[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][Hot springs from impacts]

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:

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!)

Update: May 04

Meteorites from Venus

So far no meteorites from Venus have been found on Earth. I asked Jay Melosh how we might recognise such meteorites. He replied:

Venusian meteorites would, in fact, be easy to spot and are on the list of most serious meteorite hunters.  As you know, lunar and Martian meteorites have been confirmed and there is a report (not widely accepted) of a Mercurian meteorite.  However, a Venus meteorite would be easy to spot from its composition and age.  Of course it would be an achondrite and almost certainly of basalitc composition like the Martian Shergottites.  What would stand out is that the K-Ar or Ar-Ar age would be identical to its cosmic ray exposure age, since the Venusian surface is uniquely hot enough to degas Ar as quickly as it forms and so Ar could not accumulate.  Less easily reset chronometers, such as U-Pb would presumably show its crystalization age, which would be around 700 Myr.

Regards, Jay

Related links


CCNet 69/2004 - 10 May 2004

Let's welcome the apology of John Michael Williams (CCNet, 67/2004 - 6 May 2004) for mistakenly claiming to have shown that impacts on
Mars cannot eject meteorites (CCNet 129/2002 - 11 November 2002). So seldom do scientists have the courage to admit to careless errors.

But he's wrong to still assert that "impact ejection from Earth should not be possible". We reviewed the arguments for our paper in
Monthly Notices in February (Wallis and Wickramasinghe MNRAS 348(1) 52-61, 2004).

Incoming comets can have impact speeds well above 2-3 times the 11.2km/s escape speed, the criterion used by Melosh. JMW's view may
be based on the maximum shock speed in rock being sufficient to eject spall above the 5km/s martian escape speed, but not above 11.2km/s.

But the physical model is probably incomplete because spalled ejecta are in practice blown out on the plume of fluid created in the
hypervelocity impact. Some martian meteorites (Chassigny) are so lightly shocked that JMW's analysis would doubtless exclude pure
shock ejection. Alvarez, Claeys & Kieffer (1995) argued similarly that shocked crystalline quartz from the Chicxulub crater found as
far as 10 000 km away is evidence of debris riding with the vapour plume, because ejection at the 7-8 km/s speed necessary to reach such
distances would have melted the quartz.

Metre-sized pieces of spall could not penetrate individually an atmosphere of density ~10 000 kg/m2, comparable to early Martian or
present terrestrial atmospheres, as Mileikowski et al. (2000) supposed, for such metre-sized rocks would need impossibly high
initial speeds in order to push aside several times their own mass of air.

We pointed out that Jay Melosh in his book (1988) did acknowledge that the sheer bulk of ejecta could far exceed the mass of the
atmospheric cone blown out by the plume. Some workers have speculated that the ejecta might escape up the hole punched by the
incoming impacter, but this is a trivial fraction of the air cone  blown out in a Chicxulub-sized impact.

People need to recognise that plume-ejection rather than impact ejection is the main mechanism for projecting planetary material into
space. This has substantial implications for the amounts of ejecta, for the sizes of ejecta (including plenty of smaller fragments and
soils) and for the viability of biomaterial within the ejecta.

The terrestrial atmosphere quenching of the ejection to space can be related to the minimum crater size (with some dependence on impact
speed). We estimated (Wallis and Wickramasinghe 1995) the minimum size as ~75km (for 55km/s impact) from the Melosh-Vickery approach.
This value is consistent with the 180km Chicxulub crater.

Even if the size is out by a factor two, impacts predicted from the short period comets and near-Earth asteroids of around 1 km radius
(Napier) are too small (and too low speed) to give plume ejection from the Earth - Napier's 50-60 km/s impacts from Halley-type and
long period comets (3-6 predicted per 10 Myr) remain as possibles. Since craters are ~20 times the size of such impacters, the 75km
minimum crater size for plume-ejection gives a cut-off of about 4km diameter impacter. With uncertainty to a factor two - to a factor
four in ejection frequency - improved estimates of this cut-off would be welcome.

Alvarez W., Claeys P., Kieffer S. W., 1995, Sci, 269, 930
Melosh H. J., 1989, Impact Cratering: a Geologic Process. Oxford Univ. Press, New York,
Mileikowski C. et al., 2000, Icarus, 145, 391
Napier W. M., MNRAS 348(1) 46-51, 2004
Wallis M. K. and Wickramasinghe N. C., Earth Planet Sci. Lett. 130, 69-73, 1995
Wallis M. K. and Wickramasinghe N. C., MNRAS 348(1) 52-61, 2004

Max Wallis
Cardiff Centre for Astrobiology tel. 029 2087 6436
2 North Road fax 029 2087 6424
Cardiff University CF10 2DY

c2004 CCNet
20 Mar 1999: ABC Radio Science Show had a report on Queensland research into nanobacteria (nanobes). The discovery was made by Dr Philippa Uwins. The findings have implications for:

News (latest at bottom)

Impacts, hot springs and the origin of life

Many more extremophile links at NAI