Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from holmes.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr1/ota/space/space.dl) (->ota+space.digests) ID ; Sat, 27 May 89 00:19:46 -0400 (EDT) Message-ID: <4YTW7Lq00UkZAFj05n@andrew.cmu.edu> Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sat, 27 May 89 00:19:36 -0400 (EDT) Subject: SPACE Digest V9 #459 SPACE Digest Volume 9 : Issue 459 Today's Topics: Magellan Status for 05/22/89 (Forwarded) Magellan Status for 05/23/89 (Forwarded) Magellan Status for 05/24/89 (Forwarded) Magellan Status for 05/25/89 (Forwarded) News of the Week, May 24 Re: Sun's invisible partner NEMESIS Oort cloud is not `mythical' Teach your children well Re: The late NEMESIS Theory ---------------------------------------------------------------------- Date: 25 May 89 05:28:17 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: Magellan Status for 05/22/89 (Forwarded) [I was on travel the past few days, hence the late postings. -PEY] MAGELLAN STATUS May 22, 1989 Twice daily momentum wheel desaturations were performed with nominal results Friday, Saturday and Sunday. Daily star calibrations also were performed and both stars, Alpha Boots and Gamma Crux, were detected and a full attitude update was obtained. The flight team has been authorized to implement a plan to alternate use of the high-gain and medium-gain antennas at different attitudes to collect rocket engine module (REM) temperature data over a period between days 150 and 190. The information is expected to help in developing a solution to the anticipated overheating of the REMs when the spacecraft moves closer to the sun. On Saturday, the Cruise-2 sequence was uploaded to the spacecraft. It included the trajectory correction maneuver commands for Sunday's rocket burn which project said was "to perfection." Cruise-2 also will provide commands for the next 12 days. SPACECRAFT Distance From Earth (mi) 2,642,052 Velocity Geocentric 5,802 mph Heliocentric 60,057 mph Round Trip Light Time 14.1 sec ------------------------------ Date: 25 May 89 05:29:03 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: Magellan Status for 05/23/89 (Forwarded) MAGELLAN STATUS May 23, 1989 All Magellan spacecraft systems were working well today. The Navigation Team continued to refine its estimate of the accuracy of the Trajectory Correction Maneuver (TCM) Sunday which appears to be extremely precise. Twice daily momentum wheel desaturations and the daily star calibration were performed as expected. The X-band was turned on Monday afternoon and the spacecraft maneuvered to point the high-gain antenna to Earth for 10 hours of activity. Just before midnight (PDT) the spacecraft was turned to again aim the medium-gain antenna at Earth. The first very long baseline interferometry (VLBI) measurements were taken Monday using 34-meter DSN stations at Goldstone and Madrid. Also, engineering telemetry recorded during the TCM Sunday night was successfully played back at 115.2 kilobits per second to Goldstone and relayed to JPL. SPACECRAFT Distance From Earth (mi) 2,780,923 Velocity Geocentric 5,770 mph Heliocentric 60,091 mph Round Trip Light Time 14.9 sec ------------------------------ Date: 25 May 89 05:30:14 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: Magellan Status for 05/24/89 (Forwarded) MAGELLAN STATUS May 24, 1989 The twice daily momentum wheel desaturations and the daily star calibration were performed as expected. Analysis of stored trajectory correction maneuver (TCM) data confirmed the burn last Sunday was every bit as successful as first indicated. SPACECRAFT Distance From Earth (mi) 2,919,025 Velocity Geocentric 5,738 mph Heliocentric 60,128 mph One Way Light Time 15 sec ------------------------------ Date: 25 May 89 23:13:01 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: Magellan Status for 05/25/89 (Forwarded) MAGELLAN STATUS May 25, 1989 Plans are being made to place in Magellan's Cruise 4 and 5 computer command sequences information to help develop a solution to the rocket engine module overheating problem. Starting with Cruise-4, which will be uploaded on June 9, the spacecraft will be turned 180 degrees around an axis through the medium-gain antenna (MGA) to collect thermal data in a new attitude. Also, two new stars will be added to the star calibration sequence in Cruise-4. The spacecraft will scan the stars of a different spectral class to assist in adjusting the star-scanner acceptance criteria and on-board attitude determination. Those scans will not be updated, however. The twice daily momentum wheel desaturations and the daily star calibration were performed routinely Wednesday. Project has determined the time of day Magellan will reach its aim point at Venus on August 10, 1990. Without further trajectory correction it would be 10:30 a.m. PDT. Another trajectory correction maneuver scheduled for December, however, will skew that time by several minutes. SPACECRAFT Distance From Earth (mi) 3,056,363 Velocity Geocentric 5,706 mph Heliocentric 60,169 mph One Way Light Time 15.2 sec ------------------------------ Date: 24 May 89 21:02:21 GMT From: frooz!cfa250!mcdowell@husc6.harvard.edu (Jonathan McDowell) Subject: News of the Week, May 24 Jonathan's Space Report May 24, 1989 (no. 17) Delta II launch due for tonight if weather allows; Kosmos-2020 is up. The first launch of the Ariane 44L due soon. Rather a quiet patch at the moment, though. Have a