[Swapping Rocks][News] [Carl Sagan's speculations] [ Jay Melosh's 1998 Papers] ["5th Miracle" by Paul Davies][Venus] [Nanobes] [Panspermia] [Rocks between stars] [Research in the1960s] [More links] [Updates] [Genesis radio show] [Transpermia paper] [Extremophiles]
This mechanism was recently given the name "lithopanspermia" (rock-across-seeding?) , which I find rather unimaginative. Oliver Morton came up with the term "Transpermia".
26 Aug 08 TPS: Support The Planetary Society Phobos LIFE Project - urgent request for donations to send microbes on a round trip to the Martian moon to test the transpermia hypothesis.
29 Jul 10 AMEC2010: Potential for microbe colonisation of Mars by rocks launched into space by the Chicxulub impact - paper by Michael Paine. Youtube video of the presentation (no audio) + Updates:
- 14 Apr 15 BBC: Evidence of liquid water found on Mars (strengthens my speculation) +
- 29 Sep 15: NASA Confirms Evidence That Liquid Water Flows on Today’s Mars
- 3 Mar 17 Uni Arkansas: Is Anything Tough Enough to Survive on Mars? + NASA: Microbes Could Survive Thin Air of Mars.
Translations available: Belorussian, Ukrainian, Boongoo, Swedish etc (you will have to search for them - I don't link to pages that I don't understand!)
Extract from the July 1994 issue of Planetary
The returning Apollo 11 astronauts' triumphal reception in July 1969 was somewhat delayed by a strict and lengthy biological quarantine. In those days, no one was certain that the Moon was entirely sterile. No one knew whether the lunar rocks might harbor deadly microorganisms. One wonders whether the level of concern would have been as high if scientists had known that dozens of lunar rocks had been lying in the Antarctic ice for thousands of years, or that about 10 small fragments of the Moon must fall onto Earth's surface every year. Unfortunately for the astronauts, the first lunar meteorite was not recognized until 1982. Before that time, no one seriously believed that nearly unaltered rocks could be blasted off the surface of one planet and later fall onto the surface of another.
Now, however, not only do we know that lunar rocks occasionally
fall to Earth, but we are also reasonably certain that a group of nine
meteorites, the so-called SNCs (for Shergony, Nakhla and Chassigny,
the sites where they landed), originated on the planet Mars. Although
all of the lunar meteorites were collected long after they fell, four
the SNCs were observed dropping from the sky. In 1911, a piece of
which fell near Alexandria, Egypt, killed a dog, scoring the only known
fatality (of a mammal) caused by a meteorite. [update: more recent work suggests
The total flux of martian material falling onto Earth has been estimated at about half a ton per year. Under these circumstances, it may seem silly to worry about hypothetical martian organisms contaminating Earth, since martian material has evidently rained down on our planet throughout its history. Although a good case can be made for limiting modern biological contamination of Mars by terrestrial spacecraft, the discovery of Mars rocks on Earth brings up the immediate question of whether Earth rocks have been ejected into space, eventually to fall onto Mars, thus closing the circle of potential contamination.
Older work on the maximum velocities achieved by impact ejecta focused on the relationship between the pressure in the shock wave generated by the impact and the velocity of material just behind the shock. Measured directly in laboratory experiments, the shock pressure needed to accelerate material to planetary escape velocities--2.4 kilometers per second (about 5,000 miles per hour) for the Moon, and 5.0 kilometers per second (about 11,000 miles per hour) for Mars, implying pressures of 0.44 and 1.5 megabars (a megabar equals 1 million times Earth's atmospheric pressure at sea level) for lunar and martian basalts, respectively-would have been high enough to melt or even vaporize the ejected rock. Yet study of the lunar meteorites indicates that their ejection was accompanied by no more than about 0.2 megabar of shock, and the most highly shocked martian meteorites (which contain pockets of once-melted glass) still indicate only about 0.4 megabar.
The problem with the pressure-velocity relationship is that it applies only to material completely engulfed by the shock wave. Very close to the target surface, however, the ambient pressure is zero. No matter how strong the impinging shock wave, the free surface can never be raised to a pressure higher than zero. This effectively shields surface rocks from strong compression. However, the pressure increases very rapidly with depth below the surface, which translates into a powerful acceleration that throws lightly shocked surface rocks our at speeds comparable to the original impactor's speed.
An experiment performed several years ago by Andy Gratz and colleagues at the Lawrence Livermore Laboratory has verified the general correctness of this model. An aluminum projectile about the size of a penny was fired at a granite block at about 4 kilometers per second (9,000 miles per hour). Material from the face of the block was ejected at about 1 kilometer per second (2,000 miles per hour). This material was caught in a foam cylinder and, upon analysis. proved to be composed of millimeter-size, lightly shocked fragments of granite.
