We have only one example of biology forming in the universe—life on Earth. But what if life can form in other ways? How do you look for alien life when you don’t know what alien life might look like?

These questions are preoccupying astrobiologists—scientists who look for life beyond Earth. Astrobiologists have attempted to come up with universal rules that govern the emergence of complex physical and biological systems both on Earth and beyond.

I’m an astronomer who has written extensively about astrobiology. Through my research, I’ve learned that the most abundant form of extraterrestrial life is likely to be microbial, since single cells can form more readily than large organisms. But just in case there’s advanced alien life out there, I’m on the international advisory council for the group designing messages to send to those civilizations.

Detecting Life Beyond Earth

Since the first discovery of an exoplanet in 1995, over 5,000 exoplanets, or planets orbiting other stars, have been found.

Many of these exoplanets are small and rocky, like Earth, and in the habitable zones of their stars. The habitable zone is the range of distances between the surface of a planet and the star it orbits that would allow the planet to have liquid water and thus support life as we on Earth know it.

The sample of exoplanets detected so far projects 300 million potential biological experiments in our galaxy—or 300 million places, including exoplanets and other bodies such as moons, with suitable conditions for biology to arise.

The uncertainty for researchers starts with the definition of life. It feels like defining life should be easy, since we know life when we see it, whether it’s a flying bird or a microbe moving in a drop of water. But scientists don’t agree on a definition, and some think a comprehensive definition might not be possible.

NASA defines life as a “self-sustaining chemical reaction capable of Darwinian evolution.” That means organisms with a complex chemical system that evolve by adapting to their environment. Darwinian evolution says that the survival of an organism depends on its fitness in its environment.

The evolution of life on Earth has progressed over billions of years from single-celled organisms to large animals and other species, including humans.

Exoplanets are remote and hundreds of millions of times fainter than their parent stars, so studying them is challenging. Astronomers can inspect the atmospheres and surfaces of Earth-like exoplanets using a method called spectroscopy to look for chemical signatures of life.

Spectroscopy might detect signatures of oxygen in a planet’s atmosphere, which microbes called blue-green algae created by photosynthesis on Earth several billion years ago, or chlorophyll signatures, which indicate plant life.

NASA’s definition of life leads to some important but unanswered questions. Is Darwinian evolution universal? What chemical reactions can lead to biology off Earth?

Evolution and Complexity

All life on Earth, from a fungal spore to a blue whale, evolved from a microbial last common ancestor about four billion years ago.

The same chemical processes are seen in all living organisms on Earth, and those processes might be universal. They also may be radically different elsewhere.

In October 2024, a diverse group of scientists gathered to think outside the box on evolution. They wanted to step back and explore what sorts of processes created order in the universe—biological or not—to figure out how to study the emergence of life totally unlike life on Earth.

Two researchers present argued that complex systems of chemicals or minerals, when in environments that allow some configurations to persist better than others, evolve to store larger amounts of information. As time goes by, the system will grow more diverse and complex, gaining the functions needed for survival, through a kind of natural selection.

They speculated that there might be a law to describe the evolution of a wide variety of physical systems. Biological evolution through natural selection would be just one example of this broader law.

In biology, information refers to the instructions stored in the sequence of nucleotides on a DNA molecule, which collectively make up an organism’s genome and dictate what the organism looks like and how it functions.

If you define complexity in terms of information theory, natural selection will cause a genome to grow more complex as it stores more information about its environment.

Complexity might be useful in measuring the boundary between life and non-life.

However, it’s wrong to conclude that animals are more complex than microbes. Biological information increases with genome size, but evolutionary information density drops. Evolutionary information density is the fraction of functional genes within the genome, or the fraction of the total genetic material that expresses fitness for the environment.

Organisms that people think of as primitive, such as bacteria, have genomes with high information density and so appear better designed than the genomes of plants or animals.

A universal theory of life is still elusive. Such a theory would include the concepts of complexity and information storage, but it would not be tied to DNA or the particular kinds of cells we find in terrestrial biology.

Implications for the Search for Extraterrestial Life

Researchers have explored alternatives to terrestrial biochemistry. All known living organisms, from bacteria to humans, contain water, and it is a solvent that is essential for life on Earth. A solvent is a liquid medium that facilitates chemical reactions from which life could emerge. But life could potentially emerge from other solvents, too.

Astrobiologists Willam Bains and Sara Seager have explored thousands of molecules that might be associated with life. Plausible solvents include sulfuric acid, ammonia, liquid carbon dioxide, and even liquid sulfur.

