Left: Pioneer 10’s view of Jupiter in March 1973. Right: Webb Telescope’s view of Jupiter in July 2022. Image: NASA, ESA, CSA, Jupiter ERS Team; image processing by Judy Schmidt
For centuries, astronomers were limited to ground-based observations of the planets, but now we use spacecraft to capture close-up views of our neighboring worlds. Excitingly, our views of solar system planets have been getting progressively better over the decades, as these images attest.
The dawn of the Space Age finally made it possible for humankind to capture close-up views of astronomical objects. We haven’t wasted this opportunity, sending probes to every planet in our solar system and even to Pluto, a dwarf planet located over 5 billion miles (8 billion kilometers) away.
The first missions to the planets began in the 1960s, and it’s something we still get excited about. We’ve assembled a series of photos showing some of our earliest images of the planets compared to similar portraits captured during recent missions. Regardless of the era or the quality, each one has a story to tell, and each continues to stir the imagination.
Artistic impression of Dragonfly on Titan. Image: NASA/JHU-APL
The scientific objectives of the upcoming Dragonfly mission to explore Saturn’s moon Titan are described in a new research paper, along with the instruments required to fulfill these goals.
With launch expected around 2027, Dragonfly should take to Titan’s skies at some point in the mid-2030s. By that point I’ll be in my mid-60s—a full-fledged senior citizen—but I’ll undoubtedly follow the mission with child-like enthusiasm. For you see, Titan is my favorite place in space (outside of Earth, of course), owing to its many peculiar, enigmatic, and sometimes familiar features. Also, as a dedicated fan of Frank Herbert’s Dune series, I’ve always imagined Titan—with its oily surface—as resembling the fictional Harkonnen planet of Giedi Prime.
Titan is the only moon in the solar system to feature a dense atmosphere and significant quantities of liquid on the surface, even if that liquid takes the form of hydrocarbon seas and lakes. Gigantic sand dunes drape its tropical regions, the result of cosmic rays blasting the moon’s surface ice. Titan also features a vast equatorial desert, called the Shangri-La sand sea, which hosts the occasional dust storm. In that sense, the moon also resembles Arrakis from Dune (no word yet if Titan hosts gigantic sand worms, or Harkonnens for that matter).
This is an ideal destination for a robotic probe, as Titan is brimming with scientific targets. As a mission, Dragonfly has been a go since 2019, but the formal objectives of the mission were only recently disclosed. Jason Barnes, deputy principal investigator of the Dragonfly mission and a professor of physics at the University of Idaho, is the first author of the new paper, published in the Planetary Science Journal.
Illustration of the Dragonfly mission concept, including entry, descent, landing, surface operations, and flight at Titan. Image: NASA/JHU-APL
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Dragonfly is a dual-quadrotor drone that will feature eight rotors, each measuring around 3.3 feet (1 meter) in length. With NASA’s Ingenuity helicopter currently buzzing around Mars, Dragonfly will become the second aerial vehicle to fly on an alien world and the first to take flight on an alien moon.
This won’t be the first-ever mission to Titan. NASA’s stationary Huygens probe landed there in 2005, capturing some of the eeriest photos I’ve ever seen, and the Cassini probe, which circled Saturn for 13 years, used its radio capabilities to peer through Titan’s thick cloud tops. But Dragonfly will take the scientific exploration of Titan to the next level.
“Titan represents an explorer’s utopia,” Alex Hayes, associate professor of astronomy in the College of Arts and Sciences and a co-author of the new study, said in a statement. “The science questions we have for Titan are very broad because we don’t know much about what is actually going on at the surface yet. For every question we answered during the Cassini mission’s exploration of Titan from Saturn orbit, we gained 10 new ones.”
As the new paper points out, Dragonfly will partake in what is primarily but not exclusively an astrobiology mission. The aerial drone will search for biosignatures (suggestive of previous or current biological processes) and take measurements related to the moon’s chemistry (including the molecular building blocks required for life) and the current potential for habitability.
Mission planners have chosen a landing site near Titan’s equator—a spot roughly 435 miles (700 km) north of where Huygens landed. Dragonfly will explore the Shangri-La sand sea and possibly even visit the Selk impact crater—a possible cradle of life.
The mission will primarily take place during the northern hemisphere winter. The half-ton drone should have no problem achieving flight, as Titan’s gravity is one-seventh that of Earth’s, the winds are gentle, and the atmosphere is thick enough to produce lift. Mission scientists aren’t anticipating that rain—consisting of liquid methane—will be a problem, but they’re not entirely sure.
Dragonfly, a “rotorcraft relocatable lander,” in the words of the researchers, will spend most of its time on the ground performing science and transmitting its data back to Earth. The aerial drone will only fly for between 30 minutes and one hour once every two Titan days, in which one Titan day is equal to 16 Earth days. The team will select new destinations on the fly, so to speak, in a manner similar to how target destinations are chosen for Martian rovers.
