Astronomy 330 Exam 1
Good job! This class (Lecture 12): Average: 93.5% Moon Origins 25% of you >99%!
Next Class: Too easy? Life in the Solar System Don’t forget, there
is a chance to HW 4 is due Wednesday increase Exam 1 score on the final exam.
Music: We Are All Made of Stars– Moby
Question First Presentations
Exam 1 was a)! too easy. It didn’t challenge me. I felt like I wasted time studying for it. b)! too hard. (Really?) c)! just right. d)! too easy, but I like my exams like that. e)! okay, but it didn’t have enough interpretative dance components. Outline Drake Equation Frank That’s ? planetary systems/year Drake •! What’s up with the Earth? –! Mooned! •! What do we need for a life-suitable planet?
N = R* ! fp ! ne ! fl ! fi ! fc ! L # of # of Star Fraction Fraction advanced Earthlike Fraction Fraction Lifetime of formation of stars that civilizations planets on which that evolve advanced rate with commun- we can per life arises intelligence civilizations planets icate contact in system our Galaxy today 9 ? planets/ life/ intel./ comm./ yrs/ stars/ systems/ system planet life intel. comm. yr star
ne Our Solar System Terrestrial planets and Gas Giants… but how many are valid Complex term, so let’s break it into two terms: planets/moons for np? –! np: number of planets suitable for life per planetary system
–! fs: fraction of stars whose properties are suitable for life to develop on one of its planets
http://nike.cecs.csulb.edu/~kjlivio/Wallpapers/Planets%2001.jpg
X Earth-Moon Comparison Formation of the Earth
•! Earth formed from planetesimals in the circumstellar disk. •! Was hot and melted together. Radius 6378 km Radius 0.272 Earth •! The biggest peculiarity, Surface gravity 9.8 m/s2 Surface gravity 0.17 Earth compared to the other Mass 6.0x1024 kg Mass 0.012 Earth Distance to Sun 1.5x108 km Distance to Earth 384,000 km planets, is the large Year 365.2422 days Orbital Period 27.3 days moon. Solar day 1 day Solar day 27.3 days
A Double World The Moon
Why a “double world”? Earth and Moon The Moon's surface –! Most moons are tiny together is barren and dead compared to the planet from •! The Moon is over 25% the Voyager 1 –! No water, no air, some diameter of Earth (1977) water ice. •! Jupiter's biggest moons are about 3% the size of the –! No life!! planet –! The Moon is comparable to the terrestrial planets
•! About 70% the size of Mercury
•! Nearly the same density as Mars Formation of the Moon: Smack Why is this a good hypothesis?
•! The Earth has a large iron •! Collision of Earth with a Mars-sized core (differentiation), but the body early in the solar moon does not. system’s history –! The debris blown out of •! Iron-rich core of collision came from the rocky the impactor mantles sank within Earth –! The iron core of the impactor •! Earth’s rotation merged with the iron core of sped up Earth •! Compare density of 5.5 g/cm3 •! Remaining ejecta to 3.3 g/cm3— the moon thrown into orbit, coalesced into the Moon lacks iron. http://www.flatrock.org.nz/topics/odds_and_oddities/assets/extreme_iron.jpg •! http://www.youtube.com/watch?v=ibV4MdN5wo0&feature=related
Moon Impact on Life? Implications •!! Hot, Hot, hot, Hot! hot. Even if the moon theory is •! Some think that our large Moon is very important incorrect, other smaller bodies were playing havoc for life on Earth. on the surface. –! Tides! Important to move water •! When they impact, they release in and out of pools. kinetic energy and gravitational –! Stable Axial Tilt: 23.5 deg potential. offset from the collision •! In addition, some of the decaying –! Metals! Heavy elements at radioactive elements heated up Earth’s surface may be from core of impactor. the Earth– stored supernova energy! •! The planetesimals melt, and the Earth went through a period of http://www.michaelbach.de/ot/sze_moon/index.html differentiation. http://www.udel.edu/Biology/Wags/wagart/worldspage/impact.gif Planetary Differentiation Structure
•! Luckily, not all of the iron sank to the center, else we would be still in the Stone Age. Outer Core •! Temperature increases as you go deeper underground. From Inner Core around 290 K on surface to nearly 5000 K at center. Mantle –! Heated by radioactive decay Crust –! Supernovae remnants •! Earth’s magnetic field is established early on.. after the iron catastrophe… good for life.