Furthermore, blocks up to a meter in diameter from the uppermost limestone layer surrounding the 24-kilometer diameter (l5-mile) Ries impact crater in southern Germany have been found nearly 200 kilometers away in Switzerland. Although they were not actually ejected from Earth, these blocks again show a combination of low shock damage (less than 10 kilobars. 10,000 times Earth's atmospheric pressure at sea level) and high ejection velocity (1.4 kilometers per second or about 3,000 miles per hour). Thus, current theory, experiment and observation all agree in indicating that a small quantity of material near the surface surrounding the site of an impact is ejected at high speed while suffering little shock damage.
Impacts such as the one that created the 180-kilometer diameter (110-mile) Chicxulub crater in Yucatan 65 million years ago (and incidentally caused a profound extinction that wiped out the dinosaurs, among others) may have launched millions of rock fragments 10 meters (30 feet) or more in diameter into interplanetary space. Of these fragments, a small fraction, perhaps 1 in 500, would have been so lightly shocked that internal temperatures remained below 100 degrees Celsius (212 degrees Fahrenheit). Higher temperatures would presumably kill any microorganisms present in the rock, but a few thousand of the ejected rocks, those originating nearest the free surface, could have carried viable organisms into interplanetary space. Although such impacts are fortunately rare at the present time (the only comparable craters known are the 1.85-billion-year-old Sudbury crater in Ontario and the 1.97-billion-year-old Vredefon crater in South Africa), the much higher cratering rate early in solar system history during the period of late heavy bombardment that lasted up to about 3.8 billion years ago would have made ejection of microorganisms a much more common occurrence at that time.
The most lightly shocked rocks ejected at high speed are necessarily those closest to the free surface. The surface is also the place where biological activity is highest, so that a large impact on Earth, or on an earlier life-harboring Mars, would be very likely to throw rocks that might contain microorganisms into interplanetary space. Larger organisms, even if present, would be unlikely to survive the 10,000 g accelerations accompanying the launch process.
Current cratering calculations indicate that large lmpacts even on Venus, despite its dense atmosphere, could eject surface rocks into interplanetary space. Meteorites from Venus have not yet been discovered, but there appears to be no reason why they might not someday be found on Earth. Large impacts on all of the terrestrial planets are thus capable of ejecting lightly shocked surface rocks into interplanetary space. If there should be microorganisms on the surfaces of these planets, then they too have a chance of journeying to another planet.
After a long series of such encounters. a few fragments' orbits get "pumped up" sufficiently to cross Earth's orbit. Then the more massive Earth takes over this cosmic volleyball game. changing the orbit still more, until the fragment may become Venus crossing. Sometimes the fragment is deflected all the way out to Jupiter or Saturn, which themselves may eject it from the solar system entirely. At any stage of this random walk through the solar system, the fragment may actually hit one of the planets, ending its journey.
Natural orbital perturbations thus supply the means for rocks ejected from one planer to spread throughout the solar system and eventually fall onto another planet (or leave the solar system entirely). This is presumably how the SNC meteorites reached Earth. Any microorganism contained in these rocks would thus have an opportunity to colonize the new planet, if it was able to survive both the journey and the fall to its destination.
Many microorganisms stand up surprisingly well to the space environment. Subjected to high vacuum, some bacteria quickly dehydrate and enter a state of suspended animation from which they are readily revived by contact with water and nutrients. Medical laboratories routinely use high vacuums for preservation of bacteria. Viable microorganisms were recovered from pans of the Surveyor 3 camera system after three years exposure to the lunar environment. However, these instances of preservation have only been tested over times approaching decades, not over the tens to hundreds of millions of years necessary for interplanetary travel.
Nature, however, has been kind enough to give us several instances of really long-term preservation of viable microorganisms. Chris McKay of NASA Ames Research Center has extracted microorganisms preserved for perhaps as long as 3 million years from deep cores in the Siberian permafrost. Even more impressive is the discovery of bacteria that were preserved for some 255 million years in salt beds of Permian age discovered at a site in New Mexico. Dehydrated by contact with salt and protected from radiation by the salt's low content of radioactive elements, these ancient bacteria demonstrated their viability by causing the decay of fish that had been packed with the salt.
Living bacteria can tolerate extremely high radiation doses, far higher than any multicellular organism can withstand. They can resist the effects of radiation largely because of active DNA repair systems. It is less clear that a dormant bacterium could tolerate large amounts of radiation. However, if the microorganisms happened to be living in cracks or pores of rocks that were ejected as large blocks, the rock itself might provide adequate shielding against both cosmic rays and ultraviolet light. Since it requires about 3 meters (about 10 feet) of rock to shield against high-energy galactic cosmic rays, if the impact event were to throw out rock fragments of about 10 meters (30 feet) diameter or larger, a significant interior volume would be protected against this radiation. Ultraviolet light can be screened by only a few microns of silicate dust, so the interiors of large ejecta blocks might be excellent havens for spacefaring bacteria.
