Life Beyond the Earth
Life Beyond the Earth ASTR 3420
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This 21 page Class Notes was uploaded by Willie Cummings on Monday September 21, 2015. The Class Notes belongs to ASTR 3420 at University of Virginia taught by Staff in Fall. Since its upload, it has received 17 views. For similar materials see /class/209720/astr-3420-university-of-virginia in Astronomy at University of Virginia.
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Date Created: 09/21/15
Important Factors to Note 0 1 AU E distance of the Earth to the sun 15 X 108 kin This is the scale of distances within the solar system 0 light year E the distance light travels within one year E 95 X 1012 kin Stars in the neighborhood of the the sun are separated from each other over these distances 0 1 parsec E the distance at which an object will have a parallax of 1 arc second 13600th of a degree when Earth moves from one side to the other of its orbit E 326 light years MrsI Io scale if E Siam stars 45 a Eff ff 2 HL E E 4 I d f H hhquot 3 EE If Earth a C39bi around 5m 0 1 LG E the total power output by the sun E 4 X 1026 Watts 0 Size of the Milky Way galaxy 25 kpc 8 X 1017 kin o Radius of the sun RQ 7 X 105 kin mass of the sun MG 2 X 1030 kg 0 Radius of the earth R5 6000 mass of earth M5 5 X 1024 kg 0 one galactic year E the time it takes for the sun to move about the galaxy center 220 million years 0 1 Gyr E 1 billion years 1 Giga year 1 g W J39 i 7 Note Jupiter produces more energy 7 which it radiates in the IR 7 than it re ects This energy comes from gravitational contraction NQCVAWQSH 3 A 4 39 1 SJ 1quot r 23mquot quot u v 4 Direct detection is easier in the IR Jupiter s radiation is peaked in the IR at 7v10u1n 1quot l arcsec UGO X 160 x l The sun is only 103104 times brighter l 3 miles Visible light Inlrared gm dune A11 arcsecond is a tiny angle by human standards Artist concepts Center of Mass CM Are there ways to infer the Moremassive presence Ofthe planet planet A planet does not revolve around the star They both revolve around their center of massquot CM The CM is like the balance point of a seesaw How do you find the center of mass 1111112111212 Center of Mass CM mmmg towmri 15mm obseivei 12 Period Later mm mg mm from obsener Observing Jupiter Position Change Astrometric Path of S tar Jupiter causes an oscillation in the Sun39s position of 1 R9 This would result in an angular shift of 001 arcsec Viewed from 1 pc or 0001 arcsec viewed from 10 Path of CM pc 2 Planet To star ratlo 395 blgi Atmosphere blurs to l arcsec Amplitude is bigger if 1 Star is close ie big planet amp dinky star Note that detection via this technique is easier ifthe star is close and the planet is big ETE 12 VAN KatUs Barnardls Star 0 Ma Sprou O6serzafor y Marc I980 EastWest De w39a tion Mrt 3011 if Deuz39at z39on Doppler Effect stationary wavecrests Emirred 4 All observers measure same wavelength K0 Doppler E ect moving wa vecrests Sf JD 530 Q observer S S K gt 10 redder Emifiea39 observer sees 9 lt lo bluer emitter 1 sec ago emitter 4 sec ago 9 5665 9 K0 Relative Flux 4000 5000 0000 MN 012v 7000 8000 Wavelength A Stationa SOUI EB Blue Red A machin Source Blue Red 6 W b Recedin Source Blue Red QW gt Wm w 9000 Model V 81111 L2 06 I l 1 I 7768 7770 I 7772 39 I M13 J52 14 kms I 7774 OFe 06 10 ms shifts spectrum by 000025 A 1 Wavelength A Step 1 Observe star Bpl 1 b tellmelengths New Technique Record quotlines on rulerquot and spectrum at the same time First done by Campbell et al Cell of Gas Iodine for Marcy and Butler Stellar Spectrum and Iodine Reference Lines Precision 3 ms Marcy UC B Butler Carnegie D C 30000 40000 535110 Tll Iquot ll ML REWSDI MILL x LLJLLML it bakhdbm JAL MEAJI J l l l 5350 5400 5450 Wavelength angstroms r 9 to 3 S x 9 f I x 39n 4 i 2 q if r m S I 0 43933 5quot i l l L l l L 39 l J l39 l l I J 52980 52985 r752990 52995 Wavelength A a 100 I l I I lSt planet for solar star dlscovered by Mayor amp Queloz 50 i0 ii 7 9 i g R 0 0 o a j V 3 N r v 5 M szlmer Rm t 00 AU P 4 da s ii g i 3 i c V 1 5 51 139 13mm 3 rm 7100 l l quot l t H H R 5077 g 0 3 c awe quot1 8 250 4 as Heliocentrjc Julian Date 7 2450000 AFOE and Lick observations of rhoCrB HD 143761 HR 5568 I x l l l l 100 92 gi d g i M g l 10 12 Jelecity m squot lt139U 100 9301 12 04 L26 5 H 50 Phase 7100 1 Period 422 days 702 00 o 0 4 0 6 Orbiml Phase Planetary Transits Close in Planet 0 If the planet passes in front of the star the I g gt star gets fainter i ransit occurs iforbil lies within this angle More distant planet Orbit of planet must F F gt be close to our line of sight Bigger planet produces bigger dip in light OGLE monitors millions of stars nightly Highly automated data pipeline hunts for transients Has the potential to detect hundreds of 003 mag difference 2300 decrease 1n the brightness plancm OGLETRm 133 1014 Idaysn a r 7 2453555 m At a large distance a star could appear to brighten Gravitational Microlensing when a planet passes exacty along the hue ot s1ght You must observe MANY stars 39 Planel 1 39 V 39 Method depends 011 O 323 r chance alignment of 539 background sources with