Early Earth Question
Which of the following does NOT well describe the •! No atmosphere early Earth? •! No water •! High temp a)! So hot that the surface had molten rock. •! No life……. b)! There was no water. •! Big rocks keep c)! The surface kept getting hit by really, really big falling on my head… rocks. d)! The oxygen rich atmosphere caused quick oxidation (rusting) of iron-rich rocks e)! No chance of life at this stage.
http://www.black-cat-studios.com/catalog/earth.html Differentiation: The Crust Iron Catastrophe •! Outside layer of the Earth (includes oceans) floats on top •! Average density of Earth of still hot interior is 5.5 g/cm3 –! About 50 km thick •! Average density on the –! Coldest layer – rocks are rigid 3 surface is 3 g/cm •! Mostly silicate rocks •! So, something heavy –! Made of lighter elements like silicon, oxygen, and aluminum must be inside •! Oxygen and water are abundant •! When the Earth formed it was molten •! Excellent insulator –! Heavy materials (e.g. iron, –! Keeps the Earth’s geothermal heat nickel, gold) sank inside! –! Lighter materials (e.g. silicon, oxygen) floated to the top
Today’s Earth Surface Geologically Active Surface
•! 70% of the Earth's •! The young rocks on surface is covered the Earth's surface with water indicate it is –! Ocean basins geologically active –! Sea floors are young, •! Where do these rocks none more than 200 million years old come from? •! 30% is dry land – –! Volcanoes Continents –! Rift valleys –! Mixture of young rocks –! Oceanic ridges and old rocks •! Air, water erode rocks –! Up to 4.2 billion years old •! The surface is constantly changing
http://www.solarviews.com/cap/earth/earthgal.htm Recycling Bio-elements The Earth’s 1st Atmosphere •! From gravity and radioactivity, the core stays hot. •! This allows a persisting circulation of bioelements through •! The inner disk had most continental drift— melting of the crust and re-release through gases blown away and the volcanoes. proto-Earth was not massive •! Otherwise, certain elements might get locked into sediment enough to capture these layers– e.g. early sea life. gases. •! Maybe planets being formed •! Any impacts (e.g. the moon), now, with less supernovae, would have blown any would not have enough radioactivity to support residual atmosphere away. continental drifts and volcanoes. •! The first atmosphere was (Idea of Peter Ward and Donald probably H and He, which Brownlee.) was lost quickly. http://www.pahala-hawaii.com/j-page/image/activevolcanoe.jpg
http://www.udel.edu/Biology/Wags/wagart/worldspage/impact.gif
The Earth’s 1st Atmosphere Our Atmosphere
•! The interior heat of the Earth helped •! Rocks with ages greater than with the Earth’s early atmosphere. 2 billion years show that there was •! Volcanoes released gases (water vapor little or no oxygen in the Earth’s and CO2) atmosphere. •! Another scenario is that impacted comets released – water (H O), •! The current composition: 78% 2 nitrogen, 21% oxygen, and trace carbon dioxide (CO2), and Nitrogen (N2) – the first true atmosphere. amounts of water, carbon dioxide, •! The water condensed to form the oceans etc. and much of the CO2 was dissolved in •! Where did the oxygen come from? the oceans and incorporated into •! Cyanobacteria made it. sediments– such as calcium carbonate http://www.uweb.ucsb.edu/~rixfury/conclusion.htm (CaCO ). –! Life on Earth modifies the Earth’s 3 atmosphere.
