Cassini Begins Its Final Act: A Conversation with Charles Elachi

News Writer: 
Ramanuj Basu

Charles Elachi, Vice President; Director of the Jet Propulsion Laboratory; Professor of Electrical Engineering and Planetary Science, Caltech
Credit: Lance Hayashida/Caltech

In September, the NASA/JPL Cassini mission began the last two years of the Solstice Mission, the final stretch of its explorations of Saturn, its rings, and its moons—including the giant Titan, a haze-enshrouded satellite with Earth-like features and complicated organic chemistry, and small, icy, and surprisingly active Enceladus. 

Launched in October 1997, after a decade and a half of planning, design, and construction, the Cassini spacecraft may be one of JPL’s missions that is most well remembered, says JPL director Charles Elachi (MS ’69, PhD ’71). Elachi, who is also a Caltech professor of electrical engineering and planetary science, may be forgiven a small amount of bias toward Cassini, as he has served since the mid-1980s as the team leader for the spacecraft’s radar experiment—the instrument responsible for mapping the previously hidden surface of Titan.

We recently spoke with Elachi to gain his unique perspective on Cassini’s achievements—and what will come next.

How did you first get involved in the Cassini mission?

When the mission concept was being developed in the early 1980s, JPL worked with the science community to define the mission, and one of the key instruments that the community wanted was radar. At that time, all that we knew about Titan, Saturn’s largest satellite, was that it is a ball. It is completely haze covered, and you cannot see the surface. Radar was an ideal instrument because of its capability to see through the haze to map the surface.

At the time, I was the lead scientist at JPL in radar activity. I was involved in some of the earlier radar missions like Seasat, one of the first orbiting radar satellites. I was the principal investigator of a series of shuttle imaging radar missions (SIR-A, SIR-B, SIR-C). I was a member of the Venus radar team for NASA’s Magellan mission. So I decided to propose that type of instrument for Cassini. It was selected, and I was selected as the team leader. Caltech professor of planetary science Duane (Dewey) Muhleman, who is now retired, joined me on the radar team.

Other Caltech faculty and alumni include Andrew Ingersoll, professor of planetary science, who was a member of the Cassini imaging team, as was Torrence Johnson (PhD ’70); imaging team leader Carolyn Porco (PhD ’83), who is also the director of the Cassini Imaging Central Laboratory for Operations (CICLOPS); and Dennis Matson (PhD ’72), who was the Cassini project scientist from the beginning of the mission through early part of the orbiting phase.

Do you recall what your hopes were for the mission when it first started?

At the time, some people had the theory that Titan is a water ball—with an ocean across the whole satellite. Other people were saying there is no ocean. It would be too arid. We had no idea what to expect. For me, the most exciting thing was that it was going to be a complete surprise. It was different from the case with Mars, for example, where we had some idea of what the planet looked like from ground telescopes.

My goal was to map as much of Titan as possible. The radar instrument maps Titan by serial flybys, where, with every flyby, we image a wide strip of the surface. My hope was to map at least 50 percent of Titan. So far, we have mapped almost 60 percent.

What was the biggest surprise?

In my mind, the two biggest surprises were, first, that it has lakes with rivers coming into them—all made of hydrocarbons. The lakes are roughly the same size as the Great Lakes in the U.S. It looks like Earth to some extent. The other big surprise was the sand dunes. We did not expect that there would be fields of sand dunes.

What are the sand dunes made of?

We don’t know. They could be made of hydrocarbon particles or frozen grains of snow or ice. We cannot tell what their composition is from the radar or other instruments. That’s for the next mission.

We know they are extensive. All around the equatorial region on Titan, you see sand dunes of different sizes and with different structures.

They look very similar to the sand dunes in Namibia and Saudi Arabia. The phenomenology is very similar, with the wind blowing particles around hills and mountains to create the patterns.

Have you seen changes in the radar imaging over the last 11 years?

We see changes in a couple of places, and we are very puzzled about the reason for those changes. In the lakes, some small islands have appeared a couple of times. When you see things like this you debate, is it some anomaly in the instrument or is it real? It’s perfectly conceivable it could be real, that the level of the liquid could be moving up and down, like what happens in the winter or the summer in lakes here on Earth.

Is there anything that you still hope to learn over the next two years?

