoplanets then contracted and cooled to make the planets we have today and the protosun contracted to form the Sun. Some of the leftover debris from the formation are still orbiting the sun in the form of asteroids, comets, meteroids, and asteroids. But most of the unused gas and dust was blown away by a strong solar wind. inner planets- dust grains stick together to become 10-km-diameter planetesimals. In the next panel, planetesimals grow over 10,000 years to become 2,000km diameter planetary embryos. In the next panel, gas disappears over the next 10 million years. In the final panel, the gravity of the planetary embryos changes their orbits and brings them together to form the current planets over about 100 million years. Planetesimals combine to form protoplanets. Redshift 2: History of the solar system

The planets in out Solar System were formed from countless impacts 3.8 to 4.1 billion years ago Less evidence of this on earth do to geological activity, Planets started out as tiny little dust grains that combined to form astroid sized objects, collected to make planetesamols and planets Commets outer part of solar system Moon Mercury Asteroids

Inner planets are vastly different than outer planets in terms of sizes, masses, and densities Most Voyagers Entering Mars Journey Serenely Until Nightfall My Very Enormous Martian Just Swallowed Up Neptune! If you take a look at the planets, you would realize that there are two main groups. The inner, terrestrial planets and the outer Jovian planets (gas giants). The terrestrial planets did not grow from ices because it was warmer closer to the Sun so only metals and silicates could form solids, which took a longer time than ices that would form the outer giant planets. The terrestrial planets never became massive enough to accumulate a massive atmosphere the way the giant planets did. And because the inner planets are closer to the Sun and therefore hotter, gas in their atmospheres moved relatively fast. Thus, free hydrogen and helium escaped from the Earth’s low gravity. Furthermore, the solar wind (radiation pressure from the Sun) blew most of these light gases into the outer solar system. Jovian planets began growing by the same processes that built the terrrestrial planets, but because it was colder in the outer parts of the Solar System, ices were able to condense. Since ices condence faster than rock, the Jovian planets grew faster and formed before the terrestrial planets and were able to accumulate a lot of mass quickly. The Jovian planets grew quickly and rapidly and became massive enough to sweep up large amounts of gas from the solar nebula. This is also the reason why there are larger distances between them than the terrestrial planets, because they swept up more gas and dust in between them. As of August 2006, according to the definition of a planet that was formally recognized by the International Astronomical Union, there are currently only 8 planets in our solar system. Pluto is no longer considered a planet according to their new definition. We will explain the reason why a little later when we discuss Pluto. I will expect you to know the names of these 8 planets in their correct order from the Sun. I have developed a sentence to help you remember the order of these planets. The sentence is on the slide. The first letter of the words in this sentence corresponds to the first letter of the name of the planet. Of course, taken literally, my sentence says there are only 7 planets because the Martian swallowed up Neptune (okay that was a bad joke). If you feel that you can come up with a better sentence, you can share it with the class in the discussion for this week. As mentioned earlier, because of differences in the surrounding composition and temperature, the planets that formed closer to the Sun have different properties than the ones that formed farther away from the Sun. The next two slides will summarize the differences between these two groups of planets.

Rocky Asteroids - mostly found between the orbits of Mars and Jupiter There is still minor debris left over from the formation of the solar system Rocky Asteroids - mostly found between the orbits of Mars and Jupiter

Icy Comets – found in the outer parts of the solar system There is still minor debris left over from the formation of the solar system Icy Comets – found in the outer parts of the solar system

Dwarf Planets- orbit the Sun, nearly round shape, not a planet, star or moon

New solar systems in formation! Protoplanetary Disks These Hubble Space Telescope images show circumstellar disks surrounding two young stars. These stars are believed to be surrounded by protoplanetary gas and dust. New solar systems in formation!

