Dark matter. It’s secret. It’s dark because it doesn’t give off any light. We can’t see it, taste it, touch it, smell it, or even feel it. But, astronomers can measure this dark secret of the universe. How? By looking at galaxies and galaxy clusters. Dark matter exerts a gravitational influence on those regions, and that CAN be measured.
Just take a look at this image of Abell 611. It’s a galaxy cluster that lies about 3.2 billion light-years away from us. At first glance you think, “yeah, it’s a cluster of galaxies, so what?” For astronomers though, this cluster poses a challenge. They know from measuring it that there’s not enough mass in the galaxies and the cluster to keep the whole thing from flying apart. Therefore, gravity must be holding it together. But, where’s the “stuff” that has the gravitational influence? It’s not just the stuff we can see in the galaxies. It must also be dark matter.
The Cosmic Stuff that Confounds Understanding
The existence of galaxies and clusters that aren’t flying apart is a well-known challenge to astronomers, and not just in Abell 611. Astronomer Vera Rubin and her team tackled the mismatch between a galaxy’s rotation rate and its mass back in the mid-20th century. They observed galaxies that seem to have more mass than their rotation speeds would suggest. It wasn’t a new problem—astronomer Fritz Zwicky found Hubble’s observations of the Coma Cluster of galaxies puzzling back in the 1930s. Some galaxies in that cluster appear to be moving too fast and that should have blown the cluster apart. Zwicky puzzled over it and decided that some unknown thing he called “dunkle Materie” (dark matter) might explain the anomaly.
Today, astronomers still grapple with understanding this cosmic “stuff.” Not just because galaxy clusters aren’t flying apart. Or that galaxies aren’t either. It appears that the universe is not just stars and galaxies and nebulae and planets. About 85 percent of the mass in the Universe is dark matter. Compare that to the mass we can see—also known as normal matter or baryonic matter. That comprises only about 5 percent.
A computer simulation of the distribution of matter in the universe. Orange regions host galaxies; blue structures are gas and dark matter. Credit: TNG Collaboration
So, we know it’s there in most (but not all) galaxies. But what IS dark matter? A lot of theories abound, but they boil down to two possibilities. It could be a type of particle that exists all over the Universe but doesn’t interact with light. Or, it might consist of an extensive population of massive objects that can’t be detected with our current technology. So, they’re either WIMPs (weakly interacting massive particles) or MACHOs (massive astrophysical compact halo objects. Astronomers have looked all over for these things. So far, no credible detections exist, other than to note that whatever this stuff is, it’s keeping galaxies and clusters from disintegrating.
Dark Matter and Clusters
And, that brings us back to Abell 611. It’s actually a good test subject for the idea of dark matter. Astronomers know that galaxies and clusters are dominated by their dark matter components. In Abell 611, the cluster’s appearance provides evidence for astronomers to measure the amount of dark matter there. Gravitational lensing, for example, is the best visible evidence. The curves of light within the cluster are actually images of more distant galaxies whose light is being distorted by gravity as it passes through. The mass of the galaxies in the cluster isn’t enough to make those distortions. So, something else has to be doing it—and that would be dark matter in the cluster.
The galaxy cluster SMACS 0723 as seen by NIRCam on JWST. Gravitational lensing properties (from its mass and from the mass of dark matter) are helping astronomers identify 88 distant galaxies in this field of view for further study. Courtesy NASA, ESA, CSA, STScI
In fact, clusters across the Universe show this effect of dark matter haloes surrounding them. One of JWST’s first images shows the gravitational lensing caused by the halo around the cluster SMACS J0723.3-7327. It has thousands of galaxies surrounded by a dark matter halo. Each galaxy also has a component of dark matter. The result is the amazing display of lensed galaxies seen in the image. They all lie at extreme distances behind the SMACS cluster, and their light is smeared into arcs by the gravitational domination of the dark matter. The fact that this same scene plays out across many clusters throughout the Universe tells us that dark matter is real, even if astronomers haven’t yet figured out what it is.
Most of us don’t think about ozone as we go about our daily lives. Yet, this pale blue gas plays a huge role in keeping our planet habitable. There’s a layer of it in Earth’s stratosphere, and it absorbs most of the ultraviolet radiation streaming from the Sun. Without the ozone layer, the UV would cause severe damage to most life on Earth. What would happen if we had an ozone hole?
In 1985, scientists discovered an ozone hole—or more accurately, a thinning—in the ozone layer, particularly over Earth’s southern regions. This happens every September. The loss is largely due to chemically active forms of chlorine and bromine derived from human-produced compounds in the atmosphere. They attach to high-altitude polar clouds each southern winter. Once there, they begin ozone-destroying reactions as the Sun rises at the end of Antarctica’s winter. Those actions create the ozone hole. People who live in the region deal with higher rates of sunburn, skin cancer, and other conditions thanks to the increased UV streaming through the hole. And the damage isn’t limited to humans; plants and animals on the surface and in marine ecosystems are also affected.
