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Comets and Life
10 October 2016
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 omens, 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 McNaught 2007
Siding Spring at Mars October 2014
MER
PanCam
MAVEN
IUVS
Siding Spring
Latest Rosetta Images:
Philae Landing, 12 Nov 2014
Perihelion: 13 August 2015
Orbiter Landing: 30 September 2016
Rosetta Instruments
Rosetta Target: 67P C-G
Boulder ‘Cheops’
Philae Found!
Osiris from
16km
30 September 2016: Rosetta’s last image from 51m
Comet Outbursts
•
•
•
•
Are common near perihelion
Studied by JB Vincent (MPS) etal
Published last week in MNRAS
I will show pictures and paper figures from
the paper
View through Camera 4
Approaching Perihelion
Outburst in Action
Active Pits
Location of the outburst node
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
Comets and Life
• Comets are full of organics and water
• They supplied and continue to supply these
to planet and moon surfaces
• Interstellar life could hitch a ride on a comet
from another star’s Oort cloud: may have
infected Earth with life from space:
panspermia
• They preserve the material from the early
solar system in ‘cold storage’