Planets that have been detected orbiting other stars!!! Exoplanets Our Solar system is not unique, in fact we should expect to see planets around other stars and we have found almost one hundred of them. These planets were discovered in the 1990s. The reason why it took so long to find these planets is because planets are very faint. Remember they shine predominantly by reflected starlight, thus we can not detect them directly. They have been found by detecting the wobble of the Star which the planet is orbitting around. If a star wobbled from side to side, it would reveal that a planet was wobbling invisibly the other way. In the 1990s, techniques were developed to use the Doppler effect. Doppler effect is the change in wavelengths of the light that is emitted caused by motion of the source along the line of sight. At this time we could measure the Doppler effect very precisely. The observed spectrum of the star can be compared to a simulated spectrum of a stationary star. This method allows small Doppler shifts to be detected and the speeds of stars towards and away from us can be measured. a) The orbits of some of the exoplanets overlaid on the same scale. We see circular orbits close in and eccentric orbits further out. b) The distribution of the masses of the planets. (Lower limits) since we don’t know the inclination The discovery of several planetary systems instead of just our own will change the models for how planetary systems are formed. Many theorists stick to their own ideas of how giant planets form far away from their parent stars just as Jupiter and the other giant planets are far out in our Solar system. These planets may be jostled loose from their orbits and put in orbits that bring them closer to their parent stars. Perhaps orbits shrink as they encounter the debris in the dusty disk from which they formed, or shrink along with an overall swirling of the whole disk of orbiting material. Perhaps highly elliptical orbit didn’t start that way, but were produced by gravitational interactions that ejected the planets from the system. The gravitational interactions between two planets can lead to the ejection of one planet leaving the other in a very eccentric orbit. Or interactions between the planet and the protoplanetary disk can cause high eccentricities. But once a planet has part of its orbit close to the parent star, tidal forces can circularize the orbit. Other planets can spiral into the star and be destroyed. Planets that have been detected orbiting other stars!!!

Detection of Exoplanets: Stellar Wobble Method gravity of the planet causes the star to wobble back and forth 1990s, used Doppler effect to detect stellar wobbles Our Solar system is not unique, in fact we should expect to see planets around other stars and we have found almost one hundred of them. These planets were discovered in the 1990s. The reason why it took so long to find these planets is because planets are very faint. Remember they shine predominantly by reflected starlight, thus we can not detect them directly. They have been found by detecting the wobble of the Star which the planet is orbitting around. If a star wobbled from side to side, it would reveal that a planet was wobbling invisibly the other way. In the 1990s, techniques were developed to use the Doppler effect. Doppler effect is the change in wavelengths of the light that is emitted caused by motion of the source along the line of sight. At this time we could measure the Doppler effect very precisely. The observed spectrum of the star can be compared to a simulated spectrum of a stationary star. This method allows small Doppler shifts to be detected and the speeds of stars towards and away from us can be measured. a) The orbits of some of the exoplanets overlaid on the same scale. We see circular orbits close in and eccentric orbits further out. b) The distribution of the masses of the planets. (Lower limits) since we don’t know the inclination The discovery of several planetary systems instead of just our own will change the models for how planetary systems are formed. Many theorists stick to their own ideas of how giant planets form far away from their parent stars just as Jupiter and the other giant planets are far out in our Solar system. These planets may be jostled loose from their orbits and put in orbits that bring them closer to their parent stars. Perhaps orbits shrink as they encounter the debris in the dusty disk from which they formed, or shrink along with an overall swirling of the whole disk of orbiting material. Perhaps highly elliptical orbit didn’t start that way, but were produced by gravitational interactions that ejected the planets from the system. The gravitational interactions between two planets can lead to the ejection of one planet leaving the other in a very eccentric orbit. Or interactions between the planet and the protoplanetary disk can cause high eccentricities. But once a planet has part of its orbit close to the parent star, tidal forces can circularize the orbit. Other planets can spiral into the star and be destroyed.

Exoplanets in other solar systems detected by the Stellar Wobble method

A real life Tatooine!

Earth-like Planet!

Detection of Exoplanets: Planetary Transit Method KEPLER 2009 More recent method, How much light or luminocity is lost when planet is passing in front of its star. Can detect size and composition. Goel is to find earth sized planets which can be done with the new space craft called kepler. Transiting. To far away for us to get there Detection of Exoplanets: Planetary Transit Method

One of a few images of an exoplanet around a star

Future Discovery Methods Canceled Terrestrial Planet Finder (2014, 2020) Two telescopes which would combine their light and produce bright images in space. These small telescopes act like one telescope with a very large aperture. Show from Spitzer Space Telescope: Ask an Astronomer: Do Other Solar systems exist? Are other solar systems like our own? CNN: New Solar System Movie