The Grand Finale Archives

July 27, 2017 by Matt Williams

Cassini Finds that Titan is Building the Chemicals that Might Have Led to Life on Earth

Image of Titan's atmosphere, snapped by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

Titan, Saturn’s largest moon, has been a source of mystery ever since scientists began studying it over a century ago. These mysteries have only deepened with the arrival of the Cassini-Huygens mission in the system back in 2004. In addition to finding evidence of a methane cycle, prebiotic conditions and organic chemistry, the Cassini-Huygens mission has also discovered that Titan may have the ingredient that help give rise to life.

Such is the argument made in a recent study by an international team of scientists. After examining data obtained by the Cassini space probe, they identified a negatively charged species of molecule in Titan’s atmosphere. Known as “carbon chain anions”, these molecules are thought to be building blocks for more complex molecules, which could played a key role in the emergence of life of Earth.

The study, titled “Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere“, recently appeared in The Astrophysical Journal Letters. The team included researchers from University College in London, the University of Grenoble, Uppsalla University, UCL/Birkbeck, the University of Colorado, the Swedish Institute of Space Physics, the Southwest Research Institute (SwRI), and NASA’s Goddard Space Flight Center.

*Diagram of the internal structure of Titan according to the fully differentiated dense-ocean model. Credit: Wikipedia Commons/Kelvinsong*

As they indicate in their study, these molecules were detected by the Cassini P lasma Spectrometer (CAPS) as the probe flew through Titan’s upper atmosphere at an distance of 950 – 1300 km (590 – 808 mi) from the surface. They also show how the presence of these molecules was rather unexpected, and represent a considerable challenge to current theories about how Titan’s atmosphere works.

For some time, scientists have understood that within Titan’s ionosphere, nitrogen, carbon and hydrogen are subjected to sunlight and energetic particles from Saturn’s magnetosphere. This exposure drives a process where these elements are transformed into more complex prebiotic compounds, which then drift down towards the lower atmosphere and form a thick haze of organic aerosols that are thought to eventually reach the surface.

This has been the subject of much interest, since the process through which simple molecules form complex organic ones has remained something of a mystery to scientists. This could be coming to an end thanks to the detection of carbon chain anions, though their discovery was altogether unexpected. Since these molecules are highly reactive, they are not expected to last long in Titan’s atmosphere before combining with other materials.

However, the data showed that the carbon chains became depleted closer to the moon, while precursors to larger aerosol molecules underwent rapid growth. This suggests that there is a close relationship between the two, with the chains ‘seeding’ the larger molecules. Already, scientists have held that these molecules were an important part of the process that allowed for life to form on Earth, billions of years ago.

*A halo of light surrounds Saturn’s moon Titan in this backlit picture, showing its atmosphere. Credit: NASA/JPL/Space Science Institute*

However, their discovery on Titan could be an indication of how life begins to emerge throughout the Universe. As Dr. Ravi Desai, University College London and the lead author of the study, explained in an ESA press release:

“We have made the first unambiguous identification of carbon chain anions in a planet-like atmosphere, which we believe are a vital stepping-stone in the production line of growing bigger, and more complex organic molecules, such as the moon’s large haze particles. This is a known process in the interstellar medium, but now we’ve seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules.”

Because of its dense nitrogen and methane atmosphere and the presence of some of the most complex chemistry in the Solar System, Titan is thought by many to be similar to Earth’s early atmosphere. Billions of years ago, before the emergence of microorganisms that allowed for subsequent build-up of oxygen, it is likely that Earth had a thick atmosphere composed of nitrogen, carbon dioxide and inert gases.

Therefore, Titan is often viewed as a sort planetary laboratory, where the chemical reactions that may have led to life on Earth could be studied. However, the prospect of finding a universal pathway towards the ingredients for life has implications that go far beyond Earth. In fact, astronomers could start looking for these same molecules on exoplanets, in an attempt to determine which could give rise to life.