Alien life might not be based on carbon, which forms the backbone of all life’s essential molecules—at least here on Earth. It might not even need a planet to survive.

Advanced forms of life on alien planets could be so strange that they’re unrecognizable. As astrobiologists try to detect life off Earth, they’ll need to be creative.

One strategy is to measure mineral signatures on the rocky surfaces of exoplanets, since mineral diversity tracks terrestrial biological evolution. As life evolved on Earth, it used and created minerals for exoskeletons and habitats. The hundred minerals present when life first formed have grown to about 5,000 today.

For example, zircons are simple silicate crystals that date back to the time before life started. A zircon found in Australia is the oldest known piece of Earth’s crust. But other minerals, such as apatite, a complex calcium phosphate mineral, are created by biology. Apatite is a primary ingredient in bones, teeth, and fish scales.

Another strategy for finding life unlike that on Earth is to detect evidence of a civilization, such as artificial lights, or the industrial pollutant nitrogen dioxide in the atmosphere. These are examples of tracers of intelligent life called technosignatures.

It’s unclear how and when a first detection of life beyond Earth will happen. It might be within the solar system, or by sniffing exoplanet atmospheres, or by detecting artificial radio signals from a distant civilization.

The search is a twisting road, not a straightforward path. And that’s for life as we know it—for life as we don’t know it, all bets are off.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: NASA’s Goddard Space Flight Center/Francis Reddy

Stars like the sun are remarkably constant. They vary in brightness by only 0.1 percent over years and decades, thanks to the fusion of hydrogen into helium that powers them. This process will keep the sun shining steadily for about 5 billion more years, but when stars exhaust their nuclear fuel, their deaths can lead to pyrotechnics.

The sun will eventually die by growing large and then condensing into a type of star called a white dwarf. But stars over eight times more massive than the sun die violently in an explosion called a supernova.

Supernovae happen across the Milky Way only a few times a century, and these violent explosions are usually remote enough that people here on Earth don’t notice. For a dying star to have any effect on life on our planet, it would have to go supernova within 100 light years from Earth.

I’m an astronomer who studies cosmology and black holes.

In my writing about cosmic endings, I’ve described the threat posed by stellar cataclysms such as supernovae and related phenomena such as gamma-ray bursts. Most of these cataclysms are remote, but when they occur closer to home they can pose a threat to life on Earth.

The Death of a Massive Star

Very few stars are massive enough to die in a supernova. But when one does, it briefly rivals the brightness of billions of stars. At one supernova per 50 years, and with 100 billion galaxies in the universe, somewhere in the universe a supernova explodes every hundredth of a second.

The dying star emits high-energy radiation as gamma rays. Gamma rays are a form of electromagnetic radiation with wavelengths much shorter than light waves, meaning they’re invisible to the human eye. The dying star also releases a torrent of high-energy particles in the form of cosmic rays: subatomic particles moving at close to the speed of light.

Supernovae in the Milky Way are rare, but a few have been close enough to Earth that historical records discuss them. In 185 AD, a star appeared in a place where no star had previously been seen. It was probably a supernova.

Observers around the world saw a bright star suddenly appear in 1006 AD. Astronomers later matched it to a supernova 7,200 light years away. Then, in 1054 AD, Chinese astronomers recorded a star visible in the daytime sky that astronomers subsequently identified as a supernova 6,500 light years away.

Johannes Kepler observed the last supernova in the Milky Way in 1604, so in a statistical sense, the next one is overdue.

At 600 light years away, the red supergiant Betelgeuse in the constellation of Orion is the nearest massive star getting close to the end of its life. When it goes supernova, it will shine as bright as the full moon for those watching from Earth, without causing any damage to life on our planet.

Radiation Damage

If a star goes supernova close enough to Earth, the gamma-ray radiation could damage some of the planetary protection that allows life to thrive on Earth. There’s a time delay due to the finite speed of light. If a supernova goes off 100 light years away, it takes 100 years for us to see it.

Astronomers have found evidence of a supernova 300 light years away that exploded 2.5 million years ago. Radioactive atoms trapped in seafloor sediments are the telltale signs of this event. Radiation from gamma rays eroded the ozone layer, which protects life on Earth from the sun’s harmful radiation. This event would have cooled the climate, leading to the extinction of some ancient species.