I’m always ready for some surprises. A few passes that we will be doing will cover some new areas. One thing we have been looking for is if there are lakes on the other side of Titan, the other pole, now that we know there are lakes in the north. If we detect lakes over areas that we haven’t covered, that might give us some hint about why the lakes are there. Also, because Saturn’s seasons are progressing, but very slowly, we keep looking for changes as the spacecraft goes over the same areas—changes in the lakes or changes of volcanic flow, changes in sand dune patterns, anything that gives us an indication that something dynamic is happening.

How will the Cassini mission end?

It is going to be a dramatic end. We are planning, on purpose, to have the spacecraft enter Saturn’s atmosphere and burn up before it completely depletes its fuel. In order to do that, we have to do a number of orbits that come very close to the rings. In fact, we’ll be going through the gap between the rings and the planet, so we might find something new that we haven’t seen before now.

Now, you may say, “Why are you crashing into Saturn?” The reason is there are rules for planetary protection. In the long term, once we lose control of the spacecraft, we want to ensure that it doesn’t end crashing into Titan, or crashing into Enceladus, to keep the satellites pristine.

How did the team pick Cassini’s final day, September 15, 2017?

I think it came from the orbital dynamics. We needed to do it before we completely use the control fuel. The orbit guys came up with a number of scenarios, and then the science team collectively sat down and decided on one of the scenarios.

Have you thought about how you are going to feel on September 16?

On one hand, we will be thinking, “Gee, we are losing one of our great missions.”

But this mission has been so amazing. It made so many discoveries—finding the lakes and the sand dunes on Titan; the geysers on Enceladus; details of the hexagonal hurricane in the northern hemisphere of Saturn, which is allowing us to understand the planet’s atmospheric dynamics. Cassini’s discoveries have completely changed our thinking about the whole Saturnian system. It is changing the textbooks.

The way I think about it is that Voyager gave us snapshots of all the outer planets—Jupiter, Saturn, Uranus, and Neptune. It triggered our curiosity about them. Cassini gave us an in-depth understanding of the whole Saturnian system, which is almost like a mini solar system.

It’s like this with every scientific exploration. You answer a certain question, and it raises new questions. What are the sand dunes made of? Do they change? What is the liquid made of? How deep are the different lakes? We’re starting to think about the next mission for Titan. Some people are looking at possibly dropping boats in the lakes. Some people are looking at rovers. That will be a different technological challenge at that very low temperature.

We also are looking at possibly landing on Enceladus or sending a spacecraft to fly through its plume, capture samples, and either analyze them in a mass spectrometer on the spacecraft or bring a capsule all the way back to Earth.

After Cassini’s mission ends, how much longer will you still be analyzing the data?

The mission is funded at least through 2018. Beyond that, I think people will be analyzing the data at least for a decade, if not longer.

Time brings new perspective. As you learn more about how planets form and about the tectonic activities or the atmosphere, you come up with new ideas. Then you go and look at the data and see. Does that fit with the result of the measurements that were made using a different instrument? Plus, people now are getting much more knowledgeable about analyzing data from multiple instruments that complement each other.

Will you be involved in another mission?

If I’m still alive, maybe. The next big mission is to Jupiter’s moon, Europa. I’m a member of the team doing the radar sounder to measure the thickness of the ice.

Did you ever consider stepping away from the science as your other responsibilities increased after becoming director of JPL in 2001?

I always keep a finger on the science. I have found that an important thing for the director at JPL is to stay involved in the science at the team level, so we understand what the institution is doing and understand the issues of the community. It’s part of my management style.

For the Europa mission, I felt we needed a younger person to be the team leader. I am only a team member. We structured the team so that half the team is … let me call them “mature.” More experienced. People like me. The other half is relatively younger people. We teamed each senior person with a young person. A person from the University of Texas who is in his early 30s is kind of my understudy, if you want. He will be working with me, so I will transfer my experience.

In addition, I am a team member on a very exciting Discovery Venus radar mission, which will be a major advance beyond Magellan.

Is it bittersweet, handing off the reins like this?

I tell people I’m envious of them, because there will be so many discoveries happening in the next 30 years. I wish I were 20 years younger so I could see those discoveries. I’m sure when I was young, people who were older were envious of us.

Hopefully, if I live long enough, I will see some of these results. It’s an incentive to stay in good health.

In our business, you have to be patient. It takes a long time, particularly for the outer planets. With Cassini, we had seven years to sell it to Congress, seven years to build it, seven years to get to Saturn. That’s even before we started getting the data. But, once you start getting the data, the excitement is worth every bit of that patience. I would say my career was worth it.

