A key discovery from NASA’s Cassini mission in 2008 was that Saturn’s largest moon Titan may have a vast water ocean below its hydrocarbon-rich surface. But reanalysis of mission data suggests a more complicated picture: Titan’s interior is more likely composed of ice, with layers of slush and small pockets of warm water that form near its rocky core.  

Led by researchers at NASA’s Jet Propulsion Laboratory in Southern California and published in the journal Nature on Wednesday, the new study could have implications for scientists’ understanding of Titan and other icy moons throughout our solar system. 

“This research underscores the power of archival planetary science data. It is important to remember that the data these amazing spacecraft collect lives on so discoveries can be made years, or even decades, later as analysis techniques get more sophisticated,” said Julie Castillo-Rogez, senior research scientist at JPL and a coauthor of the study. “It’s the gift that keeps giving.” 

To remotely probe planets, moons, and asteroids, scientists study the radio frequency communications traveling back and forth between spacecraft and NASA’s Deep Space Network. It’s a multilayered process. Because a moon’s body may not have a uniform distribution of mass, its gravity field will change as a spacecraft flies through it, causing the spacecraft to speed up or slow down slightly. In turn, these variations in speed alter the frequency of the radio waves going to and from the spacecraft — an effect known as Doppler shift. Analyzing the Doppler shift can lend insight into a moon’s gravity field and its shape, which can change over time as it orbits within its parent planet’s gravitational pull. 

This shape shifting is called tidal flexing. In Titan’s case, Saturn’s immense gravitational field squeezes the moon when Titan is closer to the planet during its slightly elliptical orbit, and it stretches the moon when it is farthest. Such flexing creates energy that is lost, or dissipated, in the form of internal heating. 

When mission scientists analyzed radio-frequency data gathered during the now-retired Cassini mission’s 10 close approaches of Titan, they found the moon to be flexing so much that they concluded it must have a liquid interior, since a solid interior would have flexed far less. (Think of a balloon filled with water versus a billiard ball.)  

New technique 

The new research highlights another possible explanation for this malleability: an interior composed of layers featuring a mix of ice and water that allows the moon to flex. In this scenario, there would be a lag of several hours between Saturn’s tidal pull and when the moon shows signs of flexing — much slower than if the interior were fully liquid. A slushy interior would also exhibit a stronger energy dissipation signature in the moon’s gravity field than a liquid one, because these slush layers would generate friction and produce heat when the ice crystals rub against one another. But there was nothing apparent in the data to suggest this was happening. 

So the study authors, led by JPL postdoctoral researcher Flavio Petricca, looked more closely at the Doppler data to see why. By applying a novel processing technique, they reduced the noise in the data. What emerged was a signature that revealed strong energy loss deep inside Titan. The researchers interpreted this signature to be coming from layers of slush, overlaid by a thick shell of solid ice. 

Based on this new model of Titan’s interior, the researchers suggest that the only liquid would be in the form of pockets of meltwater. Heated by dissipating tidal energy, the water pockets slowly travel toward the frozen layers of ice at the surface. As they rise, they have the potential to create unique environments enriched by organic molecules being supplied from below and from material delivered via meteorite impacts on the surface.  

“Nobody was expecting very strong energy dissipation inside Titan. But by reducing the noise in the Doppler data, we could see these smaller wiggles emerge. That was the smoking gun that indicates Titan’s interior is different from what was inferred from previous analyses,” said Petricca. “The low viscosity of the slush still allows the moon to bulge and compress in response to Saturn’s tides, and to remove the heat that would otherwise melt the ice and form an ocean.” 

Potential for life 

“While Titan may not possess a global ocean, that doesn’t preclude its potential for harboring basic life forms, assuming life could form on Titan. In fact, I think it makes Titan more interesting,” Petricca added. “Our analysis shows there should be pockets of liquid water, possibly as warm as 20 degrees Celsius (68 degrees Fahrenheit), cycling nutrients from the moon’s rocky core through slushy layers of high-pressure ice to a solid icy shell at the surface.” 