Safety from a supernova comes with greater distance. Gamma rays and cosmic rays spread out in all directions once emitted from a supernova, so the fraction that reach the Earth decreases with greater distance. For example, imagine two identical supernovae, with one 10 times closer to Earth than the other. Earth would receive radiation that’s about a hundred times stronger from the closer event.

A supernova within 30 light years would be catastrophic, severely depleting the ozone layer, disrupting the marine food chain and likely causing mass extinction. Some astronomers guess that nearby supernovae triggered a series of mass extinctions 360 to 375 million years ago. Luckily, these events happen within 30 light years only every few hundred million years.

When Neutron Stars Collide

But supernovae aren’t the only events that emit gamma rays. Neutron star collisions cause high-energy phenomena ranging from gamma rays to gravitational waves.

Left behind after a supernova explosion, neutron stars are city-size balls of matter with the density of an atomic nucleus, so 300 trillion times denser than the sun. These collisions created many of the gold and precious metals on Earth. The intense pressure caused by two ultradense objects colliding forces neutrons into atomic nuclei, which creates heavier elements such as gold and platinum.

A neutron star collision generates an intense burst of gamma rays. These gamma rays are concentrated into a narrow jet of radiation that packs a big punch.

If the Earth were in the line of fire of a gamma-ray burst within 10,000 light years, or 10 percent of the diameter of the galaxy, the burst would severely damage the ozone layer. It would also damage the DNA inside organisms’ cells, at a level that would kill many simple life forms like bacteria.

That sounds ominous, but neutron stars do not typically form in pairs, so there is only one collision in the Milky Way about every 10,000 years. They are 100 times rarer than supernova explosions. Across the entire universe, there is a neutron star collision every few minutes.

Gamma-ray bursts may not hold an imminent threat to life on Earth, but over very long time scales, bursts will inevitably hit the Earth. The odds of a gamma-ray burst triggering a mass extinction are 50 percent in the past 500 million years and 90 percent in the 4 billion years since there has been life on Earth.

By that math, it’s quite likely that a gamma-ray burst caused one of the five mass extinctions in the past 500 million years. Astronomers have argued that a gamma-ray burst caused the first mass extinction 440 million years ago, when 60 percent of all marine creatures disappeared.

A Recent Reminder

The most extreme astrophysical events have a long reach. Astronomers were reminded of this in October 2022, when a pulse of radiation swept through the solar system and overloaded all of the gamma-ray telescopes in space.

It was the brightest gamma-ray burst to occur since human civilization began. The radiation caused a sudden disturbance to the Earth’s ionosphere, even though the source was an explosion nearly two billion light years away. Life on Earth was unaffected, but the fact that it altered the ionosphere is sobering—a similar burst in the Milky Way would be a million times brighter.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: NASA, ESA, Joel Kastner (RIT)

One planet is 30 percent larger than Earth and orbits its star in less than three days. The other is 70 percent larger than Earth and might host a deep ocean. These two exoplanets are super-Earths—more massive than Earth but smaller than ice giants like Uranus and Neptune.

I’m a professor of astronomy who studies galactic cores, distant galaxies, astrobiology, and exoplanets. I closely follow the search for planets that might host life.

Earth is still the only place in the universe scientists know to be home to life. It would seem logical to focus the search for life on Earth clones—planets with properties close to Earth’s. But research has shown that the best chance astronomers have of finding life on another planet is likely to be on a super-Earth similar to the ones found recently.

Common and Easy to Find

Most super-Earths orbit cool dwarf stars, which are lower in mass and live much longer than the sun. There are hundreds of cool dwarf stars for every star like the sun, and scientists have found super-Earths orbiting 40 percent of cool dwarfs they have looked at. Using that number, astronomers estimate that there are tens of billions of super-Earths in habitable zones where liquid water can exist in the Milky Way alone. Since all life on Earth uses water, water is thought to be critical for habitability.

Based on current projections, about a third of all exoplanets are super-Earths, making them the most common type of exoplanet in the Milky Way. The nearest is only six light-years away from Earth. You might even say that our solar system is unusual since it does not have a planet with a mass between that of Earth and Neptune.

Another reason super-Earths are ideal targets in the search for life is that they’re much easier to detect and study than Earth-sized planets. There are two methods astronomers use to detect exoplanets. One looks for the gravitational effect of a planet on its parent star and the other looks for brief dimming of a star’s light as the planet passes in front of it. Both of these detection methods are easier with a bigger planet.

