04 lecture outline rev - physics and...

AstronomyA BEGINNER’S GUIDETO THE UNIVERSE

EIGHTH EDITION

CHAPTER 4

The Solar SystemLecture Presentation

© 2017 Pearson Education, Inc.

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!

• Now known: Solar system has 1 star, 185+ moonsorbiting 8 planets(added Uranus and Neptune), asteroids (meteoroids), comets, dwarf planets (Plutoids), and Kuiper belt objects.

4.1 An Inventory of the Solar System


Not shown are planet moons, and comets.

Dwarf planets and plutoidsare Kuiper belt objects.

Recall radius of Earth’s orbit is1 AU.



10 AU

4.1 An Inventory of the Solar System• New quantities: planet Mass, Radius and Density … see next page for details. Orbit eccentricities are in Chapt 1!

Density of water = 1000 kg/m3

Planet rotation periods (not in this table) are obtained by measuring the time for some feature on the planet to “re-appear”.

4.1 An Inventory of the Solar System• How are quantities in the Properties in the Table determined?

• Orbital periods can be observed

• Then use Kepler’s 3rd law to obtain the orbit semi-major axis values

• First measure the angular size. Then use the known distance (knowing the planet semi-major axis distances) to obtain the planet diameter (labelled linear size on the next slide)

• Masses from Newton’s laws (see Chapt 1 lecture notes)

• Density (= Mass/Volume) can be calculated knowing diameter and Mass: see astr0101_notes_chapt3and4.pdf

• If you are interested the class web page gives the details in a series of: “astro101_notes_chaptXXX.pdf” files


More Precisely 0.1: Angular Measure• The Angular size of an object depends on its actual (linear) size and its distance from the Earth.


Angular size = 360o x (Linear size)(2 p x Distance)

4.1 An Inventory of the Solar System• All orbits but Mercury’s are close to the same planeand are almost circular (eccentricity e near 0)


4.1 The Overall Layout of the Solar SystemBecause the

planet’s orbits, including Earth’s, 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. A straight line is close to all 5 planets!



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• While terrestrial planets have a majority of similarities, in detail there are planet to planet differences e.g.:– 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


4.2 Interplanetary Matter (mostly primordial)• Asteroids (those too small to be “seen” are calledmeteoroids and are typically <1m in size) are mostly too small to be round! (It’s a gravity thing!)

(above) Asteroid Ida with its moon, Dactyl

(below) Asteroid Mathilde

(above) Asteroid Itokawa




• Eros, a typical non-round asteroid, is: 34km x 11km

4.2 Interplanetary Matter (mostly primordial)• 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 = Left photo.

• What is a meteoroid? It is an asteroid too small to be seen by Earth based telescopes …

• What is a meteorite? Fragments of meteors that reach the ground = Right photo [UNM Earth & Planetary Science Museum]


Meteor

Meteorite

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:


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 https://www.lpi.usra.edu/science/kring/epo_web/impact_cratering/World_Craters_web/intromap.html


This is the nearby Barringer meteor crater in Arizona.

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/dinosaurs-extinction-asteroid-eruptions-doom


The simple answer is we do not know. The impact that caused the Chicxulub crater is just a very likely candidate and the other half of the story may be half-way around the world in the Deccan Traps mega-volcanic eruption in India!

4.2 Interplanetary Matter (mostly primordial)• Comets are icy, with some rocky parts.

• The basic components of a cometare detailed in the drawing.

4.2 Interplanetary Matter (mostly primordial)• The comet’s “tails” develop as it approaches the Sun and disappear as it moves away from the Sun.


4.2 Interplanetary Matter (mostly primordial)• The solar wind means the ion tail always pointsaway from the Sun.


4.2 Interplanetary Matter (mostly primordial)• The dust tail also tends to point away from theSun, 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 (i.e. comet orbit eccentricities, e, are near 1, see Chapt 1)

Way to remember: orbits with eccentricity, e near 0, look like circles and orbits with eccentricity, e near 1, look like cigars.

4.2 Interplanetary Matter (mostly primordial)Short period comets have periods that are typically less than 200 years. These comets likely originate from the Kuiper Belt.

(http://cse.ssl.berkeley.edu/SegwayEd/lessons/cometstale/glossary/glossary_6th_new/short_period.html )

Short period comets break up over time, due to their many close encounters with the Sun, and are the source of meteor showers.

4.2 Interplanetary Matter (mostly primordial)• Long period comet orbits’ extend out to what is called the “Oort cloud”: the largest structure in the solar system!


Because of their long periods, these comets have been observed only once!



• 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 cometbreaks 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):

First a cloud (nebula) of gas and dust contracts due to gravity. © 2017 Pearson Education, Inc.

4.3 The Formation of the Solar System

Second the 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.


4.3 Formation of the Solar System• Condensation theory:– Condensationoccurs when gas cools and changes its state to become tiny solid particles.

– Interstellar dust grains act as condensation nuclei.

– Planetesimalsgrow 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”!

• These imagesshow 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 whererocky (Terrestrial) planets and gas giant (Jovian) planets form!


4.3 Formation of the Solar System• This explains the gross features: e.g. terrestrial planets are rocky and Jovian moons and Kuiper belt objects are icy (Chapt 8).


Rocky compounds form here

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 in white 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, Neptuneand Jupiter are also shown!


4.4 Planets Beyond the Solar System

• The large masses of the extra-solar planets isprobably a selection effect favoring discovery of massive and/or nearby-to-star planets.


4.4 Planets Beyond the Solar System

• 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.


Extra


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 940 km

Pallas 580 km

Vesta 540 km


Vesta (photo on right) is considered a rare example of a proto-planet: a layered (i.e. differentiated [see Chapt5]) planetary building block from the earliest days of the solar system!

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 (the remainder)


04 lecture outline rev - physics and...

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