Thanks to Draper and its Hack The Moon initiative for supporting PBS Digital Studios. Humanity has always been fascinated by the stars, dreaming of ways to get closer to them. This curiosity has brought us to places like Mauna Kea in Hawaii, where we can gaze into the sky with unparalleled clarity, pondering what—or who—might be out there.
On Earth and in space, advanced telescopes have been peering into the cosmos for extended periods, revealing that many stars are orbited by planets. In fact, there seems to be at least one planet for every star. These discoveries have shown us a diverse range of planetary systems, including hot Jupiters, warm Neptunes, and even super-Earths made of lava and diamond. Such findings expand our understanding of where life might exist. The ultimate question driving astronomers is whether life is common in the universe or if we are unique.
Standing before the Keck Observatory, home to some of the most advanced telescopes on Earth, we are equipped to study distant exoplanets in detail. These instruments allow scientists to determine the size, orbit, and atmospheric composition of these planets, helping us understand where and how life might exist. This interdisciplinary effort, combining biology, physics, and chemistry, is known as astrobiology.
Decades before the first exoplanet was discovered, radio astronomer Frank Drake formulated an equation to estimate the number of technological civilizations in the galaxy. The Drake Equation considers factors such as the rate of star formation (N*), the fraction of stars with planets (fp), and the number of planets in habitable zones (np). Current estimates suggest there could be as many as 40 billion Earth-sized planets in habitable zones within the Milky Way.
To answer the question of life’s abundance, astronomers first need to find planets. This is achieved through methods like transiting, radial velocity, and direct imaging with adaptive optics. Once a planet is found, scientists determine if it lies within a habitable zone where liquid water could exist. The next challenge is analyzing the planet’s atmosphere, which requires precise measurements and advanced technology.
The next phase of exploration involves searching for biosignatures—chemical indicators of life, such as oxygen or methane, in exoplanet atmospheres. Future space telescopes and ground-based observatories will enhance our ability to detect these signs. However, the presence of certain chemicals does not definitively indicate life, prompting further investigation.
Despite the vastness of the cosmos, we have yet to encounter other intelligent life. This raises the possibility of a “Great Filter”—a barrier preventing civilizations from reaching advanced stages. This filter could be biological, technological, or environmental. For instance, the use of fossil fuels has significantly impacted Earth’s climate, posing a potential risk to our civilization’s future.
As we strive to reach the stars, we must consider whether we can sustain our technological growth without jeopardizing our future. The search for life beyond our solar system is one of humanity’s greatest quests, but so is the quest to understand life within it. Join us in exploring these profound questions and more in upcoming episodes.
Thank you to Draper and its Hack The Moon initiative for supporting PBS Digital Studios. Discover the untold stories of the engineers behind the Apollo missions at wehackthemoon.com. PBS’s Summer of Space offers a range of new science and history shows available on PBS.org and the PBS video app. Don’t miss out on this cosmic journey!
Engage in a simulation where you use virtual telescopes to discover exoplanets. Analyze data to determine the size, orbit, and potential habitability of these planets. This activity will help you understand the techniques used in real-world exoplanet exploration.
Participate in a workshop where you will apply the Drake Equation to estimate the number of extraterrestrial civilizations. Discuss the variables involved and explore how changes in these factors can affect the outcome. This will deepen your understanding of the probability of life beyond Earth.
Join a debate on the potential for life on different types of exoplanets, such as hot Jupiters or super-Earths. Use interdisciplinary knowledge from biology, physics, and chemistry to argue your position. This will enhance your critical thinking and understanding of astrobiology.
Work in teams to design a mission plan for detecting biosignatures on an exoplanet. Consider the technological and scientific challenges involved. Present your plan to the class and receive feedback. This activity will help you appreciate the complexities of searching for life.
Participate in a panel discussion about the Great Filter hypothesis. Explore the potential barriers to the development of advanced civilizations and their implications for humanity. This will encourage you to reflect on our place in the universe and the future of our civilization.