Super-Earths Are Super Habitable

Over 300 years ago, German philosopher Gottfried Wilhelm Leibniz argued that Earth was the “best of all possible worlds.” Leibniz’s argument was meant to address the question of why evil exists, but modern astrobiologists have explored a similar question by asking what makes a planet hospitable to life. It turns out that Earth is not the best of all possible worlds.

Due to Earth’s tectonic activity and changes in the brightness of the sun, the climate has veered over time from ocean-boiling hot to planet-wide, deep-freeze cold. Earth has been uninhabitable for humans and other larger creatures for most of its 4.5-billion-year history. Simulations suggest the long-term habitability of Earth was not inevitable, but was a matter of chance. Humans are literally lucky to be alive.

Researchers have come up with a list of the attributes that make a planet very conducive to life. Larger planets are more likely to be geologically active, a feature that scientists think would promote biological evolution. So the most habitable planet would have roughly twice the mass of Earth and be between 20 to 30 percent larger by volume. It would also have oceans that are shallow enough for light to stimulate life all the way to the seafloor and an average temperature of 77 degrees Fahrenheit (25 degrees Celsius). It would have an atmosphere thicker than Earth’s that would act as an insulating blanket. Finally, such a planet would orbit a star older than the sun to give life longer to develop, and it would have a strong magnetic field that protects against cosmic radiation. Scientists think that these attributes combined will make a planet super habitable.

By definition, super-Earths have many of the attributes of a super habitable planet. To date, astronomers have discovered two dozen super-Earth exoplanets that are, if not the best of all possible worlds, theoretically more habitable than Earth.

Recently, there’s been an exciting addition to the inventory of habitable planets. Astronomers have started discovering exoplanets that have been ejected from their star systems, and there could be billions of them roaming the Milky Way. If a super-Earth is ejected from its star system and has a dense atmosphere and watery surface, it could sustain life for tens of billions of years, far longer than life on Earth could persist before the sun dies.

Detecting Life on Super-Earths

To detect life on distant exoplanets, astronomers will look for biosignatures, byproducts of biology that are detectable in a planet’s atmosphere.

NASA’s James Webb Space Telescope was designed before astronomers had discovered exoplanets, so the telescope is not optimized for exoplanet research. But it is able to do some of this science and is scheduled to target two potentially habitable super-Earths in its first year of operations. Another set of super-Earths with massive oceans discovered in the past few years, as well as the planets discovered this summer, are also compelling targets for James Webb.

But the best chances for finding signs of life in exoplanet atmospheres will come with the next generation of giant, ground-based telescopes: the 39-meter Extremely Large Telescope, the Thirty Meter Telescope, and the 24.5-meter Giant Magellan Telescope. These telescopes are all under construction and set to start collecting data by the end of the decade.

Astronomers know that the ingredients for life are out there, but habitable does not mean inhabited. Until researchers find evidence of life elsewhere, it’s possible that life on Earth was a unique accident. While there are many reasons why a habitable world would not have signs of life, if, over the coming years, astronomers look at these super habitable super-Earths and find nothing, humanity may be forced to conclude that the universe is a lonely place.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: NASA Ames/JPL-CalTech

We are two scientists who study exoplanets and astrobiology. Thanks in large part to next-generation telescopes like James Webb, researchers like us will soon be able to measure the chemical makeup of atmospheres of planets around other stars. The hope is that one or more of these planets will have a chemical signature of life.

Habitable Exoplanets

Life might exist in the solar system where there is liquid water—like the subsurface aquifers on Mars or in the oceans of Jupiter’s moon Europa. However, searching for life in these places is incredibly difficult, as they are hard to reach and detecting life would require sending a probe to return physical samples.

Many astronomers believe there’s a good chance that life exists on planets orbiting other stars, and it’s possible that’s where life will first be found.

Theoretical calculations suggest that there are around 300 million potentially habitable planets in the Milky Way galaxy alone and several habitable Earth-sized planets within only 30 light-years of Earth—essentially humanity’s galactic neighbors. So far, astronomers have discovered over 5,000 exoplanets, including hundreds of potentially habitable ones, using indirect methods that measure how a planet affects its nearby star. These measurements can give astronomers information on the mass and size of an exoplanet, but not much else.

Looking for Biosignatures

To detect life on a distant planet, astrobiologists will study starlight that has interacted with a planet’s surface or atmosphere. If the atmosphere or surface was transformed by life, the light may carry a clue, called a biosignature.

