introduction to astronomy - open...

Introduction to Astronomy

Solar System I – The Inner Terrestrial Planets and the

Asteroid Belt

1 Elizabeth Charlton, 2015

Overview of the Solar System


Objects in the Solar System


Solar system

•  What do we mean by solar system •  “solar” = related to the sun •  solar system

– all objects gravitationally bound to sun –  region of space dominated by sun's gravity


What is in the solar system?

•  What do you think? •  sun •  Planets •  Dwarf Planets •  moons •  small bodies


Planets

•  the “large” bodies in orbit around the sun –  large enough that gravity forms them into a sphere –  not large enough to become a star

"Mercury in color - Prockter07 centered" by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington. Edited version of Image:Mercury in color - Prockter07.jpg by Papa Lima Whiskey. - NASA/JPL [1]. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Mercury_in_color_-_Prockter07_centered.jpg#/media/File:Mercury_in_color_-_Prockter07_centered.jpg

"Jupiter New Horizons" by NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute - National Aeronautics and Space Administration. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Jupiter_New_Horizons.jpg#/media/File:Jupiter_New_Horizons.jpg

"Neptune Full" by NASA - JPL image. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Neptune_Full.jpg#/media/File:Neptune_Full.jpg 6 Elizabeth Charlton, 2015

Definition of a Planet •  is in orbit around the Sun,

•  has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and

•  has“cleared the neighborhood" around its orbit.

2006-International Astronomical Union

"Euler diagram of solar system bodies" by SounderBruce (translated version), Ariel Provost (French version), Tahc (original version) - Derivative work of File:Diagramme d'Euler des corps du Système solaire.svg, translated from French to English. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Euler_diagram_of_solar_system_bodies.svg#/media/File:Euler_diagram_of_solar_system_bodies.svg


Planets

Terrestrial •  Mercury •  Venus •  Earth •  Mars

Jovian •  Jupiter •  Saturn •  Uranus •  Neptune

"Mars 23 aug 2003 hubble" by NASA, ESA, and The Hubble Heritage Team (STScI/AURA) - http://hubblesite.org/newscenter/archive/releases/2005/34/image/j/ (image link). Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Mars_23_aug_2003_hubble.jpg#/media/File:Mars_23_aug_2003_hubble.jpg

"Venus-real color" by NASA or Ricardo Nunes - http://www.astrosurf.com/nunes/explor/explor_m10.htm. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Venus-real_color.jpg#/media/File:Venus-real_color.jpg

"Jewel of the Solar System" by NASA/JPL-Caltech/SSI/Cornell - JPEG File: http://www.nasa.gov/mission_pages/cassini/multimedia/pia17474.html#.Um1oeeig5w0Full-Resolution TIFF: JPL Photojournal PIA17474: Jewel of the Solar System (NASA). Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Jewel_of_the_Solar_System.jpg#/media/File:Jewel_of_the_Solar_System.jpg

"Uranus2" by NASA/JPL-Caltech - http://web.archive.org/web/20090119235457/http://planetquest.jpl.nasa.gov/milestones_show/slide1.html (image link)http://photojournal.jpl.nasa.gov/catalog/PIA18182 (image link). Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Uranus2.jpg#/media/File:Uranus2.jpg


Dwarf Planets

•  Pluto •  Eris •  Ceres •  Haumea •  Makemake

"PIA19562-Ceres-DwarfPlanet-Dawn-RC3-image19-20150506" by NASA/JPL-Caltech/UCLA/MPS/DLR/IDA - http://photojournal.jpl.nasa.gov/jpeg/PIA19562.jpg. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:PIA19562-Ceres-DwarfPlanet-Dawn-RC3-image19-20150506.jpg#/media/File:PIA19562-Ceres-DwarfPlanet-Dawn-RC3-image19-20150506.jpg

"Nh-pluto-in-true-color 2x JPEG" by NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute - http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=243. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Nh-pluto-in-true-color_2x_JPEG.jpg#/media/File:Nh-pluto-in-true-color_2x_JPEG.jpg

