Transcript 87 Sr
Astronomy 101 The Solar System Tuesday, Thursday Tom Burbine [email protected] Course • Course Website: – http://blogs.umass.edu/astron101-tburbine/ • Textbook: – Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. • You also will need a calculator. • There is an Astronomy Help Desk that is open Monday-Thursday evenings from 7-9 pm in Hasbrouck 205. • There is an open house at the Observatory every Thursday when it’s clear. Students should check the observatory website before going since the times may change as the semester progresses and the telescope may be down for repairs at times. The website is http://www.astro.umass.edu/~orchardhill/index.html. HW #10, #11, #12, and #13 • Due March 30th at 1 pm What are the assumptions to get an age? What are the assumptions? • No loss of parent atoms – Loss will increase the apparent age of the sample. • No loss of daughter atoms – Loss will decrease the apparent age of the sample. • No addition of daughter atoms or if daughter atoms was present when the sample formed – If there was, the age of the sample will be inflated • These can possibly be all corrected for Radioactive Parent (P) 40K 87Rb 147Sm 232Th 235U 238U Radiogenic Daughter (D) Commonly Used Long-Lived Isotopes in Geochronology 40Ar 87Sr 143Nd 208Pb 207Pb 206Pb Stable Reference (S) 36Ar 86Sr 144Nd 204Pb 204Pb 204Pb Half-life, t½ (109 y) 1.25 48.8 106 14.01 0.704 4.468 Decay constant, l (y-1) 0.58x10-10 1.42x10-11 6.54x10-12 4.95x10-11 9.85x10-10 1.55x10-10 How do you determine isotopic values? How do you determine isotopic values? • Mass Spectrometer It is easier • To determine ratios of isotopic values than actual abundances Example • 87Rb 87Sr + electron + antineutrino + energy • Half-life is 48.8 billion years • 87Sr = 87Srinitial + 87Rb (eλt – 1) • Divide by stable isotope • = 87Srinitial + 87Rb (eλt – 1) 86Sr 86Sr 86Sr 87Sr Example • Formula for line • 87Sr = 87Srinitial + (eλt – 1) 87Rb 86Sr 86Sr 86Sr y = b +mx http://www.asa3.org/aSA/resources/wiens2002_images/wiensFig4.gif = (eλt – 1) Carbon-14 • • • • • 99% of the carbon is Carbon-12 1% is Carbon-13 0.0000000001% is Carbon-14 The half-life of carbon-14 is 5730±40 years. It decays into nitrogen-14 through beta-decay (electron and an anti-neutrino are emitted). • Due to Carbon-14’s short half-life, can only date objects up to 60,000 years old • Plants take up atmospheric carbon through photosynthesis http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html • When something dies, it stops being equilibrium with the atmosphere http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html Why is Carbon-14 still present if it has such a short half-life? Why is Carbon-14 still present if it has such a short half-life? • Cosmic rays impact Nitrogen-14 and create Carbon-14 • Cosmic rays are energetic particles (90% are protons) originating from space. From the Sun (solar cosmic rays) or outside the solar system (galactic cosmic rays) • n + 14N → 14C + p • http://en.wikipedia.org/wiki/Image:Radiocarbon_ bomb_spike.svg Composition of the Planets Different bodies have different densities • Density = Mass/Volume • M = 42d3/GP2 V =4/3R3 Life of a Star • A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2) • Temperatures like 10-50 K Region is approximately 50 light years across Condensing • Interstellar clouds tends to be lumpy • These lumps tend to condense into stars • That is why stars tend to be found in clusters Protostar • The dense cloud fragment gets hotter as it contracts • The cloud becomes denser and radiation cannot escape • The thermal pressure and gas temperature start to rise and rise • The dense cloud fragment becomes a protostar When does a protostar become a star • When the core temperatures reaches 10 million K, hydrogen fusion can start occurring Formation of Solar System • Solar Nebula Theory (18th century) – Solar System originated from a rotating, disk-shaped cloud of gas and dust • Modern theory is that the Solar System was born from an interstellar cloud (an enormous rotating cloud of gas and dust) Composition • ~71% is Hydrogen • ~27% is Helium • ~2% are other elements (Fe, Si, O) in the form of interstellar grains • Show animation • Dust grains collide and stick to form larger and larger bodies. • When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, becoming protoplanets • Protoplanets collide to form planets – Asteroids such as Ceres and Pallas are thought to be leftover protoplanets • Condensation – conversion of free gas atoms or molecules into a liquid or solid • Volatile – Elements or compounds that vaporize at low temperatures Form atmosphere and oceans If you want to find life outside our solar system • You need to find planets Extrasolar Planets • Today, there are over 400 known extrasolar planets • ~430 extrasolar planets known as of today Star Names • A few hundred have names from