TED日本語 - エリザベス・ジビ・タートル: 謎に包まれた土星の衛星タイタンを調べて生命の起源に関して何がわかるか

Picture a world with a variety of landforms. It has a dense atmosphere within which winds sweep across its surface and rain falls. It has mountains and plains, rivers, lakes and seas, sand dunes and some impact craters.

Sounds like Earth, right? This is Titan.

In August 1981, Voyager 2 captured this image of Saturn's largest moon. The Voyager missions have traveled farther than ever before, making the solar system and beyond part of our geography. But this image, this hazy moon was a stark reminder of just how much mystery remained. We learned an exponential amount as the Voyagers flew by it, and yet we had no idea what lay beneath this atmospheric blanket. Was there an icy surface with landforms like those of the other moons that had been observed at Saturn and Jupiter? Or perhaps simply a vast global ocean of liquid methane?

Shrouded by the obscuring haze, Titan's surface was a huge, outstanding mystery that Cassini-Huygens, an orbiter lander pair launched in 1997, was designed to solve. After arrival in 2004, the early images Cassini sent back of Titan's surface only heightened the allure. It took months for us to understand what we were seeing on the surface, to determine, for example, that the dark stripes, which were initially so unrecognizable that we referred to them as cat scratches, were actually dunes made of organic sand.

Over the course of the 13 years Cassini spent studying Saturn and its rings and moons, we had the privilege of going from knowing almost nothing about the surface of Titan to understanding its geology, the role the atmosphere plays in shaping its surface, and even hints of what lies deep beneath that surface.

Indeed, Titan is one of several ocean worlds, moons in the cold outer solar system beyond the orbits of Mars and the asteroid belt with immense liquid water oceans beneath their surfaces. Titan's interior ocean may have more than 10 times as much liquid water as all of the Earth's rivers, lakes, seas and oceans combined. And at Titan, there are also exotic lakes and seas of liquid methane and ethane on the surface. Ocean worlds are some of the most fascinating places in the solar system, and we have only just begun to explore them.

This is Dragonfly. At the Johns Hopkins Applied Physics Laboratory, we're building this mission for NASA's new Frontiers program. Scheduled to launch in 2026 and reach Titan in 2034, Dragonfly is a rotorcraft lander, similar in size to the Mars rovers or about the size of a small car. Titan's dense atmosphere, combined with its low gravity, make it a great place to fly, and that's exactly what Dragonfly is designed to do.

Technically an octocopter, Dragonfly is a mobile laboratory that can fly from place to place taking all of its scientific instruments with it. Dragonfly will investigate Titan in a truly unique way, studying details of its weather and geology, and even picking up samples from the surface to learn what they're made of. All told, Dragonfly will spend about three years exploring Titan, measuring its detailed chemistry, observing the atmosphere and how it interacts with the surface, and even listening for earthquakes, or technically titanquakes, in Titan's crust.

The Dragonfly team, hundreds of people across North America and around the world, is hard at work on the design for this mission, developing the rotorcraft, its autonomous navigation system and its instrumentation, all of which will need to work together to make science measurements on the surface of Titan.

Dragonfly is the next step in our exploration of this fascinating natural laboratory. In flying by, Voyager hinted at the possibilities. In orbiting Saturn for over a decade and descending through Titan's atmosphere, Cassini and Huygens pulled Titan's veil back a bit further. Dragonfly will live in the Titan environment, where, so far, our only close-up view is this image the Huygens probe took in January 2005.

In many ways, Titan is the closest known analogue we have to the early Earth, the Earth before life developed here. From Cassini-Huygens' measurements, we know that the ingredients for life, at least life as we know it, have existed on Titan, and Dragonfly will be fully immersed within this alien environment, looking for compounds similar to those that might have supported the development of life here on Earth and teaching us about the habitability of other worlds.

Habitability is a fascinating concept. What's necessary to make an environment suitable to host life, whether life as we know it here on Earth, or perhaps exotic life that has developed under very different conditions?

The possibility of life elsewhere has inspired human imagination and exploration throughout history. On a grand scale, it's why the ocean worlds in the outer solar system have become such important targets for study. It's the "what if" that drives human exploration.

We don't know how chemistry took the step to biology here on Earth, but similar chemical processes may have happened on Titan, where organic molecules have had the opportunity to mix with liquid water at the surface. Has organic synthesis progressed under these conditions? And if so, how far? We don't know ... yet.

What we will learn from Dragonfly, this fundamentally human endeavor, is tantalizing. It's a search for building blocks, foundations, chemical steps like those that ultimately led to life on Earth. We're not sure exactly what we will find when we get to Titan, but that's exactly why we're going.

In 1994, Carl Sagan wrote, "On Titan, the molecules that have been raining down like manna from heaven for the last four billion years might still be there, largely unaltered, deep-frozen, awaiting the chemists from Earth." We are those chemists. Dragonfly is a search for greater understanding, not just of Titan and the mysteries of our solar system, but of our own origins.

Thank you.