foreground sta 39 s 501191113th V V 39 observe dense star elds Gravity from starsplanet bends light from a more distant star Ms C rt771 39 Wu 3113b ba enb EOGLE 2003 BLG 175h Magni cation 39 x m wl 15a 13W 2m 3639 Txmu an s 2820 2310 2360 22880 HJD 2450000 Multi pl quot I blur om amid mu Chile FUN Farm Cm M m Auckland uzw in in us um u v 1 nlpn in 15 Fme39 mung 739 T Detector Primary N rror Unaluminized A0 secondary of the WT 2mm thick 64cm wide mirror is exed by 336 voice coils Theta l Ori B A0 ON MMT Adaptive Secondary a quot1quot 0 D on Faint companion 1 2 Binary Star systems Movie shows image W adaptive optics A0 off and A0 on 2MASSWJ1207334393254 First planet observed by an A0 system 7781nas 55AUac7Upc Ed The Brown Dwarf 2M1207 and its Planetary Companion VLTNACO ESO PF Photo 14a05 30 April 2005 ESO Signals from 2 or more telecopes are combined to quotshowquot ne detail E LBT Project EURZP39EM Fmg gw 2x84m Telescope Srrl Nulling Interferometer Roger Angel UAz At some angles planet light will reinforce W Directly Image Planet Get spectrum oxygen in the atmosphere gt Life Constructive Interference Destructive nulled image 310 J 191 Astr34224 SETI Detections Criteria for Detection What standard of evidence would be required for the scienti c community to accept a detection 1 The signal makes sense Narrow bandwidth perhaps factors like large polarization or some modulation like a regular pulse pattern Makes sense gt almost natural PSR 032954 P 071 sec PSR 095008 P 0253 sec PSR 0833 45 P 0089 sec Vela PSR 193721 P 000156 sec Perhaps a pseudopulsar that glitches between two periods Almost natural Narrowband radio continuous long duration pulses Broadband optical ashes very short pulses Something nature cannot make 2 The signal is coming from the sky Intelligent looking signals often sneak into the system from local electronics or local interference One quick check for this is to point the telescope to some other direction and a real SETI signal should go away 3 Signal originates from outside the Earth Because the Earth is moving any ET signal intelligent or not is Doppler shifted One should be able to see frequency shifts associated With the Earth39s rotation its revolution around the Sun its motion around the EarthMoon center of mass etc In ordinary radio astronomy these shifts are taken out by constantly tuning the receiver I Turn Doppler Satellites and airplanes have the wrong signature in mx mi quotLiH hm neanJaseA4473717003175L r brightness of pixel denotes intensity frequency gt Pioneer 10 detected by Project Phoenix Drifting frequency is due to the do ppler shift and shows that the signal is extraterrestrial 9 4 Signal is con rmable 0 Can be detected at different times Can be detected by different radio telescopes Having passed all the above an investigator would then try to get a totally different observing team to confirm the detection Types of Signals I Beacons A beacon is a signal purposefully designed to be easy to detect It will probably be very narrow in bandwidth to achieve maximum range and thus will have very little if any information encoded on it iThe purpose of a beacon is to call our attention to the civilization and perhaps direct us to a signal containing encoded information Beacons might be directed ie aimedspeci cally at us Or omnidirectional ie they re fishing 0 A directed beacon is not expected unless they know we are here Ie they have detected our leakage radiation This requires that the number of civilizations in the Galaxy was 1039s of millions or more Abeacon might be at a magic frequency 2 Overheard conversations Many astronomers imagine sort of a Galactic Club of communicating civilizations Ron Bracewell even has a book with this title The idea is that we try to break into their network 0 The frequencies and bandwidths are chosen for their convenience and may not be easy to detect 3 Leakage radiation 0 Any technological civilization leaks some radio radiation 0 Basically leakage radiation is wasted money We and they will stop the leakage when and if we can 4 Garbage Waste Energy The garbage of a technological civilization is its waste energy A really advanced civilization might dump enough waste energy n1 the form of IR radiation that it could be detected Extreme example A civilization which has entirely surrounded their star with a shell called a Dyson Sphere and traps all its energy which is eventually radiated in the IR 390 Radius 15x10 r n I n 0 Mercury DYSON SPHERE 8 m thickness lnfrared Radiation Leakage Radiation from Earth 1d ETI learn about us l7 The strongest regular and persistent leakage comes from UHF TV stations Even though bandwidth is 6 MHz typically 5090 of power is in a 01 Hz carrier i 1 I TV Antenna quot Pattern Arecibo can detect TV carrier at 18 ly and Cyclops could detect it at 20 ly To see a TV picture requires 104 more sensitivity Even Martians With Cyclops don t see Lucy Ricky Fred and Ethel Defects rising 6eam amtz quotHuequot 5119 651 frequency 12 10am alter Defects SC ffly 5mm witz quot red shifted frequency a From the size of the diurnal doppler shifts ET could measure the latitude of each station