From: Henry Baker <hbaker1@pipeline.com> To: math-fun <math-fun@mailman.xmission.com> Subject: [math-fun] "Ejecta" from planet to planet Message-ID: <E1SH508-0007PE-OK@elasmtp-spurfowl.atl.sa.earthlink.net> Content-Type: text/plain; charset="us-ascii"
The following video explains in pretty good detail how impact craters can eject material from the surface of a planet into the solar system & find its way onto other planets. In fact, approximately 20% of such material actually gets ejected from the solar system.
The probability appears overwhelming that over the 4.5 billion years of the solar system, there has been a relatively significant exchange of material among the planets, including some meteors that fell onto Earth from relatively recent impacts on Mars. If there were any microbial creatures in these rocks, they are highly likely to have survived the original launching (100,000 G's) and the re-entry into the second planet.
One Los Alamos scientist placed a steel object on the surface for an underground nuclear explosion in the early 1950's and this object may have achieved priority as the first man-made object to escape the Earth's gravity.
This scientist estimates that the Earth gets many tons of material ejected from Mars every year, although much of this material may have been hanging around the solar system for millions of years before finally landing on Earth.
He comments that the meteor that caused so much trouble 65 million years ago almost certainly ejected much material into space. Since the Earth was absolutely teeming with life at the time, it would be inconceivable if such life were not carried away with the ejected material.
If I understood this video correctly, if an explosion exceeds approximately 250 megatons, then the fireball itself -- i.e., a portion of the atmosphere -- may escape from the Earth. This apparently answers a question I posed here a while back about whether one or more large collisions could have carried away a significant fraction of the Earth's atmosphere -- they answer may very well be "yes".
------- Are We All Martians? The Meteoritic Exchange of Life between Planets Monday, April 20, 2009 10:38 AM
Dr. H. J. Melosh is Professor in the University of Arizona Lunar and Planetary Labs. His research interests include theoretical geophysics and planetary surfaces. Presented Feb. 24, 2009.
56 minutes.
http://deimos3.apple.com/WebObjects/Core.woa/FeedEnclosure/arizona-public-dz...
--I'm skeptical on some of your/Melosh's claims, but agree re others. Ejecting rocks from a planet via a collision is difficult if that planet has a big atmosphere. Several meteors have been found that are known to have come from Mars, which has a small atmosphere. A large number are known to have come from our moon (about 1 in every 1000 meteors). I would not be terribly surprised to see meteors from Mercury, although none have been found yet, and from other moons. However, as far as I know, no meteor has ever been found that came from Venus, Jupiter, Saturn, Uranus, Neptune (big atmospheres). Earth has an intermediate size atmosphere and I think it would be difficult to eject earth rocks. To get a meteor thru an atmosphere, it needs to be large, otherwise it vaporizes. (Small ones can land, but I think the only way that can happen is if they originally were part of something large.) The threshold size should be of this order: approximately so large that the mass of the meteor is the same as the mass of the column of atmosphere "carved out" by the meteor, which for a spherical rock with density D in grams/cc would be diameter>=1500cm/D in Earth atmosphere (pressure = 1kg/cm^2). With D=3 we get diameter>=500cm=5meters. For Venus the size threshold would be more like 3000 meter diameter! However, one might conjecture that an impact big enough to blast huge rocks to well above escape velocity would shatter those rocks, i.e. not giving us big intact ones. Melosh leaves this whole issue totally un-discussed. If so, then ejection would be very rare or impossible. So here is my conjecture: Fugeddaboudit, you are not going to get meteors from Venus. Deinococcus Radiodurans http://en.wikipedia.org/wiki/Deinococcus_radiodurans is a common microbe with amazing radiation tolerance, it has 37% survival of 15000 Grays. http://www.srl.caltech.edu/ACE/ASC/DATA/bibliography/ICRC2005/usa-mewaldt-RA... says unshielded space dose is 10 centiGray per year on average So this dose is probably about what you'd get from a 150000 year sojourn in space, and you'd survive longer the deeper you were shielded inside a rock. So anyhow I agree microbe survival would be possible.