Transcript Can Comets Contain Water?

The Cometary
Biosphere
Rob Sheldon,
Richard Hoover
SPIE SanDiego
Aug 28, 2007
Panzooia
1. Cyanobacterial fossils on comets
2. Sand accretion on short-period comets
3. Liquid water on all trans-Jovian comets
Therefore life can hop from comet to comet,
colonizing and growing in short summers
and long winters.
Comets aren’t just a bus between planets
(panspermia)--planets are a traffic
accident (panzooia).
Cyanobacteria
fossils on extinct comets are:
indisputable, identifiable,
Hoover 2005
diverse,
varied,
Hoover 2005
dense
tangled,
Hoover 2005
mats
Hoover 2005
Like these
1. Comet cyanobacterial mats
…are not just refugees from the planet Earth, they are
complete, photosynthetic ecosystems:
manufacturing organics from sunlight, modifying
their environment, recycling waste products. This is
not a bus with passengers, this is a fully loaded 60foot RV, with satellite dishes.
Stardust mission to Wild-2
Stardust
Aerogel sample-and-return
Stardust
Forsterite
1400C
A sand grain?
• Particles < 1micron are blown out of the solar
system by light pressure~9µPa. Larger
particles are pulled in by Poynting-Robertson
effect.
• This sand grain is > 1 micron and must have
been accreted in the inner solar system
• Comets accrete material as they pass through
the inner solar system.Can they accrete other
pieces from comets?
Comet particles @ Earth
Brownlee particles
collected in the
stratosphere from
comets
Note the delicate,
unshocked, nature
of this particle.
Deceleration in an
atmosphere, just
like comets
Brownlee
2. Comets accrete
…not just sand grains and dirt, but spores, chunks
of dehydrated mats, lyophilized bacteria,
whatever is left behind in orbit by previous
disintegrating comets.
Liquid Water on Comets
• There is no question that H20 exists on comets,
what is the state?
• Some have suggested radioactive heating, far from
the Sun, deep in the Oort Cloud, long ago.
• But everyone acknowledges that near the Sun,
comets vaporize, and generate a tail.
• So the $64M question:
Do they sublime or melt?
6 millibars of pressure + 273K = wet.
Temperature on Tempel-1
• Most of comet
hovers just above
freezing point
Sunshine
ice
Whipple’s sublimation cooling
• To keep the comet cool, it must reflect sunlight
and have a cooling “sublimation wind”
flowing out everywhere, through the porous
snow.
• But every comet photographed is black and
non-porous with geysers!
• R. Yelle (2004) argues that geysers must have
much higher pressure to accelerate the jet. Is it
> 6mBar?
Geysers
Deep Impact
Giotto
DS-1
Stardust
Liquid water
• The phase state diagram
of water:
T>0C + P>6mBar = water.
• Look at the IR map of Tempel-1, and see how much of the
surface is ~275K. How does one get such great thermal
conductivity? And maintained right at 275K?
Water.
• What is the consequence of a wet comet?
Enormous
A Comet’s Life (2005)
a)
Ice
Liquid
Vapor
Spin Axis
Pristine
d)
Prolate
tumbler
Melting
snowball
e)
Polar jet
c)
b)
Splitting
Cement
Spin
Flip
g)
f)
Eggshell
Rubble pile
Meltwater Heliocentric Radii
•
•
•
•
•
Input 1.4 kW/m2 /AU2 is solar radiation
Albedo 4%
Most cooling on sunlit side = s T4
AU2 =s T4 / (0.96*1400W)  2.1 AU (Mars)
If we assume a poor IR emitter and/or a
surface topography (crevice) gives 45o view of
sky: 1/6 emissions = 5.1 AU (Jupiter)
• And R-T would move this heat into the comet.
How much water?
• A 5km radius comet with albedo 0.03 passing within
the orbit of Earth will intercept enough sunlight to
melt ~1 km3, or a layer some 3m deep on the comet.
• Since the Hadean somewhere between 1 x109-14
comets have passed through our solar system close
enough to accrete on the Earth.
• From the last 200 years, Marsden’s catalogue
includes 300+ “Oort Cloud” long period comets, or
about 2/year.
• The amount of “previously melted” ice in the Oort
Cloud is approx. the volume of the Earth’s oceans.
What about Tempel-1? (2006)
• From the wet comet=critical period calculation,
T=41hr, D=20kg/m3. That’s really fluffy snow! And
completely inconsistent with cratering data.
• But that assumes uniform density. If the comet has
vapor pockets, then RT instability still operates.
R-T
R-T
g
r
If pristine comet has
D=200 kg/m3, we
estimate 90% of the
interior is vapor, 10%
pristine.
3. Comet hydrosphere is large
…and dense enough to sustain an
ecosystem of extraterrestrial life
independent of Earth.
Can life survive space transport
from comet to comet?
• Freeze-drying or lyophilization is the preferred way
to preserve bacteria. “hard” radiation is more
serious, but for short times (Apollo capsule~1week)
bacteria survived just fine.
• Relative velocities between comet & accreting
material is high, perhaps 15-50 km/s, potentially
incinerating life.
