The Cometary Biosphere

Rob Sheldon,

Richard Hoover

SPIE SanDiego

Aug 28, 2007

Panzooia1. 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 60-foot RV, with satellite dishes.

Stardust mission to Wild-2

Stardust

Aerogel sample-and-return

Forsterite 1400CStardust

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

Giotto

DS-1 Stardust

Deep Impact

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)

IceLiquid

VaporSpin Axis

Spin Flip

a)b) c)

d)e) f) g)

Cement

Melting snowball Splitting

Prolate tumbler Polar jet Eggshell

Rubble pile

Pristine

Meltwater Heliocentric Radii

• Input 1.4 kW/m2 /AU2 is solar radiation

• Albedo 4%

• Most cooling on sunlit side = T4

• AU2 = 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.

g

If pristine comet has D=200 kg/m3, we estimate 90% of the interior is vapor, 10% pristine.

r

R-T R-T

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

• Bacteria collected from salt deposits,>250Myrs

“Hard radiation” may be the limiting factor mitigated by being frozen inside a comet. 10m of shielding is virtually infinite. Bacillus permians

Hoover 2000

Vreeland

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 “non-

gravitational” 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

• 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

• 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

Probability of infection

v

n

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 galaxyT1=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

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 comets could not be colonized.

Giotto

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.