Today, most ozone-destroying chemicals are banned from use or remain heavily regulated. This is thanks to strict measures enacted through the Montreal Protocol on Substances that Deplete the Ozone Layer. It’s an environmental agreement regulating the production and consumption of nearly a hundred human-created chemicals that can deplete the ozone layer. The regulation and bans resulted in the slow restoration of the ozone layer.
NASA and NOAA Study the Ozone Hole
The annual size of the Antarctic ozone hole is now around 23.2 million square kilometers. That’s slightly smaller than last year’s measurement and indicates the hole continues to shrink. Researchers at NASA and NOAA (the US National Oceanic and Atmospheric Administration) detect and measure the growth and breakup of the ozone hole. They use instruments aboard the Aura, Suomi NPP, and NOAA-20 satellites to monitor the growth and shrinkage of the hole. While it is generally shrinking over time, there are occasional short periods where the ozone hole is slightly larger than the average. Satellite measurements help scientists understand more details about how and why the hole grows and shrinks on a seasonal basis.
The depleted area of the ozone layer over the South Pole was slightly smaller than last year and generally continued the overall shrinking trend of recent years. Courtesy NASA, NOAA
“Over time, steady progress is being made, and the hole is getting smaller,” said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center. “We see some wavering as weather changes and other factors make the numbers wiggle slightly from day to day and week to week. But overall, we see it decreasing through the past two decades. The elimination of ozone-depleting substances through the Montreal Protocol is shrinking the hole.”
Homing in on Specific Ozone Changes
Studying the ozone hole is a long-term process. It allows for the best possible understanding of the interplay between the ozone layer, human activities, and other effects. It requires specific instruments to track the various moving pieces. For example, when the polar sun rises, scientists use a Dobson Spectrophotometer to record the total amount of ozone between Earth’s surface and the uppermost regions of the stratosphere. The Dobson is an optical instrument that helps scientists compute a number called the “column ozone value”.
To give an idea of what the numbers are, the total column average across the planet is about 300 Dobson Units. On Oct. 3, 2022, scientists recorded the lowest total-column ozone value of 101 Dobson Units over the South Pole. At that time, ozone was almost completely absent at altitudes between 14 and 21 kilometers (8 and 13 miles)—a pattern very similar to last year.
That’s good news for people living at those latitudes, and also for people living at high altitudes who are also at risk from extended UV exposure. Continued regulation of ozone-destroying compounds should play a big role in reversing the damage done to our upper atmosphere.
Want to know more about the ozone hole? Check out this NASA video.
Let’s talk about Phobos. We know it’s a moon of Mars and it orbits the planet once every 7.4 hours. It has a huge impact crater called Stickney. It measures about 9 km across. That’s pretty big, considering Phobos itself is 28 km across on its longest side. But, beyond that, Phobos presents something of a mystery.
This oddly dark little world fascinates planetary scientists because of its amazingly weird cratered and striped surface. They also want to know if it’s a solid body or a floating rubble pile. If so, how did it get that way? And, more importantly, they want to know how it got to be Mars’s largest satellite. All these questions indicate that, for now, Phobos remains something of a mystery waiting for a solution.
Exploring Phobos Close-up
Recently, the European Space Agency’s Mars Express orbiter flew past Phobos as part of its regular mission. The idea was to get “up close and personal” with this moon and bombard it with low-frequency radio waves from the onboard MARSIS instrument. There was only one hitch—a typical flyby of Phobos by the spacecraft would put it too close to get useful MARSIS data. That’s because the instrument always did its best work from a distance. The original software allowed it to study the Martian surface (and beneath it) from about 250 kilometers away.
An artist’s illustration of the Mars Express Orbiter above Mars. Its MARSIS instrument has been updated so it can study the moon Phobos. Image Credit: Spacecraft: ESA/ATG Medialab; Mars: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO
The radio waves MARSIS sends mostly reflect from the surface of an object and provide valuable information about conditions and structures there. But, some signals actually penetrate the crust and reflect back from deeper layers. The reflections helped scientists map the substructures on Mars and figure out if there are different layers of ice, rock, water, or soil. The instrument also played a role in finding signs of liquid water on the Red Planet.
So, how can MARSIS help figure out the big questions about Phobos and its origin? At the moment, scientists have two hypotheses about its past. “Whether Mars’s two small moons are captured asteroids or made of material ripped from Mars during a collision is an open question, said ESA Mars Express scientist Colin Wilson. “Their appearance suggests they were asteroids, but the way they orbit Mars arguably suggests otherwise.”
MARSIS Delivers an Early Look
The best way to find out its origin is to look inside Phobos. Typical optical images can only tell scientists so much. But, instruments that can probe inside Phobos can reveal a lot. That’s where MARSIS comes in. Thanks to a major software upgrade, MARSIS made observations during the recent close approach. It can now “see” beneath the surface of this little moon as it flies by to look for structural clues.
“During this flyby, we used MARSIS to study Phobos from as close as 83 km,” said Andrea Cicchetti from the MARSIS team at the Italian National Institute for Astrophysics. “Getting closer allows us to study its structure in more detail and identify important features we would never have been able to see from further away. In the future, we are confident we could use MARSIS from closer than 40 km. The orbit of Mars Express has been fine-tuned to get us as close to Phobos as possible during a handful of flybys between 2023 and 2025, which will give us great opportunities to try.”
