1. Our Solar System
Origins of the Solar System
Astronomy 12

2. Learning Outcomes (Students will…) -Explain the theories for the origin of the solar system -Distinguish between questions that can be answered by science and those that cannot, and between problems that can be solved by technology and those that cannot with regards to solar system formation. -Estimate quantities of distances in parsec. Estimate the age of the solar system. -Describe and apply classification systems and nomenclature used in the sciences. Classify planets as terrestrial vs. Jovian, inner vs. outer, etc. Classify satellites. Classify meteoroid, asteroid, dwarf planet, planet. Classify comets as long period vs. short period. etc -Formulate operational definitions of major variables. Given data such as diameter and density describe the properties that divide the planets and moons into groups. -Tools and methods used to observe and measure the inner and the outer planets and the minor members of the solar system

3. Our Solar System Our solar system is made up of: Sun Eight planets
Their moons
Asteroids & Meteroids
Comets

4. Inner Planets
The inner four rocky planets at the center of the solar system are:
Mercury
Venus
Earth
Mars

5. Mercury Planet nearest the sun Second smallest planet
Covered with craters
Has no moons or rings
About size of Earth’s moon

6. Venus Sister planet to Earth Has no moons or rings
Hot, thick atmosphere
Brightest object in sky besides sun and moon (looks like bright star)
Covered with craters, volcanoes, and mountains

7. Earth Third planet from sun
Only planet known to have life and liquid water
Atmosphere composed of Nitrogen (78%), Oxygen (21%), and other gases (1%).

8. Mars Fourth planet from sun
Appears as bright reddish color in the night sky
Surface features volcanoes and huge dust storms
Has 2 moons: Phobos and Deimos

9. Outer Planets The outer planets composed of gas are : Jupiter Saturn
Uranus
Neptune

10. Jupiter Largest planet in solar system Brightest planet in sky
60+ moons, 5 visible from Earth
Strong magnetic field
Giant red spot
Rings have 3 parts: Halo Ring, Main Ring, Gossamer Ring

11. Saturn 6th planet from sun Beautiful set of rings 31 moons
Largest moon, Titan,
Easily visible in the night sky
Voyager explored Saturn and its rings.

12. Uranus 7th planet from sun Has a faint ring system 27 known moons
Covered with clouds
Uranus sits on its side with the north and south poles sticking out the sides.

13. Neptune 8th planet from sun Discovered through math 7 known moons
Triton largest moon
Great Dark Spot thought to be a hole, similar to the hole in the ozone layer on Earth

14. A Dwarf Planet
Pluto is a small solid icy planet is smaller than the Earth's Moon.

15. Pluto Never visited by spacecraft Orbits very slowly
Charon, its moon, is very close to Pluto and about the same size

16. Asteroids Small bodies
Believed to be left over from the beginning of the solar system billions of years ago
100,000 asteroids lie in belt between Mars and Jupiter
Largest asteroids have been given names

17. Comets Small icy bodies Travel past the Sun
Give off gas and dust as they pass by

18. SOLAR SYSTEM FORMATION

19. Bode’s Law Also known as the Titius-Bode Law
Titius: German astronomer who introduced the idea (1766) that the planets in the Solar System were spaced apart in a mathematical sequence
Bode: German astronomer who popularized Titius’s idea (1772)
Bode’s Law: hypothesis that the bodies in some orbital systems, including the Sun's, orbit at semi-major axes in an exponential function of planetary sequence.

20. Bode’s Law
Step 1: Create a sequence of 10 numbers that follow the pattern
0, 3, 6, 12, …
Pattern 3 6 12

21. Bode’s Law Step 2: Add 4 to each number in the sequence. 3 6 12 24 48
Pattern 3 6 12 24 48 96
192
384
768
Add 4 4 7 10

22. Bode’s Law Step 3: Divide by 10. Pattern 3 6 12 24 48 96 192 384 7683 6 12 24 48 96
192
384
768
Add 4 4 7 10 16 28 52
100
196
388
772
Divide by 10
0.4
0.7
1.0

23. Bode’s Law
Step 4: Compare!
Pattern 3 6 12 24 48 96
192
384
768
Add 4 4 7 10 16 28 52
100
196
388
772
Divide by 10
0.4
0.7
1.0
1.6
2.8
5.2
19.6
38.8
77.2
Distance in AU
0.39
0.72
1.52
2.77
5.20
9.54
19.2
30.06
39.44
Planet
Mercury
Venus
Earth
Mars
Asteroid Belt -Ceres
Jupiter
Saturn
Uranus
Neptune
Pluto

