tRONOMERS t amazing truck a matc tiniest tant starster and even potential ability of planets mucooremote to be seen—planets so distant t it ake us o get telescopes ture ion so preposterouslyfaint t total amount of energy collected from outside tem by all of togeting began (in 1951) is “less triking the words of Carl Sagan.

    In s, t a great deal t goes on in t astronomers can’t findo reflect t until 1978no one iced t Pluto  year, a youngastronomer named James Cy at tory in Flagstaff, Arizona, ine examination of pograpo ain but definitely oto. Consulting acolleague named Robert on,  w  was a moon.

    And it  just any moon. Relative to t, it  moon in tem.

    tually someto Pluto’s status as a planet,  anyo  to be one and t meant t Pluto was mucem, including our own, are larger.

    Noural question is ook so long for anyone to find a moon in our oem. t it is partly a matter of  trumentsand partly a matter of ruments are designed to detect, and partly it’s just Pluto.

    Mostly it’s ruments. In tronomer ClarkC people t astronomers get out at nigories and scan t’s not true. Almost all telescopes very tiny little pieces of tance to see a quasar or  for black  a distant galaxy. telescopes t scans t by tary.”

    e ists’ renderings into imagining a clarity of resolution tdoesn’t exist in actual astronomy. Pluto in Cy’s pograp and fuzzy—a piece ofcosmic lint—and its moon is not tically backlit, crisply delineated companion orbyou  in a National Geograping, but rat a tiny and extremelyindistinct  of additional fuzziness. Suc, t it took seven yearsfor anyone to spot tly confirm its existence.

    One nice touc Cy’s discovery  it aff, for it  Pluto  place. t seminal event in astronomy o t of tronomer Percival Lo Boston families (tty about Boston being to Cabots, o God), endoory t bears  is most indeliblyremembered for  Mars  by industrious Martians forpurposes of conveying er from polar regions to t productive lands nearer tor.

    Loion  ted, someune,an undiscovered nint, dubbed Planet X. Loies ected in ts of Uranus and Neptune, and devoted t years of o trying tofind t ain  tunately, least partly exed by , and to abeyance e. ly as a ing attention a), tory directors decided to resume to t end ombaugh.

    tombaugraining as an astronomer, but  and ute,and after a year’s patient searcted Pluto, a faint point of ligtery firmament. It  all triking tions on ence of a planet beyond Neptuneproved to be compreombaug once t tulated, but any reservations  ter of t  aside in tattended almost any big neory in t easily excited age. t American-discovered planet, and no one o be distracted by t t it a distant icy dot. It o at least partly because t tters made amonogram from Loials. Lo order, and tombaugten, except among planetary astronomers,o revere him.

    A feronomers continue to t X out ten times ter, but so far out as to be invisible to us. (Ittle sunlig it o reflect.) t it be a conventional planet like Jupiter or Saturn—it’s mucoo far a;alking perrillion miles—but more like a sun t never quite made it. Moststar systems in tarred), wary sun a sligy.

    As for Pluto itself, nobody is quite sure  is, or  is made of, mosp  it really is. A lot of astronomers believe it isn’t a planet at all,but merely t object so far found in a zone of galactic debris kno. t ually tronomer named F. C. Leonard in 1930,but tcive  are knos—tcome past pretty regularly—of s (among t visitors ake) come fromtant Oort cloud, about wly.

    It is certainly true t Pluto doesn’t act mucs. Not only is it runty andobscure, but it is so variable in its motions t no one can tell you exactly ury s orbit on more or less to’sorbital patipped (as it  of alignment at an angle of seventeen degrees, like t tilted rakiss orbit is so irregular t for substantialperiods on eacs lonely circuits around t is closer to us tune is. Formost of tune  tem’s most far-flung planet.

    Only on February 11, 1999, did Pluto return to tside lane, to remain for t228 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 Eart it doop of ted States, it quite y-eigates. t extremely anomalous; it means tour planetary system consists of four rocky inner planets, four gassy outer giants, and a tiny,solitary iceball. Moreover, to suppose t o findotion of space. terCy spotted Pluto’s moon, astronomers began to regard t section of ttentively and as of early December 2002 ional trans-Neptunian Objects, or Plutinos as ternatively called. One, dubbed Varuna, is nearlyas big as Pluto’s moon. Astronomers nos. ty is t many of typically tiveness, of just 4 percent, about t four billion miles away.

    And  exactly? It’s almost beyond imagining. Space, you see, is justenormous—just enormous. Let’s imagine, for purposes of edification and entertainment, t to go on a journey by rockets go terribly far—just to tem—but o get a fix on  a smallpart of it we occupy.

    No  be  t, it ake seven o get to Pluto. But of course  travel at anyt speed. e’ll o go at ther more lumbering.

    t speeds yet ac are t, ty-five thousand miles an hour.

    t ember1977)  Jupiter, Saturn, Uranus, and Neptune  o use a “gravity assist” tec  to t in a kind of cosmicversion of “crack t took to reacocross t of Pluto. t if  until January 2006 (entatively sco depart for Pluto) akeadvantage of favorable Jovian positioning, plus some advances in tec tting ake rat allevents, it’s going to be a long trip.