MARSIS data from Phobos flyby. The top-right image shows the ‘radargram’ acquired by MARSIS during the flyby of Phobos on 23 September 2022. A radargram reveals the ‘echoes’ created when the radio signal emitted by MARSIS bounces off something and returns to the instrument. The brighter the signal, the more powerful the echo. The continuous bright line shows the echo from the moon’s surface. The lower reflections are either ‘clutter’ caused by features on the moon’s surface, or, more interestingly, signs of possible structural features below the surface (e). Section A—C was recorded using an older configuration of the MARSIS software. The new configuration was prepared during the ‘technical gap’ and successfully used for the very first time from D—F. The left and bottom-right images show the path of the observation across the surface of Phobos. Credit: INAF – Istituto Nazionale di Astrofisica
The Data Indicate Something Beneath the Phobos Landscape
MARSIS output a radargram based on data captured on September 23, 2022. Essentially, the radargram depicts “echoes” created when the signal from MARSIS’s 40-meter-long antenna bounced back off of something beneath the surface. That could indicate a layered structure, which might indicate that Phobos is a captured asteroid. It could also mean that there’s a variety of objects inside Phobos that could make it a floating rubble pile. Of course, more flybys will capture more data, which should give more details about what’s lurking beneath the crust of Phobos.
The close-up studies will help scientists program the upcoming Martian Moons eXploration (MMX) mission that will land on Phobos no earlier than 2024. It will gather samples and return them to Earth in 2029. Data from those samples should help settle Phobos’s origin question once and for all.
We want to send humans to Mars eventually, and while this will be both a historic and exciting journey, it could also be tragic and terrible, and we must also address the potential pitfalls and risks of such an adventure. The intent behind this is to allow fans of space exploration to consider the full picture of such an endeavor. The good, the bad, and the ugly.
Real-life human space exploration has done a good job taking cues from science fiction, and as we prepare to send humans to Mars in the coming years, we should examine one science fiction franchise that captivated the hearts of millions. That franchise is The Martian, with both the book and film being absolute triumphs, for they depicted the full might of the human spirit as the protagonist, Dr. Mark Watney, endured countless roadblocks and setbacks as he overcame planet-sized adversity just to make it home. But as heartwarming as The Martian was, this still begs the question: Would Mark have survived in real life? The answer is….
Maybe.
Let’s first examine why Mark might not have survived, and we outline two reasons: Mechanical failures and radiation sickness. One crucial juncture in his journey was when his habitat airlock literally blew out, which destroyed his crops and depressurized the habitat. While the reason behind this was not mentioned in the film, the book describes the reason for the blowout as being from overuse. Mark said himself that his mission was designed for only 30 days but for redundancy they had ~60 days of food. NASA excels at redundancy. However, one must consider that all mechanical components have lifetimes, and at some point, they just literally fall apart or stop working entirely. Now, if his airlock gave out due to overuse, then could his other mechanical components in the habitat have done the same at some point? Most notably, the oxygenator, water reclaimer, and atmospheric regulator, which were all responsible for literally keeping him alive. If one fails and he can’t fix it, he’s dead. Also, one tiny hole in that plastic sheet he used to seal the airlock would have killed him instantly, as well.
The next reason is radiation sickness, as Mark was in a habitat on the surface for 18 months on a planet with no magnetic field or ozone layer to protect him from the cosmic rays coming down every day. It’s never mentioned whether his habitat was sufficient to offer adequate shielding from this radiation, but assuming it’s not, his health might have started to deteriorate after a while, which might have been exacerbated by his weight loss over the course of his journey. We think his mechanical components might have failed before this happened, but we digress.
Now, let’s examine why Mark might have survived, and we need only one reason, which we’ve mentioned already: redundancy. NASA is built on redundancy. They have backup plans for their backup plans, and on and on. An excellent example of this is the Apollo 13 mission, which saw three astronauts stranded in space after their oxygen tank exploded on the way to the Moon, and in the end, they swung around the Moon once and came home. While the film depicts absolute chaos in mission control and astronauts yelling at each other in space, this quite literally never happened, which can be found in the archived audio recordings. Everyone remained calm, cool, and collected because they had things under control thanks to redundancy. They knew what do to and how to do it. Before we send humans to Mars, it’s highly likely NASA will have plans in place for the worst-case scenarios, to include the probability of someone being stranded on the Red Planet.
Before we send humans to Mars, we must consider all probabilities. The good, the bad, and the ugly. We must remember that while going to Mars will be both historic and exciting, it could also be tragic and terrible. Would Mark have survived on Mars? Maybe. But as we continue to plant our flag a little farther in the cosmos, let’s take our cue from this great franchise to mitigate the potential risks and pitfalls of sending humans to Mars.