http://www.fli-cam.com/images/comet-liner.jpg This New Planet Evidence of Impacting
•! Mostly oceans and some solid land (all volcanic). •! Frequent impacts of remaining planetesimals (ending about 3.8 billion years ago). •! Impacts would have sterilized the young Earth– Mass extinctions and maybe vaporized any oceans (more comets?).
http://www.agnld.uni-potsdam.de/~frank/Images/painting.gif http://www.solarviews.com/browse/vss/VSS00105.jpg
This New Planet Question
The Earth’s first atmosphere was
a)! much like today’s atmosphere, but older. b)! Trick Question. There was no atmosphere. c)! likely just H and He, and blown away quickly. d)! made from comets. e)! a combination of volcano gases and comet collisions. Water Water as a Solvent
•! The water molecule is “polar”. The oxygen atoms have more build-up of negative charge than the hydrogen. This •! Water is a key to life on Earth. allows water molecules to link up, attracted to each other. •! Primary constituent of life– “Ugly bags of mostly •! In this way, water attracts other molecules, surrounds them water” and effectively dissolves them into solution. –! Life is about 90% water by mass. •! Primary role as a solvent –! Dissolves molecules to bring nutrients and remove wastes. Allows molecules to “move” freely in solution. –! Must be in liquid form, requiring adequate pressure and certain range of temperatures. •! This sets a requirement on planets, if we assume that all life requires water.
Example: Dissolving Table Salt Water: Our Liquid Friend
The partial charges of the water molecule are attracted to the Na+ and Cl- •! A very good temperature buffer ions. The water molecules work their way into the crystal structure and between the individual ions, surrounding them and slowly dissolving the –! Absorbs significant heat before its temperature changes salt. –! When it vaporizes, it takes heat with it, cooling its original location
•! It floats. –! Good property for life in water. –! Otherwise, a lake would freeze bottom up, killing life. –! By floating to the surface, it can insulate the water somewhat.
http://www.visionlearning.com/library/module_viewer.php?mid=57 Keeping it Useful: Atmosphere Keeping It Warm, but not too Warm
•! Need to have enough pressure to keep water from boiling •! What controls a planet’s away at low temperature temperature? –! Cooking at higher elevation requires more time. Boiling point lowered: water doesn’t –! The amount of light get as hot. received from its star. –! If pressure too low, water goes directly from
ice to vapor (like dry ice CO2) –! The amount of energy •! On the other hand, high pressure may the planet reflects back. make life more difficult to form. –! And any Greenhouse •! In addition, the range of temperature for Earth based effects of the complex life is less than 325K. planet.
http://www.astro.su.se/~magnusg/large/Boiling_water.jpg http://www.solcomhouse.com/Greenhouse_Effect.gif
Greenhouse Explained Keeping It Warm, but not too Warm
•! Earth’s greenhouse effect raises the temperature by about 15%. •! Given a star’s luminosity, a range of acceptable temperatures translates into a range of distances to the star. •! This range is called the star’s habitable zone (HZ), as planets in this range have temperatures suited for life. •! Only a rough guideline.
http://www.solcomhouse.com/Greenhouse_Effect.gif Habitable Zones– Galactic Habitable Zone Are you in the Zone? •! Long living star •! Planets with stable orbits (thus stable temps) •! Likewise the galaxy •! Liquid Water Mars has regions that are •! Heavy Elements– C, N, O, etc. better suited to life. •! Protection from UV radiation Earth •! In the inner regions of Venus our galaxy, Mercury supernovae are too frequent. •! In the outer regions, there are too few metals.