"Eris and dysnomia2" by NASA, ESA, and M. Brown - http://www.nasa.gov/mission_pages/hubble/news/eris.html . Originally uploaded to en.wikipedia by en:User:Serendipodous. For more information, see the description page. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Eris_and_dysnomia2.jpg#/media/File:Eris_and_dysnomia2.jpg

"2003 EL61 Haumea, with moons" by CalTech, Mike Brown et al. - Keck Telescope, CalTech. Licensed under Fair use via Wikipedia - https://en.wikipedia.org/wiki/File:2003_EL61_Haumea,_with_moons.jpg#/media/File:2003_EL61_Haumea,_with_moons.jpg

"Makemake hubble" by NASA - Hubble Space Telescope - Email from Mike Brown (discoverer of Makemake), December 5, 2008. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Makemake_hubble.png#/media/File:Makemake_hubble.png


Trans-Neptunian Objects


Moons and Satellites

•  satellite – any object in gravitational orbit around another larger object

•  moon – natural satellite of a planet

•  “The Moon” – the natural satellite of the Earth


Small bodies

"Asteroidsscale" by NASA/JPL-Caltech/JAXA/ESA - http://dawn.jpl.nasa.gov/multimedia/images/571372main_pia14316-43_800-600.jpg. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Asteroidsscale.jpg#/media/File:Asteroidsscale.jpg

"17pHolmes 071104 eder vga" by Ivan Eder - Ivan Eder. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:17pHolmes_071104_eder_vga.jpg#/media/File:17pHolmes_071104_eder_vga.jpg


Small bodies

•  asteroid – small, rocky, planet-like fragment

•  meteoroid – very small interplanetary rock

•  comet – ice and dust body, eccentric orbit


Kuiper Belt

•  Extends beyond the orbit of Neptune to approximately 50 AU – Home to many frozen small solar system

bodies • Pluto • Haumea • Makemake

"Kuiper belt plot objects of outer solar system" by WilyD at English Wikipedia. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Kuiper_belt_plot_objects_of_outer_solar_system.png#/media/File:Kuiper_belt_plot_objects_of_outer_solar_system.png


Scattered Disk

•  Populated by icy minor planets and small solar system bodies

•  Due to “scattering” of small bodies by the gas giant planets

•  Unstable – origin of most periodic comets


Locations of Objects


Measurements

•  How do we measure locations? •  average distance from Sun •  Astronomical Units (AU)

– average sun-earth distance – 1.5 x 1011 m

•  Heliocentric longitude – position around the sun


General Shape

! Planets all orbit in a disk

"Ecliptic plane 3d view" by Lookang many thanks to author of original simulation = Todd K. Timberlake author of Easy Java Simulation = Francisco Esquembre - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Ecliptic_plane_3d_view.gif#/media/File:Ecliptic_plane_3d_view.gif

"Solarsystem3DJupiter" by Lookang many thanks to author of original simulation = Todd K. Timberlake author of Easy Java Simulation = Francisco Esquembre - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Solarsystem3DJupiter.gif#/media/File:Solarsystem3DJupiter.gif


Inner Planets

•  Mercury 5.8 x 1010 m or 0.38 AU •  Venus 1.1 x 1011 m or 0.72 AU •  Earth 1.5 x 1011 m or 1.00 AU •  Mars 2.2 x 1011 m or 1.50 AU


"Oort cloud Sedna orbit" by Image courtesy of NASA / JPL-Caltech / R. HurtOriginal text courtesy of NASA / JPL-CaltechSVG conversion by Holek - SVG version of Image:Oort cloud Sedna orbit.jpg, which lists the following sources: [1] [2] Splitzer Space Telescope Released Images about Sedna. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Oort_cloud_Sedna_orbit.svg#/media/File:Oort_cloud_Sedna_orbit.svg


Asteroid Belt

•  most asteroids found in one region •  disk from 2.3 AU to 3.3 AU •  between orbits of Mars and Jupiter

•  Ceres 4.15x1011m or 3.0 AU


Outer planets

•  Jupiter 7.8 x 1011 m or 5.2 AU •  Saturn 1.4 x 1012 m or 9.5 AU •  Uranus 2.9 x 1012 m or 19 AU •  Neptune 4.5 x 1012 m or 30 AU

