Finding Life Beyond Earth: Science Cafes

1. Choose a Topic

To help you choose a topic for your 'Finding Life' Café, we have assembled the main ideas of NOVA's Finding Life Beyond Earth Program.

The main messages might help you craft a café's discussion to be both relevant and interesting.

Main ideas In Life Beyond Earth, Hour 1

Technology is advancing the search for life, both in our solar system and beyond. Telescopes and robotic probes are shedding light on the formation of our solar system and on how its development produced conditions suitable for life. The data suggest that the forces of nature that produced us should also have created life beyond Earth. Life requires water, nutrients, and an energy source. The show details how water can be derived from rock. It explains why comets are a likely source of organic compounds, and it identifies places where geologic activity can supply the energy that life requires. 

Technology reveals the solar system in new ways

• New technology—telescopes, robotic probes—enables us to see things never seen before. The data they return reveal how planets might produce the conditions needed to create and sustain life. This information is expanding our ideas of where life can exist and is changing how we view the universe and our place within it.

Life requires water, nutrients, and energy

• Having a liquid medium is a key to life because it allows vital molecules to come together and react. On Earth, that liquid is water. Elsewhere in the solar system, it could be liquid methane. On Saturn’s moon Titan, the Cassini spacecraft discovered a surface covered with hundreds of lakes—of methane. Liquid seems to be the key to life, so the idea of cold-tolerant life living in that methane is a possibility.
• To get started, life needs a particular set of chemicals: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. These are the building blocks of life. Since they are commonly found throughout the universe, life itself may be common in the universe.

Asteroids formed the rocky planets

• Scientists believe that asteroids could hold the answers to how planets like Earth are made. In the early development of the solar system, asteroids collided, becoming bigger and hotter. As their gravity increased, they drew in still more asteroids until they eventually became giant spheres of molten rock—proto planets. This process continued until our solar system was left with four rocky planets.

The water that is chemically bound up in rocks can be released

• Giant impacts between proto-planets may have produced huge amounts of water. When scientists violently smash solid materials together at extremely high velocities, the materials release chemically bound water. As the solar system’s early hot planets cooled, this released water could eventually fall as rain to become rivers, seas and oceans, just as it has done on Earth.

Comets delivered organic compounds

• Life requires organic molecules. Yet, the same giant collisions that produced our oceans would also have destroyed any organic molecules, removing the possibility of life. Evidence suggests that the organic molecules on Earth come from comets.
• Comets are windows back in time. They formed four and half billion years ago, before the Earth even formed, and their chemistry was frozen in time. NASA sent the Stardust probe to rendezvous with a comet, collect a sample, and return it to Earth. Among several organic molecules it found was the amino acid glycine, a critical building block of life. Stardust showed that comets could be the mechanism for delivering the raw ingredients of life to Earth.
• For 100 million years in the early solar system, a time called the Heavy Bombardment, comets smashed into all the planets. This theory suggests that comets could have set the stage for life, not only on our planet, but throughout the whole solar system. If comets delivered the seeds of life everywhere, then in theory all we need to do is find worlds with the right conditions for those seeds to spark and grow.

Mars may harbor microorganisms

• Mars exhibits considerable evidence for a past with abundant surface water. And much of that water is still there today, as ice. Satellites have revealed that, if it melted, the martian ice would cover the whole planet in an ocean 30 feet deep. Essentially, Mars is an ice-cube covered with a layer of dirt.
• Scientists are studying the place on Earth that most resembles the frozen surface of Mars—the dry valleys of Antarctica Here, buried beneath a layer of dry dirt, is ice. It turns out that microorganisms are thriving in one of the driest places on Earth. If life can exist here than maybe it can exist on Mars.
• A tantalizing sign of life on Mars is the presence of methane gas in the martian atmosphere. Living microorganisms generate most of the methane in Earth’s atmosphere. Moreover, the release on Mars is seasonal, with the most methane emitted during the martian summer. Mars’s methane could be biological or could be the result of a geological process. Either way, it’s exciting. If Mars is geologically active, then ice could be melting into water and there could be an energy source for living organisms.

THE MAIN IDEAS IN NOVA’s FINDING LIFE BEYOND EARTH:  HOUR 2

As our telescopes see further and spacecrafts voyage to distant worlds, we are beginning to unlock the secrets of how solar systems like ours are born and evolve to trigger and sustain life. We find the raw ingredients of life wherever we look. If the same forces of nature that forged life on Earth are playing out elsewhere in the universe, then it’s simply a matter of time before we finally find life beyond Earth.

Conditions for life are common in the solar system

• Our understanding of our solar system is undergoing a revolution. We have discovered that the ingredients for life are everywhere. They were delivered in a violent rain of comets and asteroids to the surface of every planet and every moon. 

Moons may host habitable conditions
Moons were long considered dead, frozen, barren worlds, like our own moon. But an armada of robotic spacecraft has returned images and data that show that several moons have the ingredients necessary for life: liquid, nutrients, and an energy source. The giant gas planets and their moons act almost like mini solar systems in themselves. As the moons go around the planets, they generate heat, melt water, create oceans, and produce potential environments for life. So now the zone where life might exist has expanded out from Earth to the outer reaches of the solar system.