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Elachi to Retire as JPL Director

Charles Elachi, Vice President; Director of the Jet Propulsion Laboratory; Professor of Electrical Engineering and Planetary Science, Caltech
Credit: Lance Hayashida/Caltech

Charles Elachi (MS ’69, PhD ’71) has announced his intention to retire as director of the Jet Propulsion Laboratory on June 30, 2016, and move to campus as professor emeritus. A national search is underway to identify his successor.

“A frequently consulted national and international expert on space science, Charles is known for his broad expertise, boundless energy, conceptual acuity, and deep devotion to JPL, campus, and NASA,” said Caltech president Thomas F. Rosenbaum in a statement to the Caltech community. “Over the course of his 45-year career at JPL, Charles has tirelessly pursued new opportunities, enhanced the Laboratory, and demonstrated expert and nimble leadership. Under Charles’ leadership over the last 15 years, JPL has become a prized performer in the NASA system and is widely regarded as a model for conceiving and implementing robotic space science missions.”

With Elachi at JPL’s helm, an array of missions has provided new understanding of our planet, our moon, our sun, our solar system, and the larger universe. The GRAIL mission mapped the moon’s gravity; the Genesis space probe returned to Earth samples of the solar wind; Deep Impact intentionally collided with a comet; Dawn pioneered the use of ion propulsion to visit the asteroids Ceres and Vesta; and Voyager became the first human-made object to reach interstellar space. A suite of missions to Mars, from orbiters to the rovers Spirit, Opportunity, and Curiosity, has provided exquisite detail of the red planet; Cassini continues its exploration of Saturn and its moons; and the Juno spacecraft, en route to a July 2016 rendezvous, promises to provide new insights about Jupiter. Missions such as the Galaxy Evolution Explorer, the Spitzer Space Telescope, Kepler, WISE, and NuSTAR have revolutionized our understanding of our place in the universe.

Future JPL missions developed under Elachi’s guidance include Mars 2020, Europa Clipper, the Asteroid Redirect Mission, Jason 3, Aquarius, OCO-2, SWOT, and NISAR.

Elachi joined JPL in 1970 as a student intern and was appointed director and Caltech vice president in 2001. During his more than four decades at JPL, he led a team that pioneered the use of space-based radar imaging of the Earth and the planets, served as principal investigator on a number of NASA-sponsored studies and flight projects, authored more than 230 publications in the fields of active microwave remote sensing and electromagnetic theory, received several patents, and became the director for space and earth science missions and instruments. At Caltech, he taught a course on the physics of remote sensing for nearly 20 years

Born in Lebanon, Elachi received his B.Sc. (’68) in physics from University of Grenoble, France and the Dipl. Ing. (’68) in engineering from the Polytechnic Institute, Grenoble. In addition to his MS and PhD degrees in electrical science from Caltech, he also holds an MBA from the University of Southern California and a master’s degree in geology from UCLA.

Elachi was elected to the National Academy of Engineering in 1989 and is the recipient of numerous other awards including an honorary doctorate from the American University of Beirut (2013), the National Academy of Engineering Arthur M. Bueche Award (2011), the Chevalier de la Légion d’Honneur from the French Republic (2011), the American Institute of Aeronautics and Astronautics Carl Sagan Award (2011), the Royal Society of London Massey Award (2006), the Lebanon Order of Cedars (2006 and 2012), the International von Kármán Wings Award (2007), the American Astronautical Society Space Flight Award (2005), the NASA Outstanding Leadership Medal (2004, 2002, 1994), and the NASA Distinguished Service Medal (1999).

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Probing the Mysteries of Europa, Jupiter’s Cracked and Crinkled Moon

New research identifies possible sites of frozen, watery deposits.
News Writer: 
Rod Pyle

Europa, as imaged by NASA's Galileo spacecraft.

The puzzling, fascinating surface of Jupiter's icy moon Europa looms large in images taken by NASA's Galileo spacecraft.
Credit: NASA/JPL-Caltech/SETI Institute

Jupiter’s moon Europa is believed to possess a large salty ocean beneath its icy exterior, and that ocean, scientists say, has the potential to harbor life. Indeed, a mission recently suggested by NASA would visit the icy moon’s surface to search for compounds that might be indicative of life. But where is the best place to look? New research by Caltech graduate student Patrick Fischer; Mike Brown, the Richard and Barbara Rosenberg Professor and Professor of Planetary Astronomy; and Kevin Hand, an astrobiologist and planetary scientist at JPL, suggests that it might be within the scarred, jumbled areas that make up Europa’s so-called “chaos terrain.”

