What A Universe We Live In! Basic Concepts to Understand Modern Discoveries

Transcription

1 What A Universe We Live In! Basic Concepts to Understand Modern Discoveries Week 4 of 5 Today s Topic: Solar Systems Instructor: Robert Arn Website: Robert@astroarn.com #OSHR October 11th, 2011

2 Whats in Our Solar System The Solar System is HUGE ~40AU, ~1,000,000x Earth s Radius, ~15000x Earth-Moon Distance The Distance from Pluto to the Sun is 1/2000th of a lightyear

3

4

5 Terrestrial and Jovian Planets On a large scale the solar system is orderly Almost all planets lie on the same plane, travel around the sun in the same direction during regular intervals On a small scale planets are chaotic Terrestrial - Mercury, Venus, Mars, and Earth Jovian - Jupiter, Saturn, Uranus, and Neptune

6 Terrestrial Planets All lie within 1.5AU of the Sun All four planets have atmospheres, but the atmospheres are about as dissimilar as we could imagine, ranging from a near vacuum on Mercury to a hot, dense inferno on Venus Earth alone has oxygen in its atmosphere and liquid water on its surface Surface conditions are distinct ranging from barren, heavily cratered terrain on Mercury to widespread volcanic activity on Venuc Earth and Mars spin at roughly the same rate, but Mercury and Venus both take months to rotate just once, and Venus rotates in the opposite sense from the others Earth and Mars have moons but Mercury and Venus do not Earth and Mercury have measurable magnetic fields, of very different strengths, whereas Venus and Mars have none

7

8 Jovian Planets Large and Gaseous made mainly of H and He Have liquid interiors; thought to contain terrestrial cores which are 10-15x Earth s Mass Each contain many moons w/ unique properties

9 Definition of a Planet By the IAU (2006), A planet is a celestial body that 1) is in orbit around the sun 2) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and 3) has cleaned the neighborhood around its orbit

10 Definition of a Dwarf Planet By the IAU (2006), A planet is a celestial body that 1) is in orbit around the sun 2) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and 3) has NOT cleaned the neighborhood around its orbit 4) is not a satellite All other objects (except satellites) orbiting the sun are called small solar system objects

11 Pluto New type of Trans- Neptunian object called dwarf planet Discovered in 1930 by Clyde Tombaugh Intersects the orbit of Neptune; takes 248 years to orbit the sun; lies 17.2 off the plane of the solar system; has a diameter of 2270km (1410miles)

12

13 In 1990 Hubble imaged the planet reveling a moon, Charon which has a diameter of 1300km; since then we have found 4 moons of pluto Little is known about the composition; though spectroscopic analysis shows the surface has frozen methane, indicating a temp <50K Stay tuned from more information on Pluto through NASA s New Horizons

14 NASA Video: New Horizons Halfway to Pluto newhorizons/main/index.html

15 Interplanetary Debris Asteroid Belt between Mars and Jupiter Thought to be a failed planet but Jupiter s strong gravitational field prevented it from forming Kuiper Belt - beyond orbit of Neptune which contains planetesimals (1km-1000km sized objects) Oort Cloud - Hypothesized spherical cloud of comets lying 50000AU (or 1ly)

16

17 Comets Small faint, fuzzy patches of light Like Planets they do not produce their own light, instead the reflect sunlight Only a handful are detected, most past by unseen

18 Ion tail - Linear Streamers made up of numerous ionized molecules (carbon monoxide, water, nitrogen, etc.) Dust Tail - Broad, diffuse, curved, made up of dust particles Tails always away from sun

19 Comets have highly eccentric (oval) orbits Many break up as they approach the sun (some even impact the sun) Long-period Comets takes 100,000s or millions of years to complete one orbit Short period comets take less than 200 years and don t go beyond pluto Icy composition complex molecules of methane, ammonia, carbon dioxide, and ice water

20 Comet Holmes (2008)

21 Asteroids Small rocky objects orbiting the sun Often called minor planets, Planetoids, or Planetismials Few are larger than 300km (diam) Most are < 1/10th km Composition is very different from planets and each other - each one is a mystery

22 Trojan Asteroids - 2 regions containing asteroids on Jupiters orbit These 2 regions are in 2 of Jupiters Lagrangian points - the other 3 points are unstable Lagrangian Points - 5 points per planet where material will revolve at the same rate around the sun Spaceweather.com (PHA)

23

24

25 Meteoroids On a Clear Night it is possible to see a few meteors - a sudden streak of light caused by friction of Earth s atmosphere and interplanetary matter (comet, asteroid, or meteoroid)