25. Why is Bode’s Law Important?
Bode’s Law correctly determined where the planets were at the time of its introduction (Mercury to Saturn, with a missing planet in between Mars and Jupiter)
Bode’s Law helped to predict where “missing” planets (Ceres, Uranus) would be found!
Bode’s Law can be used for moons around planets as well

26. Moons of Uranus

27. What are the shortcomings of Bode’s Law?
Bode’s Law is a hypothesis – there is no evidence that this is nothing more than coincidence (scientifically speaking)
Bode’s Law did not determine Neptune’s orbit accurately
Bode’s Law cannot be tested properly on other planetary systems because only 1 system has enough planets (55 Cancri)

28. Questions from Bode’s Law
1) What does Bode’s Law describe?
2) Why is Bode’s Law criticized?
3) What has Bode’s Law determined?
4) What else could Bode’s Law be used to determine?

29. How old is the Solar System?
Approximately 4.5 to 4.6 billion years old

30. Planetary Nebula or Close Encounter?
Historically, two hypothesis were put forward to explain the formation of the solar system….
#1 – Nebular Theory or Gravitational Collapse of Planetary Nebula
Solar system formed form gravitational collapse of an interstellar cloud of gas
#2 - Close Encounter (of the Sun with another star)
Planets are formed from debris pulled out of the Sun during a close encounter with another star. But, it cannot account for
Hot gas expands so planets should not form
Probability for such encounter is small in our neighborhood…
Angular Momentum Issue: most of the mass should be around the Sun
This theory also says that some of the planets may have been created around another star!
Astronomers favour Hypothesis #1

31. 6- Steps to Form a Solar System
THE NEBULAR THEORY
6- Steps to Form a Solar System

32. Step 1: Solar Nebula Huge cloud of cold gas and dust forms.
This cloud spins slowly.
The solar nebula is made up of 98% gas (H and He) but also contains 1.4% hydrogen compounds (water, methane, ammonia), 0.4% silicates and 0.2% iron/nickel/aluminum

33. Step 2: Protosun
The solar nebula (cloud) condenses into a dense central region and a less-dense outer region.
The protosun begins to spin faster and flatten into a disk.

34. Step 3: Rings and Planetesimals
Instabilities in the rotating disk caused regions within it to condense into rings. Planetesimals formed in these rings.

35. Planetesimals are a few cm to a few km in size
Planetesimals are attracted to each other by gravity
They collide to build planets

36. This process explains the orderly motion of most of the solar system objects!

37. Step 4: Gas Giants
In the outer part of the disk, the planetesimals are made of rock and ice.
When big enough, they will attract large amounts of gas around them.

38. Step 5: Rocky Planets
Near the protosun only rocky material and metals can withstand the heat.
Therefore any planets formed here will be rocky.

39. Step 6: Remaining Debris Blown Away
Radiation from the Sun blows away most of the remaining gas and loose material. Some of the leftover planetesimals form the Oort cloud.

40. Nebular Hypothesis

41. Formation of the Solar System – Nebular Theory

42. Planetesimals forming planets
From the work of George Witherill, who was the director of DTM while Harold Williams was at DTM. He wrote me my hiring letter which brought me to the Washington Metro area at Alan Boss’ request.

43.
The solar system discovery)

44. Where else has there been evidence for this theory???

45. Beta Pectoris dust disk
Possible planetary system! Too young to tell yet!

46. Evidence for Ongoing Planet Formation
Many young stars in the Orion Nebula are surrounded by dust disks:
Probably sites of planet formation right now!

47. Dust Disks around Forming Stars
Dust disks around some T Tauri stars can be imaged directly (HST).

48. Planets form from the same cloud as the star.
Planet formation sites observed today as dust disks of T Tauri stars.
T Tauri stars are YOUNG stars with less mass that are very bright due to their large radii.
Immanuel Kant, ( ) German philosopher and scientist (astrophysics, mathematics, geography, anthropology) from East Prussia University of Königsberg, Königsberg now called Kaliningrad

49. Encounter Hypothesis

50. http://channel. nationalgeographic

51. Problems with Close Encounter Theory
1) Does not explain angular momentum
2) Hot gas expands so planets should not form
3) Probability for such encounter is small in our neighborhood…(main problem!)
Angular momentum is the rate at which a planet sweeps out the elliptical area or the time it takes to orbit

52. So…How WAS the Solar System Formed?
A viable theory for the formation of the solar system must be:
based on physical principles (angular momentum, the law of gravity, the law of motions)
able to explain other planetary systems
able to explain all (or at least most) of the observable facts with reasonable accuracy
Angular momentum is why the solar nebula spun faster and faster as it collapsed on itself.

