Why is it so difficult to get to Enceladus?
Enceladus is one of Saturn's moons.
It is not the largest or closest to the planet, but it is one of the most important.
The reason is that underneath Enceladus' ice sheets is a massive ocean of water, which
could not only be in a liquid state but could even have all the necessary conditions to
support life.
However, although this natural satellite is very important for the search for extraterrestrial
life, no spacecraft has landed on the surface of this moon so far.
So why haven't we sent any space missions to study this enigmatic moon in detail?
Is it tough to get to Enceladus?
Stay with us to find out!
Famed astronomer William Herschel discovered Enceladus on August 28, 1789, while using
his new 47-inch (1.2 m) telescope, the largest in the world at the time, at Observatory House
in Slough, England.
This moon is a relatively small satellite composed of ice and rock.
With a diameter of 513 km, it ranks sixth in size, since smaller than Titan, Rhea, Iapetus,
Dione, and Thetis.
Enceladus is seven times smaller than Earth's moon.
That is why its gravity is feeble, and a person standing on the surface of this natural satellite
could jump to more than three meters high without any effort.
Like Jupiter's moons, Enceladus is in 2:1 orbital resonance with Dione.
This means that for every lap that Dione completes around Saturn, Enceladus completes two.
This phenomenon of moons in orbital resonance can be observed on both Jupiter and Saturn,
and everything seems to indicate that it is a fairly common phenomenon in the solar system.
Therefore, it is possible that it is also something common in the rest of the universe.
First Missions The first spacecraft to take sharp images
of Enceladus were the famous Voyager 1 and 2 probes in the 1980s.
These two spacecraft aimed to study the solar system's outer planets and photograph the
planets' moons.
One of those natural satellites was Enceladus, which was in the path of the Voyager probes.
Thanks to this, they were able to take a series of photos that revealed that this natural
satellite was much more interesting than we had imagined.
Enceladus cannot be seen clearly from Earth, even with the most powerful telescopes.
This is because it reflects too much sunlight, so its surface is not very well-lit.
Astronomers believed that because Enceladus reflected so much light, it might have had
some atmosphere.
However, the Voyager probes discovered this satellite was covered in a thick layer of
newly formed ice.
Images acquired from this distance had inferior spatial resolution but revealed a highly reflective
surface devoid of impact craters.
The absence of craters on the surface of Enceladus caught the attention of scientists because
giant planets' natural satellites are normally much more prone to meteorite impacts.
When a meteorite falls on a celestial body without an atmosphere, such as the Moon, the
impact crater that forms remains there for hundreds of millions of years because there
is no natural geological process to erase it.
For example, many meteorites have fallen on Earth throughout history, the most famous
being the Chixulub meteorite that fell in the Yucatan Peninsula in Mexico and ended
the age of the dinosaurs.
However, most of the impact craters on Earth are erased by geological forces and erosion
caused by the atmosphere.
So, if a meteorite falls to Earth after several million years, there is no trace of it.
But in celestial bodies without atmosphere or geological activity, this does not happen
since there is nothing to erase the crater.
It is for that reason that the craters of the Moon are millions of years old and have
not been erased until now.
The case of Enceladus drew attention because if there weren't many impact craters on its
surface, it meant something was erasing them.
But what?
Geysers Off Earth After the Voyager 1 and 2 spacecraft, scientists
had to wait more than 20 years for a new spacecraft to revisit Saturn.
Why did so many years pass between the Voyager spacecraft and the Cassini-Huygens mission?
The reason is simple.
Once the Voyager probes sent back the first images of Enceladus, scientists and astronomers
began observing this moon with the most powerful telescopes on Earth, such as the Hubble Space
Telescope.
Thanks to the combination of the information provided by the Voyager spacecraft and observations
from telescopes on Earth, it was determined that Enceladus was a very important body for
scientific research since it seemed to have a tenuous atmosphere that interacted in some
way with Saturn's rings.
In addition, thanks to the photographs of the Voyagers, scientists knew that something
was constantly renewing the surface of Enceladus.
With all this in mind, astronomers planned a mission that could provide information that
would help us answer all these questions.
So, for ten years, the mission that would help us unveil the secrets of Saturn's moons
was planned: the Cassini-Huygens mission.
The Cassini mission was launched on October 15, 1997, and arrived at Saturn seven years
later, in July 2004.
This spacecraft took longer to reach Saturn than the Voyager probes because it was heavier.
The heavier a spacecraft is, the more fuel it needs and the longer it takes to travel
long distances.
The Cassini-Huygens probe was a two-part spacecraft, the Cassini orbiter on one side and the Huygens
lander on the other.
Thanks to Cassini, the most important discoveries about Enceladus would be revealed.
NASA engineers considered Enceladus to be an extremely important body, so they made
the spacecraft get as close as possible to this moon.
In one of its approaches, Cassini managed to take one of the most impressive images
that have been taken so far in the entire history of space exploration.
This 2005 Cassini image clearly showed what appeared to be geysers or jets of water being
shot from the surface of Enceladus.
This discovery impressed all scientists as geysers were observed outside of Earth for
the first time in history.
But observing them on a small moon with no geological activity was extraordinary.
This discovery helped solve the mystery of what was constantly renewing Enceladus' surface,
but it put new questions on the table, such as
How were these vast geysers produced?
