How was the thick atmosphere of Titan formed ?
– News of July 21, 2019 –
Titan is the only moon in the solar system with a thick atmosphere. However, there is still no consensus on the cause of this exception. The large quantities of nitrogen found there could be brought in the form of ammonia by comets. Titan may have been formed by the aggregation of comet-like bodies. Then the great bombardment of meteorites could have evaporated its organic compounds to form the atmosphere we know today. It is also possible that part of this atmosphere comes from inside the moon and is ejected by gaps or cryovolcanoes.
During its descent into Titan’s atmosphere, the European space probe Huygens detected argon, an isotope that could only be formed in the rocky core of the moon of Saturn. This index seems to partially support the hypothesis of an atmosphere coming from the center of Titan. The presence of large amounts of methane is perhaps the hardest thing to explain. Methane is a gas that degrades easily. Either Titan has a mechanism that allows to produce methane regularly, a little like the Curiosity rover observes on the planet Mars, or this moon of Saturn has simply huge reserves that comes from the time of its formation.
Almost everything we know about this atmosphere is due to Cassini and Huygens. That’s what makes the future Dragonfly mission so exciting. Having a long-term observatory on site should help us answer some of these questions. It may also be possible to obtain answers elsewhere in the solar system. To understand why Titan has a thick atmosphere, we must also understand why the other big moons do not have one. The study of Ganymede by the European space probe Jupiter Icy Moons Explorer (JUICE) will be exciting.
Lakes on the surface of Titan disappear at the end of winter
– News of April 23, 2019 –
Titan, one of the moons of Saturn, is one of the largest moons of the solar system because its diameter exceeds the diameter of the planet Mercury. It is also one of the most interesting moons. Indeed, Titan is the only known body outside the Earth to have liquids on its surface. The moon of Saturn has seas, lakes and even hydrocarbon rains. This liquid cycle generates complex and variable reliefs according to the seasons. Titan was logically one of the exploration targets favored by Cassini, the only space probe in Saturn’s orbit, that completed its mission in September 2010 during a destructive dive into the atmosphere of Saturn. But a few months before, the Cassini space probe made a last flyby of Titan.
On April 22, 2010, the space probe used its radar to probe some of the lakes that run through the north pole of Titan. This was an opportunity to collect some interesting information. First, the lakes would be mainly composed of methane. We estimate that the large lake in the South Pole is much richer in methane. This regional difference shows the complexity of Titan. Cassini’s radar also analyzed the depth of Titan lakes. It seems that some of them are at least 100 meters deep. However, their surface area would be relatively small and many of these lakes would be located in altitude, on reliefs. This suggests that they formed in the same way as some lakes on Earth, that is to say by the collapse of the land.
Another discovery about the lakes of Titan was made thanks to the incredible longevity of the Cassini space probe. It has indeed remained in orbit of Saturn long enough to watch the seasons transform the landscapes of Titan. In fact, some of the lakes observed in the northern hemisphere at the beginning of the Cassini mission seem to have disappeared seven years later, that is to say the time that the winter ends in this region of Titan. These seasonal lakes may have very different characteristics than perennial lakes. In any case, it is an excellent opportunity to understand how liquids interact in the atmosphere, on the surface and in the subsoil of Titan.
With a little luck, the data collected by Cassini will reveal some more surprises about Titan. To continue studying this moon of Saturn, however, one day we will have to send a new mission. NASA should decide in 2019 whether or not it chooses to fund the Dragonfly mission that proposes to send a drone to Titan. It would be an opportunity to explore closely its lakes and seas. If the mission is funded, Dragonfly will be launched in 2025 and arrive at its destination in 2034.
Rain would fall on Titan, a Saturn’s moon
– News of January 22, 2019 –
It can take years to process the data collected by a space probe. The Cassini space probe completed its mission in September 2017. It was then burnt in Saturn’s atmosphere. One of the missions of this spacecraft was the study of Titan, a Saturn’s moon.
Titan is very particular in the solar system. It is the only celestial body with the Earth to have a liquid cycle on its surface. Titan has rains, lakes and seas, except that on Titan they are hydrocarbons, mainly methane and ethane. The Saturn‘s moon has a thick atmosphere but very low temperatures, making it one of the most fascinating places we know.
The Cassini space probe discovered several hydrocarbon lakes during its mission. But in June 2016, NASA’s space probe made an even more startling observation. On Titan, the northern hemisphere is richer in methane than the southern hemisphere. It would therefore be normal for there to be a larger liquid methane cycle, at least during summer. Cassini arrived near Titan in the middle of winter in the northern hemisphere and in the middle of summer in the southern hemisphere. In the southern hemisphere, the space probe observed hydrocarbon clouds and collected clues indicating that there had been rainfall. It observed morphologically transformed landscapes after the passage of large clouds. We were therefore looking forward to the arrival of summer in the northern hemisphere, which happened around 2016. But so far, we were rather disappointed.
One study looked at photos taken in 2016 by Cassini. On some photos of the north pole of Saturn’s moon, we can observe clouds, and ephemeral tasks. They were not here in the photos taken a few weeks earlier and disappeared a few weeks later. The team that published the study thinks it is a reflection effect due to precipitation. If this discovery is confirmed, this would be the first evidence of hydrocarbon rains in the northern hemisphere of Titan. This gives even more interest to an already exciting region. The North Pole of Titan has hydrocarbon seas similar in size to the great American lakes.
Perhaps this discovery will influence the choice of the next NASA New Frontiers mission. The US Space Agency will decide in a few months if it decides to send a drone on Titan or if it prefers to focus its efforts on a return of samples of the 67P comet. If the mission to Titan is selected, it will be an opportunity to explore deeply this Saturn’s moon. The drone, named Dragonfly, will be able to move during several terrestrial years on the surface and in the atmosphere of Titan thanks to nuclear energy. This would be an opportunity to study organic chemistry and to evaluate the habitability potential of the Saturn’s moon. We will know the final decision of NASA in July 2019. If the mission towards Titan is selected, it will be necessary to wait 2024 or 2025 for the launch, and some additional years for the travel.
Image by NASA / JPL / SSI / J. Major