For the first half of its existence, Earth sported an atmosphere without oxygen, even though it hosted simple, single-celled life. Earth’s biosignature was very faint during this early era. That changed abruptly 2.4 billion years ago when a new family of algae evolved. The algae used a process of photosynthesis that produces free oxygen—oxygen that isn’t chemically bonded to any other element. From that time on, Earth’s oxygen-filled atmosphere has left a strong and easily detectable biosignature on light that passes through it.

When light bounces off the surface of a material or passes through a gas, certain wavelengths of the light are more likely to remain trapped in the gas or material’s surface than others. This selective trapping of wavelengths of light is why objects are different colors. Leaves are green because chlorophyll is particularly good at absorbing light in the red and blue wavelengths. As light hits a leaf, the red and blue wavelengths are absorbed, leaving mostly green light to bounce back into your eyes.

The pattern of missing light is determined by the specific composition of the material the light interacts with. Because of this, astronomers can learn something about the composition of an exoplanet’s atmosphere or surface by, in essence, measuring the specific color of light that comes from a planet.

This method can be used to recognize the presence of certain atmospheric gases that are associated with life—such as oxygen or methane—because these gases leave very specific signatures in light. It could also be used to detect peculiar colors on the surface of a planet. On Earth, for example, the chlorophyll and other pigments plants and algae use for photosynthesis capture specific wavelengths of light. These pigments produce characteristic colors that can be detected by using a sensitive infrared camera. If you were to see this color reflecting off the surface of a distant planet, it would potentially signify the presence of chlorophyll.

Telescopes in Space and on Earth

It takes an incredibly powerful telescope to detect these subtle changes to the light coming from a potentially habitable exoplanet. For now, the only telescope capable of such a feat is the new James Webb Space Telescope. As it began science operations in July 2022, James Webb took a reading of the spectrum of the gas giant exoplanet WASP-96b. The spectrum showed the presence of water and clouds, but a planet as large and hot as WASP-96b is unlikely to host life.

However, this early data shows that James Webb is capable of detecting faint chemical signatures in light coming from exoplanets. In the coming months, Webb is set to turn its mirrors toward TRAPPIST-1e, a potentially habitable Earth-sized planet a mere 39 light-years from Earth.

Webb can look for biosignatures by studying planets as they pass in front of their host stars and capturing starlight that filters through the planet’s atmosphere. But Webb was not designed to search for life, so the telescope is only able to scrutinize a few of the nearest potentially habitable worlds. It also can only detect changes to atmospheric levels of carbon dioxide, methane and water vapor. While certain combinations of these gasses may suggest life, Webb is not able to detect the presence of unbonded oxygen, which is the strongest signal for life.

Leading concepts for future, even more powerful, space telescopes include plans to block the bright light of a planet’s host star to reveal starlight reflected back from the planet. This idea is similar to using your hand to block sunlight to better see something in the distance. Future space telescopes could use small, internal masks or large, external, umbrella-like spacecraft to do this. Once the starlight is blocked, it becomes much easier to study light bouncing off a planet.

There are also three enormous, ground-based telescopes currently under construction that will be able to search for biosignatures: the Giant Magellen Telescope, the Thirty Meter Telescope, and the European Extremely Large Telescope. Each is far more powerful than existing telescopes on Earth, and despite the handicap of Earth’s atmosphere distorting starlight, these telescopes might be able to probe the atmospheres of the closest worlds for oxygen.

Is it Biology or Geology?

Even using the most powerful telescopes of the coming decades, astrobiologists will only be able to detect strong biosignatures produced by worlds that have been completely transformed by life.

Unfortunately, most gases released by terrestrial life can also be produced by nonbiological processes—cows and volcanoes both release methane. Photosynthesis produces oxygen, but sunlight does, too, when it splits water molecules into oxygen and hydrogen. There is a good chance astronomers will detect some false positives when looking for distant life. To help rule out false positives, astronomers will need to understand a planet of interest well enough to understand whether its geologic or atmospheric processes could mimic a biosignature.

The next generation of exoplanet studies has the potential to pass the bar of the extraordinary evidence needed to prove the existence of life. The first data released from the James Webb Space Telescope gives us a sense of the exciting progress that’s coming soon.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: NASA/JPL-Caltech/Wikimedia Commons

For over 70 years, astronomers have been scanning for radio or optical signals from other civilizations in the search for extraterrestrial intelligence, called SETI. Most scientists are confident that life exists on many of the 300 million potentially habitable worlds in the Milky Way galaxy. Astronomers also think there is a decent chance some life forms have developed intelligence and technology. But no signals from another civilization have ever been detected, a mystery that is called “The Great Silence.”