ancient times • Betelgeuse, Algol, etc. • Another system: • A star gets name depending on what constellation it is in • With a Greek letter at the beginning – Alpha Andromeda, Beta Andromeda, etc. • Only works for 24 brightest star Star Names now • Stars are usually named after the catalog they were first listed in • HD209458 is listed in the Henry Draper (HD) Catalog and is number 209458 • HD209458a is the star • HD209458b is the first objects discovered orbiting the star Our Solar System has basically two types of planets • Small terrestrial planets – Made of Oxygen, Silicon, etc. • Large gaseous giants – Made primarily of hydrogen and a little helium – – – – Jupiter - 90% Hydrogen, 10% Helium Saturn – 96% Hydrogen, 3% Helium Uranus – 83% Hydrogen, 15% Helium Neptune – 80% Hydrogen, 20% Helium Things to Remember • The Milky Way has at least 200 billion other stars and maybe as many as 400 billion stars • Jupiter’s mass is 318 times than the mass of the Earth Question: • How many of these stars have planets? What is the problem when looking for planets? What is the problem when looking for planets? • The stars they orbit are much, much brighter than the planets • Infrared image of the star GQ Lupi (A) orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun. • GQ Lupi is 400 light years from our Solar System and the star itself has approximately 70% of our Sun's mass. • Planet is estimated to be between 1 and 42 times the mass of Jupiter. • http://en.wikipedia.org/wiki/Image:GQ_Lupi.jpg So what characteristics of the planets may allow you to “see” the planet So what characteristics of the planets may allow you to “see” the planet • Planets have mass • Planets have a diameter • Planets orbit the star http://upload.wikimedia.org/wikipedia/commons/d/de/Extrasolar_Planets_2004-08-31.png • Jupiter – – – – H, He 5.2 AU from Sun Cloud top temperatures of ~130 K Density of 1.33 g/cm3 • Hot Jupiters – – – – – – H, He As close as 0.03 AU to a star Cloud top temperatures of ~1,300 K Radius up to 1.3 Jupiter radii Mass from 0.2 to 2 Jupiter masses Average density as low as 0.3 g/cm3 10 100 1,000 (lightyears) Some Possible Ways to detect Planets • Radial Velocity (Doppler Method) • Transit Method • Direct Observation Center of Mass • Distance from center of first body = distance between the bodies*[m2/(m1+m2)] • http://en.wikipedia.org/wiki/Doppler_spectroscopy Radial Velocity (Doppler Method) http://www.psi.edu/~esquerdo/asp/shifts.jpg • http://astronautica.com/detect.htm Wavelength http://www.psi.edu/~esquerdo/asp/method.html www.physics.brandeis.edu/powerpoint/Charbonneau.ppt Bias • Why will the Doppler method will preferentially discover large planets close to the Star? Bias • Why will the Doppler method will preferentially discover large planets close to the Star? • The gravitational force will be higher • Larger Doppler Shift Transit Method • When one celestial body appears to move across the face of another celestial body • When the planet crosses the star's disk, the visual brightness of the star drops a small amount • The amount the star dims depends on its size and the size of the planet. • For example, in the case of HD 209458, the star dims 1.7%. • http://en.wikipedia.org/wiki/Extrasolar_planets#Transit_method One major problem • Orbit has to be edge on Direct Observation • Infrared Image Visible • • Infrared http://www.news.cornell.edu/stories/March05/extrasolar.ws.html http://nai.nasa.gov/library/images/news_articles/319_1.jpg http://en.wikipedia.org/wiki/Image:Extrasolar_planet_NASA2.jpg How did these Hot Jupiters get orbits so close to their stars? How did these Hot Jupiters get orbits so close to their stars? • Formed there – but most scientists feel that Jovian planets formed far from farther out • Migrated there - planet interacts with a disk of gas or planetesimals, gravitational forces cause the planet to spiral inward • Flung there – gravitational interactions between large planets Kepler Mission • Kepler Mission is a NASA space telescope designed to discover Earth-like planets orbiting other stars. • Using a space photometer, it will observe the brightness of over 100,000 stars over 3.5 years to detect periodic transits of a star by its planets (the transit method of detecting planets) as it orbits our Sun. • Launched March 6, 2009 Kepler Mission http://en.wikipedia.org/wiki/File:Keplerpacecraft.019e.jpg Kepler Mission • The Kepler Mission has a much higher probability of detecting Earth-like planets than the Hubble Space Telescope, since it has a much larger field of view (approximately 10 degrees square), and will be dedicated for detecting planetary transits. • There will a slight reduction in the star's apparent magnitude, on the order of 0.01% for an Earthsized planet. www.physics.brandeis.edu/powerpoint/Charbonneau.ppt KEY D 22255311322343524233524343125151 35254313 Any Questions?