Transcript 87 Sr
Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 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. Office Hours • Mine • Tuesday, Thursday - 1:15-2:15pm • Lederle Graduate Research Tower C 632 • Neil • Tuesday, Thursday - 11 am-noon • Lederle Graduate Research Tower B 619-O Homework • We will use Spark • https://spark.oit.umass.edu/webct/logonDisplay.d owebct • Homework will be due approximately twice a week Astronomy Information • Astronomy Help Desk • Mon-Thurs 7-9pm • Hasbrouck 205 • The Observatory should be open on clear Thursdays • Students should check the observatory website at: http://www.astro.umass.edu/~orchardhill for updated information • There's a map to the observatory on the website. Final • Monday - 12/14 • 4:00 pm • Hasbrouck 20 HW #9 • Due today HW #10 • Due Oct. 29 Exam #2 • Average was a 75 • Grades from 100s to a 27.5 • http://web.mit.edu/thb/www/exam2a.answers.doc • Average (80% exams, 20% HW) for people who took both exams is ~81 32 Extrasolar planets were just announced The new alien planets, which bring the known count beyond 400, were found with the HARPS spectrograph on the European Southern Observatory's 3.6-m telescope in La Silla, Chile. Some just five times the mass of Earth Others five times heftier than giant Jupiter http://www.msnbc.msn.com/id/33379852/ns/technology _and_science-space/ Radioactive Decay http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/radio1.gif 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 Basic Formula • Number of daughter atoms formed = number of parent atoms consumed • If there were daughter atoms originally there • D – Do = n o - n • Remember: n = noe-λt so no = n eλt • D- Do = n eλt – n • D = Do + n (eλt – 1) 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 Show animation Form atmosphere and oceans Show animation Any Questions?