Final Exam-Astro
Habitability factors
1. distance from star 2. size 3. surface atmosphere- necessary to protect against harmful solar radiation
3 giants of early rocketry
Konstantin Tsiolkovsky (Russia), Hermann Oberth (Germany), Robert Goddard (American).
rocket equation
describes how a vehicle's final speed depends on the propellant's velocity. realized it would be hard for a rocket to reach escape velocity: speed necessary to overcome gravity and leave earth
spacetime
four-dimensional universe, three dimensions of space and one of time
Stars brightness depends on
(1) its distance (2) intrinsic luminosity (3) the dimming effects of any interstellar dust that might lie between use and the star. Because the cones of our retinas do not work well in low light, looking at stars with the naked eye is a poor way to judge their hue. But any colour photograph of the stars will show a range from blue to red. So knowing stars spectral type will tell you its surface temp.
Project rover, project orion, project daedalus
-1960's NASA confident Project Rover to send humans to Mars but political climate changed, US abandoned plans -Nevada:higher speeds-toss small nuclear fusion bomb out the rear and let the resulting explosions push the craft forward- expensive and require exception to internation treaty banning nuclear detonation in space. -Britain: shoot frozen fuel pellets of deuterium and helium-3 into a reaction chamber where they undergo nuclear fusion. Fuel pellets shot into the chamber at 250/s. Encouraged to fuse by electron beams, producing rapid fire series of explosions to propel the ship.
Venus is about 30% closer to the sun than earth, and this difference was enough to be critical
-Earth:cool enough for water to rain down to make oceans in which CO2 could dissolve and undergo chemical reactions that locked it away in carbonate rocks -Venus greater intensity of sunlight made it just warm enough oceans either never formed or soon evaporated. Without oceans to dissolve co2 and make carbonate rock, co2 accumulated in atmosphere, leading to a runaway GH effect, which resulted in the extreme temps of Venus today
Consequence of warmer temps on Venus
-Higher water vapour in atmosphere- stronger GH effect, warmer temps, so more water vapour in atmosphere (+feedback loop). -UV dissociation of H2O molecules in atmosphere. -insufficient H2O to dissolve CO2 into oceans, rocks- CO2 builds up from outgassing, runaway GH effect. -lithosphere continuously loses water over planets lifetime- crust becomes thick and rigid, no plate tectonics
Reasons to colonize
-become extinction proof -if star moved out of habitable zone would be forced to move - we colonize because of our species general tendency toward aggression -intelligent life could have had up to 5 byr longer than us to develop
Nebular Theory Success
-explaining solar system: two kinds of planets, and circular orbits -explaining existence of other planetary systems Modifications: extrasolar planet observations were incomplete. Migration and gravitational encounters may be more important than previously believed
transit and ellipse- indirect method #3
-fraction of planetary orbits are aligned edge-on such that the planet passes directly in front of the star at regular times-block small fraction of starlight -half an orbit after a transit, the planet passes behind its star-block radiation from the planet Measure combined light from star and planet, so there will be a dip in brightness whenever either object blocks light from the other.
Inner boundary vs. outer boundary
-if a planet were any closer to the sun, a runaway GH effect would be triggered -if a planet were any farther from the sun, surface water would freeze. runaway GH effect would occur if earth were anywhere inside 0.84 AU from the sun, or about halfway between the orbits of Venus and the earth.
Most occupied regions
-s-shaped curve:stable stars fusing hydrogen in their cores- overwhelming amount of stars fall into this category. Sun is referred to as average star, even tho it is more massive than majority of stars -top right are giants and their somewhat bigger brethren, the supergiants-mostly cool and red, but very luminous. At the end stages of their lives, already exhausted their core hydrogen -bottom left are hot but dim white dwarfs- collapsed remains of stars that have exhausted fuel and slowly turning to ashen.
2 things in universe are absolute
1) laws of nature are the same for everyone; 2) speed of light is the same for everyone
Direct imaging of planets around other stars is very difficult
1. Stars are far away, which makes the angular separation between star and planet very small 2. planets much fainter than stars, so light from planets is easily overwhelmed by starlight. All planets reflect sunlight in the visible range-Jupiter would be the brightest planet when seen from afar. The Sun is about a billion times brighter than Jupiter, so , the glare of scattered starlight easily overwhelms the small blips of planetary light!
Direct imaging at present only works if
1. The planet is fairly far away from its parent star 2. The star is relatively close to us 3. The planet is relatively bright compared to its parent star 4. and/or we can "mask" or reduce the starlight efficiently without reducing the light from the planet.
2 reasons for lack of water on Venus
1. Venus never had much water in first place- unlikely b/c planets should have accumulated from planetesimals of similar conditions 2. venus once had more water but somehow lost it- lots of impact craters spaced evenly- surface is all roughly same age
While today's radio SETI experiments are vastly more sensitive and comprehensive than Drake's pioneering Project Ozma, they have been limited by two important constraints
1. all projects until now have used telescopes that are also in service for other astronomical research-get only limited observing time. one major advantage of an array, compared to single-dish radio telescope, is that it can be electronically focused on several stars simultaneously-speeding up the search. 2. terrestrial radio interference, is more difficult. This interference greatly hinders SETI searches, because tele-communications satellites, aircraft, and Earth-bound radar produce lots of narrow-band signals.
