PHYS 1621 Planet Formation contracting gas/dust cloud  forms stars  swirling disk of material (H, He, C, O, heavier elements, molecules, “dust”)  form planets New born star heats up material, blows out of solar nebula  planets (or at least protoplanets) need to form before material dissipates

PHYS 1622

3 see disks around new stars in Orion nebula

PHYS 1624 Planet Formation II material condensates if cool enough (gas  liquid/solid) heavier elements (metals, silicates) condense first, at higher temperatures, then molecules like water  H and He remain gases density and temperature falls with distance from star. Planet formation occurs when not too far and not too close “snow line”  separates type of planets being formed

PHYS 1625 Temperature in early Solar Nebula

PHYS 1626 “snow line” in early Solar Nebula Very, very simplistic

PHYS 1627 Planet Formation III condensation starts, protoplanets grow in size -objects collide; stick together over millions of years sweep out most smaller objects as collide with larger objects  existing planets only ~circular orbits won’t collide any further (asteroid belt between Mars and Jupiter) Possible motion of planets to/from star  may be critical

PHYS 1628 planetisimals (little dust grains)  protoplanets by accretion: collisions, gravity  smaller objects to stick together

PHYS 1629 Planet Formation IV close to star: planets = heavy elements (iron,silicon) -water may be trapped at beginning in dust grains or come later from comets hitting surface??? further from star: Gas Giants ices (water H 2 O, methane CH 4 ) froze out early  larger protoplanets  more material to accrete comets, meteors, asteroids give clues to composition of early solar system

PHYS 16210

PHYS 16211

PHYS Planets in other Star Systems test out how planets are formed with more examples first extrasolar planet observed in In Jan 2000, 28 observed and now >4500 candidates about 1000 confirmed (11/2013). Many systems with 2 or more observed planets difficult to observe directly mostly look for impact on Star: wobbles due to gravity of planets or reduction of light due to “eclipse” Planet orbits obey Kepler’s laws. If multiple planets, will have to add effects of planets (our solar system: Jupiter with 12 year orbit, Earth with 1 year, etc)

PHYS Observe Directly block out star in telescope optics Do if found exoplanet by other means

PHYS Observe by Star’s Wobble: Doppler Shift or Proper Motion the larger the planet the larger the gravitational pull the smaller the orbit the larger the gravitational pull the smaller the orbit the more rapid is the wobble  easiest to see large planets which are close to their stars

PHYS Ursae Majoris (one of first discovered) Doppler shift 2 large planets

PHYS Cancri (one of first discovered) Doppler shift very complicated. One close large planet plus 3-4 more?

PHYS Summary: some of the exoplanets found by Doppler shift - - easiest to find big planets close to a star

PHYS Observe by planet eclipsing star Jupiter would reduce Sun’s light by 1%; Earth reduces by.01% “easy” (done by 7 th grader at NIU Science Fair) once spotted can also analyze Doppler shift and try and observe atmosphere WASP-4 Wide Angle Search for Planets

PHYS Kepler telescope launched in 2009, designed to detect Earth-sized (or smaller) planets by observing them eclipsing their stars In orbit around the Sun….away from the Earth, points away from the Sun Looked 150,000 main sequence stars (every 20 minutes) measures luminosity 20 parts per million ( ) Has discovered over 3000 possible planets, ~600 confirmed (Jan 2014), rest available for analysis. Candidates often binary star systems Database at : two motors fail, can no longer “point”.

PHYS Kepler telescope orbit field of view (Cygnus + Lyra)

PHYS Kepler Results: many Earth-like planets some in habitable zones (more later) Kepler 35 – binary star Planet orbiting 4-star (2 close binaries)

PHYS Kepler telescope collected data from pointing failed. Not sensitive to long periods like Jupiter’s 12 years Sees a lot of planets between Earth and Neptune size. 603 in plot (1/14) 

PHYS Kepler telescope Kepler data can estimate the number of Earth-like planets orbiting Sun-like stars. Didn’t take data long enough to do 1 year periods

PHYS Exoplanet Highlights Jan 2014 Smallest: Kepler-37b. About the size of our Moon Earthiest: Kepler-78b has earthlike mass and diameter but 8.5 hour orbit and temp>2000 degrees C Intriguing 1: Kepler-62e and 62f are 2 Earthlike planets in habitable zone. Both ~twice Earth size at.4 and.7 AU from star ~0.2 Sun’s luminosity Intriguing 2: star Gliese667C has three planets in habitable zone. Bit 3 star system with “C” being a M1 class with 1% of Sun’s luminosity  poor for “intelligent” life

PHYS Planetary Atmospheres composition of a planet’s atmosphere depends on Surface Gravity Temperature light atoms/molecules move faster than heavy molecules if velocity = escape velocity gas leaves planet Mercury, Moon: all escape Earth: lightest (H,He) escape Jupiter: none escape

PHYS Familiar Molecules molecule mass H 2 hydrogen 2 He helium 4 CH4 methane 16 NH3 ammonia 17 H20 water 18 N2 nitrogen 28 O2 oxygen 32 CO carbon monoxide 28 CO2 carbon dioxide 44

PHYS Atmosphere of Venus vs Earth 96.5% CO2, 3% N2 runaway greenhouse effect 78% N2, 21% O2, 0.04% CO2, ~1% H20. most CO2 absorbed by oceans

PHYS Atmosphere of Jupiter and Saturn ammonia, sulfuric acid, water interiors are helium and hydrogen, core of ice/rock Titan, moon of Saturn, has ~90% nitrogen rest mostly methane and argon; pressure similar to Earth