For a long time, comets were seen only as occasional visitors, icy bodies that cross the sky and disappear for decades or centuries. This view changed radically when science began to observe them closely, not only as astronomical objects, but as… active reservoirs of water and volatile compoundsThe definitive turning point came with the mission. Rosetta, from the European Space Agency, which has been tracking the comet for years. 67P / Churyumov-GerasimenkoFor the first time in history, humanity has been able to measure, in real time, how much material a comet releases as it approaches the Sun — and the numbers are colossal.
Measurements revealed that, on each approach to perihelion, 67P ejects… trillions of liters of water…in addition to dust, organic gases, and complex molecules. This transformed comets from simple “icy bodies” into… dynamic actors in the Solar System’s water cycle.
Before Rosetta, estimates of comet composition were indirect, based on telescopic observations of the tail. The mission changed everything by orbiting the comet for over two years, tracking its activity as it approached the Sun.
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Instruments such as the spectrometer ROSINA They allowed for direct measurement of:
water vapor;
carbon dioxide;
carbon monoxide;
volatile organic compounds.
The data showed that the comet does not release water constantly. Instead, there is intermittent jets, more active regions and diurnal variations caused by the rotation of the nucleus.
During periods of increased activity, the 67P even released… hundreds of kilograms of water per second, which, over the course of months, translates into volumes equivalent to trillions of liters.
Although the term “melt” is common, the physical process is… sublimationIn the vacuum of space, ice does not change from a solid to a liquid state: it transforms directly into vapor.
When the comet approaches the Sun:
The surface heats up quickly;
The water ice begins to sublimate;
Trapped gases are released;
Dust particles are dragged along, forming the coma and tail.
This process is not superficial. Rosetta showed that heat penetrates layers of the core, activating internal reservoirs and causing… collapses, fractures and slips on the surface.
Trillions of liters of water: the real impact of this release on the space environment.
At first glance, releasing trillions of liters of water into space might seem insignificant in a gigantic Solar System. But, over billions of years, the cumulative effect is profound.
Astronomical models indicate that:
Jupiter-family comets, such as 67P, make thousands of solar passes;
Each passage contributes large volumes of water to interplanetary space;
Some of this material is captured by planets and moons.
This reinforces the idea that comets function as mobile water tanks, redistributing this resource throughout the Solar System.
One of the great questions in planetary science is: Where did Earth’s water come from?
For decades, it was believed that the oceans were formed primarily by comet impacts. Rosetta provided a more complex and interesting answer.
By analyzing the ratio between ordinary hydrogen and deuterium in the water of 67P, scientists discovered that it It does not exactly correspond to the water in Earth’s oceans.This indicates that:
Not all of Earth’s water came from comets of this type;
different classes of icy bodies contributed;
Water-rich asteroids also played a key role.
Even so, the mission confirmed that Comets are real and abundant sources of water., reinforcing its role in supplying water to rocky planets.
In addition to water, Rosetta detected a surprising variety of organic molecules in 67P, including amino acid precursors. This transformed comets into… true chemical records of the birth of the Solar System.
These bodies have preserved virtually untouched material since:
the formation of the Sun;
the collapse of the protosolar nebula;
The beginning of planetary aggregation.
By releasing trillions of liters of water mixed with organic compounds, comets act as chemical seeds, spreading essential ingredients for life.
The discovery of Rosetta broadened the concept of the water cycle. It is not exclusive to Earth. There is a The hydrological cycle on a planetary and interstellar scale., involving:
sublimation in comets;
transportation through space;
gravitational capture by planets and moons;
Incorporation into oceans, atmospheres, and ice.
This means that water is not just a planetary byproduct, but a mobile and recyclable component of the Solar System.
How Rosetta’s data changed the planning of future space missions.
Following Rosetta, new missions began to consider comets as priority targets, not only out of scientific curiosity, but also for their strategic role. Studying comets helps to:
to understand the distribution of water in space;
to plan future manned missions;
to identify usable resources outside of Earth;
Assess the risks and opportunities of impacts.
Water released by comets may, in the future, be exploited for:
fuel (hydrogen and oxygen);
life support;
Raw material for space infrastructure.
A mobile reservoir that connects the past and the future of the Solar System.
Comet 67P showed that water is not confined to oceans or polar ice caps. It circulates, migrates, and redistributes itself continuously, carried by bodies that cross billions of kilometers. By releasing trillions of liters of water with each orbit, comets:
They connect the primitive past to the dynamic present;
They help explain why water is common in rocky worlds;
They reinforce the idea that life can emerge in diverse places.
Before Rosetta, comets were seen as frozen remnants. After Rosetta, they came to be understood as… active systems, complex and fundamental to planetary evolution.
67P was not just a scientific target. It became a Living proof that water travels through space in unimaginable quantities., feeding planets, moons, and perhaps future human habitats.
Far beyond a celestial spectacle, each active comet is a cosmic source of moving water, silently shaping the Solar System for billions of years.