The fate of a meteorite entering a planetary atmosphere depends largely upon its initial size and speed. Small meteorites, smaller than a few centimeters, burn up in Earth's atmosphere. Very large ones, a kilometer or more in diameter, traverse it without slowing and make craters. Meteorites of intermediate sizes, a few meters to tens of meters, however, are significantly slowed by the atmosphere. Buffeted by kilobars of aerodynamic pressure, they break up in the atmosphere (as did the famous Peekskill meteorite that disintegrated over the eastern United States on October 9, 1992) and may eventually fall to the ground in a shower of small fragments. Even on the modem Mars, with its tenuous atmosphere, meter-size meteorites are greatly slowed before striking the surface.
This scenario of slowing and breakup of intermediate-size meteorites is nearly ideal for the dispersion of microorganisms onto the new planet. Whether or not these organisms can survive and multiply depends, of course, on conditions at their new home. It seems unlikely that terrestrial organisms arriving on the modern Mars or Venus would survive. However, in the past conditions may have been much more hospitable on Mars at least, and perhaps at that time microorganisms from Earth found a home on Mars, or vice versa.
The current impact-exchange rates among the terrestrial planets are relatively low. However, during the era of heavy bombardment, when most of the visible craters on the Moon and Mars formed, cratering rates were thousands of times higher than current rates. Blue-green algae were apparently present on Earth as early as 3.5 billion years ago. and life may have been present even earlier, overlapping the period of heavy bombardment. Given the possibility of exchange of life among the planets by large impacts, we may have to regard the terrestrial planets not as biologically isolated, but rather as a single ecological system with components, like islands in the sea, that occasionally communicate with one another.
Although this scenario is highly speculative, it may be testable: If sample returns from former lake deposits on Mars should contain evidence of the existence of a microbiota, it may be possible to extract organic molecules from the samples. If familiar terrestrial molecules such as DNA, RNA and proteins are discovered, and especially if a genetic code similar to that of terrestrial organisms is found, then it would provide very strong verification of the idea that Earth and Mars have exchanged microorganisms in the past. Naturally, any such test requires that we be very careful not to contaminate the samples beforehand with terrestrial organic molecules.
H. Jay Melosh is a professor of planetary science at the Lunar and Planetary Laboratory at the University of Arizona. His latest book, Impact Cratering: A Geologic Process, has been published by Oxford University Press.
In an article titled "Some mysteries of Planetary Science" in the May/June 1988 issue of Planetary Report, Carl Sagan wrote:
A very recent and interesting analysis by H.J. Melosh at the University of Arizona shows that in the course of generating a l00-kilometer impact crater, debris can be transferred from Mars to Earth or vlce versa; the chunks being transported are big enough that anything inside them does not suffer significant radiation damage from the solar wind or solar ultraviolet light or cosmic rays during the roughly million-year time scale it takes to be ejected from the one world and swept up by the other. This has a serious biological implication. It suggests that on time scales of tens to hundreds of millions of years microorganisms from Earth arrive at Mars.
Is this true? If they survive the journey, would they survive the martian environment? And if we go to Mars looking for microbes and find one, is it indigenous, or is it some contaminant from Earth? How do we find out? And then there's even the remote possibility that a long time ago terrestial microbes got transported to Mars, sat around and maybe proliferated a while, and then another big impact on Mars ejected their remote descendants back to Earth. How much did they change in the meantime?
Jay Melosh is also participating in a gigantic collaboration to do
a careful analysis of the transfer of viable microorganisms from one
planet to another that will be published soon in Icarus:
Mileikowsky, C., Cucinotta, F., Wilson, J. W., Horneck, G., Lindgrin, L., Melosh, H. J., Rickman, H. and Valtonen, M. (1998) Natural transfer of viable microbes in space, Part 1: From Mars to Earth and Earth to Mars, submitted to Icarus. (not published as at May 1999) - Paul Davies: "It turns out to be even easier than we thought to cross-contaminate the planets."
ATLANTA (AP) - A primordial soup of complex organic
that could be the
precursors of life is cooked up very quickly after the birth of stars, new research suggests.
``Life could have had an easier time starting than we
before,'' astronomer Sun Kwok
said Wednesday at a national meeting of the American Astronomical Society.
Kwok, of the University of Calgary, Canada, said a study by
the Infrared Space Observatory
showed that large organic molecules evolve within only a few thousand years from chemicals
in the cloud-like envelope surrounding some stars.
