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

Sun

Comet

Earth

Perihelion distance

Aphelion 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-BoppIon tail &Dust tail

Halley from Giotto

Hyakutake

Deep Impact Tempel 1

Comet ISON

4 October 2013

10 April 2013

Comet ISON

Comet ISON

8 October 2013

ISON’s path through the sky

ISON approaches the Sun

ISON is only debris cloud after passing Sun

CometHartleyjets

Comet McNaught 2007

Siding Spring at Mars October 2014

MERPanCam

MAVENIUVSSiding Spring

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

Rosetta Target: 67P C-G

Boulder ‘Cheops’

Approaching Perihelion

Outburst in Action

View through Camera 4

P67Rotation andRegions

Active Pits

Key Concepts• Kuiper Belt, exterior to Neptune is the primary source of short period (P<200yr) 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