2 basic ways to search for extrasolar planets:
1. directly: obtaining an image (or spectrum) of planet directly. More preferable because it can tell us far more about the planet's properties. Direct imaging of planets around other stars is very difficult. 2. indirectly: establishing the presence of planet by its effect on the star
Is intelligence common-2 opposing schools of thought
1. intelligence that is comparable to our own to be unlikely. Life has existed for 3.5 billions years, but only in last few mill years has life developed the capability to understand environment, and only within last half-millennium have understood the nature of Earth and begun exploration of the cosmos. Life seems to have arisen as a number of chance events. 2. there is evolutionary pressure for intelligence; various evolutionary mechanisms consistently encourage an increase in intelligence for a wise range of species. But we're the only species on our planet so no other known species directly supports the view that the evolution of technological intelligence is likely.
two possible ways in which it might lose its atmosphere
1. large impacts can blast significant amounts of atmospheric gas into space. 2. solar wind can strip atmospheric gas from any planet that lacks a global magnetic field`
fermi-hart paradox has two ideas:
1. neither we nor our planet in any way special suggests that someone should have colonized the galaxy by now 2. galactic civilization implies that we should be surrounded by evidence of this civilization-but this evidence does not exist
Early experiments were doomed for two reasons:
1. no martians sophisticated enough to assemble radio transmitters 2. these pioneers listening attempts were all made at the wrong spot on the radio dial-low frequency would have trouble penetrating Earth's ionosphere (layer of upper atmosphere that consists of particles ionized by sunlight).
two types of nuclear reactions that can generate power
1. nuclear fission: involves splitting of large nuclei such as uranium and plutonium. When uranium nucleus is split, approximately 0.07% of its mass is turned into energy. 2. nuclear fusion: power from sun and other stars is about ten times as efficient as fission. Hydrogen into helium converts about 0.7% of the hydrogen mass into energy.
Most common to be in binary star system. 3 possible situations to consider for planetary orbits in a binary star system:
1. planet could orbit around both stars. If the planet orbits stellar pair at a distance considerably greater than the separation between the two stars, then gravitationally the two stars act as one, and the planet can orbit w/o disruption around its distant twin hosts 2. a planet could orbit one star or the other. If the two stars are widely separated, then a planet near either one can't orbit steadily because it will feel little disturbing effect from the second star. 3. planet may try to orbit between the two stars, however if distance between the planet and at least one of the stars is not sufficiently different from the distance between the two stars-orbit won't be stable. Planet gets competing gravitational tugs from both stars that ultimately fling it out of the system
Nikolai Kardashev suggested that there might be 3 distinct categories of civilization
1. planetary (or type I) civilizations: use the resources of their home planet-us 2. stellar (or type II) civilizations: corral(gather together) the resources of their home star 3. galactic (or type III) civilizations: which employ the resources of their entire galaxy. Civilizations in the third category are so advanced that they might be hard for us to imagine
There are enough M stars to host a large number of inhabited worlds. This thought has two objections:
1. planets orbiting close to a star get locked into synchronous rotation, with one side of the planet perpetually facing the star. Once this happens, the side away from the star becomes perpetually dark, and the atmosphere might be expected to freeze out 2. small stars have frequent and energetic flares (sudden bursts of intense light and radiation) that might cook any complex life. Flares dangerous UV light might actually cause the production of a protective layer of atmospheric ozone, in much the way we have described for worlds orbiting stars of types A and F.
3 science fiction ideas
1. putting crew in suspended animation so don't worrying about long travel- don't know how to do this but have identified genes in animals to put them in hibernation 2. allow travelers to live long enough to cruise galaxy- depends on advance in medical technology 3. build enormous craft to accommodate large crew "ark"- very long voyages often end badly- fighting, also worry about deterioration of level of expertise of the crew.
Alien signals fall under 3 categories
1. signals used for local communication on the world where intelligent beings live. Our radio and television signals fall into this category, because they are designed for our own use and not for interstellar communication 2. signals used for communication between a civilization's home world and some other site- signals comparable in strength to those we currently use for communicating with our own interplanetary spacecraft. 3. intentional signal beacons
3 Caveats to habitable zone
1. this is based on range of distances at which worlds similar to earth could exist 2. Moon is located at essentially the same distance from the sun as earth but it is not habitable- planet's size matters 3.zones evolve with time, because stars tend to brighten as they age, so expect a star's habitable zone to move outward over time
3 solutions to fermi-hart paradox
1. we are alone 2. civilizations are common but no ones has completely colonized the galaxy- technological difficulties; sociological considerations-no desire to explore; self-destruction- many arose but destroyed themselves 3. galactic civilization- but deliberately avoided revealing its existence to us
Is CO2 cause of global warming- must look at 2 factors
1.correlation- evidence that temperatures rise and fall with CO2 concentration. 2. if there is a correlation, does this imply causality- Correlations do not automatically imply causality: often, they may be coincidental or attributable to some underlying commonality
3 ways habitability might present itself outside HZ
1.small pockets of subsurface groundwater (Mars)-water would be kept liquid by geological conditions rather than solar heat 2. subsurface oceans (Europa): some moons contain large amounts of water ice. Orbital resonance contribute to tidal heating on Io, Europa, Ganymede, Enceladus happens in any system with multiple moons. Heat from radioactive decay could also melt ice 3. surface habitability on earth-size planets outside HZ-possibly have its own internal heat to keep surface warm enough for liquid water if the surface were protected by a thick hydrogen atmosphere- not possible on planet in our solar system, because solar heat would cause the hydrogen to escape into space fairly rapidly.
sunlight was less intense on all the planets when they were young
4 byrs ago, the intensity of the sunlight was probs only 40% greater than it is on earth today. rain might have fallen on Venus, oceans could have formed- life might have been transported from meteorites.
Venus GH effect
470 degrees surface temp night and day, no liquid water, thick atmosphere- runaway GH effect. Immediate cause of heat is GH effect- atmospheric CO2, 200,000x as much CO2 in atmosphere than earth. Air pressure is weight of everything on you at this elevation.
Habitable zone
A zone in which the surface temperature of a planet could allow it to have abundant liquid water on the surface- goldilocks zone is just right. Life could exist outside this zone but difficult to detect
How did SETI begin
As the twentieth century dawned, 2 pioneers of wireless technology became convinced that they had heard aliens on the airwaves. One of these pioneers was Guglielmo Marconi- celebrated as the man who sent first transatlantic radio message. The other was Nicola Tesla- invented use of AC for transmitting electrical power rather than using copper wire.
Galactic habitable zone
Believe there is a relatively narrow ring at about our solar system's distance from the centre of the Milky Way Galaxy that makes up a galactic habitable zone. Supernovae are more common in the more crowded, inner regions of the galactic disk, making it more likely that a terrestrial planet would be exposed to the intense radiation from one of these stellar cataclysms. Radiation from supernovae could be beneficial by increasing rate of mutations and accelerating pace of evolution.
