In July 2015 the NASA space probe New Horizons, will take center
stage in the world media when it passes by Pluto. Launched in 2006 it
used a Jupiter gravity assist to accelerate to a speed of 82,000
kilometers per hour (51,000 mph) and is now nearing the end of a 9 year
voyage. Pluto is the last of the major bodies in the solar system to be
visited by spacecraft from Earth. Although Pluto has recently been
re-designated a dwarf planet, the general public and even many in the
scientific community still consider it one of the "original nine"
planets.
Pluto was discovered in 1930 by American astronomer,
Clyde Tombaugh. Observations of the planet Uranus had shown a slight
orbital disturbance that could not be entirely explained by the presence
of the eighth planet, Neptune. Astronomers concluded there had to be
another undiscovered planet even further out. Calculations pointed to an
area of the sky where this unknown planet must be and after a year of
searching, Tombaugh found it.
It soon became apparent Pluto was
too small to be the mysterious "Planet X" he was searching for. Even so,
it was mysterious enough in its own right. Despite its great distance
we've been able to determine Pluto has an atmosphere and at least five
moons, one of them more than half as big as Pluto itself. Calculations
of its mass based on moon observations indicate it is probably a tiny,
ice-covered rocky world, quite unlike the other outer planets. This will
in no way make it an uninteresting encounter. Pluto is thought to be
similar to other large bodies in the Kuiper Belt, the material beyond
Pluto left over from the formation of the solar system, unchanged after
billions of years.
New Horizons will not orbit Pluto. Instead it
will perform a flyby. The probe was unable to carry the amount of fuel
needed to slow down and reach orbit because of weight restrictions. As a
consolation there will be the opportunity to carry on and intercept one
or more Kuiper Belt Objects later on.
New Horizons weighs just over 1,000 pounds. Its scientific payload was designed to answer four basic questions:
- What does the surface look like?
- Are there any large geological features?
- What is the composition of the atmosphere?
- How does the solar wind react with the atmosphere?
At Pluto's distance, radio signals returning the data
will take more than four hours to reach Earth. Much of that data will
only be of interest to planetary scientists but the general public will
be amazed by the pictures from New Horizons's visible light camera that
will have a resolution of roughly 100 meters at closest approach. Four
filters, each one covering a different wavelength, will be used to make
color maps. It can also scan in the infrared and ultraviolet
wavelengths. New Horizons's radio package is specially equipped to
analyze signals in the latter stages of the flyby when transmissions
from Earth will have to pass through Pluto's atmosphere to reach the
probe, thereby helping to identify the specific gasses it's made of. The
final mission profile is subject to change depending on any significant
new discoveries made in the months before arrival but the current plan
is as follows:
In December 2014, New Horizons will be taken out of
electronic hibernation for the last time before the Pluto encounter.
Scientific observations will begin in January, 2015. At ten weeks out,
the on board cameras will be able to see greater detail than the
earth-orbiting Hubble telescope. Four weeks away, daily observations
begin. On July 14, 2015, New Horizons will make its closest approach to
Pluto at a distance of 10,000 kilometers traveling at 14 km/s (31,000
mph). Fourteen minutes later it will pass within 27,000 km of Pluto's
largest moon, Charon. Studies and measurements will continue for four
weeks after. Then New Horizons will use its remaining fuel to be
redirected to an as yet undetermined Kuiper Belt Object to perform
similar experiments.
Affixed to the side of New Horizons is a CD
in which 430,000 people signed up to have their name put on. They will
no doubt be the envy of all their friends. But the person most envied
will be Clyde Tombaugh himself since the payload also includes one ounce
of his ashes. It's fitting that the man who discovered Pluto will also
be the first to reach it.
A. L. Smith has had a lifelong interest in space exploration,
radio communications, hiking and sailing. Read about his adventures at http://hotelzulu.com today.
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