Take a stroll through the desert at night. Cast your gaze skyward. The blanket of stars looks infinite, but we’re seeing only the edges of its margins. If you try to count the stars in the heavens, as the angel suggests to Abraham in Genesis, you’ll arrive at 9,096 – that would be the result in both hemispheres, under conditions of optimal visibility. Our universe is inconceivably large and our human eye is amazingly tiny. Only the angel, or the scientist, sees the full picture. Our galaxy, the Milky Way, contains at least 100 billion stars, and there are at least 100 billion galaxies. In other words, the skies are speckled with at least 10,000,000,000,000,000,000,000 – 10 sextillion – stars.
In light of all this celestial abundance, as it were, we should ask ourselves, as did physicist Enrico Fermi did in 1950, “Where is everybody?” We don’t yet know whether we are truly alone in the universe, and that’s clearly one of the most profound and highly charged scientific, philosophical and emotional questions that humanity faces, but there’s a good chance that many of us will find out the answer to that question in our lifetime. A historic confluence of scientific discoveries relating to not only space but also the depths of Earth, along with groundbreaking technologies and a paradigmatic revolution in the very definition of life – these have all conspired lately to transport the question-of-questions from the realm of science-fiction into the sphere of empirical science.
NASA’s last astrobiological experiment to be carried out on another planet took place in the summer of 1976: Two separate Viking probes, the first spacecrafts to land successfully on Mars, scooped up a handful of soil, heated it to a temperature of 500 degrees Celsius and sniffed the vapors in the hope of discovering the remains of roasted microorganisms. The results were not definitive. For NASA, however, there was one clear outcome: embarrassment. The chemistry on Mars took the space agency by surprise, and its scientists lacked the tools to determine whether the source of the singular chemistry lay in a different biology than that on earth. The experiment remained controversial, and NASA never replicated it.
It’s only on paper that science consists of trial and error. In reality, and certainly in missions that cost the American taxpayer billions of dollars, experiments are expected to produce results. The speed at which Mars rotates on its axis is a question for which an experiment could be constructed that would produce a definitive answer. The question of life, on the other hand, is so complex and abstract that astrobiology was for years considered an almost philosophical field – speculation that’s not quantifiable in mathematical terms.
Almost every space mission is fueled by a vague declaration of intent about the source and presence of possible extraterrestrial life (because almost every discovery that is made has implications for the search for such life). However, in the fierce competition among scientists to have their instruments and experiments integrated into the next big mission – whether a new Mars probe, a spacecraft destined for Jupiter or a space telescope – astrobiologists always lose out to the geologists, the physicists and the astronomers. They’re the underdogs, and there’s no placed for underdogs in hyper-expensive space research.
No longer. In October 2018, the National Academies of Sciences, Engineering and Medicine submitted a report to Congress, stating that “NASA should expand the search for life in the universe and make astrobiology an integral part of its missions.” The National Academies thereby validated astrobiology as a practical scientific discipline. In effect, the definition of this interdisciplinary field is changing before our eyes: No longer a search for environments that would allow for life as we know it, it now looks for dynamics of life and environments that change together. After all, primeval Earth, too, wasn’t very hospitable to life as we know it today. It’s life that altered the chemical compositions of the atmosphere and the land over the course of billions of years, adapting them to its needs.
Though this type of circular definition might sound spiritual, the fact is that astrobiologists have found signs of life in the most severe conditions here on Earth – in the looming darkness of the ocean depths, as well as in the extreme heat at the mouths of volcanoes. There’s no reason to assume, therefore, that life can’t flourish everywhere, be it beneath the ice of Saturn’s moon Enceladus, amid the outer reaches of Venus’ clouds or in the methane lakes of Saturn’s Titan.
“Since the early 1990s, astrobiology has been a practical, empirical, experimental science that has yielded abundant results,” says Dr. Reut Sorek Abramovich, an astrobiologist from Israel’s Dead Sea and Arava Science Center. “There’s no need to paint a picture that says that until today nothing has been done to find [extraterrestrial] life and that we’ve only now remembered to start searching for it. There has been a significant leap forward, but it rests on solid research conducted in recent decades here on Earth – in areas including the genesis of life, synthetic DNA and alternatives to DNA, extreme life environments and much more.”
In May 2018, in the wake of developments in our own backyard, on Earth, NASA published, for the first time since 1976, a public call for astrobiological experiments to be conducted on a different planet in our solar system, with the aim of identifying life there directly. The space agency set forth the theoretical foundation for this undertaking in an article titled “The Ladder of Life Detection,” published in June last year, in the journal Astrobiology. It elaborates on the ways to confirm or rule out the presence of metabolic activity in soil samples.