Von Neumann Machines
Beyond simply sending out individuals robots we can expect to send more sophisticated robots in the future. Would then go to another world and build other robots- self-replicating. Because colonization would require technology slightly beyond our own, these should be widespread so Tipler concluded we are alone and so SETI is a waste of time.
one problem: with higher temp A and F stars emit many times as much UV light as does the sun
Biology is vulnerable to UV light because it breaks apart chemical bonds- 2 ways around this problem 1. UV radiation does not penetrate far into the ground, oceans, or ice. If life on Earth emerged near volcanic vents same thing might happen on watery planet near A or F star. 2. even though our sun emits far less UV light, it still emits enough to make earth's land surface sterile if not for the shielding provided by the ozone layer in the atmosphere. The additional UV light would split more atmospheric O2 molecules, producing single oxygen atoms that would then combine to form ozone.
Have another problem before the sun dies out
Brighter over time, stronger it is, habitable zone will move but we are on the inner edge of the calculations, but as things get hotter just the right spot is going to move
M1207 & 2M1207 b
Brown dwarf. Planet itself is warm (1600 K) presumably due to gravitational contraction-meaning its relatively bright in the infrared. Spectrum of planet indicates presence of water. Only time will tell whether it is really a planet-orbital period = 1700 years.
rockets today
Chemical rockets- engines ignite and burn a chemical fuel: mix of oxygen and kerosene. Chemical burning creates hot gas, expelled through a narrow nozzle propelling the spacecraft. Mass ratio: mass of the fully fueled rocket divided by the rocket mass after all the fuel is burned 39(38 + 1:1)- attain escape velocity- 11km/s and fuel that weighs 38x rest of rocket.
Carl Sagan
Considered a hypothetical rocket steady 1g- acceleration that would feel comfortably like gravity on earth- would bring ship closer and closer to speed of light. As ship gets closer to the speed of light mass becomes greater so same rocket thrust generates even less additional speed. Would take infinite energy at last step and infinity doesn't exist
Why is interstellar travel so difficult
Distance- only in 19th century did astronomers develop instruments of person adequate to measure the distances of the closest stars besides the sun.
all stars are born with basically same composition (98% hydrogen and helium)
During hydrogen-fusing phase a star's surface temp and total luminosity are determined by the star's mass. Star's mass tells us how much hydrogen fuel it has available for fusion, while its luminosity tells us how brightly the star shines and hence how rapidly it is fusing its hydrogen.
EQ line graph
EQ=1 means brain mass proportionate to body weight. Heavier animals have heavier brains- If brain mass is above this line, reasonably suppose that they are capable of elaborate behaviour. Those who fall below the line are less mentally agile than average animals in this sample. For extinct species, since we can often estimate their total body masses, we an gauge their brain masses from the volume of their fossil skulls.
Global warming
Earth's global average temperature is currently on the rise, a trend referred to as global warming.co2 is a GH gas that can enhance the GH effects and cause a rise in planet's surface temperature, and human activity is adding CO2 and other GH gases to earth's atmosphere. Due to human activity last decade has been hottest on record
Earth's water and CO2
Earth's temp remained cool enough for liquid oceans to form. Oceans dissolve atmospheric CO2, enabling carbon to be trapped in rocks CO2 content of oceans = 60 ⋅ atmosphere's CO2 content of rocks = 170,000 ⋅ atmosphere's
Detecting earth biosignature
Earthshine: doubly-reflected light from the dark side of the moon. Contains an imprint of earth's biological signature.
Arecibo Message
Encoded as 1679 frequency flashes= 23*73 (prime numbers), sent to M13 globular clusters (25,000 ly away). Information encoded- shot message to M13 cluster where there are a bunch of stars. Mostly technical details- 5 atoms in DNA; chemistry and structure in DNA; human population, shape, and size; location of earth in solar system; pictograph of sending telescope
Einstein's special theory of relativity is impossible to travel through space faster than the speed of light.
Even at this remarkable speed, light takes time to travel the vast distances between the stars, which is why we measure stellar distances in light years. c =300,000 km/s- 8.8 yrs for round trip to alpha centauri, 100,000 yrs across galaxy
Lagrange Points
Five positions in space, where effects of gravity from earth and the moon cancel in such a way that, if you floated weightlessly at one of these five points, you wouldn't be tugged toward either body. three of them are on a line passing through the centres of earth and the moon an that the other two are located 60degrees to either side of the moon. Latter two positions, are stable which means if you started at these points and drifted slightly away the competing effects of gravity from earth and the moon would bring you back to your starting point.
In 1950s and 1960s teams of academics met to study the most interesting of the UFO reports.
For a majority of the sightings, the investigators could not deduce what had been seen, but their overall conclusion was that there was no reason to believe that UFOs were either highly advanced Soviet craft or visitors from other worlds. UFO reports tell us nothing more than the fact that people sometimes see things in the sky that they are unable to identify or explain.
Energy in starlight falls off with the square distance from the star
For a planet to receive as much radiant energy as earth from a K star having one-fourth the sun's luminosity, the planet would have to orbit its star at one-half earth's distance from the sun. If star has luminosity 1% of the sun's, a similar planet would need to orbit at a distance 1/10 of earth's distance from the sun, which means it would follow and orbit about 1/4 the size of mercury's.
1961 first scientific conference on the search for extraterrestrial intelligence was held in Green Bank, West Virginia
Frank Drake was at this conference and tried to summarize the factors that would determine whether any attempt to detect intelligent extraterrestrials could succeed
G, K and M stars
G stars, make up another 7%, like our sun and prove that these have habitable planets. Need to consider the smaller suns K and M which make up 90% of all stars in the universe. K and M have long lifetimes so no limit on their ability to evolve life. 75% are M stars, because of their long lives, every M star ever born is still shining and the fact that small stars are born in larger numbers than more massive stars. Could probably support life- since they live so long could house galaxy's oldest biology
1926
Goddard lauches first liquid-fueled rocket from a field in massachusets- reach 13m. rapid development of rocketry followed the war was driven largely by german scientist who has been recruited by both the russians and the americans
Some other, unknown biological or physical barrier to interstellar travel may exist
However neither energy considerations nor lurking dangers would be enough to stop civilization from sending out self-replication Von Neumann machines.
