C
omic explorers like
Alan Stern need one
thing above all else:
unending patience.
For while ships on Earth go on
voyages that take a maximum
of several months to complete,
it takes spaceships months or
even decades just to reach their
object of study. A lot can happen
on Earth during that time—even an
astronomical revolution that turns
your own mission on its head...CAN YOU DEPOSE A PLANET?
When the New Horizons spacecraft
was launched in January 2006 under
the leadership of NASA engineers,
its target, Pluto, was still considered
the ninth planet of our solar system.
Shortly thereafter the astronomical
community downgraded its status,
and since then it has offi cially been
known as a dwarf planet. But why?
Pluto itself has remained the same,
so the reason behind the redefi nition
lies in its neighborhood: “A series of
discoveries has thrown everything
that we thought we knew about the
architecture of our solar system out
the window,” says Stern. Scientists
are slowly realizing that Pluto is just
the guardian of a territory at the very
edge of the solar system that’s both
gigantic and completely unexplored.
It is a world that no one even knew
existed 30 years ago: a ring of rock
and ice over 600 million miles wide,
beginning behind Pluto. This desert
of debris receives only one- to two-
thousandths of the Sun’s light that
reaches Earth. This so-called Kuiper
belt is therefore so dark that even a
second Earth could easily hide from
the best telescopes there. This area
covers such a broad expanse that
despite moving at 10,600 miles per
hour Pluto needs almost 250 Earth
years to orbit the Sun just once. But
on July 14, 2015, the New Horizons
probe brought the light of science to
that distant darkness and revealed
this world to us for the fi rst time...
Five other “Plutos” have already
been discovered in the Kuiper belt,
and one of these—named Eris—is
even larger and one-quarter heavier
than the original. This was the death
knell for Pluto’s status as a planet.
And there is no end in sight to the
discoveries: “I still have 107 objects
of ‘probable dwarf planet’ status on
the list. Another 428 are ‘possible,’”
says Michael Brown. The planetary
astronomer at the California Institute
of Technology is one of the principal
astronomers who decisively expelled
Pluto from the family of real planets.
And so since mid-2006, the offi cial
defi nition has been: Only the objects
that have cleared their orbit of other
objects can be called planets. After
76 years, the number of the Sun’s
companions has shrunk to eight.“Ridiculous and unscientifi c,” is
how planetary scientist Alan Stern
has described the decision of the
International Astronomical Union to
downgrade the destination of “his”
probe and relegate it to the second
tier of the solar system. “The further
a planet is from the Sun, the larger
it must be to clear out its orbit,” he
grumbles. “Not even Earth would be
a planet according to this defi nition.
It’s like designating a river a stream
just because there are other larger
rivers in its surroundings.”HOW DO YOU ACCELERATE A
PIANO TO 37,000 MPH?
To this day Pluto is still a mystery—
and this is one of the reasons for the
ongoing disputes among scientists.
We know more about foreign stars
and galaxies that are located light-
years away than we do about the
dark edge of our own cosmic home,
where all that remains of the Sun is
a mere dot of light. To date, the best
photos of Pluto (all of the others are
graphics) consist of a pile of coarse
pixels, each of which represents an
area of 300 by 300 miles. You can
imagine how a similar map of Earth
would look, since it would consist of
about 30 colored squares.
Not even the size of Pluto is clear:
It was only during the past few years
that astronomers have agreed upon
a diameter of 1,472 miles—give or
take 10 miles or so. Therefore Pluto
is only about two-thirds the size of
Earth’s Moon and half the size of the
(now) smallest planet, Mercury. Its
entire surface area is smaller than
that of South America. But after a
nine-year journey to get there, New
Horizon’s camera fi nally got a good
look at the erstwhile planet.IN PLUTO’S
HOME SECTOR,
THE EARTH
WOULD ALSO
DWINDLE
TO DWARF–
PLANET STATUS
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