In the archives of Lowell Observatory, under the excellent guidance of archivist Antoinette Beiser, I came across this typewritten memo – in its original, a few pages long.  While it’s not clear who composed this note, someone has penciled “VM?” in the upper margin — Vesto M. Slipher, director of the Observatory.

In this memo, Slipher (probably) is acknowledging that there was some delay in the announcement of the discovery of Planet X (later Pluto).  Clyde Tombaugh found the retrograding trans-Neptunian object on February 18, 1930.  Lowell Observatory didn’t announce their findings until March 13.  This happened to be Percival Lowell’s birthday — as well as, through one of this story’s many cosmically-arranged coincidences, the date on which Uranus was first discovered.

Aside from the pleasing timing, why the delay?

As I’ve written here before, the astronomers at Lowell weren’t sure what they had.  The object was too small to be the gas giant they’d been expecting.  But their mathematics seemed to indicate that a gas giant was indeed what was out there to discover; only a very large planet could perturb the orbits of Uranus and Neptune in the way that was posited.  So they were understandably puzzled to have found a very small object in just the place that Lowell’s mathematics suggested a gas giant would be.

But what’s of interest to me in this memo is the phrase “In view of the unusual character of the discovery into which the institition [sic] and its founder had given so much in the way of effort and time we had to be content to allow the momentary gusts of emotion to blow over…”

One way of reading this goes: we’d been looking for the thing for so long, and under such pressure to find something, that we wanted to make sure we had something genuine before we said anything.

That’s a legitimate reason to hesitate, of course.

But I think, too, that it’s fair to read those three weeks as a pregnant pause, during which the astronomers decided whether to call this object Planet X or not — that is, whether the accumulated pressures of history and institutional expectation outweighed the obvious problems with the object.  It wasn’t what they were expecting.

So – should they gamble?  Should they go ahead and try to call this object Planet X?

Had it been a gas giant — had they found what they’d been expecting — I bet they would have announced it the next morning.  Instead, over the next three weeks, they took countless photographs of the object, hoping to solve their conundrum.  They never did.  And in the end, of course, they didn’t call it Planet X when they finally announced it.  They just called it a “solar system object apparently trans-Neptunian.”  It was the press that called it Planet X, and so a planet was born.

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