Dragonfly goes on Titan: what an incredible mission!
On Earth it is 9:00 a.m. UT on January 14, 2005, when the small Huygens probe is released from
the Cassini mothership and plunges into the atmosphere of Titan at an altitude of 1200 km.
Huygens parachutes down for two and a half hours, measuring atmospheric pressure,
temperatures, electrical properties, humidity, wind speed, and direction. Equipped with a
microphone, Huygens also records the first ambient sounds from another celestial body.
The spacecraft descends through an atmosphere formed by hydrocarbon and nitrogen smog,
and lower down a troposphere furrowed by a few but dense cloud formations, possibly thunderstorms,
and characterized by fog formations at medium altitudes, crossed by electrical discharges;
The slow descent gives Huygens plenty of time to photograph the approaching surface,
and surprisingly the panorama of Titan recalls the orography of our mountains,
with quiet valleys crossed by rivers and streams. We can glimpse sinuous channels
of ice organized in a dense network of main branches and smaller branches, which seem to
flow into vast basins similar to large lakes, bordered by coastlines with a marked profile.
And then, islands and slabs of lighter-colored soils, perhaps shoals or sandy shores, emerging
from darker basins near the coastlines, over which misty formations stand out;
But the resemblance is only apparent... Titan is, in fact, a world totally alien to Earth
and, as far as we know, also very different from other solid bodies in 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 of ice and smog; instead of lava flows, Titan has volcanoes
that erupt ice. A very strange world that reveals its secrets only with great difficulty.
All this Huygens saw and photographed, as he descended cradled by Titan's winds. Until, after
two and a half hours of travel, he touches down in what looks like the wet bed of a stream, largely
composed of water ice, full of smooth pebbles that lie, eroded at the base by the flow of water, on
an apparently soft but solid surface, perhaps the beach of one of the many river channels or drains.
Another 72 minutes and the probe's batteries run out.
And Huygens has been there ever since,
for 17 years. Or maybe not, Titan is such a living, violent world that a flood or methane
rains could have swept her away, buried in one of the many lakes of hydrocarbons...
A little sorry, honestly. That spacecraft was brave, and it gave us the first important
insights into a truly alien world, 1.5 billion miles away from home.
Of course, the photographs it left us are of poor quality (the camera technology was that
of 15 years earlier) and deteriorated by brutal compression algorithms (a price to be paid to the
temporariness of communications and the short time available for transmission), but the mission is
still a technological and scientific success. But Huygens will not be alone for long.
Another Earth probe is preparing to land on Titan and to reap the benefits of its sacrifice…
Among the many moons in the Solar System, Titan - Saturn's largest moon,
the second largest in the Solar System - stands out for its unique characteristics, and for the
possibility of finding extraterrestrial life forms there, past or present.
Larger than the planet Mercury, its orbit around Saturn places it about 1.4 billion kilometers from
the Sun (i.e., about 10 times farther than Earth), so its average temperature is about -180°C.
Its atmosphere, dense and opaque in the visible spectrum,
is composed largely of nitrogen and methane. Methane on Earth is one of the products of
the life processes of organisms and occurs naturally in gaseous form.
On Titan, however, where the surface pressure is 50% higher than on Earth, methane is liquid and,
just like water on our planet, forms clouds and rains, fills lakes and rivers.
Titan is the only satellite in the Solar System that possesses a thick atmosphere and
liquids flowing on its surface. It even has a hydrological system similar to Earth's,
although it rains methane instead of water. Wind and rain have created surface features
similar to those found on Earth and, like Earth, Titan manifests the alternation of seasons.
At this point the question arises: could Titan host, or have hosted, some form of life?
It depends. Life as we know it needs three things: an energy source such as sunlight,
a liquid solvent such as water, and organic substances,
a wide variety of carbon-based compounds that build proteins for life as we know it.
Before life arose on Earth, our atmosphere was very different. There was almost no oxygen
and much more methane. In the sunlight, these molecules formed organic chemicals that then
rained down on the ground. We don't know exactly what those chemicals were, but when combined
with water and energy they probably formed the primordial soup from which life arose.
We can't travel back in time and see exactly what happened in the past, but fortunately, there is a
current place with a similar atmosphere: Titan! So we just have to go and see! Yes, but how?
We had a chance in 2005 with the little Huygens, but its brief existence
only served to make us even more curious. And Saturn, it's not exactly around the corner...
Fortunately, NASA has found the funding to put together a true sci-fi mission,
giving birth to the idea of a giant drone that will go "from
flower to flower" on Titan's surface. We won't be sending an ordinary lander, then.
Planetary landers move very slowly and can only explore a small region of the worlds they visit,
but Titan's low gravity and dense atmosphere will allow Dragonfly,
as it has obviously been named, to take flight and make leaps of tens of kilometers.
Dragonfly is certainly not a garden-variety drone. At 3 meters long and weighing 500 kilograms,
it's more like a small car, with four arms that each support two rotors stacked on top
of each other. Each of the eight rotors will be about one meter in diameter.
The aircraft will be able to travel at about 10 meters per second and will be able to fly up to
4 km altitude. This will allow it to make short flights from one point to another on the surface.
Each flight will be meticulously planned but will have to be done autonomously,
as a radio command sent from Earth would take more than 80 minutes to reach the drone.
