ered Planet X, located somewhere be- 
yond Pluto. This claim has been re- 
jected, although there still may be a 
little planet out there, too small and far 
away to noticeably disturb Halley. The 
comet does deviate from a precisely 
predictable path because evaporating 
gases give it some propulsion of its own. 
A reasonably accurate path, computed 
early thanks to an early sighting, might 
enable ground controllers to steer their 
space probes closer to the comet, and to 
point the Space Telescope with in- 
creased exactness so as to track Halley 
better. 
There is special interest in determin- 
ing what, besides water ice and rock 
dust, Halley or any comet is made of. 
Many atoms and molecules have been 
observed in the heads and tails of com- 
ets, but most of them are so-called 
daughter products. They are fragments 
of larger parent molecules, which evapo- 
rate from the nucleus and are then 
swiftly broken into daughter products 
by the sun’s ultraviolet rays and by 
collisions with other particles. To iden- 
tify most of the parents, it will be neces- 
sary to point or steer the sensing instru- 
ments into Halley’s inner coma, where 
the parents can still be detected before 
they disrupt. 
The viewing conditions for Halley in 
1985-86 will not be as favorable as they 
were during its 1910 appearance. When 
the comet is brightest near perihelion in 
February 1986, it will not be observable 
from the ground. Nevertheless, past ex- 
perience assures me that we will soon be 
receiving glossy brochures advertising 
comet-viewing cruises, and that suitably 
decorated Halley T-shirts, first-day 
postal covers, souvenir plates, bumper 
stickers, and crystal beer mugs cannot 
be far behind. At least one group will 
announce the end of the world, as is 
done every time a famous comet ap- 
pears. Despite the impending hoopla, 
however, serious scientific investigations 
are in the planning stages and under 
way, and much should be learned. 
Comets are widely believed to be the 
frozen debris of the material from which 
the sun and planets formed. If so, the 
intensive study of Halley’s comet over 
the next few years may establish the 
facts we need to take us back five billion 
years in time to the origin of the solar 
system. 
Stephen P Maran is a senior staff sci- 
entist in the Laboratory for Astronomy 
and Solar Physics at NASA 's Goddard 
Space Flight Center in Greenbelt, 
Maryland. 
INDIA. 
EVEN IN OUR HOTELS 
THE PAST AND 
THE PRESENT ARE ALIVE. 
Spend some time floating in your own houseboat Enioy some of our modern hotels Swimming, golf tennis anyone 0 
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about Unbelievable India. 
Please send me Information on Unbelievable India 
City. 
I 
I 
I 
I 
I State. Zip 
GOVERNMENT OF INDIA TOURIST OFFICE 
30 ROCKEFELLER PLAZA NEW YORK NY 10112 ( 212 ) 586 4901 3550 WILSHIRE BLVD LOS ANGELES CA 90010(213)380-8855 ■ 
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39 
