The solar system is a treasure trove of bizarre moons, many of which have astonishing features.
For example, Io, the most volcanic world ever discovered, or perhaps Titan, the only world
apart from Earth to have liquid flowing across its surface.
Moons such as these offer the possibility of spectacular future discoveries and in some
cases, such as with Europa or Enceladus the possibility of finding life beyond Earth.
Past all of these distant worlds, however, towards the fringes of the solar system, and
you will find Neptune's largest moon, Triton, an active, icy world with a mysterious past,
a past that If revealed may expose its true origin as not a moon, but a Neptunian prisoner,
that was captured and never released. So where did this strange moon originate? And how did
it end up orbiting the 8th planet from the sun?
The only spacecraft ever to visit Neptune was Voyager two, back in 1989. Voyager two
travelled 4.3 billion miles, or 7 billion kilometres over a 12 year period before arriving
at the ice giant and photographing it, in all its glory.
It revealed to the world a magnificent planet, wrapped in a teal and cobalt blue atmosphere
that is it dotted with enormous violent storms, one of which was dubbed the "great dark spot".
During the encounter, the team behind Voyager two carefully changed the direction and speed
of the probe, so that it could also complete a close flyby of Neptune's largest moon. The
flyby allowed humanity to catch a close-up glimpse of Triton for the first time in history,
revealing a geologically young surface, active geysers spewing icy material out from its
frozen crust and a vast south polar cap with a pinkish hue.
Covered in nitrogen frost and tholins, which are dark organic compounds, Triton is one
of the coldest places ever to be visited. Triton was, unfortunately, Voyager twos final
encounter of its grand tour of the solar system and most of what we currently know about this
strange moon came from the exploits of this historic flyby. But Although the mission was
a triumph for the ambitious spacecraft, it could only discover so much about the large
moon due to the speed of its visit and of course, it's capabilities, and so Triton still
holds many mysteries. At first glance Triton may seem like a fairly
regular large moon orbiting a distant giant Planet, however, If we look closer we start
to see that this strange world is anything but normal.
The large moons of the solar system, such as Earths moon and all of the major moons
of Jupiter, Saturn and Uranus orbit roughly the same plane as their planet and they orbit
in the same direction as their planet rotates, which is counterclockwise if you are looking
from above. But Triton does not follow any of these properties.
Instead, the bizarre world orbits in the opposite direction to Neptune's rotation and follows
a highly inclined path of 157 degrees, relative to Neptune's Equator.
This unusual orbit, which is called a retrograde orbit suggests that Triton had a very different
history, compared to the regular large moons of the solar system. Causing scientists to
wonder whether Triton was instead plucked from another region of space, rather than
forming locally around Neptune. By studying the data provided by Voyager two,
scientists also discovered that Tritons physical properties, such as density, colour and atmosphere
do not match the other large moons, but instead, share many similarities with the Kuiper Belts
Dwarf planets. The Kuiper belt is a vast region located beyond
Neptune that contains millions of icy objects, including larger worlds such as Pluto, Haumea,
Makemake and Eris. Could it be that long ago, during the time
of the early solar system, Triton was born to this cold dark region of space, but was
eventually forced into submission by a young and powerful Neptune?
If this theory Is correct, then Neptune likely had its own set of large primordial moons
at one point, similar to what can be observed around Uranus today. But over the course of
millions or possibly billions of years, a number of repeated and close interactions
with Triton within the inner edge of the Kuiper belt tugged the strange world towards the
ice giant, causing all but the innermost moons of Neptune to be eliminated.
Because Triton is larger than the dwarf planets Pluto and Eris, it would mean that the true
king of the Kuiper belt is now the 7th largest moon in the solar system.
However, according to scientists, Tritons time as Neptune's largest moon is limited.
Along with Tritons unique orbit and Neptune's gravity slowing it down, the once King of
the Kuiper belt is dropping closer and closer to the giant planet.
Triton is already closer to Neptune than our moon is to the Earth and one day in a predicted
3.6 billion years from now, Triton will pass below Neptune's Roche limit, which is the
minimum distance a large object can approach a planet without becoming overcome by its
gravity. After this point, there is no turning back,
Triton will likely be torn apart during a catastrophic event that will result in Neptune
gaining an enormous ring, possibly something as spectacular as Saturn's rings.
When Voyager two arrived at Triton, scientists expected to see a big frozen, silent moon.
But instead, they were presented with a magnificent, active world with a complicated, mysterious
past. The spacecraft provided extremely precious
data during its brief flyby of Triton, allowing us to understand the strange moon that little
bit more. But the historic mission happened over 30 years ago, and so the oddball moon
is surely due another Earthly visitor. Fortunately, One such mission has been proposed,
a NASA mission named Trident that would launch in 2025, taking advantage of a planetary alignment.
It is said that It would complete multiple gravity assist flybys, including Earth and
Jupiter to get to Neptune, which would allow a single pass of Triton. Similar to how New
Horizons passed Pluto back in 2015. The Trident spacecraft would map the surface
of Triton, study its thin atmosphere, and of course examine it's active geysers, hoping
to find evidence of a subsurface ocean. The only downside to the mission is that it
will take the probe around 13 years to arrive at Neptune, meaning that we will have to wait
until 2038 until we got see this magnificent moon once again.
Triton was likely born in the cold dark regions of the Kuiper belt, it became the companion
of a mighty gas planet and it will likely end its existence, during a spectacular event
that will transform it into a ring of glistening particles. A fitting way for the once true
king of the Kuiper belt to end its fascinating story.