Nature’s Roadtrippers
Comets and the search for life
An overview of the solar system
100,000
Distance in AU
0
1
Sun
10
Earth
100
10,000
Planet 9?
Saturn
Oort cloud
Neptune
Asteroid
Belt
1,000
Kuiper belt
The long and the short of it
Short-period comets
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Generally labeled with their catalog
number and the letter P
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Long-period comets
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Eg., 9P/Tempel
Orbital periods of less than 200 years
Orbit throughout the inner and outer solar
system
Dynamically old: have spent millions or
billions of years in their current region of
space
Generally labeled with the prefix C and the
year of their first observation
○
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Eg., C/2011 W3 Lovejoy
Orbital periods of hundreds to millions of
years
Orbits may reach deep into the Oort cloud
Some may be dynamically new, meaning
our observation of them is their first-ever
trip into the inner solar system
Visiting three wanderers
→ There have been three spacecraft missions to visit comets.
Stardust visited 81P/Wild in 2004 and 9P/Tempel in 2011
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Collected material from the tail of 81P and returned it to Earth
Deep Impact visited 9P/Tempel in 2005
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Impacted 9P in coordination with telescope observations from Earth
Rosetta has been studying 67P/Churyumov-Gerasimenko since 2014
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Dropped the Philae lander onto the surface of 67P
Stardust
Aerogel dust collector
Follow up on Deep Impact
Deep Impact
View from carrier
View from impactor
Rosetta and Philae
Rosetta and Philae
Rosetta and Philae
10 km above surface
View of surface
Enceladus
Moon
Earth
67P
So what have we learned?
Comets are:
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Exceptionally dark objects
More icy rock balls than dirty snowballs
Constantly evolving
Full of organic material
Very porous
Object
Density (g/cm3)
9P/Tempel
0.62
19P/Borrelly
0.3
81P/Wild
0.6
67P/Churyumov-Gerasimenko
0.47
Ice cube at 93 K
0.934
Comets in the context of life
→ During the early
history of the solar
system, comets may
have delivered water
and organic material to
Earth.
→ The high heat of impact
may fuse simpler organic
compounds into the more
complex ingredients
needed for life.
Comets as cosmic lifeboats?
1,000,000
Distance in AU
0
Sun
1
10
100
1,000
10,000
100,000
Planet 9?
Earth
Oort cloud
Neptune
Kuiper belt
Proxima
Centauri
Comets as cosmic lifeboats?
→ At the edge of the Oort cloud, our solar system may exchange material
with others.
The notion of panspermia is that this material may contain life, which can then
take root on any habitable planet that comet encounters.
Problems with panspermia:
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Travel times are millions of years
Space is an incredibly harsh environment
The comet’s impact on the Earth is a violent event
Summary
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Including their reservoir, the Oort cloud, comets may be the most numerous
class of solar system object
Their evolution is highly dependant on temperature
Comets have have delivered organic compounds and water to early Earth
Although there is no evidence for panspermia, comets at the edge of the
Oort cloud may facilitate material exchange between