From: Henry Baker <hbaker1@pipeline.com> To: math-fun <math-fun@mailman.xmission.com> Subject: [math-fun] Fwd: Re: Ejecta from Earth ? Venus ? Message-ID: <E1SHc69-0007aU-9C@elasmtp-curtail.atl.sa.earthlink.net> Content-Type: text/plain; charset="iso-8859-1"

FYI -- Here is Dr Melosh's response to my question:

...

From: "Melosh, Henry J" <jmelosh@purdue.edu> To: Henry Baker <hbaker1@pipeline.com> Date: Tue, 10 Apr 2012 10:06:12 -0400 Subject: Re: Ejecta from Earth ? Venus ?

Dear Dr. Baker:

The atmosphere issue was one of my concerns from the very beginning of such considerations--it is not something that I have overlooked! There is substantial evidence that impacts that produce craters greater than about 10 km diameter on the Earth and about 30 km on Venus breach the atmosphere and eject material directly into space. This evidence is not (yet!) based on the discovery of Earth or Venus meteorites, but rather on the observation of crater ejecta that has traveled immense distances before reentering the atmosphere: That is, material that nearly, but not quite, left the planet. On Venus, this comes in the form of the dark parabolas of ejecta from larger Venusian craters that blanketed the surface with ejecta more than about 10 cm deep (equal to the wavelength of the Magellan radar that detected these deposits) for distances exceeding 5000 km from the impact. On Earth, ejecta from craters like Chicxulub, Popagai, down to Bosumptwi can be found at distances ranging from thousands of km to the antipode of the crater. The 22 km diameter Ries crater in Germany threw intact rocks more than 300 km into Switzerland. These ejecta cannot have traveled this far through the atmosphere and so clearly were thrown above it as part of the plume of vaporized and melted rock, mixed with intact fragments, that expands out of any high speed impact crater.

As to nuclear explosions breaching the atmosphere, see Jones, E. M. and J. W. Kodis (1982). Atmospheric effects of large body impacts: The first few minutes. Geological Implications of Impacts of Large Asteroids and Comets on the Earth. L. T. Silver and P. H. Schultz, Geol. Soc. Amer. Sp. Pap. 190: 175-186.

I have published on this atmosphere breaching in a variety of media, as a google or ADS search would quickly show.

Sincerely, Jay Melosh

--this doesn't seem convincing to me. Here is the situation: A. meteor falls in at somewhat more than escape velocity, perhaps as much as 1.5X escape. B. ejects material presumably at large initial speeds but not as large as the impactor's speed. C. ejected material slowed and/or destroyed by atmosphere. D. hopefully still has enough speed to escape planet. Now if an ejected item (B) reaches 100s to 1000s of km from the impact site before landing, that is WAY short of reaching escape velocity. It merely indicates it reached maybe 50% of escape velocity. It is hugely more difficult to gain factor 2 in speed. This can be regarded as evidence in my favor and against Melosh, but he regards it as evidence in his favor. Furthermore, since Melosh cites a boulder in Switzerland that was found 300 km from the impact site as his best on-earth evidence, let me ask this: Where are all the boulders, that were ejected from impact sites all over earth, then fell back down in Antartica? Meteorites are very easy to find in Antartica because highly visible on top of ice, and get carried to glaciers to certain sites. Far more meteorites have been found in Antartica than everyplace else combined. It seems to me, if Melosh were right, there'd be lots of them. But there are zero. By contrast, there are loads of meteorites found that came from the moon, where there was no atmosphere to mess it up! I suggest to you that this combination of evidence and non-evidence supports me, not Melosh. Finally re Jones+Kodis, I have not seen this paper. But I can tell you right now, from the power of pure thought, that any claim (which Melosh made in the video) that a small iron disklike object (I thought he was contending it was about the size of a dinner plate) initially launched at 17 km/sec, would escape Earth, is a false claim. The air would slow it down to well below escape velocity and/or destroy it. It simply could not escape Earth. This calculation is easy and you should make your own calculation independently of me if you do not believe me. Oh wait, somebody else did that already: According to the American Meteor Society Fireball and Meteor FAQ http://www.amsmeteors.org/fireballs/faqf/ item 12, meteors weighing less than 8 tons retain essentially none of their cosmic velocity when passing through the atmosphere, they simply end up as a low speed falling rock. Only objects weighing many times this mass retain a significant fraction of their velocity, e.g 1000 tons retains 70%. So we conclude that ejected matter in (B) to escape earth would need to be a chunk weighing>8 tons and probably 1000 tons. The question is: will such chunks exist, or would they be fragmented by the postulated 100,000g acceleration? However... I found this: http://nuclearweaponarchive.org/Usa/Tests/Brownlee.html which seems to be what Melosh had in mind, although the details differ much from Melosh's oral account. In this account, the object was a 4-inch thick steel plate 4ft in diameter, and even though it was predicted by a simulation the simulator himself did not believe to reach 6X earth escape velocity, and they knew this prediction, and they intentionally tried to measure it with a pre-planned hi-speed camera, they failed massively since only one movie frame had it. (Very poor experimental planning...) And it would appear this result was never published, despite Melosh making it sound like it had been, since presumably the primary source Brownlee would have said so. Anyhow, this is much larger than a dinner plate. Could this escape earth? Such a plate would mass 924 kilograms. This is well below 8 tons. Also a randomly rotating disk is way less aero than a ball per unit mass. So the answer still is NO, it could not have escaped Earth.