•  Pluto 5.9 x 1012 m or 39 AU •  Eris 1.0 x 1013 m or 68 AU •  Haumea 6.4 x 1012 m or 43 AU •  Makemake 6.9 x 1012 m or 46 AU


"Oort cloud Sedna orbit" by Image courtesy of NASA / JPL-Caltech / R. HurtOriginal text courtesy of NASA / JPL-CaltechSVG conversion by Holek - SVG version of Image:Oort cloud Sedna orbit.jpg, which lists the following sources: [1] [2] Splitzer Space Telescope Released Images about Sedna. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Oort_cloud_Sedna_orbit.svg#/media/File:Oort_cloud_Sedna_orbit.svg


Oort Cloud

•  Furthest extent of Solar system

•  50,000 AU to 100,000 AU (approximately)

•  sun's gravity just barely enough to hold objects

•  long period comets originate here

"Kuiper belt - Oort cloud-en" by NASAThis SVG image was created by Medium69.Cette image SVG a été créée par Medium69.Please credit this : William Crochot - http://herschel.jpl.nasa.gov/solarSystem.shtml. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Kuiper_belt_-_Oort_cloud-en.svg#/media/File:Kuiper_belt_-_Oort_cloud-en.svg


Object Sizes


Size Measurements

•  most objects are spheres (or close to spheres)

•  Diameter – distance across object •  Radius – average distance from center out

to edge


Largest object?

•  Sun •  radius = 7.0 x 108 m

– 700,000,000 meters – 700,000 km =7.0 x 105 m


Other Objects

•  Planets – 1,000 km to 70,000km •  Moons – 5 km to 3,000 km •  asteroids – most < 1 km, up to 750 km •  comets – nucleus up to 100 km •  meteoroids – most in cm range, up to

100m


Planets

•  Jupiter – largest planet –  7 x 107m (70,000 km)

•  Mercury – smallest planet –  2.4 x 106m (2,400 km)

•  Size order –  Jupiter, Saturn,

Uranus, Neptune, Earth, Venus, Mars, Mercury


Relative to Earth

•  Sun = 110 •  Jupiter = 11.2 •  Saturn = 9.1 •  Uranus = 4.0 •  Neptune = 3.9

•  Earth = 1.00 •  Venus = 0.95 •  Mars = 0.53 •  Mercury = 0.38

•  Eris = 0.19 •  Pluto = 0.18 •  Makemake=0.10-0.15 •  Haumea=0.11 •  Ceres = 0.07


The Inner Planets


Major Characteristics

•  What are the major characteristics of each of the inner planets?

Elizabeth Charlton, 2015 35

Mercury


Mercury

•  smallest inner planet •  looks like Moon (gray, bare, cratered) •  essentially no atmosphere


Venus


Venus

•  a dense CO2 atmosphere, •  covered with deep sulfuric acid clouds, •  hottest planet, •  immense volcanic peaks tower over

desolate plains


Earth

"The Earth seen from Apollo 17" by NASA/Apollo 17 crew; taken by either Harrison Schmitt or Ron Evans - http://www.nasa.gov/images/content/115334main_image_feature_329_ys_full.jpgAlt: http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001138.html (direct link). Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:The_Earth_seen_from_Apollo_17.jpg#/media/File:The_Earth_seen_from_Apollo_17.jpg 40 Elizabeth Charlton, 2015

Earth

•  Great variety: •  blue seas, white clouds and ice caps, red

deserts, green jungles, mountains •  Life!!


Mars


Mars

•  Thin CO2 atmosphere •  vast red deserts with craters and dunes, •  polar caps of ice and CO2, •  canyons and dry river beds, •  ancient volcanoes,


Commonalties

•  What do they all have in common? •  What caused these characteristics?


Commonalities

•  have similar sizes and structure –  Iron/nickel core – Rocky mantle and crust

http://sse.jpl.nasa.gov/multimedia/gallery/terrest_int.jpg


Commonalties

•  What caused this common structure? – They are formed in the inner part of the solar

system from the same material – Solid material formed clumps – Gases pushed away by the Sun – Differentiation – Cooling and cratering


What makes each planet unique?