    No to realize is t space is extremely ful. Our solar system may be t trillions of miles, butall tuff in it—ts and tumblingrocks of teroid belt, comets, and oting detritus—fills less trilliont none of tem ely drao scale. Most scs ss coming one after t neigervals—ter giants actually castsrations—but t to get tune in reality isn’t just a little bit beyond Jupiter, it’s er—five times farter ter is from us, so far out t itreceives only 3 percent as muc as Jupiter.

    Sucances, in fact, t it isn’t possible, in any practical terms, to draem to scale. Even if you added lots of fold-out pages to your textbooks or used a reallylong s of poster paper, you  come close. On a diagram of tem toscale, o about ter of a pea, Jupiter ao  (and about terium, so you be able to see it anyauri, our nearest star, ten t Jupiter tence, and Pluto o ill be over ty-five feet away.

    So tem is really quite enormous. By time anning, life-giving Sun—o t is little more t star. In suco understand significant objects—Pluto’s moon, for example—tention.

    In t, Pluto il tions, Neptune  to  to contain ty moons. total no least ninety,” about a t t ten years.

    t to remember, of course, is t actually knoem.

    Noice as  Pluto is t Pluto. If you cinerary, you  trip to tem, and I’m afraid  t. Pluto may be t object marked onscs, but tem doesn’t end t, it isn’t even close to endingt get to tem’s edge until  celestial realm of drifting comets, and  reac cloud for anot ten ter edge of tem, asto is barely one-fifty-the way.

    Of course o tillrepresents a very big undertaking for us. A manned mission to Mars, called for by tPresident Bus of passing giddiness, ly dropped  it  $450 billion and probably result in torn to tatters by icles from w be shielded).

    Based on ely no prospectt any  tem—ever. It is just too far.

    As it is, even elescope,  see even into t cloud, so actually kno it is ts existence is probable but entirely ical.

    *About all t can be said  t cloud is t it starts someretco t ofmeasure in tem is tronomical Unit, or AU, representing tance from*Properly called t cloud, it is named for tonian astronomer Ernst Opik, ence in 1932, and for tcronomer Jan Oort, wions eiger.

    to to is about forty AUs from us, t of t cloud about fiftyt is remote.

    But let’s pretend again t o t cloud. t tnotice is  is out  it’s not even test star in t is a remarkable t t tdistant tiny to s in orbit. It’s not a very strongbond, so ts drift in a stately manner, moving at only about 220 miles an ime to time some of ts are nudged out of t by some sligational perturbation—a passing star perimes ted into tiness of space, never to be seen again, but sometimes to a long orbit aroundt ts, pass tem. Just occasionally tray visitors smack into somet’s oer of tem. It is  is going to take a long time to get tleast—so  for nourn to it mucer in tory.

    So t’s your solar system. And  tem? ell,not deal, depending on  it.

    In t term, it’s not perfect vacuum ever created by  asempty as tiness of interstellar space. And t deal of tilyou get to t bit of somet neigauri,ar cluster knoerms, but t is still a imes fartrip to the Moon.

    to reac by spacesake at least ty-five trip you still  be any a lonely clutcars in t no-years of travel. And so it ried to star-he cosmos.

    Just reacer of our oake far longer ted asbeings.

    Space, let me repeat, is enormous. tance betars out t speeds approac, tasticallycances for any traveling individual. Of course, it is possible t alien beingstravel billions of miles to amuse ting crop circles in iltsening ts out of some poor guy in a pickup truck on a lonely road in Arizona(t eenagers, after all), but it does seem unlikely.

    Still, statistically ty t t there is good.

    Nobody knoimates range from 100 billionor so to per one of 140 billion or so ot Cornell namedFrank Drake, excited by suc a famous equation designed tocalculate ties.

    Under Drake’s equation you divide tars in a selected portion of tars t are likely to ary systems; divide t by tary systems t could tically support life; divide t by to a state of intelligence; and so on. At eac even  conservative inputs tions just in t to be somewhemillions.

    an interesting and exciting t. e may be only one of millions of advancedcivilizations. Unfortunately, space being spacious, tance betions is reckoned to be at least t makes it sound. It means for a start t even if to see us in telescopes, tc t leftEartcion and tockings and poom is, or a gene, and y by rubbing a rodof amber ’s quite a trick. Any message o begin “Dear Sire,” and congratulate us on tery of ance so far beyond us as to be,  beyond us.

    So even if  really alone, in all practical terms ed ts in t large at 10 billion trillion—a number vastlybeyond imagining. But  of space tly scattered. “If ed into te, “t you  rillion trillion.” (t’s 1033, or a one folloy-three zeroes.) “orlds are precious.”

    is good ne in February 1999 ternational AstronomicalUnion ruled officially t Pluto is a planet. t.