nice long weekend; I'm forced to take it off as our system will be down for upgrade! -Jonathan ------------------------------ Date: 23 May 89 14:07:04 GMT From: nih-csl!jim@uunet.uu.net (jim sullivan) Subject: Re: Sun's invisible partner NEMESIS In article <723@Terra.cc.brunel.ac.uk> me85mda@cc.brunel.ac.uk (M D Ayton) writes: >>Oh, come now! I take it, Ed, that you will not consider Nemesis to >>exist unless/until it is directly observed. Does this mean you won't >>accept the existence of electrons until someone takes a photograph of one? > >No, and photographs can be faked - I may not even believe my very own mark I >eyeball! > >Martin. me85mda@me.brunel.ac.uk I hope that I am reading this right because I must get out my flame-thrower: FLAME ON Do I take it that Ayton wants Ed to "consider" the existance of Nemesis without any evidence? I know of a lot of evidence of the existance of electrons but very little if any evidence for the existance of Nemesis. And DON'T call periodic extinctions evidence. There are many theories around for the extinctions and Nemesis is the least favored. I, for one, would like to know how a binary star system could form with an orbital period of 20 million years with the companion getting close enough to disrupt the asteriod belt with the planets all seeming to have very stable orbits. If you want someone to "consider" a theory without any evidence, call it religion, and not science. FLAME OFF Jim Sullivan jim@nih-csl.dcrt.nih.gov ------------------------------ Date: Tue, 23 May 89 14:54 EST From: Subject: Oort cloud is not `mythical' Ed Nather writes: >Note that I did not say the theory was wrong, only unproven, and totally >lacking in observational evidence other than the known evidence it was >devised to explain. It has proved to be unprovable, hence "mythical." >I guess I would like it to be correct, since it's plausible, but my >gullibility was shattered as a child by an unplanned close encounter >with the tooth fairy ... I think it would be a good idea if you checked your dictionary again. Mythical does not mean unproven - rather it is something fictional, usually with supernatural overtones. And fictional means that something is not true. I agree that the location of the Oort cloud is in dispute, and that its existence is circumstantial. It is NOT, however, mythical or fictional. Rather, it is a scientific theory like any other, one that fits the available data reasonably well and better than any similar theory about the origin of comets. Your misuse of the word `mythical' insults the astronomical community, of which you are yourself a member. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Arnold Gill | If you don't complain to those who | Queen's University at Kingston | implemented the problem, you have | gill @ qucdnast.bitnet | no right to complain at all ! | -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ------------------------------ Date: Tue, 23 May 89 14:45:26 CDT From: pyron@lvvax1.csc.ti.com (Who remembers 8USER.PAR?) Subject: Teach your children well >From: cfa!wyatt@husc6.harvard.edu (Bill Wyatt) >From article <13140@ut-emx.UUCP>, by nather@ut-emx.UUCP (Ed Nather): >> In article <13325@swan.ulowell.edu>, devans@hawk.ulowell.edu (Daniel Evans) writes: >>> A couple of years back, I had read some accounts about a tiny (non- >>> identical) "twin" of our sun, which swings by every few million years or so. >>> Someone referred to it as "Nemesis". [bunch of ASCII deleted] > >>> My wife's sixth-grade students want to know... >> >> Teach them the difference between theory and observation, and you'll do >> them a life-long favor. >> >Absolutely. If anyone here wishes to make one positive impact on space or anything in the realm of science, teach your children and your neighbors basic principles of science. Observation, experimentation, the "scientific method". I am never so frustrated and morose about our prospects for the future as when I find someone misunderstanding science. Phrases like "it's been light-years since I saw home" (_Hard Time on Planet Earth_) or the number of people who use the word new-cue-ler to describe a certain energy source are just chops at our scientifc position. Kids who learn basic scientific principles and core mathematics will never be hurting for jobs. I just fear that they may find themselves in too much demand. more paranoia in the public interest form Dillon Pyron | The opinions are mine, the facts TI/DSEG Lewisville Computer Services | probably belong to the company. pyron@lvvax1.csc.ti.com | (214)462-5449 | We try, we learn, sometimes we die. | We sit on our butts, learn nothing, | and we still die. ------------------------------ Date: 23 May 89 22:35:07 GMT From: oliveb!tymix!3comvax!michaelm@apple.com (Michael McNeil) Subject: Re: The late NEMESIS Theory In article <13185@ut-emx.UUCP> ethan@ut-emx.UUCP (Ethan Tecumseh Vishniac) writes: >In article <1568@cfa.cfa.harvard.EDU>, wyatt@cfatst.HARVARD.EDU (Bill Wyatt) >writes: >>Several things would have to be verified for the entire NEMESIS theory >>to be accepted. A short list, off the top of my head: >> >>...list mostly deleted .. >>5) The iridium layer(s) must be of extraterrestrial origin. > >The original claim was that the K-T boundary had to be. One >comment that I see periodically is that the same irridium anomaly >that shows up in meteorite abundances is also present (perhaps to >a lesser degree) in the mantle. It