"Terrestrial planet sizes" by NASAMercury image: JHUAPLVenus image: JPLMars image: HST - Mercury Globe-MESSENGER mosaic centered at 0degN-0degE.jpgVenus globe.jpgThe Earth seen from Apollo 17.jpgMars 23 aug 2003 hubble.jpg. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Terrestrial_planet_sizes.jpg#/media/File:Terrestrial_planet_sizes.jpg


“Why?” is most important

•  Memorizing differences is hard and meaningless

•  Understanding the reasons gives meaning to the facts and makes it easier to remember them


Role of Mass and Radius

•  Mass and radius affect interior temperature – Smaller => not as hot internally

•  This in turn determines the level of tectonic activity – Smaller => not as active

•  Examples: – Mercury the least active, –  then Mars, –  then Venus and Earth


Role of Internal Activity

•  Internal activity affects the surface •  More activity => more lava on the surface •  More lava => features are erased more often

•  Internal activity also affects a planet’s atmosphere

•  volcanic gases are the most likely source of gases

•  Less activity => less gas


Role of Mass and Radius

•  Mass and radius affect atmosphere •  Low mass Mercury and Mars will have a

smaller source of gas than Venus/Earth •  the low surface gravity of these small planets

also means they will have trouble retaining the gases they generate

•  Examples: – Mercury the least atmosphere, –  then Mars, – Then Venus/Earth


Role of Sunlight

•  Heating depends on planet’s distance from Sun – closer => warmer further => cooler

•  Example: – Mercury daytime side is very hot (~427oC) – Mars daytime side is much colder (~20oC in

Martian Summer)


Role of Sunlight

•  Heat and high energy light from Sun can alter atmosphere – Break apart molecules – Drive off light gases

•  Example: – Mercury, lost most of the little atmosphere it had – Venus, UV breaks H2O apart with the H escaping

into space


Role of Atmosphere

•  While temperature affects the atmosphere, •  the opposite is also true…

•  Atmosphere affects the temperature: •  Warming by greenhouse effect •  Insulates surface

•  Examples: – Venus is hottest – Earth is warmer than Moon (at night)


Role of Atmosphere

•  Atmosphere can affect surface:

•  Protects against impacts •  Wind erosion covers impact craters

•  Examples: – Mercury, Mars, and Moon many impacts craters – Earth, Venus, not as many, not as visible


Role of Water Content

•  The water near Earth’s surface makes possible many chemical reactions not found elsewhere

•  Examples: •  Biological processes !!! •  CO2 removed from atmosphere by dissolving

in water

•  Water also causes large scale erosion


Role of Biological Processes

•  photosynthesis •  plants convert H2O and CO2 -> O2

– Earth’s atmosphere has oxygen

•  Planets cover and break down rocky surface

•  Animals (People) shape surface – atmosphere

•  Sea creatures turn CO2 into rock 57 Elizabeth Charlton, 2015

Combined Effects

•  Surfaces all started out smooth, •  then shaped by: •  cooling, tectonics, impacts, and erosion

•  they ended up with different surfaces


Combined Effects

•  Mars, Venus and Earth started with similar atmospheres – CO2 with traces of N2 and H2O

•  But were then modified by: •  sunlight, tectonic activity, and, in the case

of the Earth, life


Differences

•  Two main factors can be used to explain all of these differences

•  Planetary size

•  Distance from Sun


In-class Discussion

•  Discuss your answers in groups of 2 •  How would Mercury be different if it was

larger? •  How would Mars be different if it was

closer to the Sun?


Asteroids

Asteroids

•  remnants of planetisimals •  a small rocky fragment that orbits the sun •  too small to be planet •  doesn't orbit a planet

"(253) mathilde" by NASA - http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/nea_19970627_mos.html. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:(253)_mathilde.jpg#/media/File:(253)_mathilde.jpg

Composition

•  Some mostly rock •  Some mostly iron •  Some are a mixture of rock and iron

"InnerSolarSystem-en" by Mdf at English Wikipedia - Transferred from en.wikipedia to Commons.. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:InnerSolarSystem-en.png#/media/File:InnerSolarSystem-en.png

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