Astronomy A BEGINNER S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER 4 The Solar System Lecture Presentation
4.0 What can be seen with the naked eye? Early astronomers knew about the Sun, Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors. Occasionally 5 planets can be seen at one time! Do you already know these?
4.1 An Inventory of the Solar System Early astronomers knew about the Sun, Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors. Now known: Solar system has 1 star, 169 moons orbiting 8 planets (added Uranus and Neptune), asteroids (meteoroids), comets, dwarf planets (Plutoids), and Kuiper belt objects. Which of these are shown in the figure? (Plu
4.1 An Inventory of the Solar System New quantities: planet Mass, Radius and Density see next page for details.
If you are interested the class web page gives the details in a series of: astro101_notes_chaptxxx.pdf files 4.1 An Inventory of the Solar System How do we know the quantities in the Table on the previous page? Distance from Sun known by Kepler s laws Orbital period can be observed Radius known from angular size and distance Masses from Newton s laws Rotation period from observations Density (= Mass/Volume) can be calculated knowing radius and Mass: see astr0101_notes_chapt3and4.pdf
4.1 An Inventory of the Solar System All orbits but Mercury s are close to the same plane and are almost circular (e near 0): these patterns are curiously similar and must be telling us something! (see solar system formation models at the end of this Chapt)
4.1 The Overall Layout of the Solar System Because the planet s orbits are close to being in a plane, it is possible for them to appear in a straight line as viewed from Earth. This photograph was taken in April 2002; can you visualize a straight line through all 5 planets? Can you also see a 6 th planet in the photo? Where is it?
4.1 An Inventory of the Solar System Curiously : Sun is huge, then 4 small planets, then 4 large planets: what is that all about?
4.1 An Inventory of the Solar System Terrestrial planets (many common features): Mercury, Venus, Earth, Mars Jovian planets (many common features): Jupiter, Saturn, Uranus, Neptune
4.1 An Inventory of the Solar System Differences between the terrestrial planets: Atmospheres and surface conditions are very dissimilar. Only Earth has oxygen in atmosphere and liquid water on surface. Earth and Mars rotate at about the same rate; Venus and Mercury are much slower, and Venus rotates in the opposite (retrograde) direction. Earth and Mars have moons; Mercury and Venus don t. Earth and Mercury have magnetic fields; Venus and Mars don t.
4.2 Interplanetary Matter (mostly primordial) The inner solar system, showing the asteroid belt, Earth-crossing asteroids, and Trojan asteroids Find all of these in the figure!
4.2 Interplanetary Matter (mostly primordial) Asteroids are mostly rocky (for astronomers, but too detailed for us, asteroids are grouped into 3 types [see next page]) About 200,000 have been identified so far The three largest (about the size of Texas but much smaller than Earth or our Moon) are: Diameter Ceres Pallas Vesta 940 km 580 km 540 km
4.2 Interplanetary Matter (mostly primordial) Asteroids are classified into 3 types: C-type: Carbonaceous, dark (about 75% of asteroids) S-type: Silicate (rocky) (15% to 17% of asteroids) M-type: Metallic; iron and nickel (most of the remainder) Vesta (photo on right) is considered a rare example of a protoplanet: a layered (i.e. differentiated [see Chapt 5]) planetary building block from the earliest days of the solar system!
4.2 Interplanetary Matter (mostly primordial) Asteroids (those too small to be seen are called meteoroids and are typically <1m in size) are mostly too small to be round! (It s a gravity thing!) (below) Asteroid Mathilde (above) Asteroid Ida with its moon, Dactyl (above) Asteroid Itokawa
4.2 Interplanetary Matter (mostly primordial) Eros, a typical non-round asteroid, is: 34km x 11km
4.2 Interplanetary Matter: What Killed the Dinosaurs? The dinosaurs may have been killed by the impact on Earth of a large meteoroid or small asteroid. Fortunately in recent times, the larger an impact is, the less often we expect it to occur: see plot!
4.2 Interplanetary Matter: What Killed the Dinosaurs? Some meteors explode in the air much like a huge bomb! The blast from the Tunguska meteor in June 1908 flattened 770 square miles of forest!
4.2 Interplanetary Matter: What Killed the Dinosaurs? The impact of a large meteor can create a significant crater; check out http://geology.com/meteor-impact-craters.shtml This is the nearby Barringer meteor crater in Arizona What is a meteor? It is a small body of matter from outer space that enters the earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.
4.2 Interplanetary Matter: What Killed the Dinosaurs? This is the remnant of a much larger impact called the Manicouagan reservoir in Quebec Canada
4.2 Interplanetary Matter: What Killed the Dinosaurs? Could the asteroid/meteoroid/comet impact that created the Chicxulub crater have caused the extinction of the dinosaurs? An easy to read article is: https: www.sciencenewsforstudents.org/article/dinosaursextinction-asteroid-eruptions-doom The simple answer is we do not know the impact that caused the Chicxulub crater is just a very likely candidate!
