Comets in the New Millennium Dr. Erika Gibb UMSL

Comets Through History Comet as destroyer of the world 1857 Unknown Artist

Comets Through History Comet as destroyer of the world 1857 Unknown Artist Woodcut showing destructive influence of a 4th century comet (Stanilaus Lubienietski, Theatrum Cometicum,1668)

Comets Through History They marveled at the star Halley’s Comet King Harold being informed of the comet’s appearance Bayeux Tapestry Battle of Hastings, 1066

Comets Through History Chinese astronomers documented comets and the disasters attributed to them. The Mawangdui silk, a surviving record of ancient comets (~300 B.C. ) Believed to include information from back to 1500 B.C.

Comets Today Short period (<200 years) Long period (>200 years) Halley (76 years) Hale-Bopp (2537 years) Encke (3.3 years) Hyakutake (70,000-114,000 years)

Comets Today ~70,000 bigger than 100 km Source of short period comets (1000 Billion) Source of long period comets

Anatomy of a Comet Coma Dust Tail Ion Tail Nucleus Not visible!

Why are comets important? Formed near Jupiter & beyond (where temperature low enough for water to freeze) Gravitational interactions flung all over solar system Impacted early Earth, Sun, were ejected from solar system, formed Oort Cloud destruction? source of oceans? delivery of organics?

Why are comets important? If we know what comets are made of  learn how they affected Earth’s early history Difficult to study: Can’t see nucleus from Earth (coma too bright) Chemistry in coma - how to infer composition of nucleus? Not predictable Comets are like cats. They both have tails and do precisely what they want. - David H. Levy

Questions that need Answers What are comets made of? Where did they form? What is the internal structure? Have they been modified since their formation? Could they have contributed to Earth’s early oceans/organics?

Comets are ~ 1/2 ice & 1/2 dust (But how are these mixed?) Darker than coal! Evaporation of ice over only small amount of surface (jets) Snowy surface just after formation Dark surface after 4.6 billion years of radiation exposure If the surface has been modified, how do we measure the original composition?

Comets are fragile! Shoemaker-Levy 9 Ganymede: Chain of craters From a broken comet like SL9?

Models of Nucleus Easily broken implies that comets are made of smaller cometesimals? Are they made of the same material? How do we get below the modified surface to test? Smash a hole in a comet and see if the composition changes!

Deep Impact Smash 820 lb probe into comet Tempel 1 at 22,680 miles/hr Create stadium sized crater Gets below the surface

Deep Impact Image from impactor 90 seconds before impact Smooth area 20-m high scarp Craters require surface tension Impact site Rough spots

Worldwide Campaign Many telescopes, including Keck (below) observed Tempel-1 before & after impact Changes? Surface Different from Interior?

Worldwide Campaign Sample comet spectrum Every molecule emits at specific positions  what molecules are present Height  how much of that molecule is in comet What do we find? water, methanol, methane, carbon monoxide, ammonia, hydrogen cyanide, acetylene, ethane, etc

What are comets made of? model after before

What are comets made of?

Schwassman-Wachman 3: May 2006 Broke apart in 1995 As of April 10, 19 fragments Brightest will be studied with Keck in April/May Why is this a big deal?

Schwassman-Wachman 3: May 2006 Why is this a big deal? A recently broken comet = newly exposed interior! Several pieces to study = study whether composition is same throughout

Stardust Collector Return Pod Comet Wild 2 Launched 1999 Sample Return Jan 15, 2006

Stardust Pod recovery, Jan 15, 2006 Image of tracks Comet dust impacts in aerogel Want to help? http://stardustathome.ssl.berkeley.edu/

Comets in the Future Rosetta Mission launched Mar 2004 Lander:Philae island in the Nile obelisk with a bilingual inscription Enabled Champollion to decipher Rosetta Stone Land on Churyumov- Gerasimenko in 2015