Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sun, 30 Dec 1990 03:00:10 -0500 (EST) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sun, 30 Dec 1990 02:59:39 -0500 (EST) Subject: SPACE Digest V12 #695 SPACE Digest Volume 12 : Issue 695 Today's Topics: Tenth planet? U.S., European Probe To Sun Threatened By Malfunction Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: Fri, 14 Dec 90 14:44:37 PST From: fermat!r@la.tis.com (Richard Schroeppel) Subject: Tenth planet? Henry Spencer writes: hs>The chances of a tenth outer planet are not too bad, although evidence for hs>it is slim to nonexistent. (A very careful reassessment of observations hs>of the orbit of Neptune by some folks at JPL concluded that there are no hs>unexplained perturbations.) Precise ranging of the Pioneers and Voyagers hs>have already put tight bounds on it, however: it has to be small, a long hs>way out, well away from the ecliptic, or some combination. From the 1988 Astronomical Almanac, page L1 (rejustified to shorten lines; I have capitalized one sentence for emphasis): > Fundamental ephemerides of the Sun, Moon and planets were calculated by a simultaneous numerical integration at the Jet Propulsion Laboratory in a cooperative effort with the U.S. Naval Observatory. Optical, radar, laser, and spacecraft observations were analyzed to determine starting conditions for the numerical integration. In order to obtain the best fit of the ephemerides to the observational data, some modifications to the IAU (1976) System of Astronomical Constants were necessary. These modification of the constants are listed on page K7. A SATISFACTORY EPHEMERIS FOR URANUS FOR THE 1980'S COULD BE COMPUTED ONLY BY EXCLUDING OBSERVATIONS MADE BEFORE 1900. This integration, designated DE200/LE200, is available on magnetic tape for the period 1800-2050. Additional information about the new ephemerides is included in the *Supplement to the Astronomical Almanac for 1984.* [Information from The Discovery of Neptune, by Morton Grosser, 1962; I have the 1979 Dover edition.]: Uranus was discovered by William [and Caroline? --rcs] Herschel in March 1781. It was initially thought to be an unusual comet, and was widely observed. The first computed orbits, assuming a comet-like shape, failed to accurately predict its motion. In a couple of months, it was recognized as a new planet, and that some years of data taking would be required for an accurate orbit. Johann Bode guessed that Uranus might have been seen by previous astronomers, but incorrectly classified as a star. He checked old star catalogs, and in August 1781 he found a 1756 observation by Tobias Meyer. Assisted by Placidus Fixlmillner, he found (in 1784) that Flamsteed had observed Uranus in 1690 (and assigned it the name 34 Tauri). The French astronomers Lemonnier and Montaigne independently uncovered the Flamsteed observation. New orbits were computed, and perturbations by Jupiter and Saturn included. Lemonnier found he had observed Uranus as a star in 1764 and 1769. In the next thirty years, sixteen more "pre-discovery" obser- vations were turned up. As the orbit question was cleared up, interest in observing Uranus gradually waned; the first asteroids were discovered in 1801 and the following years. In 1813, Bessel found that Bradley had observed Uranus in 1753. Burckhardt found additional observations by Flamsteed in 1712 and 1715. A 1750 observation by Lemonnier was uncovered. By 1820, enough information on the orbit had accumulated that calculators were forced to reject the pre-1781 observations as inaccurate, because they didn't fit very well. Eventually, even the post-1781 observations could not be reconciled with the contemporary position of Uranus. These discrepancies led to the discovery of Neptune in 1846. In 1847, astronomers found a pair of "pre-discovery" observations of Neptune by Lalande in 1795; this allowed the computation of a reasonable orbit for Neptune. I have seen claims elsewhere that Uranus was recorded in star catalogs dating back to Greek and Roman times. Uranus is a marginal naked-eye object. Scientific American had an article a few years ago claiming that Galileo may have seen Neptune while observing Jupiter. Neptune is 8th to 9th magnitude, so pre-telescope observations are unlikely. On the other hand, it should appear in every post-telescope catalog. Astronomical photography was inaugurated in 1858. It should be possible to remeasure the position of Uranus accurately from old photos. I'm not sure how much weight we can give to spacecraft ranging data: (1) Can we determine the spacecraft position, relative to the transmitting antenna, to within a wavelength of radio? How accurately can the velocity and acceleration be measured? (2) The spacecraft maneuvers occasionally. The delta-V caused by the maneuver must be taken into account, and cannot be measured independently. (3) Are there non-gravitational forces on the spacecraft? Light pressure, outgassing, thruster leaks, and occasional ring particle impacts. It sounds to me like the tenth planet question is still open. Rich Schroeppel rcs@la.tis.com ------------------------------ X-Added: With Flames (dowjones v2.6) Filename: 27692028 Corporation: EUROP Industry: ARO GEN Government: Flags: P N T SequenceNum: 1812141469 From: DowJones@andrew To: bb+dow-jones@andrew Subject: U.S., European Probe To Sun Threatened By Malfunction Date: Fri, 14 Dec 90 10:55:57 -0500 (EST) PASADENA, Calif. -AP- A $750 million mission to study the sun's poles is in danger because the Ulysses spacecraft is wobbling for reasons U.S. and European flight controllers don't fully understand. The malfunction developed Nov. 4, about four weeks after the spacecraft was launched by the shuttle Discovery, The Associated Press has learned. The spacecraft was 40.6 million miles from Earth today. Officials of NASA and the European Space Agency confirmed the problem's existence during interviews this week. Willis Meeks, Ulysses project manager at NASA's Jet Propulsion Laboratory, said he is optimistic engineers can repeatedly use the spacecraft's thrusters to minimize the wobble when Ulysses becomes the first spacecraft to orbit the sun's poles during 1994 and 1995. ''I don't foresee that anybody here or in Europe is going to write off this mission as a failure,'' said Ed Smith, NASA's chief scientist for Ulysses. The wobble threatens the mission because it makes it difficult for Ulysses to keep its main dish-shaped antenna pointed at Earth to transmit the information it collects. 10:54 AM ------------------------------ End of SPACE Digest V12 #695 *******************