按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
nergy collected from outside the solar system by all of themtogether since collecting began （in 1951） is 鈥渓ess than the energy of a single snowflakestriking the ground；鈥潯n the words of carl sagan。
in short； there isn鈥檛 a great deal that goes on in the universe that astronomers can鈥檛 findwhen they have a mind to。 which is why it is all the more remarkable to reflect that until 1978no one had ever noticed that pluto has a moon。 in the summer of that year； a youngastronomer named james christy at the u。s。 naval observatory in flagstaff； arizona； wasmaking a routine examination of photographic images of pluto when he saw that there wassomething there鈥攕omething blurry and uncertain but definitely other than pluto。 consulting acolleague named robert harrington； he concluded that what he was looking at was a moon。
and it wasn鈥檛 just any moon。 relative to the planet； it was the biggest moon in the solarsystem。
this was actually something of a blow to pluto鈥檚 status as a planet； which had never beenterribly robust anyway。 since previously the space occupied by the moon and the spaceoccupied by pluto were thought to be one and the same； it meant that pluto was much smallerthan anyone had supposed鈥攕maller even than mercury。 indeed； seven moons in the solarsystem； including our own； are larger。
now a natural question is why it took so long for anyone to find a moon in our own solarsystem。 the answer is that it is partly a matter of where astronomers point their instrumentsand partly a matter of what their instruments are designed to detect； and partly it鈥檚 just pluto。
mostly it鈥檚 where they point their instruments。 in the words of the astronomer clarkchapman： 鈥渕ost people think that astronomers get out at night in observatories and scan theskies。 that鈥檚 not true。 almost all the telescopes we have in the world are designed to peer atvery tiny little pieces of the sky way off in the distance to see a quasar or hunt for black holesor look at a distant galaxy。 the only real network of telescopes that scans the skies has beendesigned and built by the military。鈥�
we have been spoiled by artists鈥櫋enderings into imagining a clarity of resolution thatdoesn鈥檛 exist in actual astronomy。 pluto in christy鈥檚 photograph is faint and fuzzy鈥攁 piece ofcosmic lint鈥攁nd its moon is not the romantically backlit； crisply delineated panion orbyou would get in a national geographic painting； but rather just a tiny and extremelyindistinct hint of additional fuzziness。 such was the fuzziness； in fact； that it took seven yearsfor anyone to spot the moon again and thus independently confirm its existence。
one nice touch about christy鈥檚 discovery was that it happened in flagstaff； for it was therein 1930 that pluto had been found 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鈥檚 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鈥檚 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鈥檚 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鈥檚 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鈥攁 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鈥檛 be a conventional planet like jupiter or saturn鈥攊t鈥檚 much too far away for that；we鈥檙e talking perhaps 4。5 trillion miles鈥攂ut 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鈥檛 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鈥攖hose thate past pretty regularly鈥攐f which the most famous is halley鈥檚 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鈥檛 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鈥檚orbital path is tipped （as it were） out of alignment at an angle of seventeen degrees； like thebrim of a hat tilted rakishly on someone鈥檚 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鈥檚 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鈥檚 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鈥檚 moon。 astronomers now think there may be billio