A dive into Titan's atmosphere to find the old Huygens probe!
Getting off on Titan is a breeze. I'm telling myself that all the
time these days. And I'm hearing it a lot from NASA engineers, too, all cozy in their chairs.
But they are right. Venus yes it really is hell, but Saturn's big moon, no.
Titan’s atmosphere is also unbreathable, but at ground level, the pressure is only a
little higher than on Earth. It doesn’t crush you like Venus, which is 95 times heavier.
Also, Titan doesn’t try to fuse the lander you’re down with, or your suit, with sulfuric acid
puffs! Neither does it have winds that blow like those of Jupiter, nor temperatures that threaten
to liquid you and your entire spacecraft. On Titan it is cold, it is true, but -195°C,
I don't know why, sounds better than +450°C... it gives me more confidence, it seems more human.
Let's say rather that Titan is much more out of the way than Venus, to get there.
And it's only thanks to a revolutionary "direct fusion" engine that we're about to complete the
Earth-Saturn crossing in less than two years. And it has been 41 years since - with the Huygens
probe - we had the last direct contact with Titan. Unfortunately, the Dragonfly mission
of 2035 ended in disaster, and it is only today, 23 February 2046, aboard the James Clerk Maxwell,
a spacecraft with nuclear propulsion for the first time, that we are going back again.
Tomorrow afternoon (Earth time), in fact, the Maxwell will land near Antilia Faculae,
the "marshy" archipelago where Huygens landed on January 14, 2005. If all goes well,
there will be three of us descending to the surface. But the funny thing is that I will
already be there waiting for my companions. Can you believe it? Here's what I'm going
to do... While we're still orbiting Titan, I'm going to put on a suit made for the occasion,
I'm going to go out on the balcony set up for extra-vehicular activities, and from there,
at the right time, I'm going to let myself go into free fall... It won't be the madness of
a moment, but a mission planned before departure I will slow down my speed through jets of nitrogen
emitted by the thrusters of my suit and then all I have to do is to fall towards the surface
telling the radio everything I see... everything that my senses and my instruments will collect
What do you want to do, come along?.
"Roll intro"
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Today we know that somehow Titan is a world similar to ours. Certainly not because of the
climate or the breathability of the air: Titan is in fact about a billion and a half kilometers
from the Sun, so it receives just ninetieth of the light that receives our planet and its atmosphere
is made mostly of nitrogen with a little methane. Certainly, Titan is a complex world: unlike Mars,
for example, has a very dense atmosphere, reminiscent of
that of Earth several billion years ago. Its surface, moreover, has been modeled by
phenomena that appear quite similar to those in action here on Earth, such as soil erosion by
winds and fluids. On Earth, it is obviously water - liquid or solid - the fluid capable
of modifying the landscape, while on Titan it is likely that methane plays this role.
The average temperature of the large moon of Saturn is -182°C,
very close to that of the so-called triple point of methane, of -180°C. Therefore,
small climate changes are sufficient to allow the presence of gaseous methane in the atmosphere and
liquid or frozen methane on the surface. And this makes possible a hydrological cycle of
methane similar to that of water on Earth. But the similarity with the Earth is only
apparent... Titan is, in fact, a totally alien world and, as far as we know, also very different
from the other solid bodies of the Solar System. Instead of liquid water, Titan has liquid methane;
instead of silicate rocks, Titan has rocks of compact ice; instead of dust, Titan has a
regolith made of ice and carbon compounds; instead of lava flows, Titan has volcanoes that erupt ice.
A very strange world, which reveals its secrets only with great difficulty.
However, everything we know, or almost, of this remote world we
owe to the Cassini-Huygens mission. If you remember... Cassini took
Huygens with it for 7 long years, then, upon reaching the Saturn system dropped it on Titan
(kind of what Maxwell will do with me tomorrow), and then continued its Grand Tour until 2017.
During her parachuted descent, Huygens collected data for 2 hours and 28 minutes. and after landing
continued to transmit for another 72 minutes. Tomorrow, God willing, I will go and wake her up.
February 24, 2046 - T+0. I have just detached myself from the handrail of the gallery.
The microcomputer that governs all my movements immediately activates the thrusters to decrease
my speed and above all to draw the trajectory that should bring me down very close to the
position where Huygens is right now. I am consoled by the fact that once
upon a time the ellipses of uncertainty in landings measured tens of kilometers,
while today we are able to reduce them to a hundred meters. At least, in theory...
Yeah... but where did Huygens really land? It may sound bizarre, but it wasn't easy to figure out.
The problem is that Titan is covered by a very opaque fog. In fact, the images Huygens took as
he descended are the only ones we have of the surface in the visible. To figure out where the
exact location was, yesterday we had to .hit the approximate region, located west of Shangri-La,
with a radar beam. And now that we know the exact coordinates, with the approximation of one meter,
it is up to my computer to calculate everything well and bring me to my destination!
T+5 minutes - I am still in free fall at an altitude of 90 km. At this altitude,
the atmospheric pressure is one-hundredth of the Earth's, practically the same as on Mars.
On my visor, all the data from the sensors are aligned. The temperature is -130°C.
And this very light haze that surrounds me apparently is made of tholins... a kind of
aerosol that is formed by the irradiation of methane by ultraviolet radiation from the Sun,
often combined with inorganic substances such as molecular nitrogen.