While SETI has long been a part of mainstream science, METI, or messaging extraterrestrial intelligence, has been less common.

I’m a professor of astronomy who has written extensively about the search for life in the universe. I also serve on the advisory council for a nonprofit research organization that’s designing messages to send to extraterrestrial civilizations.

In the coming months, two teams of astronomers are going to send messages into space in an attempt to communicate with any intelligent aliens who may be out there listening.

These efforts are like building a big bonfire in the woods and hoping someone finds you. But some people question whether it is wise to do this at all.

The History of METI

Early attempts to contact life off Earth were quixotic messages in a bottle.

In 1972, NASA launched the Pioneer 10 spacecraft toward Jupiter carrying a plaque with a line drawing of a man and a woman and symbols to show where the craft originated. In 1977, NASA followed this up with the famous Golden Record attached to the Voyager 1 spacecraft.

These spacecraft—as well as their twins, Pioneer 11 and Voyager 2—have now all traveled well past the orbits of the outer planets. But in the immensity of space, the odds that these or any other physical objects will be found are fantastically minuscule.

Electromagnetic radiation is a much more effective beacon.

Astronomers beamed the first radio message designed for alien ears from the Arecibo Observatory in Puerto Rico in 1974. The series of 1s and 0s was designed to convey simple information about humanity and biology and was sent toward the globular cluster M13. Since M13 is 25,000 light-years away, you shouldn’t hold your breath for a reply.

In addition to these purposeful attempts at sending a message to aliens, wayward signals from television and radio broadcasts have been leaking into space for nearly a century. This ever-expanding bubble of earthly babble has already reached many stars. But there is a big difference between a focused blast of radio waves from a giant telescope and diffuse leakage—the weak signal from a show like “I Love Lucy” fades below the hum of radiation left over from the Big Bang soon after it leaves the solar system.

Sending New Messages

Nearly half a century after the Arecibo message, two international teams of astronomers are planning new attempts at alien communication. One is using a giant new radio telescope, and the other is choosing a compelling new target.

One of these new messages will be sent from the world’s largest radio telescope, in China, sometime in 2023. The telescope, with a 1,640-foot (500-meter) diameter, will beam a series of radio pulses over a broad swath of sky. These on-off pulses are like the 1s and 0s of digital information.

The message is called “The Beacon in the Galaxy” and includes prime numbers and mathematical operators, the biochemistry of life, human forms, the Earth’s location and a time stamp. The team is sending the message toward a group of millions of stars near the center of the Milky Way galaxy, about 10,000 to 20,000 light-years from Earth. While this maximizes the pool of potential aliens, it means it will be tens of thousands of years before Earth may get a reply.

The other attempt is targeting only a single star, but with the potential for a much quicker reply. On Oct. 4, 2022, a team from the Goonhilly Satellite Earth Station in England will beam a message toward the star TRAPPIST-1. This star has seven planets, three of which are Earth-like worlds in the so-called “Goldilocks zone”—meaning they could be home to liquid water and potentially life, too. TRAPPIST-1 is just 39 light-years away, so it could take as few as 78 years for intelligent life to receive the message and Earth to get the reply.

Ethical Questions

The prospect of alien contact is ripe with ethical questions, and METI is no exception.

The first is: Who speaks for Earth? In the absence of any international consultation with the public, decisions about what message to send and where to send it are in the hands of a small group of interested scientists.

But there is also a much deeper question. If you are lost in the woods, getting found is obviously a good thing. When it comes to whether humanity should be broadcasting a message to aliens, the answer is much less clear-cut.

Before he died, iconic physicist Stephen Hawking was outspoken about the danger of contacting aliens with superior technology. He argued that they could be malign and if given Earth’s location, might destroy humanity. Others see no extra risk, since a truly advanced civilization would already know of our existence. And there is interest. Russian-Israeli billionaire Yuri Milner has offered $1 million for the best design of a new message and an effective way to transmit it.

To date, no international regulations govern METI, so the experiments will continue, despite concerns.

For now, intelligent aliens remain in the realm of science fiction. Books like The Three-Body Problem by Cixin Liu offer somber and thought-provoking perspectives on what the success of METI efforts might look like. It doesn’t end well for humanity in the books. If humans ever do make contact in real life, I hope the aliens come in peace.