Closer to home, the findings could also be significant in the search for life in our own Solar System. “The question is, could it also be happening within other nitrogen-methane atmospheres like at Pluto or Triton, or at exoplanets with similar properties?” asked Desia. And Nicolas Altobelli, the Project Scientist for the Cassini-Huygens mission, added:

“These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how complex organic molecules are produced in an early Earth-like atmosphere. While we haven’t detected life itself, finding complex organics not just at Titan, but also in comets and throughout the interstellar medium, we are certainly coming close to finding its precursors.“

Cassini’s “Grande Finale“, the culmination of its 13-year mission around Saturn and its system of moons, is set to end on September 15th, 2017. In fact, as of the penning of this article, the mission will end in about 1 month, 18 days, 16 hours, and 10 minutes. After making its final pass between Saturn’s rings, the probe will be de-orbited into Saturn’s atmosphere to prevent contamination of the system’s moons.

However, future missions like the James Webb Space Telescope, the ESA’s PLATO mission and ground-based telescopes like ALMA are expected to make some significant exoplanet finds in the coming years. Knowing specifically what kinds of molecules are intrinsic in converting common elements into organic molecules will certainly help narrow down the search for habitable (or even inhabited) planets!

Further Reading: ESA, The Astrophysical Journal Letters

April 4, 2017April 5, 2017 by Nancy Atkinson

Cassini’s Final Mission to Annihilation Starts April 22

Grab the tissues. This video nearly had the Cassini team all choked up during today’s press briefing, and virtual sobs and sniffs were abundant on social media posts sharing the video.

“We get goosebumps and get emotional every time we see it,” said Earl Maize, Cassini project manager at JPL.

On April 22 the Cassini spacecraft will begin its ‘Grand Finale’ — the beginning of the end of this tremendous mission that has provided breathtaking images and so many new discoveries of Saturn, its rings and moons. The mission will end on September 15, 2017, when it makes a dramatic plunge into the gas giant.

Here’s the video that had everyone teary-eyed. Be prepared for some stunning visuals:

Today, Maize talked about how nineteen countries and three space agencies contributed to the success of the Cassini/Huygens mission, saying the mission has been truly an international triumph and a phenomenal achievement.

“Cassini’s legacy is assured. We are in the books!” Maize said. “But the best is yet to come. We are going to dive into the gap between the rings of Saturn and Saturn’s atmosphere, a place where no spacecraft has ever gone. We’ll be going 70,000 mph (112,634 km/hr) into a 1,500-mile-wide (2,400-kilometer) gap, operating the spacecraft from a billion miles away.”

Cassini has been a relatively trouble free mission, and has made many discoveries about the Saturn system. So why crash the spacecraft?

Cassini is running out of fuel, basically running on fumes at this point.* And NASA needs to follow the protocol of planetary protection, and not allow a spacecraft with possible microbes from Earth to crash into a potentially habitable moon such as Enceladus or Titan.

“Cassini’s own discoveries were its demise,” Maize said. “Enceladus has a warm, salt water ocean. We can’t risk an inadvertent contact with this pristine body. The only choice was to destroy it (Cassini) in a designed fashion.”

Maize said that back in 2010, the team decided they would make the mission last as long as possible and use every last kilogram of propellant to explore the Saturn system as thoroughly as they could.

Cassini vs. Saturn. As depicted in this illustration, Cassini will plunge into Saturn’s atmosphere on Sept. 15, 2017. Using its attitude control thrusters, the spacecraft will work to keep its antenna pointed at Earth while it sends its final data, including the composition of Saturn’s upper atmosphere. Credit: NASA/JPL-Caltech

The final flyby of Titan on April 22 will ultimately alter Cassini’s trajectory and push it toward the spacecraft’s final demise. Maize described the gravity slingshot from Titan as a “last kiss goodbye that will push Cassini into Saturn. This is a roller coaster ride that we’re not coming out of.”

You can plot Cassini’s trajectory in JPL’s “Eyes on Cassini” special section of their Eyes on the Solar System website.

