Planet X Announcement

LOWELL OBSERVATORY

Observation Circular

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THE DISCOVERY OF A SOLAR SYSTEM BODY APPARENTLY TRANS-NEPTUNIAN

The message sent last night (March 12) to Harvard Observatory for distribution to astronomers read as follows:

“Systematic search begun years ago supplementing Lowell’s investigation for Trans-Neptunian planet has revealed object which since seven weeks has in rate of motion and path consistently conformed to Trans-Neptunian body at approximate distance he assigned.  Fifteenth magnitude.  Position March twelve days three hours GMT was seven seconds of time West from Delta Geminorum, agreeing with Lowell’s predicted longitude.”

For ease in finding object was referred to Delta Geminorum.

Position March 12.14 G.M.T.  R.A. 7h 15m 50s Dec. 22° 6′49″

The finding of this object was a direct result of the search program set going in 1905 by Dr. Lowell in connection with his theoretical work on the dynamical evidence of a planet beyond Neptune.  (See L.O. Memoirs, Vol I, No. 1, “A Trans-Neptunian Planet,” 1914).  The earlier searching work, laborious and uncertain because of the less efficient instrumental means, could be resumed much more effectively early last year with the very efficient new Lawrence Lowell telescope specially designed for this particular problem.  Some weeks ago, on plates he made with the instrument, Mr. C. W. Tombaugh, assistant on the staff, using the Blink Comparator, found a very exceptional object, which since has been studied carefully.  It has been photographed regularly by Astronomer Lampland with the 42-inch reflector, and also observed visually with the large refractor.

The new object was first recorded on the search plates of January 21 (1930), 23rd, and 29th, and since February 19 it has been followed closely.  Its rate of motion has been measured for the available material at intervals between observations with results that appear to place the object outside Neptune’s orbit at an indicated distance of about 40 to 43 astronomical units.  During the period of more than 7 weeks the object has remained close to the ecliptic; the while it has passed from 12 days after opposition point to without about 20 days of its stationary point.  Its rate of retrogression, March 10 to 11, was about 30″ per day.  In its apparent path and in its rate of motion it conforms closely to the expected behavior of a Trans-Neptunian body, at about Lowell’s predicted distance.

There has not been opportunity yet to complete measurements and accurate reductions of positions of the object requisite for use in the computation of the orbit, but it is realized that the orbital elements are much to be desired and this important work is in hand.

In brightness the object is only about 15th magnitude.  Examination of it in the large refractor – but without very good seeing conditions – has not revealed certain indication of a planetary disk.  Neither in brightness not apparent size is the object comparable with Neptune.  Preliminary attempts at comparative color tests photographically with large reflector and visually with refractor indicate it does not have the blue color of Neptune and Uranus, but hint rather that its color is yellowish, more like the inner planets.  Such indications as we have of the object suggest low albedo and high density.  Thus far our knowledge of it is based largely upon its observed path and its determined rates of motion.  These with its position and distance appear to fit only those of an object beyond Neptune, and one apparently fulfilling Lowell’s theoretical findings.

While it is thus too early to say much about this remarkable object and much caution and concern are felt—because of the necessary interpretations involved—in announcing its discovery before its status is fully demonstrated; yet it has appeared a clear duty to science to make its existence known in time to permit other astronomers to observe it while in favorable position before it falls too low in the evening sky for effective observation.

—V.M. SLIPHER

Flagstaff, Arizona
March 13, 1930