Earlier this year, NASA announced 4 new Discovery-class missions that they were considering.
These are low-cost, rapidly-built missions that will help scientists understand some
mystery in astronomy and planetary science.
One of these missions is called Trident, and it’s going to be targeting the Planet Neptune.
And more specifically, it’s going to be providing close up pictures of its largest
moon Triton.
You’re looking at Neptune.
Seen close up by NASA’s Voyager 2 spacecraft when it flew past the giant planet back in
the summer of 1989.
The spacecraft came within 5,000 kilometers of the planet’s north pole.
Five hours later, it made its closest approach to Neptune’s largest moon, Triton, passing
within 40,000 kilometers of its surface.
This brief flyby revealed a bizarre ice world that orbits Neptune in the opposite direction
from every other large Moon in the Solar System.
The moon is highly inclined to Neptune, offset by 23-degrees.
It’s believed that the huge moon, three-quarters the size of our own Moon is actually a captured
Kuiper Belt object.
When did this happen, and how?
Voyager discovered that Triton has an atmosphere, and its ionosphere - the region filled with
charged particles - is 10 times more active than any other moon in the Solar System.
This is surprising considering how far Triton is away from the Sun.
It means that some other energy sources must be generating the particles.
Triton seems to have a dynamic climate, with constant snowfalls of organic chemicals, like
nitrogen falling on its surface, piling up into snowdrifts and glaciers.
The average temperature on Triton is 38 K, or -235 Celsius, which means that atmospheric
nitrogen collects on the surface like frost.
It has a south polar cap containing methane ice.
But the most fascinating mystery is that Voyager discovered a faint hint that Triton has geysers,
just like Europa and Enceladus.
Does Triton have a liquid ocean surrounded by a thick layer of ice?
Are these icy water worlds everywhere across the Solar System?
Did it always have a liquid ocean, or did it form after it was captured by Neptune,
and the tidal interactions liquified its interior?
With so many unanswered questions, NASA is getting more and more serious about returning
to Neptune and Triton.
Back in January 2020, NASA announced a new set of Discovery-class missions that it was
considering.
These included two missions to Venus called VERITAS and DAVINCI+.
If built, these two missions will map the surface and atmosphere of Venus in more detail
than ever seen before.
Venus is a terrible terrible place, but definitely worth exploring more.
Keep your enemies closer, and all that.
There’s IVO, which would be a mission to Jupiter’s moon Io - the most volcanically
active place in the Solar System.
This spacecraft would make close flybys to Io, helping scientists understand how magma
is generated through the tidal interactions with Jupiter.
Yes, please.
Seriously, can you imagine even higher resolution images of the surface of Io than this?
But the one that really caught my eye was Trident, a mission to Neptune and Triton.
In June 2020, NASA gave us a few more clues about the Trident mission.
First, I need to address the name.
Trident.
Unlike most missions, this isn’t an acronym or even a backronym.
It references the Greek God Poseidon, aka the Roman God Neptune, known for holding a
three-pronged spear called a trident.
That said, NASA has said the mission will have a three-pronged approach to examining
Triton.
For starters, the mission will be scanning the moon for evidence of water in all its
forms, from the under-ice ocean, to the rock-like ice mountains to the plumes of steam blasting
out from its geysers.
The second objective will be to view the 60% of Triton that Voyager missed during its flyby
back in 1989.
One full hemisphere of Triton has never been seen, and this time, Trident will see almost
all of it.
The third objective will be to help understand how Triton is such an active world so far
out in the Solar System.
Even though it’s 4.6 billion years old, like the rest of the Solar System, the surface
of Triton is constantly being refreshed.
When Voyager 2 flew past, it saw very few craters, which means that the surface is easily
less than 10 million years old.
Observing Triton up close will answer questions about this moon and Kuiper belt objects in
general.
Okay, now we know the science questions, how will we get answers?
How will the mission actually work?
I’ll get to that in a second, but first I’d like to thank:
Michael Stephen Bradley Joseph Biernat
TJ Chapman David
Bill Hellmer Sara Michaele
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If chosen, Trident will be a Discovery-class mission.
These are low-cost, rapid development missions that have been sent all over the Solar System.
Let me give you a few examples.
The Lunar Reconnaissance Orbiter at the Moon, which has given us the highest resolution
images we’ve ever seen of the lunar surface.
Mars InSight, which is currently on Mars, trying to understand how volcanically active
Mars is today.
Future missions include Lucy, which will be traveling to Jupiter’s Trojan asteroid belt
and Psyche which will be going to a metal asteroid.
Past missions include Stardust, which retrieved samples from a comet, MESSENGER, which explored
Mercury, Dawn, which visited two asteroids in the belt, and Kepler, which found thousands
of exoplanets.
Small missions, big science.
If all goes well, Trident will launch in October 2025, when the Earth and Jupiter are perfectly
aligned, so the spacecraft can get a gravitational assist from the giant planet, increasing its
speed and helping it climb up the gravitational well to Neptune and Triton.
A backup date of October 2026 will provide the same alignment opportunity.
The mission would then fly through the Solar System for 13 years, finally arriving at the
Neptune system in 2038.
It will then have a total of 13-days as it flies through the system, capturing close
up images of Neptune and Triton, before speeding off into the Kuiper Belt.
This won’t be an orbiter, unfortunately, this will be a New Horizons-style flyby, giving
us a quick glimpse of the system.
During the flyby, it’ll pass within 500 km of the surface of Triton, 80 times closer
than Voyager 2 got back in 1989.
This means it’ll actually be flying direction through Triton’s atmosphere, measuring the
particles directly from within.
It’ll get close enough to the surface of Triton to make detailed maps of its magnetic
fields.
The flight path will take it through Triton’s shadow, allowing it to make observations of
the moon’s atmosphere.
The big goal is to reach Triton before 2040, that’s when the Sun moves too far north
in the skies to allow a good view to the plume activity on Triton’s surface.
Right now, we don’t know which of these 4 mission proposals will actually fly.
NASA said that they’re going to choose two out of the four by summer 2021.
I don’t envy the selection team’s job here.
Venus, Io or Triton… pick 2.
I was 17 years old, in my last year of high school, when Voyager 2 sent back those first
close up pictures of Neptune and its moons.
I was already a space nerd, and I remember that time vividly.
And if it does turn out to be the Trident mission, then we’ll see new images coming
back from the surface of Neptune and Triton 49 years after those first pictures were captured
by Voyager 2.
Even though I’ll be 67 years old, I can’t wait to see them.
What do you think?
Let me know your thoughts in the comments.
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We did a whole video about other mission concepts to both Uranus, Neptune, and their moons.
A serious flagship mission that could actually go into orbit around one or both planets and
deliver Cassini-like science of the outer Solar System.
And you can watch that video now.