We recently examined how and why the planet Mars could answer the longstanding question: Are we alone? There is evidence to suggest that it was once a much warmer and wetter world thanks to countless spacecraft, landers, and rovers having explored—and currently exploring—its atmosphere, surface, and interior. Here, we will examine another one of Saturn’s 83 moons, an icy world that spews geysers of water ice from giant fissures near its south pole, which is strong evidence for an interior ocean, and possibly life. Here, we will examine Enceladus.
In terms of space exploration, Enceladus was briefly visited by NASA’s Voyager 1 and Voyager 2 in 1980 and 1981, respectively, and wasn’t visited again until NASA’s Cassini spacecraft explored the Saturn system, ultimately performing multiple flybys of this icy moon starting in 2005. It was these flybys that revealed Enceladus’ unique geology and composition.
“Enceladus has many of the ingredients we think are necessary for life: a liquid water ocean beneath an icy shell; an energy source (tidal heating); and nutrients (we’ve detected carbon compounds, which could be used as food),” said Dr. Francis Nimmo, who is a Professor in the Department of Earth & Planetary Sciences at the University of California, Santa Cruz. “In this respect it is not so different from other moons with subsurface oceans, like Europa. What makes Enceladus unique is that it’s giving us free samples of its ocean: there are geysers which jet water vapor and ice crystals into space, where we can scoop them up with a passing spacecraft and analyze them. So, Enceladus is a very good place to go and look for potential life, because we can *directly* sample material from the ocean.”
A two-image mosaic of geysers on the south pole of Enceladus imaged by NASA’s Cassini spacecraft and published on February 23, 2010. (Credit: NASA/JPL/Space Science Institute)
NASA’s Cassini spacecraft used its mass spectrometer to discover organic materials, water vapor, carbon dioxide, carbon monoxide, and a mixture of volatile gases within these geysers, which could indicate the presence of life. Not only do the active geysers indicate the presence of an internal ocean, but it’s also indicative of a source of energy within Enceladus.
“Enceladus has captivated the astrobiology community because it is the first icy ocean world for which we have strong evidence supporting its habitability,” said Dr. Christopher Glein, who is a Lead Scientist and geochemist at the Southwest Research Institute in Texas. “Data from the Cassini mission show that Enceladus has the three ingredients that are required for life as we know it. Those are liquid water, essential elements (including organic molecules), and a source of energy that can be harnessed by life. Recently, we found that the geochemistry of Enceladus’s ocean makes phosphate minerals unusually soluble there. This strongly suggests that phosphorus availability will not impede the prospects for life but should instead serve as an opportunity.”
With the Cassini mission ending in 2017, there are currently no active missions exploring the Saturn system, let alone Enceladus. However, there are several future missions currently under study which could help us further understand Enceladus and whether it can support life. This includes NASA’s Enceladus Orbilander, whose science goals include determining if Enceladus has life, how it has life, and also to locate a suitable landing site for a potential surface mission.
“Orbilander is designed to answer the question of whether there is life in the Enceladus ocean as unambiguously as possible,” said Dr. Nimmo. “Because we don’t know what form life would take, Orbilander uses several different techniques to look for the presence of life-like attributes. And because most of the material that comes out of the geysers ends up back on the surface, Orbilander will look in the “snow” on the surface for signs of life, as well as in material that goes into orbit around Enceladus. After Orbilander, we should have a very good idea of whether or not Enceladus is inhabited.”
While we wait for another spacecraft to re-visit Enceladus, scientists continue to pour over data from the Cassini mission to try and squeeze every last bit of science about Saturn’s icy moon. We know it has an ocean, which indicates the possibility for life, but what kinds of life could be thriving in its oceanic depths? How has it evolved, and is it similar to life on the Earth?
“Enceladus is perhaps the most puzzling of ocean worlds. It’s so small that it should not have an ocean, yet it does. After over a decade of study, we now have a better understanding of how powerful tidal forces keep the interior warm and make Enceladus geologically alive. Could those same forces also sustain biological activity?”
And with this, we wonder if Enceladus will finally answer, “Are we alone?”
As always, keep doing science & keep looking up!
Featured Image: Saturn’s moon, Enceladus, taken by NASA’s Cassini spacecraft on October 9, 2008, after it skimmed within 25 kilometers (15.6 miles) of the surface. (Credit: NASA/JPL/Space Science Institute)
In a recent study accepted to The Astrophysical Journal Letters, a team of researchers at the University of Nevada, Las Vegas (UNLV) investigated the potential for life on exoplanets orbiting M-dwarf stars, also known as red dwarfs, which are both smaller and cooler than our own Sun and is currently open for debate for their potential for life on their orbiting planetary bodies. The study examines how a lack of an asteroid belt might indicate a less likelihood for life on terrestrial worlds.
For the study, the researchers observed several M-dwarf systems with exoplanets within the habitable zone (HZ) and noted a lack of giant planets outside what they refer to as the “snow line radius”, which is the distance from a star where water ice permanently forms. In our own solar system, the giant planets beyond the asteroid belt also orbit beyond our own snow line radius. The researchers note that it is because of these giant planets that the asteroid belt exists, thus resulting in some of those asteroids being pushed to the inner solar system, and possibly bringing life with it. The findings concluded that, “None of the currently observed planets in the habitable zone around M-dwarfs have a giant planet outside of the snow line radius and therefore are unlikely to have a stable asteroid belt.” Given these findings, should we, therefore, increase or decrease our search for life in M-dwarf systems?