What force or energy produced them?
What was the geysers expelling?
Was it water?
If so, where did that water come from?
Origin of the E ring The images of the geysers on Enceladus helped
answer many questions, one of which was the influence this moon had on the rings.
Since the discoveries made by the Voyager probes, it has been known that this moon interacts
in some way with Saturn's E ring.
The E ring is one of Saturn's innermost rings.
The interesting thing about this ring is that it is made up of very small ice particles.
The Sun's radiation sublimates them, and the ring disappears slowly.
The problem is that at the rate that the material of this ring evaporates, by this point the
ring should have disappeared completely, but it doesn't, as if the particles that make
up the ring were constantly renewed in some unknown way.
This is where Enceladus comes in.
With images of geysers at Enceladus' south pole, scientists were finally able to test
one of their theories: that Enceladus is the main source of particles in Saturn's E ring.
Cassini's images reveal that Enceladus is not only very close to the E ring but is also
entirely inside it.
This means that without Enceladus constantly feeding the flow of materials, Saturn's E
ring would not exist.
But back to the initial question: What produces the geysers on Enceladus?
Did Enceladus have tectonic activity even though it was so small?
The answer will surprise you!
An ocean of temperate, liquid water As we mentioned earlier, Enceladus is in Orbital
Resonance with Dione, another moon of Saturn; this synchrony around a planet causes the
satellite closest to the planet to experience enormous tidal forces internally caused by
the stretching and contraction of the gravitational forces of the objects with which it is synchronized.
This is what causes the intense volcanic activity of Io, a moon of Jupiter.
This moon is in orbital resonance with Europa and Callisto.
Because it is synchronized with two other moons and also with its planet, the tidal
forces within Io are immense.
As its innermost layers heat up, this produces an enormous number of volcanoes.
It was previously thought that very small natural satellites like Enceladus could not
have this kind of geological activity, as the tidal forces on Enceladus are not as large
as they are on Io.
However, scientists found that they were wrong and that the tidal forces on Enceladus are
enough to produce geysers, but how are they produced?
For now, the most widely accepted theory is that the tidal forces produced by Dione and
Saturn on Enceladus stretch and contract it, causing its inner rock core to heat up.
The heat produced on Enceladus doesn't compare to that produced on Io, but it's enough to
warm the ice sheet above the hot rock.
This heat melts the ice, turning it into water and then into steam.
Then, this vapor expands and, due to the high pressures, shoots out towards the surface
of Enceladus, giving rise to the geysers that Cassini captured.
In the planetary sciences, this process gives rise to something known as cryovolcanoes.
These are ice volcanoes that behave very similar to volcanoes on Earth but with completely
different materials.
On Earth, volcanoes occur because the planet's internal heat heats the rock until it melts
and turns it into lava, which is expelled to the outside.
When it cools, it hardens to become rock again.
Something very similar happens on Enceladus but with ice.
The ice that forms the outermost layer of Enceladus is heated by tidal forces.
It turns into water and then into steam, which is ejected to the surface.
In the same way that lava hardens when it reaches the surface of the Earth, water, and
vapor from Enceladus turn back to ice when they reach the surface.
In cryovolcanoes, water serves as lava, ice as rock, and steam as ash.
They're like volcanoes on Earth but made of ice.
Did you know that something like that could exist?
Does this mean that there is water underneath Enceladus' ice sheet?
The answer is yes.
The evidence is compelling.
Beneath the surface of Enceladus is an ocean of liquid water that is kept at warm temperatures
thanks to the warming caused by Saturn's tidal forces.
But... if there is an ocean of water beneath the surface of Enceladus, could there also
be living things swimming in that ocean?
Enceladus Habitability For years, scientists wondered if Enceladus'
ocean might have the conditions for living things to live inside.
Still, they could not know for sure without a sample of water from Enceladus' inner ocean,
so they devised a way to obtain it with the help of the Cassini spacecraft.
In 2015, the Cassini spacecraft made a close flyby of Enceladus' south pole, flying 30.0
miles (48.3 km) from the surface and through a plume of smoke from one of the geysers.
A mass spectrometer aboard the spacecraft detected molecular hydrogen (H2) from the
plume, and after months of analysis, scientists concluded that the hydrogen in the sample
was most likely the result of hydrothermal activity beneath Enceladus' surface.
If microbes or bacteria were present in Enceladus' inner ocean, they could combine hydrogen with
carbon dioxide dissolved in the water to form methane.
This chemical reaction is known as methanogenesis, and scientists believe it took place in the
early days of Earth's life.
Unfortunately, for now, there is no way to prove if life exists on Enceladus, and that
is why new missions are being planned to explore this fascinating world and reveal once and
for all if we are not alone in the universe.
Not since the Cassini mission have spacecraft been sent to explore Enceladus because it
is a highly distant and cold world.
However, there are currently several proposals to return to Enceladus.
One of them is the Enceladus Orbilander mission proposed by NASA, which plans to land on the
surface of Enceladus to try to obtain ice samples to help us discover if Enceladus has
any evidence of life inside.
Now we'd like to know your opinion: Do you think there could be living things in Enceladus'
internal ocean?
Would you like us to discuss NASA's new mission to explore this moon?
Let us know what you think in the comments!