More definitive information could come from NASA’s next mission to Saturn. Launching no earlier than 2028, the agency’s Dragonfly mission to the hazy moon could provide the ground truth. The first-of-its-kind rotorcraft will explore Titan’s surface to investigate the moon’s habitability. Carrying a seismometer, the mission may provide key measurements to probe Titan’s interior, depending on what seismic events occur while it is on the surface. 

More about Cassini 

The Cassini-Huygens mission was a cooperative project of NASA, ESA (European Space Agency), and the Italian Space Agency. A division of Caltech in Pasadena, JPL managed the mission for NASA’s Space Mission Directorate in Washington and designed, developed, and assembled the Cassini orbiter. 

To learn more about NASA’s Cassini mission, visit:

https://science.nasa.gov/mission/cassini/

News Media Contacts 

Ian J. O’Neill 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-2649 
ian.j.oneill@jpl.nasa.gov 

Karen Fox / Alana Johnson 
NASA Headquarters, Washington
202-358-1600 / 202-358-1501 
karen.c.fox@nasa.gov / alana.r.johnson@nasa.gov 

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Good morning, readers, and happy Friday. Welcome to This Week in Space, our Friday morning roundup of the week’s most important space news. Today we’ve got a bunch of good news, including a newfound exoplanet and a dozen new moons orbiting Jupiter. We’ve also got a report of an absolutely wild idea — a literal moonshot — for fighting climate change with moon dust.

SpaceX Starship Aces Static Fire Test

Thursday afternoon, SpaceX ran a successful static fire test of its gigantic Starship rocket. With 33 separate Raptor engines, Starship has the most engines of any rocket ever. Together, their thrust is twice that of a Saturn V or the Space Launch System. Is anyone else amazed the struts can hold that thing on the gantry?

Only 31 of the 33 engines fired. However, that’s actually good news because it means Starship can handle multiple engine failures.

Views from drone of Booster 7's static fire test pic.twitter.com/KN4sk1nohf

— SpaceX (@SpaceX) February 9, 2023

SpaceX hopes to attempt a test flight for Starship in March. “That first flight test is going to be really exciting. It’s going to happen in the next month or so,” said Gwynne Shotwell, SpaceX’s president and chief operating officer.

“We will go for a test flight and we will learn from the test flight and we will do more test flights,” Shotwell added. “The real goal is to not blow up the launch pad. That is success.”

ISS Astronauts Work On Plasma Crystals, Space Plumbing

We’ve talked about how the folks aboard the International Space Station have to become polymaths to keep up with the demands of life in orbit. This winter, among many other pursuits, NASA astronauts on the ISS have been tending tomatoes and working on avant-garde methods of space propulsion. But the most recent projects in low-earth orbit make space tomatoes sound outdated. Over the past few days, crew on the ISS have been working on plasma crystals, servicing jetpacks, and… doing space plumbing.

NASA astronaut Frank Rubio and JAXA astronaut Koichi Wakata spent Thursday doing maintenance on the station’s water recovery system and orbital plumbing for the station’s bathroom, respectively. Meanwhile, station commander Sergey Prokopyev worked inside the Columbus lab “configuring video hardware that records how clouds of highly charged particles, or plasma crystals, behave in microgravity.”

Hubble Captures New Portrait of Tarantula Nebula

The Tarantula Nebula is the brightest star-forming region in our cosmic neighborhood. It’s not even in our galaxy — it’s in the Large Magellanic Cloud, one of the Milky Way’s satellite galaxies. But it’s so bright that it dazzles even at that distance. Astronomers recently used the Hubble space telescope to capture this image of the Tarantula Nebula in all its splendor:

What you see here is actually a joint effort between two different astronomy projects. One team sought to analyze the properties of dust grains floating between stars — a proposal dubbed Scylla by the Hubble team. Those dust grains create the dark, wispy clouds spread across the frame. The other, called Ulysses, studies interstellar dust and starlight interactions.