“I think M-dwarfs are still a great place to look for life since these systems can offer the most detailed observations of Earth-sized planets,” said Dr. Anna Childs, who is a Postdoctoral Scholar at the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern University, lead author of the study, and conducted the research while a PhD student at UNLV. “Because M-dwarf stars are so small and the habitable zone is closer to the star than around larger stars, it allows us to detect smaller planets and to also better characterize the atmospheres of planets that are potentially habitable. This is what the James Webb Space Telescope will be doing with some planetary systems around M-dwarfs such as TRAPPIST-1. Having more detailed information on the atmospheres of Earth-sized planets will provide us with a lot more information about the planet’s climate, composition, and formation process. There are still a lot of uncertainties when it comes to these important details about exoplanets. More detailed observations of smaller planets around M-dwarfs will place better constraints on these parameters which will help us characterize these planets in a more complete way.”
As stated, M-dwarf stars are both smaller and cooler than our own Sun, and range in size from 0.08 to 0.6 solar masses while exhibiting luminosities from 0.0001 to 0.1 times our Sun. This means the HZ is also much farther in towards the star, which could result in some interesting star-planetary interactions. So, what can M-dwarf stars teach us about planetary formation and evolution?
“The M-dwarf systems that have been discovered are fascinating because they are so different from the solar system,” said Dr. Childs. “We are finding more super-Earths and less giant planets around low mass stars than we are around larger stars like our Sun. For a long time, planet formation theory was dominated by theories that did a good job at explaining the solar system. But these M-dwarf systems suggest that either we need a more generalized planet formation theory that is able to explain systems that form around both low mass and high mass stars or, that planet formation does take different formation pathways around low mass and higher mass stars. New theories for planet formation around low mass stars are still being put forward and new detailed observations of these planets offer an exciting opportunity to test these new theories.”
Our Sun is classified as a G-type star and including M-dwarfs there are seven types of stars in our universe: O, B, A, F, G, K, and M that range from largest to smallest in both size and luminosity, but range from smallest to largest in terms of lifetimes. While our Sun’s lifetime is on the order of approximately 10 billion years, M-type stars like the one in this study can live up to approximately 200 billion years, which makes them intriguing for the study of life beyond Earth. So, which star-system should we most aggressively search for life beyond Earth?
“Right now, we know of only one place in the universe that has life and that’s around our Sun,” said Dr. Childs. “While there are a lot of practical reasons for looking for life around M-dwarfs, there might come a time when we’ve exhausted our methods and we’ll need to change our tactics and our targets. If we are unsuccessful at finding life around M-dwarfs the next logical place to look will be around Sun-like stars–specifically in systems that have planetary architectures similar to the solar system.”
For now, the search for life beyond Earth continues at a fever pitch. With new tools just the James Webb Space Telescope, and more ground-based telescopes coming online in the coming years, it could be only a matter of time until we find even the smallest traces of life beyond Earth. Unless we’ve already found, and just don’t know it.
“It’s possible that we’ve observed planets that do host life, but we just don’t yet have the technology capable of observing any subtle traces of it,” said Dr. Childs. “Life elsewhere could also be so drastically different from our current understanding of it that we fail to recognize it when we do observe it. I think it’s an important philosophical and scientific question: Would we recognize life on another world if we observed it? Continuously asking this question and attempting to answer it in a fundamental way will increase our chances of finding life elsewhere.”
As always, keep doing science & keep looking up!
Featured Image: Artist’s rendition of a very active red dwarf star. (Credit: NASA, ESA and D. Player (STScI))
The hits just keep on streaming back to Earth from James Webb Space Telescope (JWST). This time, arriving to help celebrate Hallowe’en, data from the MIRI mid-infrared instrument onboard JWST shows another view of the Pillars of Creation. Thousands of stars are embedded in those pillars, but many are “invisible” to MIRI.
In the latest image, the Pillars have a steely gray look about them. They almost look like cosmic gravestones instead of stellar birthplaces. Why is this? Mid-infrared light is an important part of the spectrum for astronomers interested in studying clouds of dust. It reveals gas and dust in extreme detail. The densest areas of dust in the pillars show up as the darkest shades of grey. The red V-shaped region toward the top is where the dust clouds are thinner and cooler.
At these wavelengths, MIRI is only able to “see” the young stars still embedded in their gas and dust cocoons. They glow a mysterious red—almost like the eyes of jack-o-lanterns—at the tips of formations in the pillars. The blue-looking stars are older ones that have burst free and eaten their birth clouds away.