• Brownlee particles survive deceleration in 100km at
Earth if r<100microns. Cometary atmospheres
extend ~1 Gm and so max size is r < 3mm. Outflow
of 1km/s  a minimum size too.
How long can life survive space?
• Antarctic glacier at T<273K,
viable > 8 Myrs
• Spores in amber at ambient
T; viable > 40Myrs
Hoover 2000
• Bacteria collected from salt
deposits,>250Myrs
“Hard radiation” may be the
limiting factor mitigated by
being frozen inside a comet.
Vreeland
10m of shielding is virtually
Bacillus permians
infinite.
Comet biosphere is at least 3.5Ga
…and potentially even older.
Can comets seed the galaxy?
• The 1 km/s jets on comets give them “nongravitational” forces, that can convert a bound,
elliptical orbit, to an unbound, hyperbolic orbit
• Marsden’s catalog list 33/307 Oort Cloud comets on
hyperbolic trajectories. 23/33 begin trapped and end
hyperbolic (ejected), 10 begin hyperbolic.
• Using a 2km/s interstellar speed (after climbing out
of the solar system gravity well), the nearest star
system is reached in 600,000 yrs.
• Life can survive when frozen in 10m of ice.
Can another star trap a fast
comet?
• The deceleration must be gentle to avoid sterilizing
all the life.
• It need not land on a terrestrial planet, merely be
injected into elliptical orbit, gravitationally bound.
• The non-gravitational forces (jetting) is proportional
to stellar radiation, so the closer the comet passes
near a star, the likelier it will decelerate.
• The excess energy of comet to be shed = ½ mv2
• Rocket equation: v ln(m/M)=V where jet = 1km/s,
m/M ~ 2, V~2km/ssx
Probability of infection
• Interaction time, I = 1/n σ v
– Cross section σ~ π(4AU/v)2
– n=0.01 stars/ly3 average for Milky Way
– v=2km/s  I=1e16 years, longer than the Universe!
• But many comets are ejected in this time.
– Interaction probability = dt/I
– Ejection rate P= 0.1/yr
n
• 1 = 0∫T1 Pt dt/I  T1=400Myr
– Repeat for T2, T3…and sum the series,
• N= 0.6031 exp(0.83806 T √I/P)
• Galaxy is infected in 10Gyrs
v
σ
Other locations & rates
• The comet production rate of our solar system was
much much higher 4 Gyr ago. Delsemme (1996)
estimates a rate 10,000 higher than today. Such a
“pulse” would reduce T1  50Myrs
• Density of stars in a globular cluster is 100x greater
than galaxyT1=40Myr first infection, entire
cluster of 50,000 stars in 100 Myr. This produces a
“pulse” within the galaxy.
• So galactic infection time is overestimated using the
homogeneous density, and 1Gyr is closer.
What about other galaxies?
• Andromeda is 250Mly away.
• Comet must travel some 200km/s to reach
Andromeda (we assume a Kolmogorov spectrum of
comet speeds, (200/2)-5/3=0.04% of production rate)
• Cross-section for capture is now very small, about
0.001% σ, aerocapture & Jovian gravity assist.
• Then a comet going fast enough to reach
Andromeda, has small probability of capture, so that
in 10Gyr with entire comet output of Milky Way, it
remains a 1:100 bet that Andromeda remains sterile.
Panzooia
If our solar system has a hydrosphere of infected ice
equal to the Earth’s ocean, then the galaxy of 200
billion stars, must have 10billion or so Oort Clouds,
not including the reservoir of interstellar comets.
If these comets are infected as we claim, then
cyanobacteria are not evolved for Earth life, but for
comet life, and continually raining down on the
Earth.
Cyanobacteria adaptions
Giott
1. Lyophilization
2. Mats-- (why didn’t they evolve leaves?)
3. Polysaccharide sheaths--plug the pores of comets,
increase tensile strength, blacken to keragen under
UV, increase thermal transfer, stick to surfaces…
(What is albedo of all comet nuclei observed?)
4. DNA conservation-- (Prochlorococcus marinus
smallest genome, yet duplicates
nucleotidases)
5. N2 fixing--Only organism that both fixes
nitrogen and photosynthesizes, without which
Conclusions
• Panspermia sees the habitat for life as an
Earth-like planet with liquid water, and comets
as the bus transferring life between habitats.
• Panzooia sees the major habit for life as
comets, and Earth-like planets are an
insignificant blip in terms of DNA mass.
• Just as Copernicus removed Earth from the
center of the physical universe, so this model
removes Earth from the center of the
biological universe.
Conclusions
• Quran, Sura 21:30 The heavens and the earth were a
closed-up mass, then We [God] opened them out. And
We made from water every living thing.
• Genesis 1:1-2 In the beginning, God created the
heavens and the earth. The earth was without form
and void, and darkness was over the face of the deep.
And the Spirit of God was hovering over the face of
the waters.
• If “earth” = matter & “formless”=stellar nebula before
star burning had begun, then “waters” = Oort Cloud.
And since “Spirit“= the awakening of Adam, then
“Spirit hovering” =“life evoking” waters.
• Even for creationists, life began with comets.