A paper about the work has been accepted to The Astronomical Journal.

“We have known for a long time that Europa’s fresh icy surface, which is covered with cracks and ridges and transform faults, is the external signature of a vast internal salty ocean,” Brown says. The areas of chaos terrain show signatures of vast ice plates that have broken apart, shifted position, and been refrozen. These regions are of particular interest, because water from the oceans below may have risen to the surface through the cracks and left deposits there.

“Directly sampling Europa’s ocean represents a major technological challenge and is likely far in the future,” Fischer says. “But if we can sample deposits left behind in the chaos areas, it could reveal much about the composition and dynamics of the ocean below.” That ocean is thought to be as deep as 100 kilometers.

“This could tell us much about activity at the boundary of the rocky core and the ocean,” Brown adds.

In a search for such deposits, the researchers took a new look at data from observations made in 2011 at the W. M. Keck Observatory in Hawaii using the OSIRIS spectrograph. Spectrographs break down light into its component parts and then measure their frequencies. Each chemical element has unique light-absorbing characteristics, called spectral or absorption bands. The spectral patterns resulting from light absorption at particular wavelengths can be used to identify the chemical composition of Europa’s surface minerals by observing reflected sunlight.

The OSIRIS instrument measures spectra in infrared wavelengths. “The minerals we expected to find on Europa have very distinct spectral fingerprints in infrared light,” Fischer says. “Combine this with the extraordinary abilities of the adaptive optics in the Keck telescope, and you have a very powerful tool.” Adaptive optics mechanisms reduce blurring caused by turbulence in the earth’s atmosphere by measuring the image distortion of a bright star or laser and mechanically correcting it.

The OSIRIS observations produced spectra from 1600 individual spots on Europa’s surface. To make sense of this collection of data, Fischer developed a new technique to sort and identify major groupings of spectral signatures.

“Patrick developed a very clever new mathematical tool that allows you to take a collection of spectra and automatically, and with no preconceived human biases, classify them into a number of distinct spectra,” Brown says. The software was then able to correlate these groups of readings with a surface map of Europa from NASA’s Galileo mission, which mapped the Jovian moon beginning in the late 1990s. The resulting composite provided a visual guide to the composition of the regions the team was interested in.

Three compositionally distinct categories of spectra emerged from the analysis. The first was water ice, which dominates Europa’s surface. The second category includes chemicals formed when ionized sulfur and oxygen­­—thought to originate from volcanic activity on the neighboring moon Io­­—bombard the surface of Europa and react with the native ices. These findings were consistent with results of previous work done by Brown, Hand and others in identifying Europa’s surface chemistry.

But the third grouping of chemical indicators was more puzzling. It did not match either set of ice or sulfur groupings, nor was it an easily identified set of salt minerals such as they might have expected from previous knowledge of Europa. Magnesium is thought to reside on the surface but has a weak spectral signature, and this third set of readings did not match that either. “In fact, it was not consistent with any of the salt materials previously associated with Europa,” Brown says.

When this third group was mapped to the surface, it overlaid the chaos terrain. “I was looking at the maps of the third grouping of spectra, and I noticed that it generally matched the chaos regions mapped with images from Galileo. It was a stunning moment,” Fischer says. “The most important result of this research was understanding that these materials are native to Europa, because they are clearly related to areas with recent geological activity.”

The composition of the deposits is still unclear. “Unique identification has been difficult,” Brown says. “We think we might be looking at salts left over after a large amount of ocean water flowed out onto the surface and then evaporated away. He compares these regions to their earthly cousins. “They may be like the large salt flats in the desert regions of the world, in which the chemical composition of the salt reflects whatever materials were dissolved in the water before it evaporated.”

Similar deposits on Europa could provide a view into the oceans below, according to Brown. “If you had to suggest an area on Europa where ocean water had recently melted through and dumped its chemicals on the surface, this would be it. If we can someday sample and catalog the chemistry found there, we may learn something of what’s happening on the ocean floor of Europa and maybe even find organic compounds, and that would be very exciting.” 

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California Wildfires Are Abrupt Climate Change, Ecological Collapse


California is collapsing ecologically

It’s OK America, pop pills and watch TV. Don’t worry about abrupt climate change, environmental collapse, or perma-war blowback from your oil addiction.

“California is a nice place to visit, but soon no one may be able to live there.” – Dr. Glen Barry


Only a couple centuries ago California was mostly covered in lush naturally evolving ecosystems that surrounded and provided ecological habitat for relatively small settlements of Native Americans. Grizzly bears roamed and redwood forests towered. Now the heavily industrialized state is an over-populated ecologically collapsing mess. Remaining tawdry natural ecosystems are surrounded by an endless sprawl of human filth, and the very climate is abruptly changing.