The presence of tholins on Titan is intriguing because they are thought to
contain some of the chemical precursors of life. However, I passed through it at more than 110 km
per hour and after a few minutes, at 80 km altitude, I plunged into the densest
layer of tholins, the one that when seen from the outside totally dulls the view of Titan's surface.
Meanwhile, the thrusters slowed me down to a speed of 32 km per hour.
T+12 minutes - The computer commands the opening of the parachute and from
this moment the descent becomes slower and slower. Visibility is much more reduced than
before... I am descending through orange gas clouds, but I can still see the Sun above me.
No trace instead of the surface looking down. The atmospheric pressure tripled compared to
before and the temperature dropped to -170°. The shift due to the wind is getting stronger
and stronger and I pray with all my strength that the computer will take this into account.
T+56 minutes - at an altitude of 60 km I suddenly emerge from the layer of dense mist. I almost
fainted from the surprise: I see the surface of Titan and I am the first human being to do so!
I see among some clouds branched channels carved by a liquid that perhaps flowed in
times not far away. Now they seem empty but at the bottom, there is perhaps organic material,
hydrocarbon deposits. The jagged outlines of seas and lakes become clearer.
I descend through what the viewer tells me is a fog of hydrocarbons.
The temperature has reached -200°, which should be the minimum measurable on Titan.
From here on it should start to rise again.
T+1h 21m - I am at 30 km. Some turbulence is starting to be felt. The wind thrust
is discontinuous. I have reached an altitude where large white clouds composed of methane
and molecular nitrogen are hovering. I look down and try to understand if the computer is
pushing me in the right direction, towards Shangri-La. I still can't get my bearings.
T+2h 11m - At an altitude of 20 km I suddenly find myself in the middle of
a thunderstorm with violent bursts of rain. NASA scientists had told me that on Titan
it very rarely rains at low latitudes (and here I am on the vertical of the equator),
but that when it rains, it pours. And in fact, I'm having a very bad time,
with strong winds and continuous electrical discharges between clouds.
The worry does not prevent me from noticing that the methane droplets are very large,
up to a couple of centimeters in diameter, and, due to gravity, which on Titan is only
one-seventh of Earth's, also very slow. Much slower than me, so much so that I am the
one raining down on them! Slow as snowflakes. It is these rains that form the methane lakes,
at least at higher latitudes, where it rains more frequently.
All around the sky is stormy and dark, but underneath I see plains sprinkled with dunes
that stretch for dozens and dozens of kilometers, probably formed by the tholines that descend from
the upper atmosphere and are then deposited on the surface. The fact is that on Titan,
again due to the reduced gravity, lower than that of our Moon, the deposits can be as high
as a hundred meters. Hills and sand dunes are then carved by branched channels and canyons.
T+3h 01m - At an altitude of 10 km I emerge from the storm and finally manage to see and recognize
the dark spot of Shangri-La. A little further west is the jagged coastline of Antilia Faculae, where
Huygens has been waiting for me for 41 years. At this altitude, the air pressure is exactly
the same as on earth, while the temperature has risen to -190°.
Towards the east I can see a column of gas rising from the horizon,
a plume that bends sharply northwards higher up. I don't want to be wrong,
but I have the almost absolute certainty that it is an erupting volcano. I feel like I am
dreaming... it could be the confirmation of the existence of volcanism on Titan,
which would explain the origin of methane... With enthusiasm sky high I prepare to touch down.
T+3h 59m - After almost four hours of descent I touch down with the lightness of a feather,
slowed down to a crawl by the thrusters that are almost empty.
I immediately activate the release of the plate that binds me to the parachute,
to prevent the wind from dragging me away. A wind that does not exceed 17 km per hour.
I look around me. Incredulous. The landscape is disturbing: silent and cold.
A flat landscape, a ground with the consistency of wet sand sprinkled with smooth stones. I hold one
in my hand... and it feels as compact and heavy as real rock, and not made of ice as someone thought.
But I don't have much time. I ask the computer to calculate the distance between me and the
Huygens...and I don't like the answer. .and I don't like the answer: 277 meters!
Luckily the terrain is flat until the horizon, apparently without obstacles.
I set off, and in the meantime, I make sure Maxwell has detected my position.
The daytime sky has a decidedly dark orange color and appears uniform in all directions due to the
significant scattering of the high-altitude haze layers. The Sun should be very high, but instead,
it is not visible. The light is that of a cloudy, gloomy terrestrial sunset.
Absolutely invisible Saturn, which should appear gigantic and looming on the eastern horizon.
T+4h 27m - I'm out of breath from the effort. It was not easy to walk in this suit and with
this gravity, but I finally managed to reach the site indicated by the computer.
The problem is that I don't see the probe. Huygens is a kind of cylinder 130 cm wide and 80 cm high.
So it should be clearly visible, but ... nothing. So I try to look for it by moving away on an
increasingly wide spiral. But the only result is to realize that my boots get heavier and heavier
collecting a sticky slush. There must be liquid methane flowing down there,
I tell myself, and maybe in all these years, the probe has been carried further
downstream by the movements of the ground... And indeed... there it is! About thirty meters
to the south, practically buried... Only the radio antenna still sticks out from the surface.
I kneel down and remove the rocks and mud covering the top.
Then I stay there, and I'm not ashamed to say that for the first time
since the beginning of my descent, I no longer feel alone
and abandoned to myself. We stand there together,
Huygens and I, waiting for Maxwell to come and get us. And bring us home at last.