This time NASA’s scientists believe they will be able to design an experiment that will produce results, so it’s not improbable that by the end of the coming decade we will see a reprise of the Viking experiment, perhaps to Mars or to one of Jupiter’s or Saturn’s icy moons. But along with the confidence the agency is displaying about its ability to identify life in soil samples, it’s also adopting the opposite path: remote sensing. According to this approach – whose advocates include British scientist James Lovelock, a formulator of the Gaia hypothesis, which holds that living organisms are integral and inseparable parts of the chemistry of planet Earth – it’s not necessary to land on a planet in order to know whether it harbors life, because the biology transforms the chemistry of an entire planet. Accordingly, there’s no need to embark on interstellar voyages to discover life: It’s virtually enough to look at a planet to know whether it’s alive or dead.
In fact, at least one “living” world – namely, ours – has already been identified remotely. In 1990, while the Galileo probe was on the way to Jupiter, it executed an overflight of Earth. Astronomer and pioneering astrobiologist Carl Sagan took advantage of the opportunity to identify the chemical signature that life leaves in our atmosphere. Using only a spectrometric analysis of sunlight reflected back into space from Earth, Galileo discovered an atmosphere not in chemical equibrium – testimony to life constantly renewing the reserve of oxygen and methane in the air, as well as irregular and uneven absorption of light, attesting to plant photosynthesis.
“In its December 1990 fly-by of Earth,” Sagan and his co-authors wrote in a classic article published in the journal Nature in 1993, “the Galileo spacecraft found evidence of abundant gaseous oxygen, a widely distributed surface pigment with a sharp absorption edge in the red part of the visible spectrum, and atmospheric methane in extreme thermodynamic disequilibrium; together, these are strongly suggestive of life on Earth.” In 2017, incidentally, the spacecraft OSIRIS-Rex replicated that experiment on its way to the asteroid Bennu. It found a sharp rise in the levels of carbon dioxide and methane in the atmosphere, showing that intelligent life on the planet had multiplied and had severely polluted its world.
When Sagan found signs of life on Earth in 1990 by remote means, there was no definitive knowledge about the existence of other planets outside the solar system. Today, thanks mainly to the Kepler space telescope, we know of 3,500 worlds outside our solar system. Statistically, around every star we see in the night sky we should imagine that we see two, three or seven worlds, some of them gaseous giants like Jupiter, others rocky and Earth-like and situated at the right distance from their star to enable the existence of (liquid) water on the surface. This is the region known as the “habitable zone” or the “Goldilocks Zone,” after the line in “Goldilocks and the Three Bears” about porridge that is “not too cold and not too hot.”
So, how many habitable, earth-like exoplanets are we talking about? The numbers are – what else? – astronomical. Even if we take into account all the variables, the minimum estimates are of about 40 billion Earths in our galaxy alone, and six sextillion Earths in the universe. Because that number cannot be grasped by the human brain, it’s usually compared to the number of grains of sand on our planet. According to calculations by astrophysicist Jason Marshall, all the seashores in the world contain a total of “only” five sextillion grains of sand. If so, when the angel promised Abraham that he could multiply his seed like the stars in the sky and like the sand on the shores, Abraham should have opted for the former.
And here, at last, the scientific discoveries made on and about our planet converge with those relating to other solar systems. We know how to identify metabolic activity and now we also where to search. An additional report by the National Academies of Sciences, Engineering and Medicine, published last September, recommends that NASA build a space telescope capable of collecting photons of light reflected from Earth-like exoplanets in other solar systems – in other words, a telescope that would be able to replicate Sagan’s experiments in distant worlds.
But all these reports and recommendations are only a prologue to the great drama: the Decadal Survey on Astronomy and Astrophysics, aka Astro2020. Approximately every decade, the National Academies embark on this endeavor, which aims to “identify and prioritize leading-edge scientific questions and the ways to answer them,” according to its website, and suggests projects deserving of support by Congress and federal agencies including NASA. The last survey, published in 2010, recommended finding an answer to the question of the nature of dark energy and an explanation of how the galaxies in the universe came into being. The astrobiologists hope that the current survey, which should be coming to its conclusion soon, will focus on the whether there is extraterrestrial life. Their dream may yet come true.
“The Kepler space telescope discovered that about a quarter of the stars in our galaxy, the Milky Way, are accompanied by an Earth-like planet with a temperature that allows liquid water and life on its surface,” says Israeli-born Avi Loeb, who heads the astronomy department at Harvard University, and is in charge of the decadal survey, in his capacity as chairman of the National Academies’ Board on Physics and Astronomy.
“Accordingly,” Loeb adds, “the subject of the search for life – in the meantime, only simple life – is generating broad resonance and will appear as a central theme in the next decadal survey.”