The Sun http://astronomy.swin.edu.au/GHZ/GHZmovie.html 0.5MSun star
Question The Sun’s Variation
The Greenhouse effect •! As the Sun ages, it gets slightly brighter. •! When it was younger, its luminosity was 70% current values. a)! will destroy our planet. •! A young Earth should have been 20K colder– iceball! b)! will hopefully stop this crazy winter. •! During our ice ages, the temperature only changed by c)! keeps the Earth warmer than it would be about 1%. otherwise at its distance from the Sun. d)! is all Man-Made. e)! keeps the Earth colder than it would be otherwise
at its distance from the Sun. http://www.cherishclaire.com/iceball.htm The Sun’s Variation Earth’s Atmosphere: Trapping CO2 for Fun and Profit •! There is evidence that the Earth did nearly freeze over– 2.8 billion years •! Most recent studies suggest an efficient planet negative-feedback ago and 700 million years ago. mechanism (like a thermostat). –! CO2 cycles from atmosphere (greenhouse gas) and oceans (buried •! Probably changes in the Greenhouse sediment especially carbonate rock). gases. –! CO2 in atmosphere: temporarily dissolved CO2 in rainfall reacts •! This implies that the habitable zone with weathered rocks, trapping it. can vary with time, thus the real habitable zone is smaller than shown •! Negative feedback process before? –! Increase in temperature: evaporation of oceans, more rainfall, more weathering and CO2 •! Some have postulated that real zone is reduction, so decrease in temperature. only 0.95 to 1.01 AU! If the Earth –! This negative feedback stabilizes the were 1% farther away– Iceballed. http://www.soest.hawaii.edu/gerard/GG108/images/bylot.jpg Earth’s temperature. And np would be very small ~ 0.1.
http://www.wildtech.org/images/feedback.gif
Life Adds to Feedback Life in the Solar System?
•! Life increases the weathering of •! We want to examine in more detail the backyard of rock. humans. •! J.E. Lovelock has proposed that •! What we find may change our estimates of n . life also stabilizes the planet e temperature. •! Regardless, the negative feedback helps with the habitable zone, so we can estimate perhaps np is more around 1– more Earth chauvinism? Earth – Venus comparison What We Used to Think
Venus must be hotter, as it is closer the Sun, but the cloud cover must reflect back a large amount of the heat.
In 1918, a Swedish chemist and Nobel laureate concluded: •! Everything on Venus is dripping wet. Radius 0.95 Earth •! Most of the surface is no doubt covered with swamps. Surface gravity 0.91 Earth Venus is the hottest •! The constantly uniform climatic conditions result in an Mass 0.81 Earth entire absence of adaptation to changing exterior conditions. planet, the closest in Distance from Sun 0.72 AU size to Earth, the closest Average Temp 475 C •! Only low forms of life are therefore represented, mostly no in distance to Earth, and Year 224.7 Earth days doubt, belonging to the vegetable kingdom; and the the planet with the Length of Day 116.8 Earth days organisms are nearly of the same kind all over the planet. longest day. Atmosphere 96% CO2 http://www.daviddarling.info/encyclopedia/V/Venuslife.html
Turns Out that Venus is Hell Our “Twin”
•! The surface is hot enough to melt lead •! Always covered in thick clouds of CO , which • There is a runaway greenhouse effect 2 ! make it the hottest planet •! There is almost no water in the Solar System. •! There is sulfuric acid rain •! Pressure on surface is 90 •! Not a place to visit for Spring Break. times that on Earth– like 1 km under the sea
http://antwrp.gsfc.nasa.gov/apod/ap960923.html Our “Twin” Soviet Satellites on Venus •! Often called the morning star or the evening star. 3rd brightest object in the sky. •! Often mistaken for a UFO. •! Retrograde rotation – Sun rises in west •! No moons, no magnetic field
Mostly Basalts-like rocks, indicative of volcanoes http://antwrp.gsfc.nasa.gov/apod/ap960923.html
The Venusian Surface Revealed Surface of Venus: Radar
•! We can’t see Venus’ surface in visible light, clouds block the view •! Magellan’s Radar showed the surface •! Most of surface is smooth lava flows •! Many large volcanoes •! Probable ongoing http://www.solarviews.com/cap/venus/vidven1.htm volcanism Venus: surface features
10,000 km
Maxwell Montes (65N 5E) (Highest mountain range in the solar system 11km high– Everest is 8km)
http://www.geology.smu.edu/~dpa-www/venus.html