The first thing to do would be to look for repetition
If aliens really wanted us to detect and decode their signal, they would repeat the entire broadcast many times, since otherwise we'd have to be listening at just the right moment to catch the signal. It might be that we would never be able to understand an alien broadcast.
Radio waves
In general, it requires far less energy to send an interstellar signal via radio than via visible light, so researchers guessed that radio would be the aliens' technology of choice. The way our atmosphere is built allows radio waves to travel. Atmospheric capacity will let light in. Because of long wavelength of these radio waves, need to build large telescopes
EQ (encephalization quotient)
In principle, we can test whether intelligence is evolutionarily favourable by measuring the brain power of a variety of animal species over time. Those animals that have brain mass falls on this line are said to have an EQ (encephalization quotient) of 1, which means a typical allotment of mental ability for creatures of their size.
According to many psychologists, such abduction experiences are probably attributable to sleep paralysis
It seems quite reasonable to imagine that a small percentage might believe they had experienced some type of alien abduction. The one thing going for the claims of ancient visitation is that they at least attempt to rely on archaeological artifacts that can in principle be studied by anyone.
Kepler-10b
Kepler-10b is orbiting a star very much like our own Sun, but with an age greater than 8 billion years, at a distance of 560 light years. Kepler-10b is the smallest exoplanet discovered to date and the first unquestionably rocky planet orbiting a star outside our Solar System.
1920's
Marconi stated he had picked up signals that came from extraterrestrial intelligence. These experiments culminated in 1924, during one of the periods when Earth and Mars were closest to each other in their orbits. Marconi and others encouraged anyone with radio set to listen for martian broadcasts, and even the U.S. army joined in the search-mistook thunderstorms- distant lighting whispers for Martians
Drake Equation
N = Nhp x flife x fciv x fnow. Look for civilizations within our own galaxy, if we want to explained to the entire universe multiply the number we find by 100 billion. Nhp- # of habitable planets in the galaxy- can be answered by astronomy, planet frequency in stellar habitable zones (10%-30%) flife- fraction of habitable planets, inhabited- if life is probable (100%), so far no evidence (0%) fciv- This gives us a way to calculate the # of civilizations capable of interstellar communication, there has been plenty of time for evolution to work on numerous planets fnow- fractions of civilization-bearing planets that happen to have a civilization now. Only interstellar communication available for 60 years-if typical likely to find a signal at random time would be 1 part in 170million
Gravitational Tugs
Newton's version of Kepler's laws tells us that two bodies will orbit their center of mass. This means that planets are not orbiting the Sun, but are orbiting the center of mass of the Solar System. Sun is orbiting the center of mass too. Allow us to determine planets distance, mass, orbital characteristics
O-stars, B-stars
O stars don't last long enough to allow the formation of earth-sized planets. We can also rule out stars of type B, although lifetime is long enough, the star's death would probably occur before the process of accretion had settled down long enough for life. These are rare.
cattle mutilations and the reputed killings of various small animals by short, bipedal creatures have been attributed to alien activity.
Only evidence connected to these attacks to extraterrestrial beings is uncertainty over who or what is doing the killing. The lack of confirmed culprit does not mean we are seeing the work of aliens.
optimistic estimate vs. conservative estimate
Optimistic: inner boundary may be 0.84 AU if no runaway GH effect. Sufficient GH warming would be 1.7 AU. Conservative: 0.95 AU if we allow for water loss by a moist GH effect. No CO2 snow <1.4 AU
Fermi-Hart Paradox
Our Galaxy is about 100,000 lyrs across. Though the laws of physics may prevent travel at speeds greater than the speed of light, an advanced civilization could reasonably be expected to travel, 1% of the speed of light. At this speed, even going to neighbouring star and taking time to colonize each system, one could get across the galaxy in say 100,000 trips (civilization could spread across the galaxy in 20 mil yrs). Reason you can't get to speed of light, last step would take infinite amount of energy, and infinity does not exist.
E.T. Kepler
Over a period of 12 years, this star wobbles around a point. Looks like a gravitational tug so there must be a planet! E.T. Kepler's third law says the period of a planet and its distance are related - a period of 12 years means there must be a planet orbiting at an average distance of about 5.2 AU- given this must have mass of 1.9x10^27 for centre of mass to be outside star. Also not moving at constant speed, therefore has eccentricity of 0.05
4 planetary probes travelling away from the solar system
Pioneers 10 and 11 and Voyagers 1 and 2. Pioneer 10 took 12 months to reach jupiter- first to attain escape velocity from the solar system. Would take 115,000 yrs to get to nearest star alpha centauri
because the spacecrafts themselves should survive unscathed for millions of years in the near-vacuum of interstellar space, we have included messages in case any extraterrestrial beings someday find them
Pioneers probes carry plagues of man and woman as well as diagrams of giving the layout of the solar system and our general location in the galaxy. Voyager carries messages of pictures, multilingual greetings, and two dozen musical selections on a gold-plated copper record.
Bright planets
Planets emit primarily at infrared wavelengths and are thus much brighter in the infrared! At infrared wavelengths, a star is "only" a thousand to a million times brighter than the planet.Young planets tend to be hotter, so even brighter in the infrared! This still looks bad, but at least it improves our chances for finding planets
1911, Hertzsprung plotted colours and luminosities of stars in two clusters
Pleiades and Hyades- stars not scattered at random but fell into two broad categories: (1) most in swath running diagonally through the diagram, named main sequence; (2) nearly all remainder were in a part of the diagram he called the giants.
Caveat to doppler effect
Reveals only the part of a star's motion directed toward or away from us. If we view orbit face-on, no doppler shift. We have precise determination of the period and the orbital shape, but the mass of planet we determine from amplitude is the lowest possible mass, so mass likely larger than determined by doppler effect. This has found planets orbit close to their stars and has not found any planets with earth-like masses--may be selection effects
By 1687, newton described how rockets work
Rockets work by vaporizing fuel that is shot out the back. Its newtons third law of every force having an opposite reaction force that causes the rocket to move
Neutrinos and Gravity waves
Some people have also suggested that advanced civilizations might send messages via the ghostlike subatomic particles called neutrinos or via the gravity waves that Einstein predicted by that we have not yet directly detected- however, might involve physics that might not be discovered, or might use ways of disguising signals so that our detectors cannot distinguish them from natural background signals
Changes in sun's habitability
Sun's was about 30% since sun's birth 4.5 byrs ago b/c core temp has increased. sun shines by fusing hydrogen into helium- makes core denser. Each fusion reaction converts 4 hydrogen nuclei into 1 helium nucleus. The total number of independent particles in the solar core gradually falls with time. The slow shrinkage gradually increases the core temp. Gradual temp increases causes a corresponding increase in the fusion rate, which is why the sun slowly brightens. The habitable zone gradually moves outward from the sun. Sun will die in about 5 byrs.
