Even though Cassini ended its mission nearly two years ago, data from all of the spacecraft’s flybys of the Saturnian moon Titan continue to help scientists unlock the mysteries of this world shrouded by a thick, dense atmosphere.
Now, NASA is planning a return to this extreme object of interest in the solar system – a location that is quite favorable for harboring life in its methane-rich environment.
Titan offers up secrets to its methane lakes
During its final flyby of Titan in 2017, the Cassini spacecraft trained its radar instruments onto the moon – peering beneath the obscuring cloud layer that envelops Titan to gather data on a series of small liquid methane lakes in the moon’s northern hemisphere.
The data, analyzed by scientists and published earlier this year in Nature Astronomy, offer new glimpses into the depths of the lakes and surrounding terrain at which they reside.
On Titan, the mysteries run deep. During its final flyby of Saturn’s giant moon, Cassini revealed that some of Titan's methane lakes are surprisingly deep and perched atop hills. Learn more: https://t.co/39BS2VyLAQ pic.twitter.com/MjhXYynzpu
— Cassini (@CassiniSaturn) April 15, 2019
Specifically, Cassini data shows that these methane lakes are surprisingly deep and are perched atop hills.
“Every time we make discoveries on Titan, Titan becomes more and more mysterious,” said lead author of the new study Marco Mastrogiuseppe, Cassini radar scientist at Caltech in Pasadena, California. “But these new measurements help give an answer to a few key questions. We can actually now better understand the hydrology of Titan.”
The data from Cassini revealed that some of the northern hemisphere methane lakes are more than 100 m (300 feet) deep.
Aside from Earth, Titan is the only other known body in the solar system that has stable liquid on its surface; whereas water is that stable liquid on Earth, methane and ethane are those liquids on Titan.
The intriguing thing about these liquid methane lakes and hydrologic cycle is that research from the University of California has shown that life – as it did on Earth with water – can evolve with methane as its liquid medium instead of water, providing tantalizing possibilities into what might be happening in the methane lakes on Titan.
For the lakes investigated in 2017, it is their elevation and depth that adds a whole new set of information to the Titan puzzle – specifically that the hydrologic cycles in the moon’s eastern and western portions of its northern hemisphere are completely different.
“It is as if you looked down on the Earth’s North Pole and could see that North America had completely different geologic setting for bodies of liquid than Asia does,” said Cassini scientist and co-author of the study Jonathan Lunine of Cornell University in Ithaca, New York.
On the eastern side of Titan’s northern hemisphere, methane concentrations are grouped into large seas at low levels of elevation, canyons, and islands.
But on the western side of the northern hemisphere, methane is grouped into small lakes (tens of kilometers/miles across) located atop large hills and plateaus.
And it is specifically the lakes’ depth and high-elevation that provide scientists with evidence that they formed when the surrounding bedrock of ice and solid organics chemically dissolved and collapsed – just like karstic lakes in Germany, Croatia, and the United States that form when water dissolves limestone bedrock.
The new data has allowed scientists to better understand how Titan’s hydrologic cycle is quite similar to that of Earth’s, just with methane instead of water.
During Cassini’s final distant encounter with Titan, the spacecraft captured this view of the north polar landscape of lakes and seas, filled with liquid methane and ethane. (Credit: NASA)
The information also provides a stronger link to Titan’s similarities to Earth and continues to enshrine the moon’s position as a key location for research in the solar system and one of the prime locations where life might have developed and still exist off Earth.
The data gathered by Cassini for this study was acquired by the spacecraft on 22 April 2017 as it performed its final close flyby of Titan.
“This was Cassini’s last hurrah at Titan, and it really was a feat,” said Lunine.
But, thankfully, it will not be NASA’s or humanity’s last hurrah on Titan.
Dragonfly – a drone for Titan
While additional flybys of Titan by other spacecraft to Saturn would certainly allow scientists to learn more about the moon, the best way to learn the most information at this point is to simply go to the moon itself instead of flying by it.
The Cassini mission brought with it the European Space Agency’s Huygens lander, which was dispatched to Titan and successfully entered its atmosphere and then descended under parachute to the moon’s surface in January 2005.