26 NASA s Astronomy Picture of the Day August 21st, 2010

27 Meteoroid - same thing as an asteroid but <100m in size If a piece of interplanetary debris hits the ground it is called a meteorite - though most burn up in the atmosphere Smaller meteoroids are rocky remains of broken up comets - pebble and dust size Traveling together we call them meteoroid swarms Individual small meteoroids are called micrometeoroids

28 Meteor Showers (Draconids 2011) Earth has >100 craters 0.1km or larger

29 Properties of our Solar System 1) Each planet is relatively isolated in space 2) The orbits of the planets are nearly circular 3) The orbits of the planets all lie in nearly the same plane 4) The direction in which the planets orbit the Sun is the same as the direction in which the Sun rotates on its axis

30 5) The direction in which most planets rotate on their axis is roughly the same as the direction in which the Sun rotates on its axis 6) Most of the known moons revolve about their parent planets in the same direction that the planets rotate on their axes 7) Our planetary system is highly differentiated 8) The asteroids are very old an exhibit a range of properties not characteristic of either the inner or the outer planets or their moons

31 9) The Kuiper belt is a collection of asteroid-sized icy bodies orbiting beyond Neptune 10) The Oort-cloud comets are primitive, icy fragments that do not orbit in the plane of the ecliptic and reside primarily at large distances from the Sun

32 Modeling Planet Formation Recall the formation of a sun-like star Material at the center of a protostar gets more dense, more material starts to fall into the star; star and material start to rotate Due to the conservation of angular momentum the rotating material outside begins to flatten into a disk

33

34 As the dust starts to cool dust grains form condensation nuclei, providing the first clumps of solid matter which are spinning and moving around the sun in the disk Over time these clumps grow by accretion - colliding and sticking to other clumps Once these clumps reach a size of 1km they are called planetisimals and have a gravitational field strong enough to attract their neighbors

35 When the sun begins nuclear fusion there is a strong shockwave (solar wind ) Heavier planetisimals (large or dense) are not pushed far; unlike lighter (smaller or less dense) The rocky planetisimals that are close to the sun continue to collide, eventually forming Mercury, Venus, Earth, and Mars The Jovian Planetisimals have enough mass to collect the small dust and gas particles left over and eventually become Jupiter, Saturn, Uranus, and Neptune

36

37 The Role of Catastrophes Still does not explain all 10 points Very broad theory with room for special events to describe current situation Mercury s exceptionally large Nickel-Iron core may be the result of a collision between two partially differentiated protoplanets. The cores may have merged, and much of the mantle material may have been lost

38 Two large bodies could have merged to form Venus, giving it its abnormally low rotation rate The Earth-Moon system may have formed from a collision between the proto-earth and a Marssized object A late collision with a large planetisimals may have caused Mars s northsouth asymmetry and ejected mush of the planet s atmosphere

39 The tilted rotation axis of Uranus may have been caused by a grazing collision with a sufficiently large planetisimals, or by a merger of two smaller planets Uranus s moon Miranda may have been almost destroyed by a planetisimals collision, accounting for its bizarre surface terrain Interactions between the jovian protoplanets and one or more planetisimals may account for the irregular moons of those planets and Triton s retrograde motion

40 Pluto may simply be a large representative of the Kuiper belt, and the Pluto-Charon system may be the result of a collision or near-miss between two icy planetesimals before most were ejected by interactions with the jovian planets It is impossible to test these theories but is possible to exist with current model - while leaving room for very diverse exo-solar systems

41 Cosmic Evolution We identify 7 phases with the history of the universe Particulate, Galactic, Stellar, Planetary, Chemical, Biological, and Cultural The First 4 were discussed in the first 4 weeks of class

42

43 Life in the Universe No definite definition of life, but Organisms that can react to their environment Heal when damaged Grow by taking nourishment and converting to energy Reproduce by passing along characteristics Capacity for genetic change

44 The Good Assumptions of mediocrity: 1) Because life on earth depends on just a few basic molecules, and 2) because the elements that make up these molecules are present in most stars 3) and if the laws of physics are the same throughout the universe, then given enough time, life must have originated elsewhere

45 The Bad Intelligent life is the product of a series of extremely fortunate accidents Astronomical, geological, chemical, and biological All are unlikely events which may not occur anywhere else We know very little about life, the Universe, and Everything Else - it is possible that life can form under many diverse conditions

46 The Ugly (Math!)

47 Take-Home Messages Our solar system is imaginable large and infinitesimally small It contains a very diverse range of objects Our model of solar system formation is very dependent on our model of stellar formation yet it is diverse enough to describe our current solar system as well as exo-solar systems Life can be found on earth but may have beginnings elsewhere