Thank you to Draper and its Hack The Moon initiative for supporting PBS Digital Studios. People have always dreamed of ways to be closer to the stars. That’s what brought us here to Mauna Kea in Hawaii. From this spot, we can stand nearer to the sky and see farther and clearer than almost anywhere else on Earth to wonder what and perhaps even who is out there.
On Earth and in space, advanced telescopes have stared for weeks, even months, into patches of sky, and they’ve seen that other stars are surrounded by planets of their own—at least one planet for every star. But what sort of planets are they? Astronomers have learned that our galaxy is home to many kinds of planet/sun systems: from hot Jupiters to warm Neptunes, even super-Earths of lava and diamond. These planets have expanded our view of where life may be possible. But what drives astronomers to study them is to find an answer to that ultimate question: Is life abundant or are we unique?
We’re standing in front of two of the most sensitive, precise, and advanced ground telescopes ever constructed – the Keck Observatory. These instruments, and others that are being designed, will allow scientists, for the first time, to characterize these far-off exoplanets, to paint a detailed picture of their sizes, their orbits, even the chemicals in their atmospheres, to understand where and how life might exist. Combined with knowledge from biology, physics, and chemistry, we’re learning a great deal about how life and planets coevolve. We call it the science of astrobiology.
Decades before we discovered the first exoplanet, one scientist asked what we’d need to know in order to determine whether another intelligent, technological civilization is, or was, or might one day be out there. That scientist was a young radio astronomer named Frank Drake. He gave us a way to estimate the number of technological civilizations that are out there.
N* tells us how often stars are born. It’s now known that around one star per year is born in the Milky Way, so we put a “1” there. f sub p is the fraction of stars with planets, which we now believe is 1, or at least one planet for every star. Solar systems are the rule, not the exception. n sub p is the estimate of how many planets orbit their stars at distances that allow for liquid water. We think as many as 1 in 5 planets sit in these so-called “habitable zones,” or a value for n sub p of 0.2. In all, there may be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way.
Now so far, our discoveries have filled nearly half of the equation and expanded what is possible, but the Drake Equation is still incomplete. We don’t yet know how many host life (f sub L), if any of that life is intelligent (f sub i), if it’s built a civilization (f sub c), or how long that civilization might last so that we might find it.
When astronomers are searching for that ultimate question of whether life is abundant or unique, what sorts of actual experiments are they doing here to try and get at that question? Well, the first thing you have to do is find the planets. That’s one of the things that Keck does wonderfully well and many other telescope facilities do as well. We find them, either by transiting when the planet goes in front of its star and dips the light down a bit, or through the radial velocity method, or through direct imaging with Keck adaptive optics. So you’ve got to find the planets; that’s step one.
Step two is determining if the planets are at a distance from their host star where water could be liquid on the surface. Then you want to know something about the atmosphere of that planet. And that’s when things get really challenging. To measure the atmosphere of that planet, you either have to have an extremely precise measurement of the star before and during these eclipses, or you have to measure the light that’s bouncing off of that planet and analyze the chemistry in its atmosphere. Both of those things require extremely precise instrumentation, very large telescopes, and just sheer determination to keep in the game.
This telescope is amazing. Each of its 36 hexagonal mirror segments is polished so smoothly that if they were the size of the Earth, their largest imperfections would only be three feet high. Twice every second, these segments’ positions are adjusted with an accuracy of 4 nanometers, or 1/25,000th of a human hair.
The next phase of exoplanet exploration will be the search for biosignatures—these are telltale chemical signs like oxygen or methane in those far-away atmospheres. These will be detectable from future space telescopes and giant ground-based observatories planned on Earth. Then comes the big question: How many of them actually show hints of life in their atmosphere? And are we being misled? Just because you see ozone, methane, carbon dioxide, and water vapor in the atmosphere, is that a definitive sign of life? Not necessarily.
We want to be able to determine that, and then we want to get at the essence of the question: if we look at a hundred planets, and they’re all in the habitable zone, and we see nothing, then that tells you something statistically. If you look at a hundred planets, and fifty or sixty of them have something, that tells you something really amazing about the universe. So we need to have the power and precision to explore as many planets as possible, but at the same time, just by exploring Earth, we’re finding out that life is thriving in places where we thought it was impossible.