The conclusion is based on the infrared spectra readings of
short-lived, carbon-rich stars that
are engulfed in clouds of gas and dust. Kwok said the clouds are rich in some of the most
advanced organic molecules ever detected in outer space.
``There is no doubt now that such complex molecules exist
the stars are able to make them
with no difficulty,'' said Kwok.
Such chemicals would eventually be ejected into interstellar
space, he said, which makes it
possible that they could end up on planets such as Earth where, under the right conditions, life
could have evolved.
Among the chemicals detected was acetylene, a building block
for benzene and other aromatic
molecules that, in turn, can form complex hydrocarbons, the chemical stuff of life.
Kwok said it is possible that amino acids could be
manufactured around stars, but this
molecule, essential to life, cannot be detected by the current generation of space telescopes.
The Infrared Space Observatory is operated by the European Space Agency.
Another international team has made calculations that
that life could have arisen on
Mars and then been transferred to Earth by meteorites jolted away from the surface of Mars
by asteroid impacts.
A team of astronomers from nine institutions and five
countries made a serious study of the
possibility and found that, if life ever existed on Mars, then there could have been up to five
trillion life-bearing rocks from Mars that landed on Earth over the last four billion years.
``The question is, are we really Martians?'' said Mauri
Valtonen of the Turku Observatory in
The international team also studied the possibility of
life-carrying asteroids from solar systems
beyond the sun landing on the Earth and found the probability of this to be very low.
``The ancestral cell for life on Earth must have originated
somewhere in our own solar
system,'' said Curt Mileikowsky, an astronomer of the Royal Institute of Technology in
Stockholm, Sweden, and a leader of the research team.
In their calculations, the astronomers considered how
frequently Mars would have been hit by
asteroids that blasted rock away from the Red Planet and sent it flying toward Earth. Although
only a few asteroids from Mars have been found on Earth, the team calculated that tons of
Martian rock is here.
The team also calculated the pressure, temperature,
acceleration and radiation a microbe
would have to endure to survive such a journey from Mars to Earth.
At least two well-known microbes, Deinococcus radiodorans
Bacillus subtilis, said
Mileikowsky, would be capable of surviving the trip. He said the microbes have been tested in
laboratories and found to be highly resistant to heat, radiation and acceleration forces.
Mileikowsky said the microbe would have to be near the core
of a Mars rock to be protected
enough to survive the journey through the vacuum of space and endure the searing fall to
``If the size (of the rock) is more than a football,'' he
said, ``heat would not have time to get
The astronomers estimated that up to one and one-half
of the microbes inside such a
rock would survive.
The existence of life on Mars is now unlikely, but
astronomers say that early in solar system
history the planet had water, an atmosphere and mild temperatures. For this reason, it is
believed that life could have once existed there. Scientists at the Johnson Space Center in
Houston say they have found evidence that life once existed inside a Martian asteroid, but the
conclusions are controversial.
Early in solar system history, it is also calculated that up
a trillion Earth rocks were blasted into
space and traveled to Mars. This means that life from Earth could have once seeded Mars.
``Because of the heavy traffic between Earth and Mars, we
couldn't decide which came first,''
Martian life on Earth, or the reverse, said Mileikowsky.
There is however a mechanism that might increase the chances of
exhange of rocks between planetary system - THE STARS MIGHT COME TO
US.In 1981 Jack Hills published a paper 'Comet showers and the
steady-state infall of comets from the Oort cloud'. He was looking at a
possible cause of comet bombardments. As part of this work he derived
estimates of the mean time between stars passing within a given
distance of our Sun. I don't know
if there have been updates to these estimates but here is a summary of
Minimum distance between Mean interval
star and Sun (au) (years)
500au 5 billion
1,000au 1 billion
5,000au 40 million
10,000au 10 million
This suggests that over the lifetime of the Earth about 4 star systems may have come within 1,000au of the Sun. It would be interesting to work out the odds of a microbe-bearing Earth rock finding its way into this region of the solar system (perhaps through encounters with Mars and/or Jupiter - the estimate is that several hundred kilograms of Earth rocks reach the surface of Mars each years so a reasonable number must just miss Mars and receive a slingshot to the outer solar system). Then the odds of it being "picked up" by a passing star and landing on a suitable planet - all within, say, 1 million years. No doubt they are extremely poor odds - but it would just take one successful exchange for panspermia to succeed.
One positive factor in this speculation is that it would take several years for the star to pass "through" the solar system. During this time there may be a major bombardment of the Earth by comets disturbed from the Oort cloud. The number of launches of rocks bearing microbes would therefore increase during this period (the delay in comets reaching the inner solar system may defeat this idea).
Michael Paine 5 Dec 2000
P.S. Jay Melosh advises that he is looking at this possibility for a forthcoming article in Icarus.
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Many more extremophile links at NAI