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Comets : Comets Astronomy 311 Professor Lee Carkner Lecture 22


Which of the following is not true about Pluto ? : Which of the following is not true about Pluto ? Its composition is different from that of any other planet Its orbit is highly inclined It has several moons HST has imaged craters on its surface It crosses the orbit of Neptune


Which correctly lists TNO regions from closest to the sun to furthest away? : Which correctly lists TNO regions from closest to the sun to furthest away? Centaurs, Kuiper belt, Scattered disk Scattered disk, Kuiper belt, Centaurs Kuiper belt, Scattered disk, Centaurs Kuiper belt, Centaurs, Scattered disk Scattered disk, Centaurs, Kuiper belt


Upcoming : Upcoming Quiz #3 on Monday, Nov 5 Covers Gas Giants through The Sun Final exam Monday Nov 12, 3pm Covers entire course Observing project due next Friday, Nov 9


Comets Throughout History : Comets Throughout History People throughout history have observed the passing of comets “When beggars die, there are no comets seen; The heavens themselves blaze forth the death of princes.” --Julius Caesar, Act II, Scene II


Edmund Halley : Edmund Halley


Comet Halley : Comet Halley He used Newton’s new laws to determine its orbit (P=76 years so A=18 AU) He was the first to realize that comets are solar system objects on highly elliptical orbits Comet Halley will return again in 2061


Finding Comets : Finding Comets Large observatories do not have time to spend looking for them If you see a faint fuzzy patch in the sky with your telescope, that is a good candidate for a new comet More and more comets are being found by automated observatories


Observing a Comet : Observing a Comet When we look at a comet with our eyes (or a small telescope) we see: Tail: Long streamer of gas and particles that can be more than 100 million km long


Structure of a Comet : Structure of a Comet


Comet Tails : Comet Tails A comet generally has 2 tails: Ion Tail (blue) Always points away from the Sun Dust Tail (yellow) Points roughly away from the Sun, but is curved back towards the Sun by gravity


The Two Tails of a Comet : The Two Tails of a Comet


The Heart of the Comet : The Heart of the Comet This is what the comet looks like far from the Sun and is the source of the tail and the coma Composed of rock and ice


Comet Jets : Comet Jets The heat from the Sun boils off material Sometimes volatiles boil inside the comet and are released as a jet Comet orbits cannot be strictly predicted by Newton’s laws


Comet Composition : Comet Composition A comet is a mixture of ice and rock “dirty snowball” Comets are composed of: Silicates (rock) Water (ice) Carbon Dioxide (“dry ice”) Ammonia Organic material Comets contain many carbon compounds including C2, CH, CN (cyanogen)


Comet Orbits : Comet Orbits Comets have highly elliptical orbits that bring them close to the Sun and then back to the Kuiper Belt or Oort Cloud Short period comet orbits are constantly being altered by Jupiter and Saturn


Meteor Showers : Meteor Showers As the comet circles the Sun its orbit fills up with lost material When the Earth passes through this material we get a meteor shower Meteors are small dust particles and thus burn up before they reach the ground


Anatomy of a Meteor Shower : Anatomy of a Meteor Shower


The Perseid Meteor Shower : The Perseid Meteor Shower Occur every year around August 12 Get about 50 meteors per hour Meteors appear to come from the direction of the constellation Perseus The Perseids are debris from Comet Swift-Tuttle


Comet Deliveries : Comet Deliveries Comets could be a source of volatiles, including water Could the Earth’s water have come from comets?


Death of a Comet : Death of a Comet At each passage, the comet loses material Eventually all the volatiles will boil off Comets can also hit a planet or be ejected from the solar system in a close encounter


Spacecraft Studying Comets : Spacecraft Studying Comets Imaging Giotto (1985) -- took close-up pictures of Comet Halley in 1986 Gathering Impacting Deep Impact (2004) – blasted a 25m deep crater into Comet Temple (2005) Landing Rosetta (2004) -- will land a probe on the nucleus of Comet 67P/Churyumov-Gerasimenko (2014)


Next Time : Next Time Read Chapter 16


Summary : Summary Comets are small (10 km) bodies that have highly elliptical orbits that originate in the Kuiper belt or Oort cloud The Sun boils off material making the comet visible Comets can produce meteor showers and large impacts


Summary: Comet Structure : Summary: Comet Structure Nucleus: small (10km) core that is the source of the comet material Coma: large (~1 million km) cloud of gas around the nucleus Tail: comets have two tails, both pointing away from the Sun: Ion -- pushed by solar wind Dust -- pushed by solar light pressure Jets: gas expelled from the nucleus under pressure