1901
Tesla noted that his apparatus was picking up electrical disturbances, which he ascribed to interplanetary communication. That same year, Marconi successfully sent a radio signal across the Atlantic, proving that this invention was useful for communication over large distances.
Jupiter's tug
The centre of mass between the sun and jupiter lies just outside the sun's visible surface. b/c sun and jupiter are always on opposite sides of the centre of mass, sun must orbit this point with same 12-year period, so sun orbits this centre of mass in 12 years too. With precise measurements could detect this orbital movement of the sun and thereby deduce the existence of jupiter without ever seeing this planet.
radial velocity curve
The period we see in the radial velocity curve tells us the average distance of the planet through Newton's version of Kepler's 3 law. At that distance, a more massive planet will cause larger velocities, so the amplitude of the variations tells us the planet's mass. The shape of the radial velocity curve tells us the shape of the planet's orbit.
Planetary migration may have important implications for the question of whether solar systems can harbour life.
Theoretical work suggests that even if terrestrial-size planets were born in these systems, they could face severe problems, because the migration of a large planet might disrupt the inner solar system. If migration occurs before terrestrial planets have finished forming, the material that would have accreted onto the terrestrial worlds might be swallowed instead by the larger world. W/o migration we expect rocky planets to form and to remain stable orbits, and many of these orbits should be within the habitable zones of their stars.
In 1959, Giuseppe Cocconi and Phillip Morrison wondered how difficult it would be to send radio signals over interstellar distances
They realized that the galaxy is considerably older than our solar system and consequently that there could be civilizations among the stars that have been around far longer than ours-surviving for many millions of years. Instead of searching all frequencies turned receivers to: 1420 MHz
Leading hypothesis for Venus losing water
UV light broke apart water molecules in atmosphere. Hydrogen atoms escaped through thermal escape. Oxygen molecules lost to some combination of chemical reactions with surface rocks and stripping by solar wind- no magnetic field because of slow rotation
Plate tectonics may be necessary to long-term habitability
Venus's lack of plate tectonics might be caused by its runaway GH effect- high temps baked water out of the rock in Venus's crust and upper mantle, making the crust too stiff to allow subduction and thereby suppressing plate tectonics
why did Venus keep its atmospheric co2 and earth did not?
Venus: all co2 in atmosphere, lacks co2 cycle because no liquid water to dissolve co2 in; Earth: co2 locked in carbonate rocks or dissolved in oceans. Difference in co2 is direct consequence of diffs in liquid water
2 lines of evidence of volcanic activity
a) venus's clouds contain sulfuric acid made from sulfur dioxide and water. Sulfur dioxide enters atmosphere through volcanic outgassing b) recent observations show evidence of geologically recent lava flows.
centre of mass
all objects in a star system, including the star itself, orbit the system's centre of mass, which is the balance point for all the mass of the system. The centre of mass of our solar system lies close to the sun because sun is more massive than all the planets combined, but it is not exactly at sun's centre.
Mars' size
allowed interior to cool more quickly than that of a larger planet like earth. Cooler interior means no global magnetic field, and if martian volcanoes remain active at all, they do not erupt frequently enough to resupply lost atmospheric gases. Best candidate other than earth
Star's luminosity
another factor that influences the range of distance that form the habitable zone. a brighter star may have a wider and more distant habitable zone than the sun, while a dimmer star must have a narrower and closer-in habitable zone. Brighter stars have shorted lifetimes
Moist GH effect
at high altitudes water molecules would be above much of the ozone layer and could be broken apart to UV light from the sun. Hydrogen would escape to space, causing earth to lose this water and thereby allowing more water to rise into the upper atmosphere and be lost
# of habitable planets
based on our own system, suggests the possibility to have more than one habitable planet per system, since we now suspect Mars was habitable some time in the past. For the moment we have no reasonable way to get flife. The fact that life apparently rose rapidly on earth suggests that the origin on life was fairly easy, in which case we might expect that most habitable planets would also have life.
The close-in orbits also are often highly elliptical, rather than nearly circular like the orbits of most of the planets in our own solar system.
because these orbits bring the planets so close to their stars, the planets must be quite hot. As a result, they have been dubbed hot jupiters, meaning that they are jupiter-like in size but have very high surface temps. Could have moons that are habitable especially around semi-hot jupiters that orbit within the habitable zones of their stars.
Methanogenesis
before photosynthesis raised the oxygen level, the atmosphere may have been altered by another metabolic process, known as methanogenesis, where microbes expel methane rather than oxygen.
Proto Star
before the centre gets hot enough to ignite nuclear fusion. All stars spend most of their life fusing hydrogen into helium. a star that exhausts its core hydrogen begins to grow larger and brighter, becoming a giant or supergiant star- the rapidly changing nature of these stars makes it unlikely that any planets could remain habitable for long.
planetary migration
believe hot jupiters were indeed born with circular orbits far from their stars and that those that now have close-in or highly elliptical orbits underwent some sort of planetary migration or suffered gravitational interactions with other massive objects. Young planet's motion can create waves in planet-forming disk. Matter in waves can tug on planet, causing orbit to migrate inward
Extrasolar planets name
by placing a lowercase letter after the star name. "b" for the first planet found, "c" for the second and so on. The "a" was reserved for the star itself as opposed to the entire system. E.g. "51 Peg b" is the first planet around 51 Peg. Letters are assigned based on order of detection, NOT on their position.
