Comets 30 October 2015 Introduction The history of

Comets 30 October 2015

Introduction • The history of comet watching dates back to 1000 BC from the Chinese records and Chaldea, a place in present Iraq. • Comets have been regarded as omen, even as recently as 1986. – Battle of Hastings – 1066 – Bayeau Tapestry • Today Astronomers study Comets from scientific perspectives, and our understanding of these fascinating objects have grown tremendously.

Dirty Snowballs • Comets are dusty chunk of ice • During each orbit around the sun they partially vaporize • Have elliptical Orbits Courtesy: Calvin J. Hamilton

Orbits of Comets • Elliptical in Shape • Randomly oriented Aphelion distance Comet Sun Earth Perihelion distance

Comet Hunters • Comet are named by International Astronomical Union (IAU) after the person who first discovers them. • Many comets are discovered by amateur astronomers. • Charles Messier, E. E. Bernard, Shoemaker and Levy, Hale and Bopp, Ikeya, Seki and Hayakutake are popular comet hunters.

Origins of Comets • Comets are thought to be the left over debris from during the time of formation of the solar system. • The elliptical orbits of comets suggest that they underwent gravitational pull from the giant planets. • This all lead us to infer two possible locations where comets could start their journey towards the sun: Oort Cloud for long period comets; Kuiper Belt for short period.

Comets Tails • Ludwig Biermann propose the idea of solar wind to explain comet tails. Mariner 2 spacecraft captured the one such event in 1962.

Comet Collisions Courtesy: NASA/JPL

Kohoutek

Comet West

Shoemaker-Levy 9

Shoemaker-Levy hits Jupiter

Hale-Bopp Ion tail & Dust tail

Halley from Giotto

Hyakutake

Deep Impact Tempel 1

Comet ISON 4 October 2013

Comet ISON 10 April 2013

Comet ISON 8 October 2013

ISON’s path through the sky

ISON approaches the Sun

ISON is only debris cloud after passing Sun

Comet Hartley jets

Comet Mc. Naught 2007

Siding Spring at Mars October 2014

MER Pan. Cam

MAVEN IUVS Siding Spring

Latest Rosetta Images: Landing, 12 Nov 2014 Perihelion: 13 August 2015

Rosetta Target: 67 P C-G

Boulder ‘Cheops’

Approaching Perihelion

Outburst in Action

View through Camera 4

P 67 Rotation and Regions

Active Pits

Key Concepts • Kuiper Belt, exterior to Neptune is the primary source of short period (P<200 yr) comets • Oort Cloud, 10, 000 AU from Sun, reservoir of long period comets, stored there billions of years • Small objects much more abundant • Cometary activity is triggered by sunlight • Comet tails: dust, shaped by solar radiation; ion or plasma tail shaped by solar wind • Comet grains: CHON + refractory matter • Comet nucleus: dirty snowball