Far beyond Earth, Mars and the mighty gas giants, within a region known as the Kuiper
belt, hides the small, icy world, Pluto and its 5 moons.
Once considered the ninth and most distant planet in the solar system, Pluto was discovered
by the American astronomer Clyde Tombaugh in February 1930. For more than 70 years Pluto
was categorised as one of the main planets, but in 2006, the distant, icy world was reclassified
as a dwarf planet, a change that attracted controversy and still stirs debate even today.
For decades after its discovery very little was known about Pluto and because of its enormous
distance from the sun, it was largely thought of as a lifeless rock, lurking at the edge
of the solar system. But in July 2015, after nearly 10 years of travelling through the
darkness of space, an incredible spacecraft called New horizons changed our view of Pluto
forever.
Before New Horizons arrived at Pluto, this was one the best photos we had of the dwarf
planet, a pixelated blob that was taken by the Hubble space telescope in 1996.
(Pluto approach video) New Horizons historic flyby, on the other hand, was able to capture
thousands of high resolution close up images. Revealing a complex, evolving world unlike
any other in the solar system.
The spacecraft collected about 6.25 gigabytes of data during its brief encounter with Pluto,
a download that took over 15 months to officially complete. And it's because of this extraordinary
data, that scientists now have a much broader understanding of this mysterious world, giving
us the chance to explore some Pluto's fascinating surface features like never before.
The study of Pluto revealed a colourful, but complex world that is covered in tall icy
mountain chains, deep chasms, overlapping craters and vast almost featureless plains.
A small Jewell of astonishing beauty.
One of the largest and most spectacular features on Pluto is the iconic Heart. Named Tombaugh
Regio, the bright area consists of two very different sides.
The eastern lobe is a chaotic mountain range that is made of water ice frozen harder than
granite. Whereas the western lobe is a fairly flat nitrogen ice plain, that is believed
to be a gigantic ancient impact crater. This region of the heart is called Sputnik Planitia
and was possibly created by a massive object 1200 miles wide, which is 1930 kilometres
wide.
It is thought that over hundreds of thousands of years the impact basin slowly filled with
vast amounts of soft but frozen nitrogen ice via glacial flows. But the most surprising
part of Sputnik Planitia is the strange textures and deep crevasses that separate the plain.
These repeating patterns suggest that below the thick ice a process known as convection
is occurring, which happens when fluid is warmed unevenly. Meaning that something deep
within Pluto is warmer than the surface and is causing this gigantic sea of frozen nitrogen
to slowly churn possibly concealing a slushy water ocean.
Towards the south of Pluto's magnificent heart is another bizarre feature that has been named
Wright Mons and is an enormous Cryovolcano. Unlike volcanoes we see on Earth, Wright mons
once erupted melted volatiles such as water and ammonia onto Pluto's frigid surface.
The giant ice volcano measures about 90 miles across, which is 145 kilometres across and
is 2.5 miles high, which is 4 kilometres high, making it the largest feature of its kind
ever discovered in the outer solar system.
One of the more perplexing things about Wright Mons is that there is only one identified
impact crater on its slopes, indicating that this mighty Cryovolcano must have formed relatively
recently.
Along the western margins of Sputnik planitia, just above the Wright Mons cryovolcano is
Pluto's highest and steepest mountain range, an area that has been named the Tenzing Montes.
These ginormous, icy peaks tower 3.9 miles or 6.2 kilometres above the surface and have
a mean slope of 19.2 degrees. Although most of Pluto is covered in methane and nitrogen
ice, to create big mountains like these requires a much stronger material, and so Tenzing montes
are most likely made of frozen water because, at these frigid temperatures, water-ice behaves
more like rock. Like other large features on Pluto, these
tall peaks are fairly young, likely shaping no more than 100 million years ago and they
may even still be in the process of forming.
One of the more striking and obvious features on Pluto is the massive red patch that stretches
around the equator. This bizarre, but beautiful region has been named Cthulhu Macula and is
made up of a varied landscape of flat plains, scarps, mountains and craters.
The enormous patch is roughly 1860 miles long, which 2990 kilometres long and is the darkest,
largest feature on the dwarf planet. Cthulhu macula is also pockmarked with craters, suggesting
that it is billions of years old, much older than the crater-less heart feature that we
have already explored.
The reason this bizarre region of Pluto is a deep red colour isn't fully understood,
but it's likely a result of methane and nitrogen in Pluto's thin atmosphere interacting with
the Sun's ultraviolet light, creating organic particles known as tholins.
Another gigantic feature is a spectacular canyon that stretches more than 1000 miles
or 1600 kilometres across. But this deep geological scar isn't on Pluto, instead, it is on the
dwarf planets mighty moon, Charon.
At over half the diameter of Pluto, Charon is the largest natural satellite relative
to its planet in the solar system, making the two objects more a binary planet system.
The gigantic chasm is at least four times longer than Arizona's Grand Canyon and twice
as deep in certain areas. It spans from one side of the giant moon to the other and was
likely caused by a violent geological event. However what that event was or how it occurred
is still a mystery.
To the Romans Pluto was the God of the underworld, to us, it is a complex, frozen object billions
of miles away that has captured the imaginations and interests of millions. Many still consider
Pluto the 9th planet and denounce the dwarf planet title that has been placed upon it.
But regardless of its planetary status, Pluto is by far the solar systems bright pearl,
a small but mighty world that boasts some of the greatest geological features ever discovered.