Curiosity Finds Clues to Mars’ Watery Past

NASA’s Perseverance rover went to Mars with a plan: Scour the planet’s surface for evidence that can teach us about Mars’ history and tell us whether the Red Planet might once have supported life. During its two years on Mars, the rover has found silicate clay and other minerals, signs that liquid water once flowed across Mars’ surface. But none of its discoveries have had evidence of water as visually obvious as a photograph that the agency’s Curiosity rover recently captured. The rover caught a photo of sandstone rock with ripples carved out of its surface, showing that the rock was once at the bottom of a lake.

The ripples support our observations of Mars’ weather and climate. Gentle, constant winds create standing ripple patterns like these. This fits with the constant prevailing winds and planetwide dust storms we’ve seen on Mars. It’s also exciting evidence that Mars indeed had liquid water once upon a time.

Russia Launches Progress Spacecraft to International Space Station

Russia successfully launched a Progress capsule aboard a Soyuz rocket this week, bound for the International Space Station. The rocket launched from Russia’s Baikonur aerodrome early Thursday morning, local time. This capsule, ISS Progress 83 (83P), carries about three tons of supplies, including food, water, and air. It will dock with the Russian Zvezda module on Saturday morning, replacing the Progress capsule that left Monday afternoon.

What happens to Progress 82 once it departs? Progress capsules are expendable. This means that the crew on the ISS loads the capsules with trash from the station while it’s docked. Then, hours or days after the capsule undocks, it burns up in the atmosphere.

CAPSTONE Lunar Satellite Reports In After 11-Day Glitch

NASA’s CAPSTONE satellite is finally responding to hails after nearly two weeks incommunicado. A software glitch left the probe unresponsive on Jan. 26 until it rebooted itself Monday.

“The spacecraft remained overall healthy and on-course throughout the issue,” NASA said in a blog post. “On Feb. 6, an automatic command-loss timer rebooted CAPSTONE, clearing the issue and restoring two-way communications between CAPSTONE and the ground.”

The satellite has made twelve successful circuits in its near-rectilinear halo orbit (NRHO) — twice what its original mission expected. That’s great news for NASA. CAPSTONE is trying out the fancy new NRHO orbit because it’s more fuel efficient than other lunar orbits we’ve used. In twelve orbits, CAPSTONE has only had to fire its engine twice. This smashing success means the agency may use the new orbital pattern for lunar support satellites under the aegis of its Artemis project.

Rolls-Royce Building Nuclear Engine For Spaceships

Did you know Ball makes Mason jars — and parts for space telescopes? Ball made parts for Hubble and the mirrors for the JWST. In a similar fashion, Rolls-Royce appears to be branching out. Way out. The luxury automaker’s subsidiary, Rolls-Royce Holdings, has announced plans to build a nuclear engine for deep space exploration.

According to Rolls-Royce, the micro-reactor will use uranium as fuel for nuclear fission. The company hopes to use the micro-reactor as an energy source for trips to the Moon, Mars, and beyond.

Webb Telescope Breaks Own ‘Speed Limit’ Tracking DART Impact

NASA’s Guaranteed Time Observation program gives a certain amount of telescope time to those who worked on the JWST. One GTO project: Making observations of NASA’s DART kinetic asteroid redirect test. However, the project brought an unlooked-for surprise. Wednesday, JWST deputy project scientist Stefanie Milam explained how the telescope broke its own speed limit watching the asteroid impact.

Webb launched with the ability to track objects moving through the sky as fast as Mars. But scientists who study fast-moving small bodies like asteroids, comets, and interstellar objects “really wanted to study objects that moved faster than Mars,” said Milam. So, the team set out to show that not only could Webb exceed this “notional speed limit,” it could go much faster. Their efforts paid off when it came time to observe the DART asteroid impact.