Cassini will make 22 passes through the gap, and in doing so, further our understanding of how giant planets, and planetary systems everywhere, form and evolve.

Project Scientist Linda Spilker said Cassini will be able to make close up measurements of Saturn and its rings to finally help us understand the mass and internal structure of Saturn. And the images should be absolutely stunning.

There’s the risk of dust or debris hitting the spacecraft, potentially crippling Cassini. But the risk is worth it, because if the spacecraft survives through even just a few of the close passes, the scientific payback will be incredible. However, even if the spacecraft is crippled and can’t send back its final science observations, the end is inevitable, as the path toward destruction will be written by the final ‘kiss’ from Titan.

“This is something we couldn’t try at any other time,” Maize said. “But now is time.”

A computer-generated representation of all Cassini’s Saturn orbits -affectionately called the “ball of yarn” by mission planners. The time frame spans Saturn Orbit Insertion on July 1, 2004 to the end of mission on Sept. 15, 2017. Credit: NASA/JPL-Caltech.

The Cassini team said the end of the mission will likely be a combination of excitement, pride and a sense of loss.

“I think that once the signal is lost, it would mean the heartbeat of Cassini is gone,” said Spilker. “I think there will be tremendous cheers and applause for the completion of an absolutely incredible mission. Hugs, tears — the Kleenex box will be passed around — but we will rejoice at being part of such a wonderful mission.”

See more images and information about the Grand Finale here.

For more of an inside look at Cassini, I devote a chapter of my book to the mission, with more insight from Earl Maize, Linda Spilker and others about the history and discoveries of the Cassini/Huygens mission, and additional details about the Grand Finale. “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Channging Our View of the Cosmos.”

Artist’s concept of Cassini orbiter crossing Saturn’s ring plane.
Credit: NASA/Jet Propulsion Laboratory.

*One of the Cassini team members said that as of today (April 4, 2017) Cassini has 36kg of hydrazine left for the thrusters, which are used everyday to orient the spacecraft, point the antenna towards Earth, point the instruments to their desired targer, etc. For the Titan flyby on April 22, about 10-15 kg. As for the bipropellant that runs the main engines, that’s a little more unknown and the one the team is worried most about running out of fuel. The team member said there is about 10 kg of that fuel left, “plus or minus 20 kilos [meaning there is true uncertainty about how much of this fuel remains]. We could run out today, or we could have 30 kilos left.”

March 8, 2017 by Fraser Cain

What Did Cassini Teach Us?

Ask me my favorite object in the Solar System, especially to see through a telescope, and my answer is always the same: Saturn.

Saturn is this crazy, ringed world, different than any other place we’ve ever seen. And in a small telescope, you can really see the ball of the planet, you can see its rings. It’s one thing to see a world like this from afar, a tiny jumping image in a telescope. To really appreciate and understand a place like Saturn, you’ve got to visit.

And thanks to NASA’s Cassini spacecraft, that’s just what we’ve been doing for the last 13 years. Take a good close look at this amazing ringed planet and its moons, and studying it from every angle.

Space Probes — Cassini orbiting Saturn. Credit: NASA

Throughout this article, I’m going to regale you with the amazing discoveries made by Cassini at Saturn. What it taught us, and what new mysteries it uncovered.

NASA’s Cassini spacecraft was launched from Earth on October 15, 1997. Instead of taking the direct route, it made multiple flybys of Venus, a flyby of Earth and a flyby of Jupiter. Each one of these close encounters boosted Cassini’s velocity, allowing it to make the journey with less escape velocity from Earth.

It arrived at Saturn on July 1st, 2004 and began its science operations shortly after that. The primary mission lasted 4 years, and then NASA extended its mission two more times. The first ending in 2010, and the second due to end in 2017. But more on that later.

Before Cassini, we only had flybys of Saturn. NASA’s Pioneer 11, and Voyagers 1 and 2 both zipped past the planet and its moons, snapping pictures as they went.

