Astronomy and Space articles
by Martin George of the Launceston Planetarium
1 August 2015
Goodbye, Pluto
As you read this, the New Horizons spacecraft is speeding away from the dwarf planet
Pluto, as it has been doing for over 17 days. Now, about 20 million kilometres separates
the two. As seen from New Horizons, Pluto would currently appear about the same size
as a five-cent coin seen from about 160 metres away.
The excitement of the close approach to Pluto is now over, but the science will go on for
a long time. New Horizons, billions of kilometres from a home to which it will never
return, has been transmitting a wealth of information about Pluto, and spectacular
pictures. We shall receive more and more information as the signals from the craft
continue to arrive.
Most significantly, Pluto amazed us. It was not what anyone had expected, and I have to
admit to being quite taken aback by what I have seen so far.
The main thing that surprised us all was the Pluto is clearly an active world. It is not a
body that has remained unchanged for billions of years: far from it. A hint that Pluto was
more special than we realised came with the discovery of Pluto's nitrogen atmosphere in
the 1980s, but we know know that there is far more to the dwarf planet.
Pluto's atmosphere, appearing as a fuzzy ring around the dwarf planet as
New Horizons was receding.
CREDIT: NASA/JHUAPL/SwRI
One of the most important discoveries is that there is strong evidence of moving ices on
Pluto. An image of part of Pluto where the now famous bright heart-shaped feature
Astronomy and Space articles
by Martin George of the Launceston Planetarium
1 August 2015
meets a mountainous region reveals that the ice appears to have flowed around objects
in its path.
Scientists have likened the effect to the behaviour of glaciers on Earth. Of course, if
you've ever seen a glacier, you will have noticed that a casual observation does not
reveal its movement: even the fastest glacier on Earth moves as a speed of only about
two metres per hour, and a typical speed is one metre per day.
It is not clear how fast the ice is moving on Pluto. But it is certain that this is not just
ordinary water ice. The bright 'heart' of Pluto has been shown to be a mixture of at least
three kinds of ices: nitrogen, carbon monoxide and methane.
Scientists have deduced that in this icy region on Pluto, there are glacier-like flows.
CREDIT: NASA/JHUAPL/SwRI
It may seem remarkable that it is possible to deduce the surface composition of an object
without landing on it and performing a direct analysis. However, astronomers have been
doing this for a long time by carefully examining the wavelengths of light reflected by, or
emitted by, an object.
In a supermarket vegetable stand, we can quickly locate the carrots because of their
colour, which represents the predominant wavelengths of light they reflect. However,
what astronomers do, of course, is far more complex than that everyday example!
Astronomy and Space articles
by Martin George of the Launceston Planetarium
1 August 2015
There is so much more that we shall be learning. But to most people — indeed, to most
astronomers — the first really exciting results are the pictures of objects never before
seen close up.
One of the most wonderful pictures of Pluto is, surprisingly, an image that shows no
surface detail at all. After its passage past Pluto, New Horizons briefly passed through
the dwarf planet's shadow, experiencing a special kind of total eclipse of the Sun. The
Sun's light shone through Pluto's atmosphere, which showed up as a fuzzy ring. To me,
this is rather like a 'goodbye' picture, but it will help greatly in our understanding of the
atmosphere.
Now that we have had this great achievement, I am sure that I shall be writing about the
science of Pluto for a long time to come.
Article by Martin George, Launceston Planetarium, QVMAG.
Reproduced with permission of the Mercury newspaper.