The video Webb captured of the Dimorphos impact showed that the telescope can move its field of regard at more than triple its original maximum speed. Most of the time, though, Milam says the telescope will confine itself to double its original turning speed. Darn.

Chris Hadfield Meets With King Charles III

On Thursday, Canada’s favorite astronaut, Chris Hadfield, met with King Charles III at Buckingham Palace. The two sat down to discuss “efforts to encourage sustainability in space,” according to the Royal Family’s official Twitter.

“What a pleasure and privilege to be asked to advise and assist, and make the King laugh,” Hadfield wrote afterward.

What a pleasure and privilege to be asked to advise and assist. And make the King laugh :) https://t.co/3dGxNLCkUJ pic.twitter.com/DH9dgkq9t9

— Chris Hadfield (@Cmdr_Hadfield) February 9, 2023

While we don’t yet have specifics, Charles is a longtime environmentalist. Could it be that the King is interested in cleaning up space junk?

A Shield of Lunar Dust Could Help Cool Earth

Astrophysicists are pondering the pros and cons of a literal moonshot to blunt the effects of climate change. In a recent study, a group of researchers proposed launching moon dust into orbit around Earth to create a dusty shield that would reduce Earth’s exposure to the Sun. Evidently, lunar dust grains are just the right size and composition to block some of the solar energy that would hit the Earth.

For six days out of the year, the researchers say, the dust cloud would shield Earth from a few percent of the Sun’s radiation. To carry out this plan, the researchers’ numbers require dredging up some 22 billion pounds of lunar dust. They could fire the dust into orbit from the Moon or a platform in orbit — potato, poterrible idea. Surely there is some lower-hanging fruit?

Scientists Find a Dozen New Moons Orbiting Jupiter

In October 2019, astronomers at the Carnegie Institution for Science found 20 new moons orbiting Saturn. This made Saturn the “moon king” of the Solar System, with a total of 83. However, the same team has announced they’ve found a dozen new moons orbiting Jupiter.

Stealing the crown back from Saturn, Jupiter now has 92 known moons. Nine of the twelve new moons are retrograde, meaning they orbit “backward” against Jupiter’s orbit. All the new moons are quite small, and they had been lost in Jupiter’s glare until now.

Astronomers Spot Nearby, Potentially Habitable Exoplanet

An international team of astronomers has reported a newfound exoplanet in our cosmic backyard. The new planet, Wolf 1069 b, is between 1 and 1.4 Earth masses and just 8% bigger. Calling it Earth-like might be a stretch: Wolf 1069 b zips around its low-mass red dwarf star in just 15 Earth days. However, it’s just 31 light-years away.

Unlike our nearest neighbor, Proxima Centauri, Wolf 1069 doesn’t show the characteristic bursts of violent flares we frequently see in red dwarf stars. This could mean it has managed to retain an atmosphere. If so, the planet’s surface temperature could be about 55 degrees Fahrenheit. If not, it’s more likely an iceball, too cold to sustain liquid water.

Skywatchers Corner

Comet C/2022 E3 (ZTF) is a once-in-an-epoch visitor from the outer solar system. We haven’t seen it since the time of the Neanderthals, but it’s come back for one last visit. The outbound comet passed close to Earth last week. Now, it’s buzzing Mars.

The green comet will be near Mars in the constellation of Taurus for the next several days. After sunset, look high in the sky for the best shot at catching it through binoculars or a telescope. After Feb. 14, the comet will start heading toward Orion and Eridanus.

If you don’t have a good shot at viewing the comet where you are, you can still catch it online. This weekend, the Virtual Telescope Project is webcasting a free livestream of the comet’s approach to the Red Planet. The livestream will begin this Saturday, Feb. 11, at 2 p.m. EST (1900 GMT). You can watch it on the project’s website and YouTube channel.

Feature image: This week’s waning gibbous moon, taken from the International Space Station. Courtesy of NASA HQ Flickr.

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