The Pillars of Creation in Retrospect
This star-birth region has a long history of observations. It’s certainly visible to astronomers using backyard-type telescopes. However, it takes Hubble Space Telescope and now JWST to dig into the rich detail of this massive cloud. HST first looked at it in 1995, using the Wide Field and Planetary Camera 2. It returned 32 images, which were combined into a mosaic. The pillars are part of the Eagle Nebula. It’s a diffuse emission nebula that covers a region of space about 70 x 55 light-years across. It lies about 6,500 light-years away from us. The pillars are a part of the nebula, and some of its tiniest stellar birthplaces are larger than our solar system.
Eagle Nebula Pillars of Creation as seen by Hubble Space Telescope in 2005. (Credit NASA, ESA, STScI, J. Hester and P. Scowen (ASU)
When the first HST image appeared, astronomers could see the places where stars were born and are eating away at their gas clouds but couldn’t see INTO the clouds. Those hungry stellar babies in their cocoons were dubbed “evaporating gaseous globules”, or EGGs. They’re in other stellar nurseries, giving astronomers a good idea of how star birth progresses in thick clouds of gas and dust.
The Pillars of Creation have since been imaged by the Chandra X-ray Observatory (which found no x-ray sources associated with the newborn stars). Spitzer Space Telescope also studied this region of space. It found evidence of hot gases that suggested a supernova exploded in the area. If it did, there’s little evidence of the shock wave hurting the stellar newborns or evaporating the rest of the cloud away.
JWST’s Looks at the Pillars
The latest steely gray view of the Pillars of Creation set against the glowing red and gray backdrop isn’t JWST’s first rodeo with this region of space. Earlier in October, the science teams released a NIRCam (Near Infrared Camera) image of it. That view revealed many of the protostars forming inside those cosmic stalagtites in space. Thanks to NIRCam, we can peer right through the gas and dust, lifting the veil on star birth.
A compare and contrast of a 2014 HST view of the Pillars of Creation and the October 19, 2022, JWST image. Both views show us what is happening locally. Although Hubble highlights many more thick layers of dust and Webb shows more of the stars, neither shows us the deeper universe. Dust blocks the view in Hubble’s image, but the interstellar medium plays a major role in Webb’s. It acts like thick smoke or fog, preventing us from peering into the deeper universe, where countless galaxies exist. Courtesy of NASA, ESA, CSA, STScI, Hubble Heritage Project (STScI, AURA) Image processing: Joseph DePasquale (STScI), Anton M. Koekemoer (STScI), Alyssa Pagan (STScI)
The protostars as seen by NIRCam are the ones with multiple diffraction spikes. They’re still accreting mass, and when they get enough, they’ll collapse under their own gravity and slowly heat up. When they’re hot and massive enough, fusion will ignite in their cores. That’s when they become stars. The young stars in these pillars are probably only a few hundred thousand years old and won’t be finished forming for millions of years.
The stellar birth process often creates jets that shoot out from the newborn stars. Those jets eat away at the remaining birth cloud materials. They sculpt the clouds, which is why the pillars look wavy and deformed.
Understanding Star Formation from JWST Images
Both of these JWST images of the Pillars of Creation give astronomers a more detailed look at star formation. While scientists have a pretty good overall view of how stars form, the intricate details are what they need. All that data about star birth will help create better models of such an important process.
Compare and contrast the NIRCam view (left) with the MIRI view (right) from JWST to understand how each instrument sees the Pillars of creation. NASA, ESA, CSA, STScI; J. DePasquale (STScI), A. Pagan (STScI), A. Koekemoer (STScI)
By looking at populations of newborns like the ones in the Pillars, and mapping the huge clouds of gas and dust in this region, they’ll add to the store of knowledge about star birth. Images such as these also give a good look at what our own region of space must have looked like about five billion years ago. That’s when our own Sun and its stellar siblings began to form from a similar type of gas and dust cloud..
In the beginning, there was hydrogen and helium. Other than some traces of things such as lithium, that’s all the matter the big bang produced. Everything other than those two elements was largely produced by astrophysical rather than cosmological processes. The elements we see around us, those that comprise us, were mostly formed within the hearts of stars. They were created in the furnace of stellar cores, then cast into space when the star died. But there are a few elements that are created differently. The most common one is gold.
While gold can be produced in a stellar core, the gold we have on Earth wasn’t produced that way. Gold is a very heavy element, so when a star explodes most of the gold stays in the core. So where does our gold come from? Neutron star collisions. When two neutron stars collide, they are ripped apart creating a kilonova. All that nuclear matter within the neutron stars is freed from the crushing weight of gravity and quickly forms into elements such as gold. We know this because the amount of gold we see in the galaxy agrees with the rate of neutron star collisions.
For a while now astronomers have assumed neutron star collisions are also the primary source of other heavy elements, particularly the lanthanide series, also known as rare earth elements. But that’s just been a theory. We don’t have a good measure of the cosmic abundance of rare earth elements, so it’s a hard idea to prove. But that has changed, thanks to a recent study.
Back in 2017, gravitational wave observatories captured an event known as GW170817. Unlike gravitational events that were the merger of two black holes, this one was a merger of two neutron stars. The resulting kilonova was observed by 70 observatories across the world, making it the first great multi-messenger observation, combining data gathered from electromagnetic and gravitational waves. Some of the electromagnetic observations included spectral line data, so in principle, we should be able to identify which elements were formed by the collision.
