Module 4 Follow THE Water PDF

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ERSC 1P94 lecture, Astride Silis...

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MODULE 4: FOLLOW THE WATER Follow the Water -

Water = 2 hydrogen + 1 oxygen Hydrogen – most common element in universe Oxygen – 3rd most common

Physical States of Water -

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3 physical states: water, ice, vapour (steam) Temp at which state changes occur depend on atmospheric pressure Atmospheric pressure = weight of column of air acting on given surface, increases w increasing height of column of air o At sea lvl = 1 atm, 1.013 bars, 101.3 kilopascals o At Mt Everest summit = 0.337 bars, 33.7 kilopascals Phase Diagram used to characterise state changes w changing temp + pressure o Point T (triple point) – specific temp + pressure where 3 water phases are stable o Point C (critical point) – temp + pressure conditions great enough that liquid + steam indistinguishable from each other

Anomalous Properties of Water -

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Most substances contract (+ become denser) w cold & expand w warmth WATER is different – ice is less dense than water o Frozen water becomes solid + requires more volume o Density increases from 0-4 degrees C o Starts decreasing beyond 4 degrees C Solids dissolve in water (ex. Sugar, salt, minerals) o Salt reduces freezing point of water o Ions floating in water change conductivity

Water In Inner Solar System -

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Earth o 71% of earth covered in water o Avg ocean depth: 4km o Volume of water in oceans = 1.37billion km3 o Antarctica + Greenland + glaciers lock up water in ice form Mercury o No atmosphere, temp reaches 427 degrees C o Near the poles, ice may be found in dark holes created by craters are locations of eternal shade

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Water is left over from initial outgassing during planet’s formation/deposited on surface later during bombardment

Venus o Surface temp = 464 degrees C, but is dry heat so would not expect to find water o If water vapour in atmosphere condensed, layer on planet would only be 3 cm thick (compare to earth = 3km deep) o Probably had water earlier – lost by sunlight breaking up molecules in atmosphere that then escaped into space Mars o Had more water + was warmer 3-4 billion years ago  Lost 86% of early water o Possible large lakes in past w/in craters w channels like earth o Curiosity rover examining Gale Crater (154km wide)  GC notable for large (5.5 km tall) mound (Mound Sharp/Aeolis Mons) of layered rock  Found signatures of water-bearing clay, sulfate, iron oxide in mound which must have formed in wetter environment  Peace Vallis (outflow channel) also evidence of wetter environment  Alluvial fan – water going down outflow channel deposits large pebbles in fan shape when reaches flatter surface  Fluvial conglomerate – rocks composed of rounded, cm-sized pebbles (deposited from fast-flowing water)  Mudstone – thinly layered rocks composed of fine grains o Valles Marineris – location of past large lakes  400km long system of chasms 11 km deep  Floor of chasms filled w sediments (interior layered deposits)  Candor Mensa (a layered deposit) – located at centre, 8 km high  Lakes may have been frozen for much of time o Outflow channels + valley networks are evidence o Groundwater probably existed in past o Currently:  Ice form could be stable but would sublimate/vaporize if exposed to open air  Salty, briny solution seeps out of rocks & runs down slops, but was determined to not be liquid water

Water in Outer Solar System -

Jupiter + Saturn = large gas giants Uranus + Neptune = ice giants Gas Giants o Traces of water + methane, but no significant role o Jupiter  90% hydrogen, 10% helium

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Saturn  75% hydrogen, 25% helium Ice Giants o Rocky core surrounded by liquid mantle, gaseous atmosphere o Atmosphere has some water vapour, bulk of water is in mantle (also contains ices such as methane + ammonia) o Core of Uranus = 5,000 K, Neptune possibly higher o Core pressures double earth o Layer of superionic water (very conductive)  Has properties of both solid + liquid o Neptune has 15% chance of liquid ocean  Chance will increase when sun becomes cool white dwarf (few billion years) Icy Satellites o Voyager spacecrafts took pics of Jupiter + its larger moons  Moon Io has active volcanism  Not good candidate for water though bc it is hot and rocky  Europa is icy world + active, ice forms large % of mass Icy Geysers on Enceladus o Cassini did multiple fly-bys of one of Saturn’s moons, Enceladus o Eruptions on Enceladus not coming from single point-source vents like volcanoes  Material erupting from long fractures in icy shell  Material erupting is not pure water, contains amts of nitrogen, methane, carbon dioxide + hydrocarbons (propane, acetylene, formaldehyde)  Implies internal, salty, liquid ocean  Liquid ocean is global, extends around entire satellite o Cassini ended by plunging into Saturn o

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Tidal Heating -

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When large satellite orbits giant planet, gravitational interactions due to eccentricity of orbit deform surface of satellite by raising large tidal bulge on surface o Bulge is higher when satellite closer to large planet Provides energy to small icy satellites to melt parts of interior + keep it in liquid form Icy satellites covered in icy crust, believed to have rocky core & liquid/slushy mantle

Europa’s Sub-Surface Ocean -

Young surface (few craters) Surface can only be active if layer below it (mantle) is not solid/rigid Europa must have flowing mantle which could suggest sub-surface ocean 2 possibilities for interior o Liquid ocean

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o Solid icy mantle that convects (like earth) Estimate of ocean – saline (conductive), 25-100km thick

Pluto -

Avg temp -223C Water’s most likely form = ice Small mass so no expectation of internal activity (ex. Mantle convection) Not circling massive planet, so no good possibility of tidal heating New Horizon mission found possible ice volcanoes o Liquid erupting – not pure water, probably some kind of slushy mixture of water, nitrogen, methane or ammonia...