It was not clear from Bill's posting where the science left off and the
fiction began in his "Dark Visitor" story. If it was intended that the
discovery of Pluto was achieved because of supposed unattributed
perturbations in Neptune's orbit, that is not the case. Pluto was
discovered by hard work, observing the sky all the way around the
ecliptic photographically over a long period of time. That story is
utterly unlike the discovery of Neptune based on unattributed
perturbations in the orbit of Uranus. Neptune was discovered by Galle
after an hour's visual search, about one degree from where it was
predicted to be by Leverrier based upon those perturbations.
Supposed anomalies in Neptune's orbit, unattributable to the known
planets, led to speculation (and some search effort) that a tenth
planet of significant mass lay beyond Neptune. Such speculation was put
to rest, however, when a more accurate historical ephemeris for Neptune
was established. The story behind that is one I love to tell, and none
the less significant because it led to a null result rather than the
discovery of another planet.
Johann Galle discovered Neptune in 1846. The period of Neptune's orbit
is about 165 years. By the 1970's it hadn't even gone around the Sun
once since its discovery, hence its orbit was somewhat imprecisely
determined. The supposed anomalies in its ephemeris that led to the
tenth planet speculation were near the uncertainty limit; they were not
robust. In 1979 a Caltech astronomer, Charles Kowal wanted to know if
there were prediscovery data on Neptune that might aid in refining its
ephemeris, a technique that is frequently employed when refining the
orbit of a near Earth asteroids near the time of its discovery by
searching astronomical photographic archives. He noted that Neptune had
appeared very near the apparent position of Jupiter on 23 January 1613,
a phenomenon called an "appulse". Kowal contacted Stillman Drake, a
Galileo scholar at University of Toronto. He asked Drake to have a look
at Galileo's notebooks for the period around that time and report
anything unusual he might find therein. Drake did so, and it seems that
Galileo did see and record the presence and position of Neptune! (1,2)
This is the best example I know to illustrate the value of a well kept
notebook.
Leigh
1 C. T. Kowal and S. Drake, "Galileo's Observations of Neptune",
Nature, 28, 311 (1980)
2 S. Drake and C. T. Kowal, "Galileo's Sighting of Neptune", Scientific
American 243 (6) (1980) 52-59