California’s recent drought and wildfire outbreak is an exemplar of what surpassing a bioregion’s carrying capacity and resultant ecological collapse looks like. For centuries naturally evolved ecosystems which make California habitable have been treated as resources to be devoured for industrial development. California’s fragmented and no longer connected natural ecosystems have been further destabilized by abrupt climate change and are no longer able to stably provide human habitat.

Everywhere one looks in California one sees over-populated over-consumption, over-development’s destruction of natural ecosystems, and resultant ecological collapse further worsened by industrial emissions. For four years California has been ravaged by a climate change intensified epic drought. In the worst impacted communities, hundreds of households have no access to running water.

California’s drought, a state of emergency since January 2014, has reached unprecedented levels, the worst in recorded history. The state’s mountain snowpack – which provides 30% of California’s water – is at the lowest level in at least 500 years, 5% of its usual water content. Parts of the state have a four-year precipitation deficit of more than 70 inches. 2015 is expected to be the warmest ever recorded.

Ecologists strongly agree that climate change is linked to California’s wildfires. Human-caused warming is clearly contributing to drier conditions, which make forests more susceptible to burning. One estimate is that 20% of the California’s forest trees are sick or have died from the drought. Record heat has increased evaporation and dried out the soil and tinder dry vegetation has become literally explosive. This has caused harsh wildfires as fragmented and sick forest ecosystems are ablaze.

In recent months, two of the most destructive wildfires in state history have raged across Northern California, and over 1 million acres have burned. Forest ecosystems are a mess after a century of terrible land uses including suppressing fire, allowing sheep and cattle to graze forest understories, and endless sprawl fragmenting natural forest ecosystems. Today’s forests are more dense and filled with combustible materials, allowing fires to spread more easily from the ground to the forest canopy, more often killing trees. Since 1970 climate change has extended the California fire season by 78 days.

California’s ecological tragedy only shows signs of worsening as warm ocean temperatures are 5 degrees above normal and the El Niño weather phenomena show signs of unleashing dramatic flooding upon the heat hardened Earth. Two weeks ago a record 1.81 inches of rain fell in Southern California in 30 minutes, a once every 1,000-year rain event. Extreme weather events threaten California’s existence.

It is no wonder that California is ablaze as forest ecosystems collapse. Grizzly bears are long gone, and redwood forests tiny remnants.

Recently the California state legislature passed a new climate bill which requires greater use of renewables by 2030. But far more must be done if state-wide ecological collapse is to be averted. There must be an immediate end to building in forests. Forests must be allowed to age and recover, and in most cases forests allowed to burn naturally to renew ecosystems. Emissions must be cut far more and faster than currently proposed – in order to end the use of fossil fuels as quickly as possible. And people are going to have to have fewer children and live less-consumptive lifestyles.

Worldwide our last great forests that support the biosphere are crashing as a result of climate change. Hotter droughts that are associated with climate change are causing stress and death for trees, and these increasingly unnatural forest conditions are leading to apocalyptic forest fires like have never before been seen.

The world continues to be in a state of perma-war as distant societies and ecosystems are plundered for oil. As more ecosystems collapse, the entire biosphere is threatened by death.

The situation in California, similar in so many other locales, is a direct result of ecocidal industrial growth destroying natural ecosystems, and our addiction to fossil fuels. The impacts of California’s collapse will be felt far beyond, as over half of America’s fruits, nuts and vegetables come from California.

California is a nice place to visit, but soon no one may be able to live there.

Large and connected natural ecosystems surrounding human communities are a prerequisite for sustainability and well-being. In California and throughout the world we must allow forests to regenerate, age, and become large and reconnected, surrounding human communities. Old-growth forest logging must end. Large and intact natural ecosystems are required as the context for humanity in order to continue providing the ecological services which make Earth habitable. Otherwise we all face the sort of ecological collapse occurring in California.

Americans don’t know or appreciate what is being lost as California collapses, as we self-medicate and watch TV. And we are all going to needlessly die as a result.

Entire bioregions like California are collapsing and will become uninhabitable and have to be abandoned. It is absolutely stunning that with ecological collapse so far progressed in California, many continue to deny the problem, and we do not yet have a coherent policy in place that is ecologically sufficient to ensure bioregional and global ecological sustainability.

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