This story was updated on 5/10/22 to clarify where the Pioneer and Voyager spacecraft are in relation to the Solar System.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: Graham Holtshausen / Unsplash

I’m an astronomer with a specialty in observational cosmology—I’ve been studying distant galaxies for 30 years. Some of the biggest unanswered questions about the universe relate to its early years just after the Big Bang. When did the first stars and galaxies form? Which came first, and why? I am incredibly excited that astronomers may soon uncover the story of how galaxies started because James Webb was built specifically to answer these very questions.

The ‘Dark Ages’ of the Universe

Excellent evidence shows that the universe started with an event called the Big Bang 13.8 billion years ago, which left it in an ultra-hot, ultra-dense state. The universe immediately began expanding after the Big Bang, cooling as it did so. One second after the Big Bang, the universe was a hundred trillion miles across with an average temperature of an incredible 18 billion degrees Fahrenheit (10 billion degrees Celsius). Around 400,000 years after the Big Bang, the universe was 10 million light-years across and the temperature had cooled to 5,500 degrees Fahrenheit (3,000 degrees Celsius). If anyone had been there to see it at this point, the universe would have been glowing dull red like a giant heat lamp.

Throughout this time, space was filled with a smooth soup of high energy particles, radiation, hydrogen, and helium. There was no structure. As the expanding universe became bigger and colder, the soup thinned out and everything faded to black. This was the start of what astronomers call the Dark Ages of the universe.

The soup of the Dark Ages was not perfectly uniform and due to gravity, tiny areas of gas began to clump together and become more dense. The smooth universe became lumpy and these small clumps of denser gas were seeds for the eventual formation of stars, galaxies, and everything else in the universe.

Although there was nothing to see, the Dark Ages were an important phase in the evolution of the universe.

Looking for the First light

The Dark Ages ended when gravity formed the first stars and galaxies that eventually began to emit the first light. Although astronomers don’t know when first light happened, the best guess is that it was several hundred million years after the Big Bang. Astronomers also don’t know whether stars or galaxies formed first.

Current theories based on how gravity forms structure in a universe dominated by dark matter suggest that small objects—like stars and star clusters—likely formed first and then later grew into dwarf galaxies and then larger galaxies like the Milky Way. These first stars in the universe were extreme objects compared to stars of today. They were a million times brighter but they lived very short lives. They burned hot and bright and when they died, they left behind black holes up to a hundred times the Sun’s mass, which might have acted as the seeds for galaxy formation.

Astronomers would love to study this fascinating and important era of the universe, but detecting first light is incredibly challenging. Compared today’s massive, bright galaxies, the first objects were very small and due to the constant expansion of the universe, they’re now tens of billions of light-years away from Earth. Also, the earliest stars were surrounded by gas left over from their formation and this gas acted like fog that absorbed most of the light. It took several hundred million years for radiation to blast away the fog. This early light is very faint by the time it gets to Earth.

But this is not the only challenge.

As the universe expands, it continuously stretches the wavelength of light traveling through it. This is called redshift because it shifts light of shorter wavelengths—like blue or white light—to longer wavelengths like red or infrared light. Though not a perfect analogy, it is similar to how when a car drives past you, the pitch of any sounds it is making drops noticeably.

By the time light emitted by an early star or galaxy 13 billion years ago reaches any telescope on Earth, it has been stretched by a factor of 10 by the expansion of the universe. It arrives as infrared light, meaning it has a wavelength longer than that of red light. To see first light, you have to be looking for infrared light.

Telescope as a Time Machine

Enter the James Webb Space Telescope.

Telescopes are like time machines. If an object is 10,000 light-years away, that means the light takes 10,000 years to reach Earth. So the further out in space astronomers look, the further back in time we are looking.

Engineers optimized James Webb for specifically detecting the faint infrared light of the earliest stars or galaxies. Compared to the Hubble Space Telescope, James Webb has a 15 times wider field of view on its camera, collects six times more light, and its sensors are tuned to be most sensitive to infrared light.

The strategy will be to stare deeply at one patch of sky for a long time, collecting as much light and information from the most distant and oldest galaxies as possible. With this data, it may be possible to answer when and how the Dark Ages ended, but there are many other important discoveries to be made. For example, unraveling this story may also help explain the nature of dark matter, the mysterious form of matter that makes up about 80 percent of the mass of the universe.

