Landing on a comet may seem like a feat from science fiction books, but in reality this is what happened exactly 10 years ago, the November 12, 2014when at 17:05 UTC the Philae lander of the probe Rosette landed on the comet 67P/Churyumov-Gerasimenko. These solitary travelers who ply the expanses of the cosmos, crossing the darkness and absolute silence of space, have long remained only a spectacular sight from Earth during their fleeting crossing of the inner Solar System. However, in 2014, after a 10-year journey, the European Space Agency (ESA) managed to first time in history human to place a probe into orbit around a comet to study its characteristics and composition up close.
The probe got it surprising scientific resultsshowing for example that the water in Earth’s oceans does not appear to come predominantly from cometsas previously believed. Furthermore, these objects, remnants of the formation of our Solar System, have an abundance of organic moleculesthat is, the “building blocks” considered necessary for the development of life. The mission, which started in 2004, ended in 2016 when the probe was made crash into the cometary surfacebut the scientific data and spectacular images collected are still the subject of investigation by scientists and inspiration for astronomy lovers.
What the Rosetta probe discovered
With 12 years of mission and over 8 billion km traveled in interplanetary space, the Rosetta probe it has carried out tens of thousands of scientific analyzes and produced over 16,000 images. He not only took some of the most spectacular images ever obtained from human space exploration, but he also shed light on them fleeting visitors of the inner Solar System. The probe’s first discovery, obtained as soon as it approached the comet, concerns the 67P shape. From Earth the comet appeared potato-shaped due to the low spatial resolution of the images taken. However, Rosetta showed what the comet actually looks like made up of two objects which merged in a low-speed collision. This collision probably occurred during the early stages of the formation of the Solar System.
The mission was specifically designed to ensure that the probe observed the comet both during its inactivity phase and during its “awakening” as it approaches the Sun again. We have therefore obtained for the first time images, videos and scientific data of a “cometary awakening”observing how frozen rock transforms as regions that have remained in darkness for years are illuminated by the Sun. Solar radiation has caused the ssublimation of the cometary nucleusallowing the probe to estimate the amount of water vapor which sublimates and the quantity of dust lost. The latter rise from the comet at the rate of a ton per secondhelping to form the queue millions of km long. Spectroscopic analysis of these jets has shown how they contain carbon-based moleculesthe building blocks of life, and noble gases that we find in the Earth’s atmosphere, thus suggesting that at least part of the Earth’s noble gases come from these space travelers.
A discovery in some ways unexpected was the one relating to isotopic composition of water vapor of the comet. One of the hypotheses made by scientists that explains the abundance of water on Earth is that in the primordial Solar System the Earth underwent a cometary bombardment which transported large quantities of water to the earth’s surface. The scientists then jumped out of their chairs when the Rosetta probe showed how the isotopic composition (ratio between deuterium and hydrogen) of the water vapor of 67P pits different from that of the Earth’s oceansonce again reigniting the debate about the origin of water on Earth.
Even after the mission ended, the incredible amount of data obtained continued to lead to new discoveries. Four years after the end of the mission, in fact, scientists discovered some auroras on 67P which, however, unlike terrestrial ones, occur in ultraviolet wavelengths, therefore invisible to the human eye.
The story of the Rosetta mission
There design of the Rosetta mission is started in the 1980s with an initial concept that involved tracking the nucleus of a comet, collecting samples and returning them to Earth for in-depth analysis. In 1993 ESA realized that such a mission would require an outlay of money well beyond the capacity of the European space agency alone, so it turned to a mission concept that involved theon-site analysis of cometary samples.
After almost 20 years, the mission was finally ready to leave on January 12, 2003 towards another comet, the 46P/Wirtanen. However, the launch was postponed for more than a year, as the Ariane 5 rocket, which was supposed to launch the probe, failed a launch in December 2002, thus requiring additional controls on future launches. The mission left on March 2, 2004changing objectives and heading towards the comet 67P/Churyumov-Gerasimenko.
After a 10 year journeythe Rosetta probe entered orbit around the comet on August 6, 2014. The scientists’ goal was to put the probe into a very slow orbit around the comet, progressively slowing it down so as to allow the release of the Philae lander for on-site analysis of cometary samples. The probe spent the first months around the comet mapping it through the various chambers on board, in order to identify the best place for the lander to land.
After Philae’s release, the probe remained in orbit around the comet for others two yearsgiving us scientific analyzes and breathtaking images like the one abovewhich shows the dust surrounding the cometary nucleus, almost like sleet, with moving stars in the background. The mission ended on September 30, 2016. The scientists decided to crash the probe in a controlled manner, using these final moments to have a rare front row view of the comet’s surface and take ever-closer images of the probe’s final resting place, as the video below shows.
The probe owes its name to the Rosetta Stonein an analogy of the probe as a stele that allows us to “translate” in an intelligible way the first moments of life of the Solar System, of which the comets were spectators. The Philae lander instead it owes its name to a small island on the Nile where Giovanni Battista Belzoni found, in 1817, an obelisk with Greek inscriptions and hieroglyphics.
The unfortunate landing of Philae
The highlight of the mission was represented bylanding of the Philae lander on the surface of the comet. After identifying the landing site, the Rosetta probe released the lander November 12, 2014. After a free fall of approximately 7 hours, the lander impacted the surface speed of approximately 4 km/h. Unfortunately, the probe bounced on the surface since his anchor harpoons did not open and the thruster designed to keep the probe on the surface failed to ignite. Philae it bounced twicefinally managing to “settle” on the cometary surface.
The uncontrolled landing meant that Philae found himself in a non-optimal positionwith one incorrect inclination of the solar panels. Despite this, the resilient lander managed to make the first historic analysis of cometary samples on the surface of the comet itself, sending precious data to Earth on the chemical composition of the surface and on degassing from the subsurface, discovering water ice rich in organic material.
After two months of transmitted data, the probe was put into operation hibernation following the discharge of the batteries which were not properly recharged by the incorrect inclination of the solar panels. After this hibernation, scientists attempted to get back in contact with Philae, unfortunately without success. Only two years later, in September 2016high-resolution photos taken by the Rosetta probe showed the place where Philae will rest probably forever. Philae, now silent, lies on his side in a deep crevice in the shadow of a cliff.
Comet 67P/Churyumov-Gerasimenko
The comet 67P/Churyumov-Gerasimenko owes its name to astronomers Klim Ivanovich Churyumov And Svetlana Ivanovna Gerasimenko who discovered the comet in 1969. Although originally from Kuiper belta cold region beyond the orbit of Neptune made up of small icy bodies, remnants of the formation of the Solar System, 67P is currently a periodic comet of the inner Solar System, with an orbit that takes it to one minimum distance of approx 1.2 astronomical units from the Sun and to one maximum distance Of 5.7 astronomical unitsjust above the average Sun-Jupiter distance. 67P is approximately 4.3 by 4.1 km at its longest and widest dimensions. The comet’s next perihelion is expected in four years, on April 9, 2028.
The comet appeared potato-shaped from images from Earth, but thanks to the close encounter with the Rosetta probe, we discovered that it is actually made up of two lobes connected through a narrower neckrotating with a short period of 12.4 hours. The peculiar shape is probably due to the collision between two different objectsat a very low relative speed which allowed the comet to survive the impact as a fusion of the two celestial bodies.