Spectrum showing various elements from the neutron star merger. Credit: Domato, et al
This is fairly easy for lighter elements but more challenging for heavier ones. In this study the team ran supercomputer simulations of kilonova explosions, calculating where absorption lines should appear based on different elements. When they compared their calculations to the observed spectra of GW170817, they were able to identify several rare earth elements, including strontium, lanthanum, and cerium. It’s the first time these elements have been confirmed as by-products of a neutron star merger.
This is just the first multi-messenger observation of colliding neutron stars. In time we will have several more, and that will give this team and others a chance to discover even more rare earth elements in the debris.
There’s a monster black hole in our backyard (astronomically speaking). Life could survive underground on Mars for hundreds of millions of years. Starlink was hacked and now works as GPS. Bad news for Arecibo.
Enjoy the video version of all the latest space and astronomy news in our latest episode of Space Bites. Everything you need to know that happened last week in a convenient bite-size video format.
The Closest Black Hole Ever Discovered
A monster black hole was discovered relatively close to us. It’s just 1550 light years away, which is our backyard, astronomically speaking. The exciting thing is how it was discovered. Astronomers looked into Gaia’s data on stars and their motion. Among them, they found a star that looked like it was in a binary system. But there was no visible companion. Further analysis revealed that it was a 12-solar mass black hole. So, it’s an interesting new technique that can reveal more black holes in the future.
There is an interesting paradox about life on Mars. New studies suggest the following scenario. If there was life on Mars in its early stages, when the planet was wet and warm, it could have wiped itself out. By producing CO2, methane and other gases, it could have weakened the greenhouse effect. So, by replacing hydrogen with those gases they made the planet colder, which eventually lead to losing its atmosphere and therefore conditions for life.
Researchers managed to hack Starlink and use it as a positioning system. All that without any consent from SpaceX. By analyzing the signals from the satellites they managed to reverse-engineer it and extract timing data. Combining this information with the positions of the satellites, which are well-known and opened to the general public, it effectively turned into a GPS alternative. The precision is about 30-meters. It can be improved, if SpaceX wanted to cooperate. But whether they will want to do so is yet to be determined.
Lucy Gets a Portrait of the Earth and the Moon
Whenever spacecraft make a gravity-assisted flyby of Earth, it’s the perfect opportunity to test their optics and science instruments. During its recent flyby, Trojan-bound Lucy captured this image of planet Earth when it was about 620,000 km away. It also captured a picture of both the Earth and the Moon in the same photo, showing how far away they are from each other.
We know that red dwarf stars can blast out powerful flares, but in the case of one system, the results were catastrophic. Astronomers studied the earth-sized planet GJ 1252b, which orbits a red dwarf star every 12 hours. They found that the intense flares from the star scoured away the atmosphere from the planet. This could be the case for many other exoplanetary systems, but there’s some good news. If the worlds are farther away from the star, their atmosphere could hold under this barrage, protecting life until the star settles down.
It’s official. The famous Arecibo radar telescope won’t be rebuilt. It’s a sad but expected moment. But still, Arecibo has left a huge heritage both in science, as new studies are still being published with its data, as well as in popular culture.
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Trees are like sentinels that preserve a record of shifting climates. Their growth rings hold that history and dendrochronology studies those rings. Scientists can determine the exact ages of trees and correlate their growth with climatic and environmental changes.
But they also record the effects of more distant changes, including the Sun’s activity.
Carbon is life’s primary building material. It’s the backbone of life on Earth because it forms bonds with itself and other atoms in a wide array of compounds. Carbon is present in almost 10 million different compounds. Trees are made of mostly cellulose, a carbon-rich organic compound with the formula (C6H10O5)n.
But all carbon isn’t created equal. It exists naturally in three different isotopes: Carbon 12 (12C), carbon 13 (13C), and carbon 14 (14C). Carbon always has 6 protons, but the different isotopes have different numbers of neutrons. 14C is different than the other isotopes because it’s a radioisotope. That means it decays, and since 1949, scientists have been using 14C to find the ages of ancient things through radiocarbon dating.
The three naturally-occurring carbon isotopes exist on Earth. Carbon 14 is the rarest and is radioactive. It’s used in radiocarbon dating. Image Credit: NASA
Trees absorb carbon daily as they take in carbon dioxide and expel oxygen. Trees don’t discriminate between the different isotopes of carbon. So when scientists analyze the chemical contents of trees’ growth rings, they find all three naturally occurring carbon isotopes.
Some events cause a bump in the amount of 14C in Earth’s atmosphere. Scientists can date tree rings accurately, so by finding which tree rings have more 14C, scientists can determine when Earth experienced a carbon-14 bump.
This all goes to the heart of a new study published in the Proceedings of the Royal Society A. The paper is “Modelling cosmic radiation events in the tree-ring radiocarbon record.” Dr. Benjamin Pope from the University of Queensland’s School of Mathematics and Physics led the study.
Carbon-14 has unearthly origins.