James Webb is the most technically difficult mission NASA has ever attempted. But I think the scientific questions it may help answer will be worth every ounce of effort. I and other astronomers are waiting excitedly for the data to start coming back sometime in 2022.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: Hubble Deep Field / NASA

For the first half-century of the space age, only governments launched satellites and people into Earth orbit. No longer. Hundreds of private space companies are building a new industry that already has US$300 billion in annual revenue.

I’m a professor of astronomy who has written a book and a number of articles about humans’ future in space. Today, all activity in space is tethered to Earth. But I predict that in around 30 years people will start living in space; and soon after, the first off-Earth baby will be born.

The Players in Space

Space started as a duopoly as the United States and the Soviet Union vied for supremacy in a geopolitical contest with loud military overtones. But while NASA achieved the moon landings in 1969, its budget has since shrunk by a factor of three. Russia is no longer an economic superpower, and its presence in space is a pale shadow of the program that launched the first satellite and the first person into orbit.

The new kid on the block is China. After a late start, the Chinese space program is surging, fueled by a budget that has recently grown faster than their economy. China is building a space station, the country has landed probes on the moon and Mars, and it is planning a moon base. On its current trajectory, China will soon be the dominant space power.

Governments will continue to launch rockets, but it would be safe to say that the future of private space flight arrived in 2016 when, for the first time, commercial launches outnumbered launches by all the world’s countries combined. But the most exciting progress is being made by private space companies that are marketing space for tourism and recreation. Elon Musk’s goal for SpaceX is to carry 100 people at a time to the moon, Mars, and beyond, although in public presentations he is coy about giving a timeline. Jeff Bezos’ company, Blue Origin, also aims to colonize the solar system. Such grandiose plans have skeptics, but remember that these are the two richest people in the world.

Living on the Moon or Mars

For a spacecraft, the trip to Mars is about 1,000 times farther than a trip to the moon, so the moon will be humanity’s first home away from home.

China is partnering with Russia to build a long-term facility at the moon’s South Pole sometime between 2036 and 2045. NASA plans to put “boots on the moon” in 2024 and establish a a permanent settlement called the Artemis Base Camp within another decade. As part of the Artemis mission, NASA is also planning to launch a lunar space station in 2024 called Gateway. NASA is teaming up with SpaceX for this and future lunar projects, and the lunar station will make it easier for SpaceX to resupply the future lunar colony.

After the moon comes Mars, and the collaboration between SpaceX and NASA is accelerating the timeline for getting there. NASA’s plans are purposeful, but the organization hasn’t given a timeline. Elon Musk, on the other hand, has loudly proclaimed that he intends to have a colony on Mars by 2050. Humanity’s attempt to colonize the moon will give us a good sense of the challenges we might face on Mars.

Sex and Babies in Space

For a civilization to be really free from Earth, the population needs to grow, and that means babies. Living on the moon or Mars will be arduous and stressful, so the first inhabitants will probably spend only a few years there at a time and are unlikely to start a family.

But once people do take up permanent residency off-Earth, there are still many unknowns. First, little research has been done on the biology of pregnancy and reproductive health in a space or low-gravity environment like the moon or Mars. It’s possible there will be unexpected hazards to the fetus or mother. Second, babies are fragile, and raising them is not easy. The infrastructure of these bases would have to be sophisticated to make some version of normal family life possible, a process that will take decades.

With these uncertainties in mind, it seems likely that the first off-Earth baby will be born much closer to home. A Dutch startup called SpaceLife Origin wants to send a heavily pregnant woman 250 miles up just long enough to give birth. They talk a good story, but the legal, medical and ethical obstacles are formidable. Another company, called Orbital Assembly Corporation, plans to open a luxury hotel in orbit in 2027 called the Voyager Station. Current plans show that it would hold 280 guests and 112 crew members, with its spinning-wheel design providing artificial gravity. But the breathless news reports omit any discussion of the difficulty and cost of such a project.

However, on April 12, 2021, NASA announced that it is considering allowing a reality TV show to send a civilian to the International Space Station and film them for 10 days. It’s plausible that this idea could be extended, with a wealthy couple booking a long-term stay for the entire process from conception to birth in orbit.

At the moment, there’s no evidence anyone has had sex in space. But with about 600 people having been in Earth orbit, including one NASA couple who kept their marriage a secret, one space historian was able to gather plenty of space age salacious moments.

My guess is that sometime around 2040, a unique individual will be born. They may carry the citizenship of their parents, or they may be born in a facility operated by a corporation and end up stateless. But I prefer to think of this future person as the first true citizen of the galaxy.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Image Credit: NASA/Dennis Davidson/WikimediaCommons