If a new space telescope is to be built, it will likely be launched in the 2030s. Two plans have been proposed: HabEx (Habitable Exoplanet Observatory) and LUVOIR (Large UltraViolet/Optical/InfraRed). Whichever format is chosen, the telescope will be launched to the second Lagrange Point, a point in space that is about 1.5 million kilometers from Earth. From that point it will scan thousands of nearby (relatively speaking) exoplanets similar to Earth, located in the habitable zones in relation to their respective suns. Within light refracted from the atmospheres, the search will be for biosignatures – chemical indications of the existence of life. They needn’t be broadcast via radio waves for us to find them: If they metabolize and thereby disturb the “natural” chemical balance, resulting in a suspicious absorption of water molecules or emission of carbon dioxide, their atmosphere will be “signaling” us that their world is inhabited by life of some kind.
Because the light from planets is far weaker than the dazzling illumination of stars, the two telescopes would make use of a new instrument called a stellar coronagraph that blocks the sun’s light, enabling reception of the dim light of the worlds orbiting it. An additional technology, called a “starshade,” and developed by NASA, is used in conjunction with the space telescope and makes it possible to photograph planets located tens and hundreds of light-years away from us. Starshade is a separate spacecraft that would fly at a distance hundreds of thousands of kilometers from the telescope and open up into a flower-like form, blocking out dazzling starlight so that planets can be photographed through its “petals.”
HabEx and LUVOIR are not the only telescopes under discussion. The two astrobiological endeavors are competing with two missions in the realms of physics and astrophysics that are intended to investigate the origin of the universe, the evolution of galaxies and stars, and the content of the interstellar void. These are the Origins Space Telescope and the Lynx X-ray Observatory. The four groups developing these projects are vying for a place in the coming National Academies survey as a springboard to becoming NASA’s flagship project. The choice of an astrobiological undertaking will make scientific history: A fringe branch, which often elicits skepticism, will get its own space telescope.
The National Academies will rank the proposals in the coming months; the final report is scheduled to be sent to Congress after the 2020 presidential election. If President Donald Trump is reelected, a battle with Congress will be in the offing. Trump wants to cancel NASA’s flagship project in order to fund his own mission – landing astronauts on the moon in the next five years.
In any event, there is little or no likelihood of all four telescopes being built and deployed. NASA has informed the competing groups that they must confine themselves to a budget of $3 billion to $5 billion, but this is very unlikely since space missions tend to overrun their funding. For example, the multipurpose James Webb Space Telescope was supposed to cost between $1 billion and $3.5 billion and to be launched between 2007 and 2011. At the moment, its launch is scheduled for 2021 and its budget has skyrocketed to $9 billion. The problem with space telescopes is that it’s impossible to bring them back for a tune-up or repairs. And no one wants to discover in retrospect that they launched billions into space and produced nothing.
Even if we don’t take into account possible delays and budget problems, HabEx is expected to cost $5 billion and LUVOIR’s unprecedented price tag is $20 billion. If chosen, the latter would be the biggest telescope in history. Its mirror will have a circumference of 15 meters – 1.5 times the circumference of the mirror of the largest astronomical observatory. But for that $20 billion, humanity could find out, in the fourth decade of the 21st century, whether it is alone in the universe.
For her part, Dr. Sorek Abramovich isn’t enthusiastic about the idea of a space telescope. “Let’s say you’ve aimed the telescope at planet X and it looks dead – what does that tell you?” she says. “There could be infinite variations of life. On Earth, for example, life emerged four billion years ago, but we find fossils of multicellular life from only 600 million years ago...And even after the appearance of multicellular organisms, there were at least five mass extinctions, some of them going on over tens of millions of years, in contrast to periods of peak development.
“What prevents us from discovering life isn’t technology,” she continues, “but the fact that the average lifespan of human beings is appallingly short compared to life processes in the history of another planet. So, instead of frighteningly expensive telescopes, we need to work within the solar system and understand how we look for life here, with the aid of robots and humans. Yes, that’s expensive too, but we will get a very high ‘added value’: a deeper understanding of the history of life throughout the solar system and not only on our marvelous planet.”
Concurrently, in April 2018, Congress ordered NASA to allocate resources to search for intelligent life in space – that is, to propose ways to search for what is called technosignatures, in addition to biosignatures. Thus, we can expect to see broader use of existing and future telescopes, in space and on Earth, to hunt for civilizations.
“I think that technological life in the spirit of human society is also widespread in the galaxy,” Prof. Loeb observes. “We also need to search for other technological markers, such as artificial lights, industrial pollution and structures in space.”
One way or another, simple or intelligent, directly or indirectly, what has been perceived for many years as an eternal question might soon get an unequivocal empirical answer. If there is other life in the universe, or at least life in our small corner of it, some of us may be able to know it in our lifetime. Alternately, at least we will know once and for all that we are in fact alone – that this vast adventure known as space-time rests on our shoulders alone.