Ion engine
charges particles fired rearward as the rocket exhaust. Both Nasa and ESA have used these successfully but can not be started in space. So powerful could in principle reach speeds approaching 1% of light. Energy collection as you go
Allen Telescope Array
designed to take advantage of technological improvements, will be able to examine approximately a million targets by the year of 2035. Once detection verified, news would be released to the public. Given potential implications of discovery of an extraterrestrial civilization, this step would have to be taken with some care. SETI researchers have agreed to follow protocol: Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence.
Planetary migration in our solar system
did not play a major role, probably because the solar wind cleared out the gas before it could have much effect. Also possible that a jovian planet could migrate inward as a result of multiple close encounters with much smaller planetesimals.
CO2 concentration
direct measurements of CO2 in the past: ice cores are frozen equivalent of sedimentary rock, layering in ice cores show the year-to-year history of snowfall, and counting layers allows us to date them, trapped bubbles in ice can be analyzed and oxygen isotopes within them give clues to past temps. Antarctic air bubbles indicate current CO2 concentration is highest in at least 500,000 yrs. Most CO2 increase happened in last 50 yrs.
Continuously habitable zone
distances from the sun at which conditions have remained habitable from 4 billions years ago to present. It has been habitable at all times since the end of the heavy bombardment- Earth and Mars have remained in this zone. Earth will stay in this zone for another 0.5-1 byrs. In 3-4 byrs: Venus-like runaway GH effect.
Earth has remained habitable
due to the climate regulation provided by the co2 cycle.About a byrs from now, water vapour will begin to circulate into earth's upper atmosphere, where UV light will break apart water molecules and allow the hydrogen to escape into space, as it did with Venus. At this point unlikely life will survive on earth. when the habitable zone first moves past the orbit of earth, Mars will be well within it
Gravitational lensing
effect predicted by Einstein's general theory of relativity that occurs when one object's gravity bends or brightens the light of a more distant object.
time dilation
einsteins theory tells us when a spaceship travels close to the speed of light its length becomes noticeable shorter in the direction of movement, its mass becomes greater, and time measured aboard proceeds slower
Dolphins and sharks
evolved from earlier mammals and fish, but both have streamlined body forms that makes for greater speed underwater and clear survival for a predator. The evolution of originally quite different animals has converged on this optimized underwater shape
Sentinel Hypothesis
extraterrestrials place monitoring devices near star systems that show promise of emerging intelligence and patiently wait until these devices record the presence of civilizations
Star called 51 Pegasi
first clear-cut discovery of a planet around another sun-like star, came in 1995. Hundreds of other extrasolar planets have been discovered since that time, using several different strategies.
Coral Model
first few colonies are located within a few light-years. These colonies than lead to other colonies at greater distances, as well as unexplored locations. Growth tends to expand the empire around the edges of existing empire, much like growth of coral in sea. If it takes 150 yrs before sending out further colonizers from a new colony, expansion speed is 1% c- entire galaxy could be colonized in 10 MYRs
Zoo hypothesis
galactic civilization might declare planets like ours off-limits to explorations. Objective: even if civilizations wanted to hide from us, we would still be able to intercept their communications among themselves.
Crop circles
geometric patterns made in wheat fields. The continuing increase in complexity of the patterns over the years suggests that their creators are getting better at their craft, and the fact they are only made at night suggests human subterfuge.
The conclusion about global warming is clear
global average temps have risen by about 0.5 degrees C, in the past 50 years. Warming trend seems to be accelerating, and the past decade was the hottest on record. Polar regions warming faster than equatorial regions, Northern hemisphere is warming more rapidly than Southern hemisphere.
If we do nothing
global temps will be 3-5 degrees higher than it is now, being warmest climate generation. While some regions get warmer some may actually get colder-warm oceans increase intensity of hurricanes, warming of atmosphere means more increased evaporations from oceans so more rainfall and snowfall
Champions of alien visitation generally explain away the lack of compelling evidence in one of two ways:
government cover-ups or a failure of the mainstream scientific community to take the relevant phenomena seriously. The fact that few scientists are engaged in such study reflects not a lack of interest but a lack of evidence worthy of study.
Warp drive
hang something of dense mass in front of spacecraft, black hole on a stick would shorten spatial distances in front of the rocket, works like scrunching up carpet and straightening it behind you. Can ride the wave to accelerate to high speeds and time travel. Requires either capturing black hole or creating one using enormous amounts of energy.
Average M
has a mass about 20% that of the sun; although the smallest M stars have masses about 8% of the sun. An object with this small of a mass, gravity isn't strong enough to compress the core to high enough temps to sustain hydrogen fusion.
runaway GH effect
heat the planet until oceans were completely evaporated and carbonate rocks released all their co2 back into the atmosphere
Supernovae
higher-mass stars die in titanic explosions, in which cores collapse to form stellar remnants that may be either neutron stars or black holes.
Annie Jump Cannon
hired by Pickering in 1896, personally classified the spectra of more than 400,000 stars. The earlier method of spectra types A to O included some redundancies and the spectra fell into a much more natural order than he had supposed. 7 major spectral types which could be ordered OBAFGKM: the spectral sequence. subdivided each type by a number: G0-G9 where G0 is most similar to the F stars.
Black holes
holes in spacetime- space becomes so distorted it is a bottomless pit. The only known black holes are themselves extremely far away, so getting to them would be problem. We do not know of any way we could survive close encounter with black hole
How doppler technique works
if an object is moving toward us, then its entire spectrum is shifted to shorter wavelengths. Because shorter wavelengths of visible light are bluer, the doppler shift of a star coming toward us is called a blueshift. If an object is moving away from us, its light is shifted to longer wavelengths, called red shift, because longer wavelengths of visible light are redder. Faster object is moving-greater the amount is blueshift or redshift. If orbiting planet causes star to move should shift more to blue/red end
Hyperspace
if space had no curvature two parallel light beams would be side by side, but general relativity says the presence of matter can cause a warping of space that will lead these parallel beams to cross. Matter produces a distortion of ordinary three dimensions of space.
Wormhole
if two distortions met up in hyperspace could connect distant places in ordinary space via a short, hyperspace tunnel. Do not know how to stabilize and require a lot of energy to control
Implication of fermi-hart for humans
if we are alone, destruction of our civilization would represent an inglorious end to something that took the universe some 14 billion years to achieve.