• Jupiter’s moon, Io. The Voyager spacecraft discovered active volcanism on Io, Jupiter’s closest moon. Io’s volcanoes changed the assumptions of where else life could exist, beyond a zone (called the habitable zone) around the Sun where energy is derived primarily from the Sun. Io presents an alternate process that can generate heat within a planet and lead to conditions that could support life. The extreme swings in the gravitational pull that Io experiences make Io the most volcanically active place in the solar system. As Io orbits Jupiter, its solid rock is flexed by over 330 feet. This continual flexing is like bending a piece of metal, and Io heats up. This is the ultimate source of Io’s volcanic energy.
• Jupiter’s moon, Europa. Jupiter’s second moon, Europa, was visited by the Galileo spacecraft. Images showed a network of mysterious cracks and formations on its icy surface. In addition, Galileo detected an ocean of salty liquid water beneath the ice. The same tidal forces that flex Io’s rocky interior have melted Europa’s ice to create an ocean of water. Galileo’s data suggests that the ocean could be 60 miles deep, meaning Europa has twice as much water as in all the oceans on Earth.
• Saturn’s moon, Enceladus. The Cassini spacecraft visited Enceladus, an ice-covered moon orbiting Saturn. Jetting out of Encedadus’s surface were giant fountains of fine crystals, showing Enceladus to be geologically active. Enceladus is being flexed as it orbits Saturn, creating internal heat. Scientists think the heat maintains liquid under the surface. Cassini flew through the plumes and detected evidence of liquid water and complex organic molecules. With liquid water, an energy source, and organic materials, Enceladus has everything needed for life as we understand it. Scientists believe that any life on Enceladus would be simple, microbial life built of the same compounds and powered by the same chemistry as on Earth.
• Saturn’s moon, Titan. Titan’s freezing lakes of liquid methane might be home to different kinds of organisms. Liquid is the basis of life. For life to exist on Titan, organic molecules have to dissolve in the liquid methane so they can mix and react. Scientists mixed liquid methane with organic materials and applied electric sparks to simulate the reactions in Titan’s atmosphere. They are looking to see how much organic material builds up over time and if those components might form the basis of a biochemistry that could ultimately lead to life.

Investigating whether life can exist in Earth’s extreme environments

• Beneath the ice in Antarctica. To test whether anything could live beneath miles of ice where there is no energy from the sun, scientists looked beneath the antarctic ice sheet, the most analogous place on Earth. There, they found volcanic vents on the seafloor spewing minerals. These vents provide the chemicals and energy source required for life and suggest a way that life could exist on Europa.
• In a toxic lake in California. Can life work under a different set of rules than those we’re familiar with? One of life’s primary building blocks is phosphorous. It is chemically similar to arsenic, which is toxic to many organisms. Scientists asked whether microbes could grow using arsenic instead of phosphorous. They discovered that even in the most extreme concentrations of arsenic, the microbes used the arsenic and continued to grow. The fact that a microbe could substitute arsenic for phosphorous suggests that life could be much more flexible than previously thought.

Questioning whether there are different ways that life can develop

• When we first started looking for life on other worlds we were looking for Earth-like conditions—water, an energy source, carbon, etc.  But now, we’re finding worlds that are different in ways that open up new possibilities for life.

Looking for life beyond the solar system

• Looking for the right kind of star. Our sun also plays an important role in making life possible in the solar system. Its energy powers life on Earth and produced the conditions that allowed life to first develop. A star’s energy output determines if a star can support life. Knowing that the sun is the kind of star that is “friendly” to life, scientists are looking for other suns in the universe that could also sustain life. Despite its unimaginable power as a nuclear furnace, its intense solar radiation, and its gigantic solar flares, our sun is considered a calm star. If it had been more active or produced more intense radiation, it would have been difficult for life to form on the Earth because the radiation would actually destroy cells. Our sun is such a common star it seems reasonable to suppose that life also could be common.
• Planets hunting. Using telescopes, scientists have discovered thousands of planets beyond the solar system. Most are gas giants, far too hot to sustain life. But space-based telescopes have discovered a few rocky planets. The goal now is to find a planet in a star’s habitable zone, the zone that’s not so close to the star that the water boils away or too far from the star that the water is locked up as ice. In the habitable zone, water can exist in liquid form.
• Looking for Earth-like planets. For life to exist around a star, it needs a rocky planet or moon. Studying young stars shows how solar systems like ours begin. In general, a vast cloud of gas and dust begins to collapse under its own gravity. This cloud starts to spin, flattening into a disk. As the disk spins faster, the friction and temperatures in the center become intense, ultimately giving birth to a star. In the outer disk, the seeds of planets begin to grow. Proto-planetary disks seem to be as common as the stars themselves, which suggests that the process by which planets form is common and that most stars have planetary systems.
• Spotting extraterrestrial life. Life on Earth produces gases like oxygen and methane. By analyzing a planet’s atmosphere, even planets that are trillions of miles away, scientists hope to find gasses associated with life. Finding telltale signs of life will be as close as we could probably ever get to finding life beyond the solar system. Telescopes are already powerful enough to read the atmospheres of giant gas worlds. Currently, Earth-like planets are too small to observe in such detail.