The drone’s payload will consist of eight scientific cameras, two spectrometers, and a drill to sample for complex organics. Dragonfly will also carry a geophysics and meteorological suite with 11 different instruments capable of measuring air temperature, air pressure, wind speed and direction, and humidity.
Where Cassini was able to provide grainy radio images from space, Dragonfly will do the ground truthing needed to confirm or disprove theories about the moon’s chemical processes and atmospheric surface interactions. The team will also study the role of tropical deserts in Titan’s global methane cycle.
“My primary science interests are in understanding Titan as a complex Earth-like world and trying to understand the processes that are driving its evolution,” said Hayes. “That involves everything from the methane cycle’s interactions with the surface and the atmosphere, to the routing of material throughout the surface and potential exchange with the interior.”
The search for potential biosignatures will include “life as we know it,” that is, life that needs liquid water to survive, and “life, but not as we know it,” such as life capable of finding a home in Titan’s liquid hydrocarbons, according to the paper.
Finding the ways in which Titan is similar to Earth, or the ways in which a young Earth may have resembled Titan, is obviously very important, but I’m just as interested in knowing all the ways Titan is not like Earth. Come the 2030s, I’ll be on the lookout for the exotic stuff, including further validation of Titan as the most alien place in the solar system.
More: A methane sea on Saturn’s moon Titan could be over 1,000 feet deep.
A false-color mosaic Titan’s polar regions. Kraken Mare is the dim splotch to the right of center. Image: NASA/JPL-Caltech/University of Arizona/University of Idaho
Data gathered by NASA’s Cassini probe has allowed scientists to estimate the depth of Kraken Mare—the biggest methane sea on Saturn’s moon Titan.
New research published in the Journal of Geophysical Research is expanding our knowledge of Titan’s hydrocarbon seas, specifically Kraken Mare. This sea, approximately 600 miles (1,000 km) long, is larger than all five of North America’s Great Lakes combined and holds around 80% of the moon’s surface liquids. The seas on Titan contain lots of methane and ethane and are comparable to liquified natural gas on Earth.
Titan is the only moon in the solar system known to host an atmosphere. The thick, nitrogen-rich blanket that covers the moon hides a complex hydraulic system on the surface, but instead of liquid water, the rivers, lakes, and seas on Titan consist of oily black methane. Titan features other curiosities as well, such as gigantic dust storms, ice volcanoes, and enormous sand dunes.
As the new research shows, the deepest parts of Kraken Mare could be more than 1,000 feet (300 meters) deep. The team, led by Valerio Poggiali, a research associate at the Cornell Center for Astrophysics and Planetary Science, can’t actually be sure of that figure, because the radar pings used to determine sea depth never actually reached the seafloor.
False-color image of Kraken Mare. Image: NASA/JPL-Caltech/Agenzia Spaziale Italiana/USGS
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NASA’s Cassini spacecraft orbited Saturn from 2004 to 2017, and scientists have already studied some of the smaller seas on Titan using Cassini’s onboard altimeter. On August 21, 2014, Cassini flew to within 600 miles (970 km) of Titan’s surface and was able to send radar pings into Kraken Mare. Interestingly, this was the same flyby that resulted in the discovery of Ligeia Mare—a “magic” vanishing island on Titan.
Researchers at Cornell and NASA’s Jet Propulsion Laboratory devised a neat technique for determining the depth of Titan’s seas, which involves measuring differences between the time it takes radar to bounce back from the surface of the sea as opposed to the sea bottom. This technique helps to estimate sea depth, but the researchers have to make certain assumptions about the density of fluids on Titan and how quickly radio waves pass through them.
Using this technique, the team measured the depth of Moray Sinus, a northern estuary on Kraken Mare, which they found to be 280 feet (85 meters) deep. The absorption rate of the radar waves suggests the liquid in this part of the sea consists of 70% methane, 16% nitrogen, and 14% ethane. The scientists were expecting more methane than this due to the size and location of the sea, but this discovery suggests a more uniform distribution of chemicals across the moon’s various bodies of water.
Altimeter scans done across the main portion of Kraken Mare were less conclusive. As the authors write in the study, the NASA probe found “no evidence for signal returns from the sea floor, suggesting the liquid is either too deep or too absorptive for Cassini’s radio waves to penetrate.” That said, if the liquid in this part of the sea is similar in composition to the liquid found at Moray Sinus, then it must be deeper than 330 feet (100 meters) and possibly as deep as 1,000 feet (300 meters), according to the study.
Poggiali is hopeful that a robotic submarine might be sent to Titan one day to explore Kraken Mare or some other body of water. And in fact, he sees the new research as a step in that direction.
“Thanks to our measurements, scientists can now infer the density of the liquid with higher precision, and consequently better calibrate the sonar aboard the [future robotic submarine] and understand the sea’s directional flows,” explained Poggiali in a Cornell University statement.
A conceptual plan from 2015 showed how such a mission might look, but nothing has actually been approved in this regard. That said, NASA will be sending an aerial drone, called Dragonfly, to Titan, which should arrive at the moon at some point in the mid-2030s.