"Hey, guys, just a moment before we continue... BE sure to join the Insane
Curiosity Channel... Click on the bell, you will help us to make products of ever-higher quality!"
Titan's gravity is about one-seventh that of Earth, slightly weaker than the gravity
of our Moon. With an atmosphere four times denser than Earth's - about the pressure you
feel one meter underwater - conditions are therefore perfect for flight. A human being
with flapping wings could probably fly to Titan! At Saturn's distance, sunlight is a hundred times
weaker than on Earth. And Titan's haze blocks out most of the rest. Therefore,
Dragonfly will move through a perpetually frigid, twilight landscape, and it won't be able to rely
on solar power. It will run on batteries during the day and recharge at night from
a nuclear power source similar to those used on NASA's Curiosity and Perseverance rovers.
In this way, NASA hopes that in nearly three years of the mission Dragonfly will be able to
fly from one point to another covering a total distance of 175 km - almost double the distance
covered to date by all Martian rovers combined. With NASA's Ingenuity helicopter currently
operating on Mars, Dragonfly will become the second aerial vehicle to fly to an alien world
and the first to take flight on an alien moon. As a project, Dragonfly has been active since
2019, but formal mission objectives have only recently been disclosed.
Dragonfly's purpose will be primarily, but not exclusively, astrobiological in nature. The drone
will go in search of biosignatures, which stand for present or past biological processes, and
make measurements on the chemistry of the surface, including those concerning molecular structures
necessary for life, as well as try to understand if Titan could potentially be habitable.
The planned landing point is in the dunes of a region known as Shangri-La; almost on the Equator,
about 750 km north-northwest of where the Huygens probe lies. From there, Dragonfly will proceed
to explore the vast equatorial desert, also attempting to reach the Selk impact crater,
60 km in diameter, considered an excellent place to look for possible traces of life.
Selk's crater floor might have held a warm, wet pond when it formed and for a few hundred (or
thousand) years after. Once Dragonfly arrives at Selk, scientists can use Dragonfly's suite
of instruments to search for prebiotic molecules - the building blocks of life
as we know it - and determine how, or if, biomolecules are formed on Titan.
The mission will take place primarily during the boreal winter. It could rain,
but mission experts think that rain, of liquid methane, will not be a problem for Dragonfly,
although this is not yet entirely certain. Fortunately, it rains very rarely on Titan,
and there is also very little wind, due to its slow orbital dynamics, distance from the sun, and
foggy atmosphere. All factors keep temperatures relatively constant from latitude to latitude.
In short, it will be much easier than flying on Mars, and in practice, the sequence of flights
will follow this routine: Every 15 days the aircraft takes off and flies for about 10 km, uses
its sensors to explore new scientific targets, and then return to the original site until new landing
sites are verified as safe by mission control. The aircraft will remain on the ground during
the nights of Titan, which will last about 8 Earth days.
The drone's payload will consist of eight cameras, two spectrometers,
and a drill to sample complex organics. Dragonfly will also carry a geophysical and meteorological
station with 11 different instruments that can measure air temperature, air pressure,
wind speed and direction, and humidity. Wherever it goes, Dragonfly will study Titan's
surface, which should have picked up organic chemicals raining down from the atmosphere.
Mounted on each of the probe's two sled rails is a drill that will grind the
materials so they can be sucked into an instrument called a mass spectrometer.
The spectrometer will be able to measure the masses of molecules in each sample,
including the heavier organic compounds that are the building blocks of life as we know it.
Dragonfly will also carry a suite of instruments that will analyze the atmosphere,
allowing scientists to know how it changes with the days and seasons.
The drone will also measure any earthquakes with a seismometer. And,
of course, it will have cameras at various resolutions to capture the surface as it
flies over it up to miles high. These photos will help the mission team identify the most
interesting areas to visit later and will offer the public breathtaking views of an alien world.
Dragonfly will also make use of special ultraviolet light LEDs to aid in the
search for organic compounds, some of which fluoresce when illuminated with UV light.
Dragonfly is expected to launch in June 2027 and will take nine years to reach
Titan, arriving by 2036. The spacecraft will perform a gravitational assist flyby of Venus,
and three passes by Earth to gain additional velocity.
The cruise stage will separate from the entry capsule ten minutes before encountering Titan's
atmosphere. The lander will descend to the surface of Titan using an aeroshell and a series
of two parachutes, while the spent cruise stage will burn up in uncontrolled atmospheric entry.
The duration of the descent phase is expected to be 105 minutes.
At a speed of 1800 km per hour, a drogue parachute will deploy, to slow
the capsule to subsonic speeds. Due to Titan's comparably thick atmosphere and low gravity,
the drogue chute phase will last for 80 minutes. A larger main parachute will replace the drogue
chute when the descent speed is sufficiently low. During the 20 minutes on the main chute,
the lander will be prepared for separation. The heat shield will be jettisoned, the landing skids
will be extended, and sensors such as radar and lidar will be activated. At an altitude
of 1.3 km, the lander will be released from its parachute, for a powered flight to the surface.
It will be really terrible for us, for those who watch from Earth, having to wait
all these years before we can witness this extraordinary spectacle. Don't you agree?