Astronomy 100 Exploring the Universe Tuesday, Wednesday, Thursday Tom Burbine [email protected] Composition of the Planets Different bodies have different densities • Density = Mass/Volume • M = 4π2d3/GP2 V =4/3πR3 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 • ~463 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 Earth- sized planet. • On June 15, 2010 the Kepler Mission released data on all but 400 of the ~156,000 planetary target stars to the public. • 706 targets from this first data set have viable exoplanet candidates with sizes as small as that of the Earth to larger than that of Jupiter. www.physics.brandeis.edu/powerpoint/Charbonneau.ppt KEY D 22255311322343524233524343125151 35254313 • http://www.hulu.com/watch/119620/cosmic- journeys-the-search-for-earth-like-planets Any Questions?.