Comets spread Earth-life around galaxy, say scientists

Cardiff University ^ | 10 February 2004 | Staff

[PatrickHenry]

If comets hitting the Earth could cause ecological disasters, including extinctions of species and climate change, they could also disperse Earth-life to the most distant parts of the Galaxy.

The "splash-back" from a large comet impact could throw material containing micro-organisms out of the planet’s atmosphere, suggest scientists from Cardiff University Centre for Astrobiology.

Although some of this outflowing material might become sterilised by heat and radiation, they believe that a significant fraction would survive. As the Earth and the Solar system go round the centre of the galaxy every 240 million years, this viable bacterial outflow would infect hundreds of millions of nascent planetary systems on the way. Hence, they suggest, the transfer of Earth life across the galaxy is inevitable.

These ideas are discussed in detail in two papers appearing in the current issue of the Monthly Notices of the Royal Astronomical Society.

The authors of the two papers are Professor Chandra Wickramasinghe and Dr Max Wallis, of the Cardiff Centre for Astrobiology, and Professor Bill Napier, an astronomer at Armagh Observatory and an Honorary Professor at Cardiff University.

Interstellar routes for transmission of micro-organisms supports the view that life may not have originated on Earth but arrived from elsewhere, strengthening the "panspermia theory" that Professor Wickramasinghe and the late Sir Fred Hoyle had been developing since 1974.

It is known that boulders and other debris may be thrown from the Earth into interplanetary space. Professor Napier finds that collisions with interplanetary dust will quickly erode the ejected boulders to much smaller fragments and that these tiny, life-bearing fragments may be driven out of the solar system by the pressure of sunlight in a few years.

The solar system could, therefore, be surrounded by an expanding `biodisc’, 30 or more light years across, of dormant microbes preserved inside tiny rock fragments. In the course of Earth history there may have been a few dozen close encounters with star-forming nebulae, during which microbes might be injected directly into young planetary systems.

If planets capable of sustaining life are sufficiently common in the Galaxy, the Cardiff based scientists conclude that this mechanism could have infected over 10,000 million of them during the lifetime of our Galaxy.

Dr Wallis and Professor Wickramasinghe have also identified another potential delivery route. They point out that fertile Earth ejecta would, on impact, bury themselves in the radiation-shielded surface layers of frozen comets. A belt of such comets, the Edgeworth-Kuiper belt, lies beyond the planetary system. This belt gradually leaks comets into interstellar space, some of which will eventually reach proto-planetary discs and star-forming nebulae. There they are destroyed by collisions and erosion, releasing any trapped micro-organisms and seeding the formative planetary systems.

[Junior]

Those are only the "visible" stars within 50 light years. Gliese lists something like 700 total stars within that sphere.

[Junior]

During the past 4.6 billion years, the local neighborhood has changed considerably. Some of the stars nearby were much further away and those further away were once much closer. One must also take into account the "wake" of debris our Solar System has smeared along its orbit around the center of the galaxy during its several rotations in that time. Other stars are passing through that wake all the time, some of them are hundreds, if not thousands of light years away.

[Junior]

In order to infect 10,000 million systems in the period of life 65 million years we would have to on average pass within 15 light years of 153 new stars each and every year.

Try 3.8 billion years, which is how long life has been on this planet.

Also, we seem to be working from the assumption that Earth is the origin of life. Earth may have been a secondary host and the primary could be a long way off...

[PatrickHenry]

One must also take into account the "wake" of debris our Solar System has smeared along its orbit around the center of the galaxy during its several rotations in that time.

It seems that we are very unsanitary, leaving all this biological debris in our wake. A truly advanced species would take care to avoid such unseemly littering. No wonder the aliens avoid our planet. It's so ...yucky around here!

[RightWhale]

Certainly this seems possible. Whether the virus or whatever form the life takes as it drifts through interstellar space with or without comets would then find a good home that is just right so it can then evolve into intelligent forms seems near impossible. Yes, there is life everywhere; no, intelligent life exists only here. So say Ward and Brownlee and their view of the matter seems sound.

[edwin hubble]

This theory could be tested by the presence or absence of life-molecules on Mars.

The nearest Petrie dish.

[LRS]

I shudder to think of the life forms spread by Comets..

[js1138]

One must also take into account the "wake" of debris our Solar System has smeared along its orbit around the center of the galaxy during its several rotations in that time.

Sorry. but the wake travels with us, just like the bags of peepee ejected by astronauts.

[Junior]

If the ejecta is travelling fast enough to escape the Sun's pull (which would be the case with any object capable of reaching another solar system), it won't necessarily be dragged along with the rest of the Solar System. It'll trail along the orbit the Solar System makes as it moves around the galaxy, spreading out like the wake of a ship.

[js1138]

Correct. I jumped in without reviewing the original article. But I'm pretty sure it would still have a lot of the earth's/solar system's momentum.

The boat moves absolutely with reference to the water. The earth moves with the rotation of the galaxy. So the spreading of the wake would be much slower than the rotational velocity.

Am I all screwed up on this one?

[Junior]

True. However, the Solar System has been "around the block" several times (something like 200 million years per rotation) since life appeared on Earth).

[js1138]

So the question would be, what is the rate of expansion of our wake reletive to the size of the galaxy.

[Junior]

Methinks this would be a job for RadioAstronomer. For the lower limit, you would need to know the escape velocity of the Sun and the orbital speed of the Solar System.

[VinayFromBangalore]

In Britain,a billion is a million million.In America,a billion is a thousand million.Now get the picture?

[Doctor Stochastic]

Often the main difference between science reportage and political reportage is the the political reporters actually may have voted at least once.

[jennyp]

True. However, the Solar System has been "around the block" several times (something like 200 million years per rotation) since life appeared on Earth).

That is amazing.

[Condor51]

"panspermia theory"

Hey, weren't they part of the Superbowl Halftime show?

(just kidding. I know they were canceled)
kidding again :-)

[SunkenCiv]

Note: This topic is from 2004.