But Cassini was here to stay. To orbit around and around the planet, taking photos, measuring magnetic fields, and studying chemicals.

For Saturn itself, Cassini was able to make regular observations of the planet as it passed through entire seasons. This allowed it to watch how the weather and atmospheric patterns changed over time. The spacecraft watched lightning storms dance through the cloudtops at night.

This series of images from NASA’s Cassini spacecraft shows the development of the largest storm seen on the planet since 1990. These true-color and composite near-true-color views chronicle the storm from its start in late 2010 through mid-2011, showing how the distinct head of the storm quickly grew large but eventually became engulfed by the storm’s tail. Credit: NASA/JPL-Caltech/Space Science Institute

Two highlights. In 2010, Cassini watched a huge storm erupt in the planet’s northern hemisphere. This storm dug deep into Saturn’s lower atmosphere, dredging up ice from a layer 160 kilometers below and mixing it onto the surface. This was the first time that astronomers were able to directly study this water ice on Saturn, which is normally in a layer hidden from view.

Natural color images taken by NASA’s Cassini wide-angle camera, showing the changing appearance of Saturn’s north polar region between 2012 and 2016.. Credit: NASA/JPL-Caltech/Space Science Institute/Hampton University

The second highlight, of course, is the massive hexagonal storm churning away in Saturn’s northern pole. This storm was originally seen by Voyager, but Cassini brought its infrared and visible wavelength instruments to bear.

Why a hexagon? That’s still a little unclear, but it seems like when you rotate fluids of different speeds, you get multi-sided structures like this.

Cassini showed how the hexagonal storm has changed in color as Saturn moved through its seasons.

This is one of my favorite images sent back by Cassini. It’s the polar vortex at the heart of the hexagon. Just look at those swirling clouds.

The polar vortex, in all its glory. Credit: NASA/JPL-Caltech/Space Science Institute

Now, images of Saturn itself are great and all, but there was so much else for Cassini to discover in the region.

Cassini studied Saturn’s rings in great detail, confirming that they’re made up of ice particles, ranging in size as small a piece of dust to as large as a mountain. But the rings themselves are actually quite thin. Just 10 meters thick in some places. Not 10 kilometers, not 10 million kilometers, 10 meters, 30 feet.

The spacecraft helped scientists uncover the source of Saturn’s E-ring, which is made up of fresh icy particles blasting out of its moon Enceladus. More on that in a second too.

Vertical structures, among the tallest seen in Saturn’s main rings, rise abruptly from the edge of Saturn’s B ring to cast long shadows on the ring in this image taken by NASA’s Cassini spacecraft two weeks before the planet’s August 2009 equinox. Credit: NASA/JPL/Space Science Institute

Here’s another one of my favorite images of the mission. You’re looking at strange structures in Saturn’s B-ring. Towering pillars of ring material that rise 3.5 kilometers above the surrounding area and cast long shadows. What is going on here?

They’re waves, generated in the rings and enhanced by nearby moons. They move and change over time in ways we’ve never been able to study anywhere else in the Solar System.

Daphnis, one of Saturn’s ring-embedded moons, is featured in this view, kicking up waves as it orbits within the Keeler gap. Credit: NASA/JPL-Caltech/Space Science Institute

Cassini has showed us that Saturn’s rings are a much more dynamic place than we ever thought. Some moons are creating rings, other moons are absorbing or distorting them. The rings generate bizarre spoke patterns larger than Earth that come and go because of electrostatic charges.

Speaking of moons, I’m getting to the best part. What did Cassini find at Saturn’s moons?

Let’s start with Titan, Saturn’s largest moon. Before Cassini, we only had a few low resolution images of this fascinating world. We knew Titan had a dense atmosphere, filled with nitrogen, but little else.

Cassini was carrying a special payload to assist with its exploration of Titan: the Huygens lander. This tiny probe detached from Cassini just before its arrival at Saturn, and parachuted through the cloudtops on January 14, 2005, analyzing all the way. Huygens returned images of its descent through the atmosphere, and even images of the freezing surface of Titan.