Sun's gradual death has begun
in about 5 byrs the sun will completely run out of hydrogen in its central core. During first few hundred million years of this period, sun will gradually swell to about 100x present radius, and surface temp will drop, becoming a red giant star. In final death throes, sun will expel outer layer into space, creating planetary nebula. All that will remain will be hot central core; no more nuclear fusion will occur. The remaining core known as white dwarf, will then gradually cool over time.
the absoluteness of the speed of light
in principle, we can test this premise by measuring the speed of light coming from many different objects and going in many different directions and verifying that the speed is always the same. If the speed of light were not always the same, we could not see distinct stars in binary star systems
Humans EQ
is 7-higher than any other known species. Toothed whales and dolphins weight was estimated by measuring the size of some of the bones around the eye socket, a parameter known to be strongly correlated with body mass. High-performance brains need a vigorous metabolism, so intelligence is most likely to arise in warm-blooded animals. Long periods of parental care of offspring is probably also a necessary precondition for intelligence, which wouldn't be that useful without a time to learn from parents.
our ability to communicate through space is less than a century old
it derives from the emergence of science-itself an endeavour that has developed only gradually over the past 2500 years.
Stars of type A and F
lifetimes of 1-2 billion years-suggests that life on these planets would most likely be much simpler than life on earth.These are hotter than the sun, so habitable zone is wider and lies at greater distance from central star. Make up 3% of stars
taxonomy
long before biologists know anything about DNA or even that cells exist, they were busy setting up categories for the life they could observe called taxonomy- meaning to classify, and a science or study.
most obvious characteristic is how bright its appears in the sky
luminosity: total amount of light it emits into space, also depends on distance. To learn more about their properties required invention of spectroscopy
first report of UFO made by Kenneth Arnold in June 1947
lying private plane near Mount Rainier, in State of Washington, when he saw 9 shiny objects having wings, but no tails, that appeared to be streaking across the sky at 2000 km/h. Several later investigators have suggested that the objects seen by Arnold were meteors, streaks of light caused by small particles entering Earth's atmosphere
Sky Survey
makes no assumptions about where intelligent aliens might be located.
Astrometry-indirect method #1
measure the position of stars over time. If star wobbles gradually around its average position, we must be observing the influence of unseen planets. Primary difficulty: looking for changes in position that are very small. Stellar motions largest for massive planets orbiting far from stars but long orbits take decades to notice motions. 2 planets have been detected with this, most recently in Jan 2014.
Modeling of climate change
models suggest recent temp increase in consistent with human production of GH gases. Choas theory- very small changes in initial conditions, but models are very shoddy- although issues, what is predicted could be very problematic. Do see somethings being predicted.
Deuterium atom
most hydrogen nuclei contain just a single proton, but tiny fraction of hydrogen atoms contain a neutron in addition to the proton. These are twice as heavy as ordinary hydrogen atom and do not escape to space as easily when the water molecule is broken apart. # of these is 100x higher on Venus than earth.
Solution to death of sun
move to another star system. Recycling of stealer material cannot continue forever, b/c dying stars return to space only part of the gas from which they were made. About 100 byrs from now, the Milky way Galaxy will contain so little gas that new stars will no longer be born. Our technology is only ~10,000 yrs old. Could create sun-shade, move to other solar-systems like Mars, move earth farther away, or possibly interstellar travel
Problem with Drake Equation
no way to improve our estimate of the number of civilizations by knowing other terms well- only as strong as the weakest link. Main value is point out factors that are important and underscoring the implications of our lack of knowledge about particular factors
How do we account for the close-in orbits of hot jupiters, or with planets with highly elliptical orbits?
one possibility is that something is fundamentally wrong with our model of solar system formation. However, more than a decade of re-examinations has not turned up any obvious pawn in the basic theory. Discovery of hot jupiters forced up to re-examine nebular theory (jupiter-like planets should not form inside front line)
matter-animatter annihilation
particles that are in some ways the mirror images of normal particles, differing principally in their electric charge. positron (1932): animatter twin of the electron. antiproton (1955)- if you were to introduce this to a positron they would form atom of antihydrogen. When these meet it results in total annihilation with 100% mass turning into energy. No practical reservoirs are known-can't store them.
Climate stability and habitability
plate tectonics-carbon dioxide cycle so earth has remains habitable. Plate tectonics probably weren't necessary for the origin of life, but it seems to have been quite important in keeping the climate stable long enough for the evolution of plants and animals. 3 facts: 1. changes in axis tilt depend on rotation rate 2. solar system formation models indicate few giant impacts should be expected in planetary systems 3. even if axis tilt changes dramatically, may not have major impact on life
Targeted Search
proceeds on the assumption that not all locations in space are equally probable sites for intelligent life
Selection effects
properties of the planets found by this method are not representative for the entire population of planets. Small mass--changes in radial velocity too small to measure large distance--time to complete an orbit takes longer than we've been measuring
Solar sails
pushed by pressure exerted by sunlight. In the vacuum of space, where friction is absent, steady pressure of sunlight infringing on a mirrored sail could push a spacecraft to impressive speed- fairly inexpensive. Up to 3% of c, but fact that sunlight weakens with distance limits this
Radio vs. Light communication
radio is ideal for a situation that wants a signal to be picked up by people living in all directions from the station, visible light is a better medium if you want to signal some one in a particular place. experiments look for short pulses of light that are bright enough to outshine the background shower of photons naturally produced by the alien world's host star.
Most celebrated case of alien artifacts concerns the so-called Roswell incident of 1947
rancher ground crash remnants in a pasture, reported the debris and several military personnel drove out to the ranch, picked up the debris, and explained to the local pears that they had recovered remnants of a flying disk. An air force officer stated the debris was a crashed weather balloon, however in 1978 UFO investigator Stanton Friedman began looking at these events again and claimed it was from a spacecraft with alien occupants had been picked up as well. Declassified government records tell us that the crash was of then-secret military balloon experiment designed to detect soviet nuclear tests.
White Dwarf
relatively low-mass stars like our sun end their lives comparatively gently, ejecting their outer layers into space as planetary nebulae and leaving behind a type of dead star.