follows that extensive volcanism >*might* have a similar effect. Any geologists following this? I'm not a geologist, though I've been trying to follow this subject. From what I've been able to determine, a number of geologists agree with you. However, there's stress on the *might*. There's little evidence for such a major episode of volcanism at the proper time. >>6) There must be an Ir or other tracer layer at every extinction boundary. > >Although there have been some claims along these lines, I believe that >the K-T boundary is the only well accepted instance. Given the claimed >periodicity and the existence of at least one more drastic (although >earlier) extinction this seems somewhat damning. I agree that the evidence for meteoric impacts as the cause of other major extinction events is not particularly convincing. >One point which I haven't seen treated much is the question of whether >it is even necessary to explain the (debatable) periodicity using >astronomy. Mass extinctions appear to follow from some combination >of climate and biology. Dropping rocks on everything (or comets) is >simply a crude way to ensure this. However, climate and ecology are >coupled, extremely complicated nonlinear systems. One might add >geological processes, including continental drift, to the list as >the source of episodes of intense volcanism, disruption of ecological >systems due to the creation of land bridges, and changes in climatic >patterns. It is my understanding that such systems frequently show >oscillations on somewhat unpredictable time scales that may appear, >at first glance, crudely periodic. The nice thing about the iridium layer and other evidence (see below) for an impact catastrophe as the explanation for the K-T extinction events is that it *is* evidence. In the past there were an endless number of theories explaining the demise of the dinosaurs (everything from egg-eating mammals to little green hunters in flying saucers), but nary a shred of evidence for any of them. This is much better. I shan't argue in favor of periodicity -- I don't see it myself. However, "mere" climate change, although certainly capable of instigating large scale extinction events (and, I admit, once such extinctions begin in tightly coupled ecologies, who knows where they will end), still seems to me wholly insufficient in causing the extinction of every land animal over 1 Kg in size, and three quarters of all species, land and water, on the Earth. >To take an extreme example, suppose mass extinctions are due entirely >to episodes of volcanism and the K-T boundary is either a coincidence >(comet(s) happened to hit close to such an episode) or simply reflective >of an unusually deep upwelling of mantle material during this episode. >Then one really needs to explain an approximate periodicity in certain >kinds of flow patterns in the Earth's core. I don't think this would >strike anyone as particularly outrageous. Extreme volcanism as a explanation of the K-T extinctions, though perhaps not ruled out by the iridium layer (due to the possibility of an unusually deep upwelling of mantle material, as you say), *does* seem to be eliminated by the occurrence of shocked quartz, which has been found at the K-T boundary all over the world. Not only is it thought that no volcanic eruption is violent enough to produce the shocked quartz in the first place (I understand it has been found in the past only at meteorite impact sites and nuclear tests), but it is also believed that no volcanic eruption is violent enough to have blasted the shocked quartz fragments out of the atmosphere so they could thereupon rain down on the opposite side of the Earth. The evidence for the reality of a single meteoric-impact extinction catastrophe says nothing, of course, about the existence of Nemesis. It seems to me that detractors of the impact explanation of the K-T extinctions (I'm not accusing you of this, Ethan!) *and* proponents of the Nemesis explanation for "periodic" extinction events are both being reduced to arguing *possibility* rather than probability. Yes, it *might* be possible that a massive volcanic eruption would mimic at least some of the evidence for a K-T impact. It *might* be possible that a Nemesis star could withstand eons of extremely tenuous orbit around the sun, in order to generate the not-particularly-glaring periodicities we think we see in the geological record. But where, pray tell, is the evidence for a volcanic eruption? Where is Nemesis? These are handwaved away with talk about "But... it's *possible*!" > I'm not afraid of dying Ethan Vishniac, Dept of Astronomy, Univ. of Texas > I just don't want to be {charm,ut-sally,emx,noao}!utastro!ethan > there when it happens. (arpanet) ethan@astro.AS.UTEXAS.EDU > - Woody Allen (bitnet) ethan%astro.as.utexas.edu@CUNYVM.CUNY.EDU -- Michael McNeil michaelm@vax.3Com.Com 3Com Corporation hplabs!oliveb!3comvax!michaelm Mountain View, California work telephone: (415) 969-2099 x 208 A luminous star, of the same density as the Earth, and whose diameter should be two hundred and fifty times larger than that of the Sun, would not, in consequence of its attraction, allow any of its rays to arrive at us; it is therefore possible that the largest luminous bodies in the universe may, through this cause, be invisible. P. S. Laplace, *Le Systeme du monde*, vol. II, 1795 ------------------------------ End of SPACE Digest V9 #459 *******************