Dust Storms on Titan observed for the First Time by Cassini

Dust Storms on Titan observed for the First Time by Cassini

Cassini Spacecraft made the first-ever observation of dust storms on the largest moon of Saturn.

NASA, the Italian Space Agency (ASI), and the European Space Agency (ESA) collaborated to send a probe to study Saturn, its natural satellites (moons), and its rings in 1997. The name given to this mission was Cassini-Huygens (after astronomers Giovanni Cassini and Christiaan Huygens). It was the 1st probe to enter the orbit of Saturn despite being the 4th to visit the planet of rings. The original mission of Cassini was expected to last for 4 years between 2004 and 2008. However, it was extended two times. The first extension was for 2 years (till September 2010) while the second one allowed it to live for another 7 years (till September 2017).

The name of this robotic spacecraft came from its instruments. In addition to a Cassini probe (NASA), it had a Huygens lander (ESA) which landed on Titan, the largest moon of Saturn. Titan is the only known moon which has a dense atmosphere. Similarly, it is the only celestial object in space, other than Earth, where clear evidence of surface liquid was found. For these reasons, it is regularly described as a planet-like moon. Titan is the 2nd largest moon of our solar system as only Ganymede, a moon of Jupiter is bigger than it. All these feasibilities urged scientists to explore this natural satellite of Saturn and Cassini mission was the result.

Cassini made some outstanding revelations about Titan including the discovery of liquid hydrocarbon lakes in the polar regions of the moon. It continued to do so even in its dying moments as it captured massive dust storms in equatorial regions of Titan. This makes it only the 3rd body of our solar system to experience dust storms. All these findings were explained to the world in a paper published in the journal, ‘Nature Geoscience’. Sebastien Rodriguez, the Lead Author of the paper who is an Astronomer at the Université Paris Diderot in France, referred to their findings by saying,

Titan is a very active moon. We already know that about its geology and exotic hydrocarbon cycle. Now we can add another analogy with Earth and Mars: the active dust cycle, in which organic dust can be raised from large dune fields around Titan’s equator.”

Although Titan is an intriguing world with all the similarities with Earth, there is a massive difference between both the celestial bodies. The surface liquid on our planet is water while hydrocarbons (Methane and Ethane) flow through the liquid reservoirs on the surface of Titan. The molecules of these hydrocarbons evaporate, condense into clouds, and rain back onto the ground (which is quite similar to what we get on Earth except for the difference of the compound). The fact that the weather on Titan changes from one season to another adds to the list of similarities. For instance, powerful methane storms are observed on the moon around the ‘Equinox’.

Cassini captured three unusual equatorial brightenings around the moon during the northern equinox of 2009. Initially, the researchers considered them to be methane clouds but a detailed investigation revealed something which no one was expecting. Rodriguez mentioned that some factors forced them to rethink about their initial supposition and they decided to have another look at it. He talked about that in the following words:

From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of the year are not physically possible. The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude — much higher than the 6 miles (10 kilometers) that modeling tells us the new features are located.”

The fact that these bright features were visible for a shorter period of time (11 hours to 5 weeks) strengthened the idea that this was something different. In addition to that, computer modeling showed that these features must be atmospheric but still stay close to the surface. As they were found right over the dune fields around the equator of Titan, researchers were left with only one option that these spots were clouds of dust. Rodriguez explained that although this is the first-ever observation of a dust storm on Titan, it is not surprising at all. He said,

We believe that the Huygens Probe, which landed on the surface of Titan in January 2005, raised a small amount of organic dust upon arrival due to its powerful aerodynamic wake. But what we spotted here with Cassini is at a much larger scale. The near-surface wind speeds required to raise such an amount of dust as we see in these dust storms would have to be very strong — about five times as strong as the average wind speeds estimated by the Huygens measurements near the surface and with climate models.”

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