A short video footage has leaked from the Russian Space Agency showing Russian astronauts reaching Saturn’s orbit and exploring the planet’s moon Titan with their spacecraft. The mission took almost seven years.
Saturn is the sixth and the remotest planet in our solar system. It’s visible to the naked eye. It doesn’t always have the same distance from the sun due to the fact that it travels in an elliptical path rather than a circular one.
The distance between the Earth and Saturn is subject to continual change as both of the planets travel through space. The closest distance measures around 746 million miles (1.2 billion kilometers), which is eight times the distance between the Earth and the sun. The largest distance between the two, when they lie on opposite sides of the sun, reaches just over a billion miles (1.7 billion km). This is 11 times the distance between the Earth and the sun.
Space travel is never a straight line movement because spacecrafts often take advantage of planets, moons, and even the sun to increase speed with minimum use of fuel. Interestingly, older missions may have reached outer planets in less time than those using more modern propulsion systems. For instance, Pioneer 11, launched in April 1973, was the first mission to see Saturn six years after takeoff, in September 1979.
The Voyager spacecrafts also took advantage of an optimal lineup in order to explore the outer planets. Voyager 1, launched in September 1977, used a gravitational assist from Jupiter to pass by Saturn in November 1980, merely three years after takeoff. Voyager 2, launched a month earlier than Voyager 1, took a longer, more circular course, taking full four years to reach Saturn. It landed in August 1981.
Launched in October 1997, the Cassini mission used Venus for gravitational assists on two occasions, catapulting off of the cloudy planet. The spacecraft also passed by Jupiter, imaging the gas giant on its way. Nearly seven years later, the craft entered Saturn’s orbit in July 2004, where it will remain to study the planet until at least 2017. One of the things the mission focuses on is studying lightning in Saturn’s atmosphere.
Heading to the dwarf planet Pluto, the New Horizons mission took off in January 2006. The spacecraft reached the fastest launch speed to date passing by Mars and Jupiter, and brushing past Saturn in June 2008. It means the mission took only a year and a half to reach the largest planet in the solar system.
All of these data point to the fact that the time to reach Saturn varies depending largely on the path selected for the mission, rather than the speed of the spacecraft.
A recent discovery by NASA scientists revealed an unexpected high-altitude methane ice cloud on Saturn’s moon Titan, which resembles the unusual clouds identified far above Earth’s poles.
This dense cloud, imaged by NASA’s Cassini spacecraft, was part of the winter cap of condensation over Titan’s North Pole. It took scientists more than eight years since the cloud was first identified to determine that it contains methane ice, which accounts for a much denser cloud compared to the ethane ice that was previously identified there.
Carrie Anderson, a Cassini participating scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study said “The idea that methane clouds could form this high on Titan is completely new. Nobody considered that possible before.”
Methane clouds had already been identified in Titan’s troposphere – the lowest layer of the atmosphere. These clouds result from a cycle of evaporation and condensation, when vapor rises from the surface then meets cooler and cooler temperatures and falls back down as precipitation – a process similar to the formation of rain and snow clouds on Earth. But, the vapor on Titan is methane rather than water, and this lofty cloud formed in the stratosphere – the layer above the troposphere.
On the other hand, our planet has its own polar stratospheric clouds, which normally form above the North Pole and South Pole at an altitude between 49,000 and 82,000 feet (15 to 25 kilometers), exceeding the cruising altitude for airplanes. However, these clouds only form when the temperature reaches minus 108 degrees Fahrenheit (minus 78 degrees Celsius).
The scientists have already identified other stratospheric clouds on Titan, including a very thin, diffuse cloud of ethane, a chemical formed after methane breaks down. In addition, delicate clouds made from cyanoacetylene and hydrogen cyanide, which form from reactions of methane byproducts with nitrogen molecules, have been found there.
What’s surprising is that methane clouds were nor expected in Titan’s stratosphere. The thing is the troposphere locks most of the moisture, and stratospheric clouds require extreme cold. Just for an illustration, even the stratosphere temperature of minus 333 degrees Fahrenheit (minus 203 degrees Celsius), measured by Cassini south of the equator, was not cold enough to allow the scarce methane in this region of the atmosphere to condense into ice.
As found by Anderson and her Goddard co-author, Robert Samuelson, temperatures in Titan’s lower stratosphere are not the same at all latitudes. The high-altitude temperature near the North Pole was much colder than that just south of the equator according to data from Cassini’s Composite Infrared Spectrometer and the spacecraft’s radio science instrument.
Apparently, this temperature difference of 11 degrees Fahrenheit (6 degrees Celsius) is what allows the formation of methane ice.
The process of formation of high-altitude clouds is not the same with the process of cloud formation in the troposphere. The thing is Titan has a global circulation pattern in which warm air in the summer hemisphere arises from the surface and enters the stratosphere, thus making its way to the winter pole. It’s here that the air mass drops back down, cooling as it descends, thus allowing the stratospheric methane clouds to form.
According to Michael Flasar, Goddard scientist and principal investigator for Cassini’s Composite Infrared Spectrometer (CIRS), “Cassini has been steadily gathering evidence of this global circulation pattern, and the identification of this new methane cloud is another strong indicator that the process works the way we think it does.”
This methane cloud was found near the winter pole, above 65 degrees north latitude, similar to Earth’s stratospheric clouds. According to Anderson and Samuelson, this type of cloud system, named subsidence-induced methane clouds, or SIMCs, possibly forms between 98,000 to 164,000 feet (30 to 50 kilometers) in altitude above Titan’s surface.
“Titan continues to amaze with natural processes similar to those on the Earth, yet involving materials different from our familiar water,” explained Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “As we approach southern winter solstice on Titan, we will further explore how these cloud formation processes might vary with season.”