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Incredibly, 5 years have now passed since the New Horizons flyby of Pluto back in 2015.
It took a couple of years since then simply to send the data back to Earth, transmitting
many GBs of data from beyond Pluto using data transfer speeds equivalent to dial up internet.
We’ve also had some years to closely analyse the data and produce working models, and some
new findings have also been unearthed that we didn’t immediately notice.
So, what have we discovered?
And what’s new since the last Pluto video?
I’m Alex McColgan, and you’re watching Astrum, and together we will have a deep dive
into the Pluto data, showcasing the remarkable and unique Pluto system like you may never
have seen it before.
Let’s first of all give you a quick bit of context in case you are new to Pluto, or
if it’s been a while since you last heard about it.
Pluto is a remarkably pretty, tiny world, much smaller than our moon.
It’s found in the Kuiper Belt, a disperse belt of asteroid or comet type objects beyond
the orbit of Neptune.
Its surface consists of predominately nitrogen ice, and small amounts of carbon monoxide,
methane and water ice.
It is also covered in part by a red and orange substance known as tholins.
Tholins are organic compounds that have been irradiated by cosmic rays or ultraviolet light.
Pluto also has several small moons, and one really big moon named Charon.
Charon is so big compared to Pluto that their centre of mass - or the point in which they
orbit each other - is a point in space, and not within Pluto itself.
From this, you could actually say that Pluto and Charon are in fact a double dwarf planet
system.
Pluto also has a thin atmosphere, again mainly consisting of nitrogen, although methane and
carbon monoxide have also been detected.
So, what’s new?
Well, there have been some remarkable findings.
In June 2020, scientists released a paper stating that under Pluto’s surface is believed
to be an ocean of liquid water, very much like the icy moons of the gas planets.
It was originally thought that Pluto formed cold, being so far away from the Sun.
However, evidence from New Horizons suggests that this is not the case, but rather it started
off hot.
This means it’s always had an ocean, and if that is true, then there is a case that
habitability on Pluto may be just as good as habitability on the closer, icy moons.
In fact, if Pluto is the standard for dwarf planets found in the Kuiper belt generally,
there may be many more habitable worlds out there.
How do we know it had a hot start?
There is evidence of expansion, not contraction on its surface.
These cracks show that the crust is moving apart, not folding over itself.
If this is true and Pluto had a hot start, perhaps with bombardments from other planetesimals
heating it up during the early stages of solar system, it could be that shortly after it
was formed it would have had enough thermal energy that it was once an ocean world.
This really puts a new perspective on how the solar system formed.
Another discovery is to do with the reddish-orange substance found on Pluto’s surface.
Scientists suspected this substance was tholins as soon as New Horizons started sending images
back, but its distribution over Pluto’s surface was baffling.
Why are only some areas covered?
Also, how dynamic are the processes surrounding the distribution of tholins?
Has Pluto looked like this for a while, or is this a changing environment?
It turns out that these tholins may well be connected to the cryovolcanism found on Pluto.
Pluto is one of the few objects in our solar system where cryovolcanoes are actively shaping
its surface.
Water from either the mantle or from pockets of water trapped in the crust erupt over the
surface of Pluto, creating a varied landscape.
But it turns out that it’s not just water found in these eruptions, but tholins are
clearly mixed in too.
Data from Hubble suggested that Pluto was getting redder, and New Horizons may have
passed by during Pluto’s reddest time of its year.
And New Horizons may have found out why.
Here, in a region called Viking Terra, we see a cryovolcano that fountained this water
tholin slurry across the immediate surroundings.
Just next to this region, we see a crater and a trough filled by this slurry during
another eruption.
By the trough, you can see where this slurry flowed down and pooled.
This can also be seen in another region by Virgil Fossae, another trough where this slurry
has travelled down.
However, the most interesting thing about tholins is not found on Pluto itself, but
rather on its twin dwarf planet, Charon.
In this enhanced colour image of Charon, what do you immediately notice?
The red cap over its north pole.
Incredibly, because Pluto’s gravity is so weak, when it erupts this slurry mixture some
of it escapes Pluto altogether and makes the 19,000km journey to Charon.
The tholins are localised here because Pluto and Charon are tidally locked to each other,
they only ever show each other one face.
Poetically speaking, Pluto is always hiding its heart from Charon in this eternal waltz.
This means that more tholins fall on a specific spot on Charon, rather than all over.
And speaking of Charon, some interesting discoveries have been made about it too.
It is a water ice world, unlike Pluto whose surface is predominately nitrogen ice.
As such, it doesn’t really have an atmosphere like Pluto does, as the water ice is locked
to the surface.
On Pluto, the nitrogen ice sublimates depending on Pluto’s seasons, meaning Pluto’s atmospheric
density can vary by many orders of magnitude over the course of its year.
With this sublimating and refreezing of the atmosphere, Pluto’s appearance may change
dramatically over the course of its 248-year-long seasonal cycle.
The last discovery I want to share with you today is about the beating heart of Pluto,
a region known as Sputnik Planitia.
This is a totally unique region of the solar system; we haven’t seen anything like it
before.
It’s a region of nitrogen and carbon monoxide ices, divided up into polygonal cells by shallow
troughs.
It is clear that this is a region that is constantly changing, as no craters are found
here.
Ices sublimate and freeze here regularly, creating troughs and pits, meaning these polygons
are likely to be convection cells.
These cells are moving and can be seen pouring into the mountain ranges surrounding the region
through slow moving glaciers.
Sputnik Planitia could be compared to Greenland and Antartica, in that it controls the climate
of Pluto heavily.
While the total absence of craters is limited to Sputnik Planitia, it is amazing how few
craters there are on Pluto and Charon generally.
This might not just be because their surfaces are young, but perhaps the Kuiper Belt is
more devoid of smaller objects than we may have first thought.
Now, New Horizons has already left Pluto far behind it.
And it has even encountered another object beyond Pluto known as Arrokoth, which I will
do a video about soon.
The data from this flyby is still in the process of being transmitted back to Earth, although
that should wrap up really soon.
Beyond Arrokoth, New Horizons is studying the environment of the Kuiper Belt.
Its extended mission will take it to 2021, but it doesn’t have a new target to go and
fly by, so New Horizons may end up like the Voyagers, wandering through space until it
leaves the solar system.
One can only hope that there are other objects to observe along New Horizon’s flight path,
but nothing has been discovered yet.
All being well, New Horizons could last into the late 2030s before its power runs out.
But I wanted to leave you with this really interesting image.
New Horizons has travelled so far from Earth that when it looks at our closest star system,
Alpha Centauri, it’s in a clearly different place from New Horizons’ perspective than
from ours.
This is due to the parallax effect, something I’ve done a video about here if you want
to see more astronomical examples.
It’s just mind boggling to me to think about how far New Horizons has travelled relative
to us, so much so that Alpha Centauri has moved from New Horizon’s perspective.
Conversely, however, New Horizons has travelled all that way, and that’s the only difference
it’s made to the view of our closest neighbour.
Space is just so big.
So, there we have it, a recap on all the new data New Horizons sent back about Pluto.
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