Venus's surface might have been repaved by tectonics and volcanism
repaving would have covered up any shorelines or other geological evidence of past oceans. rocks couldn't tell us about high temps- would have baked out any gases that might once have been incorporated into surface rock. Tectonic forces in the past, forces that fractured and twisted crust, also mantle plumes
Primary issue for K and M
size of their habitable zones, temp on orbiting planets will be lower in these systems than on planets the same distances from the sun in our solar system.
Rare earth hypothesis
specific circumstances that have made it possible for evolution to progress beyond microbes to complex creatures might be so rare that ours might be the only inhabited planet in the galaxy that harbours anything beyond the simplest life. One in six stars examined have turned out to have planets. Others may still have smaller planets that we cannot detect
interstellar ramjets
starship could collect its fuel as it goes, using a giant scoop to sweep up interstellar gas-mostly hydrogen. Funneled into nuclear reactor fused into helium and expelled back to propel starship. Density of gas between is only few atoms/cubic cm, so scoop would need to be hundreds of km. A particle this size pack energy equivalent to 100 kilos of tnt-need shielding
hard to make sense of the spectra
suggested classifying by visibility of hydrogen lines in their spectra, using type A to designate stars with the strongest hydrogen lines, type B for those with slightly fainter lines, and so on down the alphabet to type O for stars showing the weakest lines.
Venus' habitability
surface of Venus is too hot for liquid water, orbits sun at distance about 72% earth's distance. Enshrouded in thick cloud cover. W/o GH effect, surface temp would be ~35 degrees C.
Dyson Spheres
technologically adept civilization could capture all of its star's energy by fashioning a large, thin-walled sphere around its solar system and covering the inner surface with solar cells or their equivalent
Convergent Evolution
tendency of organisms of different evolutionary backgrounds that occupy similar ecological niches to resemble one another. -vision is a useful adaption-evolutionary relationship show that eyes evolved independently at least eight different times -If we could establish presence of an evolutionary trend favouring intelligence, we would be encouraged to think that the emergence of technological intelligence elsewhere is not enormously improbable
the energy required to put an object into motion depends on
the object's mass and the speed with which you want it to move. as well the energy required to slow down the ship for a soft landing once we arrive at the colony is the same as the required accelerate it to cruising speed.
Bandwidth
the range of transmitted frequencies is called the bandwidth of the signal. As a practical matter, the bandwidth is governed by how much information the broadcast contains
For each search project
the search type is indicated, along with the number of narrow-band channels being examined and the overall band of frequencies covered in each search.
# of extrasolar planets
there are 2001 known planets (Nov 23, 2015), and 3,704 Kepler Exoplanet Candidates
Radial velocity
these are small: Sun's motion due to Jupiter's gravitational tug is about 13 meters/sec. We can measure these velocities with great precision-down to 1 meter/sec; i.e.we can see stars moving at walking speed
another issue raised by rare earth proponents concerns the rates of impacts by asteroids and comets on planets in other solar systems.
thousands of asteroids still roam the region between Mars and Jupiter. By studying the orbits of comets that enter the inner solar system, astronomers concluded that as many as a trillion comets must orbit the sun at distances far beyond the orbit of pluto, making up the Oort Cloud.
Habitable zone dependence on Galactic location
too close to the centre: too many stars. Too far from the centre: not enough stellar evolution and heavy element enrichment. Intermediate zone: perhaps best suited for life
Total time required for Fermi-Hart Paradox
travel time=100yr x 100,000 trips colonization time=100 yrs x 100,000 star systems =10million years.If these estimates are correct, ETI should be able to cross the Galaxy in 20 million years. May be the strongest argument against widespread intelligence, but this is only an estimate.
another challenge of interstellar travel
tremendous amount of energy it would require, particularly if we wanted to send people and not just lightweight robotic probes to the stars. as you get closer to the speed of light, your mass increases accelerating a 5000-person spaceship to 10% of c requires ~4.5 * 1022 joules
multiple star systems
two or more stars orbit each other closely. Alpha Centauri (star nearest to our own) actually triple star system: largest and brightest member (Alpha Centauri A) G star, second largest (Alpha Centauri B) is a K star, separated from G star by roughly the distance that separates our sun and the planet Uranus, and third star (Proxima Centauri) is an M star that orbits the other two at a distance of about 1/5 of a light-year. Upsilon Andromedae was first known multi-planet system
Doppler Technique-indirect method #2
use spectroscopy to measure changes in the star's radial velocities. We can only detect velocities toward or away from us, so only looking at the star from a different perspective than before Radial velocity: that part of the velocity that is directed toward or away from us. Best for massive planets that orbit relatively close to their star.
Radio station
uses electronics to convert the information content of the sound into long-wavelength light waves. it's possible that alien civilizations might choose to communicate with forms of light besides radio, and some SETI efforts are designed to search for such signals
Brown Dwarf
very dim and difficult to detect. They have much hotter surfaces than planets, which means they emit moderate amounts of infrared radiation that can allow us to detect them if they are nearby. Have masses between about 10 and 80 times that of Jupiter. These have no habitable zones, still orbited by planets and possible Europa-like moons
Saturn V
was most powerful rocket ever built carried astronauts to the Moon. Design entails multiple (usually 3) stages to avoid carrying weight of entire rocket into space- each stage has a fuel-to-payload mass ratio of ~3.4. overall mass ratio is 40-60. Impractical for interstellar travel- 100 stage rocket only attain speed of 0.1%c
Nuclear fusion rockets
we have managed to achieve nuclear fusion, but only in thermonuclear bombs and as yet not in a well-controlled, commercially useful way.
Band
when we build a radio receiver, it is sensitive only to a particular set of frequencies within this wide range, which we refer to as its band of operation. Radio stations do not broadcast their signals over this entire band-if they did, no matter where you tuned your radio you'd hear the overlapping sounds of all the radio stations that were transmitting. Narrow band carrier used to focus antennae
CO2 thermostat
works on much longer time scales- 400,000-10 million yrs. Artificial rise of CO2 could be like long-term change of thermostat setting. Has everything we done here on earth (CO2, carbon footprint, industrialization, population) broken this. If we changed our ways could earth reset itself, or already in beginning of runaway GH effect,