Message-ID: <obTNtdy00VcJ83jU5T@andrew.cmu.edu>
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.

<end of crib from Grosser's book>

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
*******************