When you combine those two things and consider solar systems that are radically unlike ours, the mind really starts to stretch and think that life could be abundant out there in the universe, and we should stop being so Earth-centric when we think about that.
But if the cosmos is so vast and full of so many places where life and intelligence may arise, then where are they? Perhaps there’s some “Great Filter” that prevents other life-bearing planets from reaching our level of civilization. Maybe the appearance of even simple life on habitable worlds is so unlikely that biology itself is the Great Filter. Or while life is common, maybe the emergence of even simple intelligence is rare.
But there is another option: maybe the Great Filter lies in technological civilizations themselves. In the millennia since human civilization started, our most important discovery is the one that’s enabled us to burn 100 million years of stored energy to power our technological growth: fossil fuels. As a rule, it takes energy to build and grow a technological civilization, and harnessing massive amounts of energy has some impact on a civilization’s environment.
Over there is the place where we measure the planet’s atmospheric carbon dioxide concentration. It’s just crossed 415 parts per million for the first time since humans came into existence. As evidenced by the measurements taken there, human activities are changing our planet’s climate, and those changes may have dire consequences for us. We’re not the first life form to change the climate on Earth. Billions of years ago, ancient microbes breathed the first oxygen into the atmosphere, making possible life as we know it today. But the result of that shift was the death of massive amounts of Earth’s early life, to whom oxygen was poisonous. It’s an environmental shift that completely changed the course of how life unfolded on this planet.
Are we now about to shift the course of life on Earth again? Is self-destruction in the process of harnessing energy an inherent risk in the development of all civilizations, human or alien? Whether or not we are ever able to find another technological civilization might depend on the question of whether civilizations can harness energy without destroying their own future.
So, as we build ourselves up to be closer to the stars, we should at least ask: will the same be true of us? Whether there’s life outside of our solar system is one of the biggest questions we’ve ever asked, but so is whether there’s life in the solar system. Check out the next episode with Dianna from Physics Girl.
Thank you to Draper and its Hack The Moon initiative for supporting PBS Digital Studios. You know the story of the astronauts who landed on the moon. Now you can log on to wehackthemoon.com to discover the story of the engineers who guided them there and back safely. Hack The Moon chronicles the engineers and technologies behind the Apollo missions. Brought to you by Draper, the site is full of images, videos, and stories about the people who made it happen.
PBS is bringing you the Universe with the Summer of Space, which includes six incredible new science and history shows airing on PBS and streaming on PBS.org and the PBS video app. Watch it all on pbs.org/summerofspace.
Cosmos – The universe seen as a well-ordered and harmonious system. – The study of the cosmos allows scientists to understand the fundamental laws that govern the universe.
Exoplanets – Planets that orbit a star outside the solar system. – The discovery of exoplanets has expanded our understanding of planetary systems beyond our own.
Astrobiology – The branch of biology concerned with the study of life on Earth and in space. – Astrobiology seeks to answer the profound question of whether life exists elsewhere in the universe.
Drake Equation – A formula used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. – The Drake Equation provides a framework for scientists to discuss the factors involved in the search for extraterrestrial intelligence.
Biosignatures – Indicators that provide scientific evidence of past or present life. – Detecting biosignatures in the atmosphere of an exoplanet could suggest the presence of life.
Telescopes – Instruments that aid in the observation of remote objects by collecting electromagnetic radiation. – Modern telescopes have enabled astronomers to observe distant galaxies and study their properties.
Habitable – Having the conditions necessary to support life. – Scientists are particularly interested in finding habitable exoplanets that might support life as we know it.
Atmosphere – The envelope of gases surrounding a planet or celestial body. – The composition of a planet’s atmosphere can provide clues about its potential to support life.
Exploration – The action of traveling through or investigating an unfamiliar area, especially in space. – Space exploration has led to numerous technological advancements and a deeper understanding of our universe.
Civilization – A complex society characterized by the development of cultural, technological, and governmental structures. – The search for extraterrestrial civilizations involves looking for signs of advanced technology or communication in space.