BIG NEWS: The next @NASASolarSystem mission is… #Dragonfly – a rotorcraft lander mission to Saturn’s largest moon Titan. This ocean world is the only moon in our solar system with a dense atmosphere & we’re so excited to see what Dragonfly discovers: https://t.co/whePqbuGBq pic.twitter.com/BQdMhSZfgP
— Jim Bridenstine (@JimBridenstine) June 27, 2019
But in a futuristic move, NASA does not wish to send a static lander to Titan.
The agency doesn’t even want to send a rover.
Instead, NASA is sending a large drone which will fly from scientific location to scientific location racking up more than 175 km (108 miles) flying distance over a 2.7 Earth-year mission.
“It’s remarkable to think of this rotorcraft flying miles and miles across the organic sand dunes of Saturn’s largest moon, exploring the processes that shape this extraordinary environment.” said Thomas Zurbuchen, NASA’s associate administrator for Science at the agency’s Headquarters in Washington.
“Dragonfly will visit a world filled with a wide variety of organic compounds, which are the building blocks of life and could teach us about the origin of life itself.”
Launching in 2026, the drone, named Dragonfly, will arrive and land on Titan in 2034 after a 6.5 year interplanetary cruise.
Thanks to data collected by the Cassini mission, NASA already knows the landing location for Dragonfly, the equatorial Shangri-La dune fields that have linear-similar dunes to those found in Namibia in southern Africa.
The Shangri-La dune fields offer a diverse sampling location that Dragonfly will explore during its first series of short, hopper flights before eventually building up into “Leapfrog” flights of up to 8 km (5 miles).
Over the course of its 2.7 Earth-year mission, Dragonfly will travel to the Selk impact crater, where it will investigate evidence of past liquid water, organics, and energy – which together make up a cocktail for life.
To accomplish its mission, Dragonfly’s design calls for it to be an octocopter, using eight, one meter rotors to fly itself and its science payload to repeated targets across the moon’s surface.
The rotors will enable Dragonfly to travel at a maximum speed of 36 km/hr (22.4 mph) while traveling at an altitude of no more than 4 km (4 miles).
Despite Titan being much smaller than Earth, its atmosphere is 4 times denser than our planet’s and local gravity is 13.8% that of Earth’s – making it an ideal location for drone flight.
Dragonfly’s entry, descent, and landing sequence at Titan. The rotorcraft will then begin a 2.7 year scientific flight program. (Credit: NASA)
Unlike drones on Earth, Dragonfly will have to operate in a surface temperature environment of -179° C (-290° F) with an average surface pressure 50% higher than Earth’s.
After atmospheric entry, the craft’s heatshield will fall away and Dragonfly will drop from inside the back shell, and then start its rotors to perform a precision soft landing onto the surface of titan.
Power for the spacecraft during flight will come from batteries that will be recharged from a Multi-Mission Radioisotope Thermoelectric Generator.
A single battery charge will allow Dragonfly to travel 60km – farther than all the Mars rovers have driven, combined – and stay airborne in Titan’s atmosphere for 2 hours at a time.
During each of Titan’s 8-Earth-day nights, Dragonfly will be grounded to perform scientific observations until daybreak.
The rotorcraft will also sport LED lights to allow for night-time scientific and photographic operations, just as the Phoenix polar lander and Curiosity rover on Mars did and do, respectively.
Dragonfly is anticipated to weigh 450 kg (990 lb) – roughly the size of the Mars rovers Spirit and Opportunity – and fit within a 3.7 meter diameter heatshield that will protect it during entry into Titan’s atmosphere.
The Titan atmospheric entry craft (left) and Dragonfly -upside-down – inside the entry craft (right). (Credit: NASA)
The craft will carry four scientific payloads including a mass spectrometer, a gamma-ray and neutron spectrometer, a geophysics and meteorology package, and a camera suite.
The scientific payloads will allow for the identification of chemical components, especially those relevant to biological processes, in surface and air samples; characterization of Titan’s weather and hydrologic cycle; and surveying of the local terrain for science targets.
The ultimate scientific objective of Dragonfly is to measure the composition of materials in different geologic settings on Titan to reveal how far prebiotic chemistry has progressed in the moon’s environments that provide known key ingredients for life: pyrimidines and amino acids.