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in the first place。 that seminal event in astronomy waslargely to the credit of the astronomer percival lowell。 lowell； who came from one of theoldest and wealthiest boston families （the one in the famous ditty about boston being thehome of the bean and the cod； where lowells spoke only to cabots； while cabots spoke onlyto god）； endowed the famous observatory that bears his name； but is most indeliblyremembered for his belief that mars was covered with canals built by industrious martians for purposes of conveying water from polar regions to the dry but productive lands nearer theequator。
lowell’s other abiding conviction was that there existed； somewhere out beyond neptune；an undiscovered ninth planet； dubbed planet x。 lowell based this belief on irregularities hedetected in the orbits of uranus and neptune； and devoted the last years of his life to trying tofind the gassy giant he was certain was out there。 unfortunately； he died suddenly in 1916； atleast partly exhausted by his quest； and the search fell into abeyance while lowell’s heirssquabbled over his estate。 however； in 1929； partly as a way of deflecting attention awayfrom the mars canal saga （which by now had bee a serious embarrassment）； the lowellobservatory directors decided to resume the search and to that end hired a young man fromkansas named clyde tombaugh。
tombaugh had no formal training as an astronomer； but he was diligent and he was astute；and after a year’s patient searching he somehow spotted pluto； a faint point of light in aglittery firmament。 it was a miraculous find； and what made it all the more striking was thatthe observations on which lowell had predicted the existence of a planet beyond neptuneproved to be prehensively erroneous。 tombaugh could see at once that the new planetwas nothing like the massive gasball lowell had postulated； but any reservations he or anyoneelse had about the character of the new planet were soon swept aside in the delirium thatattended almost any big news story in that easily excited age。 this was the first american…discovered planet； and no one was going to be distracted by the thought that it was really justa distant icy dot。 it was named pluto at least partly because the first two letters made amonogram from lowell’s initials。 lowell was posthumously hailed everywhere as a genius ofthe first order； and tombaugh was largely forgotten； except among planetary astronomers；who tend to revere him。
a few astronomers continue to think there may be a planet x out there—a real whopper；perhaps as much as ten times the size of jupiter； but so far out as to be invisible to us。 （itwould receive so little sunlight that it would have almost none to reflect。） the idea is that itwouldn’t be a conventional planet like jupiter or saturn—it’s much too far away for that；we’re talking perhaps 4。5 trillion miles—but more like a sun that never quite made it。 moststar systems in the cosmos are binary （double…starred）； which makes our solitary sun a slightoddity。
as for pluto itself； nobody is quite sure how big it is； or what it is made of； what kind ofatmosphere it has； or even what it really is。 a lot of astronomers believe it isn’t a planet at all；but merely the largest object so far found in a zone of galactic debris known as the kuiperbelt。 the kuiper belt was actually theorized by an astronomer named f。 c。 leonard in 1930；but the name honors gerard kuiper； a dutch native working in america； who expanded theidea。 the kuiper belt is the source of what are known as short…period ets—those thate past pretty regularly—of which the most famous is halley’s et。 the more reclusivelong…period ets （among them the recent visitors hale…bopp and hyakutake） e fromthe much more distant oort cloud； about which more presently。
it is certainly true that pluto doesn’t act much like the other planets。 not only is it runty andobscure； but it is so variable in its motions that no one can tell you exactly where pluto will bea century hence。 whereas the other planets orbit on more or less the same plane； pluto’sorbital path is tipped （as it were） out of alignment at an angle of seventeen degrees； like thebrim of a hat tilted rakishly on someone’s head。 its orbit is so irregular that for substantialperiods on each of its lonely circuits around the sun it is closer to us than neptune is。 for most of the 1980s and 1990s； neptune was in fact the solar system’s most far…flung planet。
only on february 11； 1999； did pluto return to the outside lane； there to remain for the next228 years。
so if pluto really is a planet； it is certainly an odd one。 it is very tiny： just one…quarter of 1percent as massive as earth。 if you set it down on top of the united states； it would cover notquite half the lower forty…eight states。 this alone makes it extremely anomalous； it means thatour planetary system consists of four rocky inner planets； four gassy outer giants； and a tiny；solitary iceball。 moreover； there is every reason to suppose that we may soon begin to findother even larger icy spheres in the same portion of space。 then we will have problems。 afterchristy spotted pluto’s moon； astronomers began to regard that section of the cosmos moreattentively and as of early december 2002 had found over six hundred additional trans…neptunian objects； or plutinos as they are alternatively called。 one； dubbed varuna； is nearlyas big as pluto’s moon。 astronomers now think there may be billions of these objects。 thedifficulty is that many of them are awfully dark。 typically they have an albedo； orreflectiveness； of just 4 percent； about the same as a lump of charcoal—and of course theselumps of charcoal are about four billion miles away。
and how far is that exactly？ it’s almost beyond imagining。 space； you see； is justenormous—just enormous。 let’s imagine； for purposes of edification and entertainment； thatwe are about to go on a journey by rocketship。 we won’t go terribly far—just to the edge ofour own solar system—but we need to get a fix on how big a place space is and what a smallpart of it we occupy。
now the bad news； i’m afraid； is that we won’t be home for supper。 even at the speed oflight； it would take seven hours to get t