4.2 Interplanetary Matter (mostly primordial) Comets are icy, with some rocky parts. The basic components of a comet are detailed in the bottom right drawing.
4.2 Interplanetary Matter (mostly primordial) The comet s tails develop as it approaches the Sun and disappears as it moves away from the Sun. The solar wind means the ion tail always points away from the Sun. The dust tail also tends to point away from the Sun, but the dust particles are more massive and lag somewhat, forming a curved tail.
4.2 Interplanetary Matter (mostly primordial) Comets that come close enough to the Sun to be detectable from Earth have very eccentric orbits (eccentricity, e, are near 1, see Chapt 1)
4.2 Interplanetary Matter (mostly primordial) The size, shape, and orientation of cometary orbits depend on their orbit period. Long period comet orbits extend out to what is called the Oort cloud : the largest structure in the solar system!
4.2 Interplanetary Matter (mostly primordial) Meteor showers have many meteors/hour that appear to radiate from a common point in the sky (see time exposure image).
4.2 Interplanetary Matter (mostly primordial) Meteor showers are associated with short period comets they are the debris left over when a comet breaks up.
4.3 The Formation of the Solar System How might our solar system have formed? In the nebular contraction model (more in Chapt 11): Cloud (nebula) of gas and dust contracts due to gravity; conservation of angular momentum means it spins faster and faster as it contracts.
More Precisely 4.2: The Concept of Angular Momentum Conservation of angular momentum says that the product of radius and rotation rate must be constant. Therefore, as a dust cloud collapses, its rate of rotation will increase.
4.3 Formation of the Solar System More is needed in the model! We must now form modern structures. Condensation theory: Condensation occurs when gas cools and changes its state to become tiny solid particles. Interstellar dust grains act as condensation nuclei. Planetesimals grow and merge through collisions.
4.3 Formation of the Solar System Planetesimals grow and merge through collisions:
4.3 Formation of the Solar System While it is too late to observe this happening for our solar system, other solar systems are constantly forming today! The star Beta Pictoris is surrounded by a disk of warm matter, which may indicate planetary formation.
4.3 Formation of the Solar System These images show two other possible planetary systems in the process of formation.
4.3 Formation of the Solar System Temperature in the cloud determines where various materials condense out (become solid think about it: you can not make a snowball out of water or water vapor). See plot in top right à This determines where rocky (Terrestrial) planets and gas giant (Jovian) planets form!
4.3 Formation of the Solar System Here is another version of the same plot. Temperature in the cloud determines where various materials condense out; this determines where rocky planets and gas giant planets form.
4.4 Planets Beyond the Solar System Many planets have been discovered in other solar systems: these are called extra-solar planets. This figure shows recently discovered extra-solar planets compared to Neptune and Earth.
4.4 Planets Beyond the Solar System Some extra-solar planets are discovered through the wobble they create in their parent star s orbit.
4.4 Planets Beyond the Solar System Other extra-solar planets are discovered through the periodic dimming of the parent star s brightness. Do you understand how a planet can reduce the brightness of the parent star?
4.4 Planets Beyond the Solar System These are the orbits of many extra-solar planets discovered so far (see Earth s orbit for comparison).
4.4 Planets Beyond the Solar System This plot shows the masses of about 1000 discovered extra-solar planets (vertical axis) VS their distance from their star (horizontal axis). Earth, Neptune and Jupiter are also shown! Most have masses closer to the mass of Jupiter or Neptune than that of Earth.
4.4 Planets Beyond the Solar System Most have masses closer to the mass of Jupiter or Neptune than that of Earth this is a selection effect favoring discovery of massive and/or nearbyto-star planets. Nevertheless many of these do lie in a habitable zone favorable to Earth-like life!
Summary of Chapter 4 The solar system consists of the Sun and everything orbiting it. Asteroids are rocky, and most orbit between the orbits of Mars and Jupiter. Comets are icy and are believed to have formed early in the solar system s life. Major planets orbit the Sun in same sense, and all but Venus rotate in that sense as well. Planetary orbits lie almost in the same plane.
Summary of Chapter 4 (con t) Four inner planets terrestrial planets are rocky, small, and dense. Four outer planets Jovian planets are made of gas and liquid and are large. Nebular theory of solar system formation says that a cloud of gas and dust gradually collapsed under its own gravity, spinning faster as it shrank. Condensation theory says dust grains acted as condensation nuclei, beginning formation of larger objects.
Summary of Chapter 4 (con t) Planets have been discovered in other solar systems. Most of those discovered so far are large and orbit much closer to the Sun than the large planets in our solar system do.