53. How was the Solar System Formed?
A viable theory for the formation of the solar system must account for 4 characteristics or observable facts:
Patterns of motion
Two types of planets
Asteroids & comets
Exceptions to patterns

54. Patterns of Motion All the planets orbit the Sun in the same direction
The rotation axis of most of the planets and the Sun are roughly aligned with the rotation axis of their orbits (fairly vertical axis).
Orientation of Venus, Uranus, and Pluto’s spin axes are not
similar to that of the Sun and other planets. (axial tilts >> 30’)
Why do they spin in roughly the same orientation?
Why are they different?
Axial Tilt: all planets (and the Sun) have small axial tilts (less than 30’) except Pluto, Uranus and Venus.
An axial tilt of 0’ would have no seasons.
These planets also rotate clockwise as opposed to the typical counterclockwise rotation of Earth, Mercury, Mars, etc.

55. Patterns of Motion
The rotation axis of most of the planets and the Sun are roughly aligned with the rotation axis of their orbits (fairly vertical axis).
Orientation of Venus, Uranus, and Pluto’s spin axes are not similar to that of the Sun and other planets. Their axial tilts are much greater than 30’.
Axial Tilt: all planets (and the Sun) have small axial tilts (less than 30’) except Pluto, Uranus and Venus.
An axial tilt of 0’ would have no seasons.
These planets also rotate clockwise as opposed to the typical counterclockwise rotation of Earth, Mercury, Mars, etc. 55

56. Questions
1) Explain how all the planets orbiting the Sun in the same direction makes sense using the Solar Nebula theory.
2) What problems are still evident in this theory in terms of patterns of motion?
It was a flat disk that was rotating!

57. Two Types of Planets: Terrestrial and Jovian
Why are there 2 types of planets according to the Solar Nebular theory?

58. The Story of Planet Building
Planets formed from the same protostellar material as the Sun, still found in the Sun’s atmosphere.
Rocky planet material formed from clumping together of dust grains in the protostellar cloud.
Mass of less than~15 Earth masses:
Mass of more than~15 Earth masses:
Planets cannot grow by gravitational collapse. These planets are made of metal and rock and can withstand the Sun’s heat.
Planets are large enough to grow by gravitationally attracting material from the dust/gas cloud
Earthlike planets
Jovian planets (gas giants)

59. What about Pluto???

60. Exceptions to Patterns
Uranus has different axial tilt
Some moons larger than others
Some moons have unusual orbits

62. So…
1) Uranus’ tilt must have occurred due to an impact after it formed.
2) Moons are formed either by collisions of planetesimals or by disks of gas/dust around the planets (similar to how the planets formed).
3) Unusual orbits…

63. The Jovian Problem Two problems for the theory of planet formation:
Two problems for the theory of planet formation:
1) Observations of extrasolar planets indicate that Jovian planets are common.
2) Protoplanetary disks tend to be evaporated quickly (typically within ~ 100,000 years) by the radiation of nearby massive stars.
 Too short for Jovian planets to grow!
Solution:
Computer simulations show that Jovian planets can grow by direct gas accretion without forming rocky planetesimals.

64. Clearing the Nebula
Remains of the protostellar nebula were cleared away by:
Radiation pressure of the sun
Sweeping-up of space debris by planets
Solar wind
Ejection by close encounters with planets
Surfaces of the moon and Mercury show evidence for heavy bombardment by asteroids.

