In the late 1800s a little girl asked the New York Times if there was
a Santa Clause. The reply is now famous. Someone thought it would be
fun to ask the scientists at NASA the same question. Here is their
reply:

No known species of reindeer can fly. But there ARE 300,000 species
Of living organisms yet to be classified, and while most of these are
Insects and germs, this does not completely rule out flying reindeer,
which only Santa has seen.

There are two billion children (under 18) in the world. But since
Santa doesn't appear to handle Muslim, Hindu, Buddhist and Jewish
children, that reduces the workload to 15% of the total - 138
million or so. At an average rate of 3.5 children per household,
that's 91.8 million homes.

One presumes there is at least one good child in each.

Santa has 31 hours of Christmas to work with, thanks to time zones
and the rotation of the earth, assuming he travels east to west.
This works out to 822.6 visits per second. This is to say that for
each household with good children, Santa has 1/1000th of a second to
park, hop out of the sleigh, jump down the chimney, fill the
stockings, distribute the remaining gifts under the tree, eat
snacks, get back up the chimney, get back into the sleigh, and move
to the next house.

Assuming that each of these 91.8 million houses are distributed
evenly(which we know to be false but for the sake of these
calculations we will accept) we are now talking about 0.78 miles per
household, a total trip of 75.5 million miles, not counting bathroom
stops. This means that Santa's sleigh is travelling at 650 miles per
second, 3,000 times the speed of sound. For comparison, the fastest
man made vehicle, the Ulysses space problem moves at a poky 27.4
mps. The average reindeer runs at 15 mph.

The sleigh's payload adds another interesting element. Assuming that
each child gets nothing more than a medium sized Lego set (2
pounds), the sleigh is carrying 321,300 TONS, not counting Santa,
who is invariably described as overweight. On land, conventional
reindeer can pull no more than 300 pounds. Even granting that
"flying reindeer" (see first paragraph) could pull TEN TIMES the
usual amount, we cannot do the job with 8 or even 9. We need 214,000
reindeer. This increases the weight, not even counting the sleigh,
to 353,430 tons. Again, for comparison this is 4 times the weight of
the British liner Queen Elizabeth 2.

353,000 tons travelling at 650 miles per second creates an enormous
air resistance. This will heat the reindeer in the same manner as a
spacecraft re-entering the earth's atmosphere. The lead pair of
reindeer will absorb 14.3 QUINTILLION joules of energy..... Per
second.....Each! In short, they will burst in flame almost
instantaneously, exposing the next pair of reindeer, and creating
deafening sonic booms in their wake. The entire team will be
vaporized within 4.26 thousands of a second. Santa, meanwhile, will
be subjected to centrifugal forces 17,500.06 times the force of
gravity. A 300 pound Santa would be pinned to the back of his
sleigh by 4,325,015 pounds of force.

CONCLUSION: There was a Santa, but he's dead now.

Merry Christmas,