Huygen’s view of Titan. Credit: ESA/NASA/JPL/University of Arizona

But Cassini’s own observations of Titan took the story even further. Instead of a cold, dead world, Cassini showed that it has active weather, as well as lakes, oceans and rivers of hydrocarbons. It has shifting dunes of pulverized rock hard water ice.

If there’s one place that needs exploring even further, it’s Titan. We should return with sailboats, submarines and rovers to better explore this amazing place.

A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

We learned, without a shadow of a doubt, that Mimas absolutely looks like the Death Star. No question. But instead of a megalaser, this moon has a crater a third of its own size.

Saturn’s moon Iapetus. Image credit: NASA/JPL/SSI

Cassini helped scientists understand why Saturn’s moon Iapetus has one light side and one dark side. The moon is tidally locked to Saturn, its dark side always leading the moon in orbit. It’s collecting debris from another Saturnian moon, Phoebe, like bugs hitting the windshield of a car.

Perhaps the most exciting discovery that Cassini made during its mission is the strange behavior of Saturn’s moon Enceladus. The spacecraft discovered that there are jets of water ice blasting out of the moon’s southern pole. An ocean of liquid water, heated up by tidal interactions with Saturn, is spewing out into space.

And as you know, wherever we find water on Earth, we find life. We thought that water in the icy outer Solar System would be hard to reach, but here it is, right at the surface, venting into space, and waiting for us to come back and investigate it further.

Icy water vapor geysers erupting from fissures on Enceladus. Credit: NASA/JPL

On September 15, 2017, the Cassini mission will end. How do we know it’s going to happen on this exact date? Because NASA is going to crash the spacecraft into Saturn, killing it dead.

That seems a little harsh, doesn’t it, especially for a spacecraft which has delivered so many amazing images to us over nearly two decades of space exploration? And as we’ve seen from NASA’s Opportunity rover, still going, 13 years longer than anticipated. Or the Voyagers, out in the depths of the void, helping us explore the boundary between the Solar System and interstellar space. These things are built to last.

The problem is that the Saturnian system contains some of the best environments for life in the Solar System. Saturn’s moon Enceladus, for example, has geysers of water blasting out into space.

Cassini spacecraft is covered in Earth-based bacteria and other microscopic organisms that hitched a ride to Saturn, and would be glad to take a nice hot Enceladian bath. All they need is liquid water and a few organic chemicals to get going, and Enceladus seems to have both.

NASA feels that it’s safer to end Cassini now, when they can still control it, than to wait until they lose communication or run out of propellant in the future. The chances that Cassini will actually crash into an icy moon and infect it with our Earth life are remote, but why take the risk?
For the last few months, Cassini has been taking a series of orbits to prepare itself for its final mission. Starting in April, it’ll actually cross inside the orbit of the rings, getting closer and closer to Saturn. And on September 15th, it’ll briefly become a meteor, flashing through the upper atmosphere of Saturn, gone forever.

This graphic illustrates the Cassini spacecraft’s trajectory, or flight path, during the final two phases of its mission. The view is toward Saturn as seen from Earth. The 20 ring-grazing orbits are shown in gray; the 22 grand finale orbits are shown in blue. The final partial orbit is colored orange. Image credit: NASA/JPL-Caltech/Space Science Institute

Even in its final moments, Cassini is going to be sciencing as hard as it can. We’ll learn more about the density of consistency of the rings close to the planet. We’ll learn more about the planet’s upper atmosphere, storms and clouds with the closest possible photographs you can take.

And then it’ll all be over. The perfect finale to one of the most successful space missions in human history. A mission that revealed as many new mysteries about Saturn as it helped us answer. A mission that showed us not only a distant alien world, but our own planet in perspective in this vast Solar System. I can’t wait to go back.

How have the photos from Cassini impacted your love of astronomy? Let me know your thoughts in the comments.