65. What does the solar system look like from far away?
Sun, a star, at the center
Inner (rocky) Planets (Mercury, Venus, Earth, Mars) ~ 1 AU
Asteroid Belt ~ 3 AU
Outer (gaseous) Planets (Jupiter, Saturn, Neptune, Uranus) ~ 5-40 AU
Kuiper Belt ~ 30 to 50 AU
-includes Pluto
Oort Cloud ~ 50,000 AU

66. Sedna – most distant body that orbits the Sun
Dwarf planet (a little smaller than Pluto)

67. Extrasolar Planets
An extrasolar planet, or exoplanet, is a planet beyond our solar system, orbiting a star other than our Sun.
Information obtained primarily from wikipedia.org

68. Types of Extrasolar Planets
Terrestrial Planets
Small, rocky planets that orbit close to the star

69. Types of Extrasolar Planets
Gas Giant
A type of extrasolar planet with similar mass to Jupiter and composed of gases
Example 1: Corot-9b
This gas giant was discovered
March 17, 2010 over 1500
light years away!
Example 2: 79 Ceti b

70. Types of Extrasolar Planets
Super Earth
A super-Earth has a MASS between that of Earth and the Solar System's gas giants. This term does not imply anything about the surface conditions or habitability of the planet!
Example 1: Corot-7b
Example 2: GJ 1214b
Neptune
Earth
Corot-7b
Up to 10 Earth masses…

71. Types of Extrasolar Planets
Hot Jupiter
A type of extrasolar planet whose mass is close to or exceeds that of Jupiter (1.9 × 1027 kg), but unlike in the Solar System, where Jupiter orbits at 5 AU, hot Jupiters orbit within approximately 0.05 AU of their parent stars (about one eighth the distance that Mercury orbits the Sun)
Example: 51 Pegasi b
Found orbiting a star (51 Pegasi) in
the constellation Pegasus about 50
light years away…

72. Types of Extrasolar Planets
Eccentric Jupiter
A gas giant that orbits the star in a highly eccentric path (like a comet)
Examples: 16 Cygni Bb and HD b

73. Types of Extrasolar Planets
Pulsar Planet
A type of extrasolar planet that is found orbiting pulsars, or rapidly rotating neutron stars
Example: PSR B in the constellation Virgo
A neutron star is a remnant of a gravitationally collapsed massive star

74. Types of Extrasolar Planets
Theoretical Extrasolar Planets…
Ocean Planet
Hot Neptune

75. Key Terms – Types of Extrasolar Planets
1) Terrestrial Planet – small, rocky
2) Gas Giant – large, gaseous
3) Super Earth – size is up to 10 Earths (not as large as the gas giants)
4) Hot Jupiter Planet: mass is close to Jupiter (1.9 x 1027 kg) and orbit is within 0.5 AU of star
5) Eccentric Jupiter Planet: mass is close to Jupiter but orbit is highly elliptical
6) Pulsar Planet: orbits pulsars (a pulsars is a neutron star which is a remnant of a gravitationally collapsed massive star)

76. Key Terms – Types of Extrasolar Planets
Theoretical Planets
1) Ocean Planet
2) Hot Neptune

77. http://channel. nationalgeographic

78. Methods of Detecting Extrasolar Planets
Transit Method
If a planet crosses ( or transits) in front of its parent star's disk, then the observed visual brightness of the star drops a small amount.
The amount the star dims depends on the relative sizes of the star and the planet.

79. Methods of Detecting Extrasolar Planets
Astrometry
This method consists of precisely measuring a star's position in the sky and observing how that position changes over time.
If the star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit.
If the star is large enough, a ‘wobble’ will be detected.

80. Methods of Detecting Extrasolar Planets
Doppler Shift (Radial Velocity)
A star with a planet will move in its own small orbit in response to the planet's gravity. The goal now is to measure variations in the speed with which the star moves toward or away from Earth.
In other words, the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star's spectral lines (think ROYGBIV) due to the Doppler effect.
A red shift means the star is moving away from Earth
A blue shift means the star is moving towards Earth

81. Methods of Detecting Extrasolar Planets
Pulsar Timing
Pulsars emit radio waves extremely regularly as they rotate. Because the rotation of a pulsar is so regular, slight changes in the timing of its observed radio pulses can be used to track the pulsar's motion.
Like an ordinary star, a pulsar will move in its own small orbit if it has a planet. Calculations based on pulse-timing observations can then reveal the geometry of that orbit

82. Methods of Detecting Extrasolar Planets
Gravitational Microlensing
The gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned.
If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect.

83. Methods of Detecting Extrasolar Planets
Direct Imaging
Planets are extremely faint light sources compared to stars and what little light comes from them tends to be lost in the glare from their parent star.
It is very difficult to detect them directly. In certain cases, however, current telescopes may be capable of directly imaging planets.