When cosmic rays from the Sun and more distant stellar objects strike Earth’s upper atmosphere, the rays interact with nitrogen, which is abundant in Earth’s atmosphere. The interaction creates 14C, which mixes freely in the atmosphere, where it’s taken in by living things. The amount of carbon-14 is relatively constant as long as the Sun behaves “normally.”
But when the Sun is highly active, it releases more energy towards Earth’s atmosphere, creating more 14C. Trees that are alive when the Sun experiences an outburst of energy keep a record of that outburst by absorbing more of the carbon isotope into their tissue. And since trees grow seasonally, one ring at a time, each ring is a record of stellar activity.
Some of the Sun’s behaviour is still a mystery. Miyake Events occur on the Sun and create “spikes” in the amount of carbon-14 in Earth’s environment. The researchers in this study used the link between carbon-14 and tree rings to understand Miyake Events. The effort involved advanced statistics and special software.
The Miyake Event is also called the Charlemagne event because Charlemagne ruled western Europe at the time. It’s also called the 774–775 carbon-14 spike. It produced the most significant rise in 14C that we know of.
This graph shows the carbon-14 spike around 774. Coloured dots are measurements in Japanese (M12) and German (oak) trees; black lines are the modelled profile corresponding to the instant production of carbon-14. Image Credit: By Isosik – Own work, CC BY-SA 4.0, https://ift.tt/4IOnHFh
“These huge bursts of cosmic radiation, known as Miyake Events, have occurred approximately once every thousand years, but what causes them is unclear,” Dr. Pope said in a press release. “The leading theory is that they are huge solar flares.”
If a solar flare caused the carbon-14 spike, it was the most powerful flare ever known, but still within the Sun’s capabilities. The flare wasn’t catastrophic for life and may have gone largely unnoticed at the time.
But it would’ve been ugly if the same event occurred in our modern technological times. Modern technology, especially satellites, would bear the brunt of the effects. In our world, we rely on satellites for communications and navigation. Add the risk of damage to electrical infrastructure, and these events are nothing to take lightly.
“We need to know more because if one of these happened today, it would destroy technology, including satellites, internet cables, long-distance power lines and transformers,” Dr. Pope said. “The effect on global infrastructure would be unimaginable.”
This is where tree rings come into the picture.
The paper’s first author Qingyuan Zhang is an undergraduate math student at U of Q. He developed software for the research that analyzes tree ring data.
“Because you can count a tree’s rings to identify its age, you can also observe historical cosmic events going back thousands of years,” Mr. Zhang said. “When radiation strikes the atmosphere, it produces radioactive carbon-14, which filters through the air, oceans, plants, and animals, and produces an annual record of radiation in tree rings.”
“We modelled the global carbon cycle to reconstruct the process over 10,000 years to gain insight into the scale and nature of the Miyake Events,” said Zhang.
They’re called Miyake events because Japanese scientist Fusa Miyake was the first author of a paper describing them. There’ve been six Miyake Events. The oldest known one occurred in 7176 BC, and the Charlemagne event is the most recent.
This figure from the study shows the 6 Miyake events and their durations. Image Credit: Zhang et al., 2022.
The most widely-held theory is that extremely powerful solar flares created the spikes in carbon-14. But in her 2012 paper, Miyake and her co-authors argued that solar flares can’t be responsible. This study also challenges the idea that solar flares are responsible.
“But our results challenge this,” Mr. Zhang said. “We’ve shown they’re not correlated with sunspot activity, and some actually last one or two years. Rather than a single instantaneous explosion or flare, what we may be looking at is a kind of astrophysical ‘storm’ or outburst.”
An astrophysical storm doesn’t sound very pleasant. Earth is at the mercy of the Sun, and the Sun’s usually placid behaviour allows our civilization to thrive. So finding evidence of powerful events that we don’t understand and can’t predict is troubling.
People in 774-775 noted unusual things in the sky, though they knew nothing about radiation, carbon, or astrophysics.
The front page (l) and the A.D. 774 entry of the Anglo-Saxon Chronicles. Image Credit: (l) By Photographed by en:User: George, original author, monastic scribes in Peterborough – English Wikipedia, Public Domain, https://ift.tt/NQaodXU. Image Credit: (r) Google Books/Public Domain.
The Anglo-Saxon Chronicle said, “This year also appeared in the heavens a red crucifix, after sunset;” What might that have been? (The same chronicle also says, “… wonderful serpents were seen in the land of the South-Saxons,” so a grain of salt is prudent.) The Chinese talked about an aurora in 776, the only one they mentioned during the 770s. They also recorded an unusual thunderstorm in 775. Were these observations related to whatever happened to the Sun?
Nobody’s certain.
A 2015 paper examined the 774–775 carbon-14 spike. It concluded, ” These events probably had no optical counterpart, and a short gamma-ray burst, giant flare of a soft gamma-ray repeater or a terrestrial ?-ray flash could all be candidates.” If that paper was correct, nobody on Earth would’ve noticed a thing.
The research team found that whatever solar activity drove the 14C spikes isn’t correlated with the solar cycle. The spikes’ amplitude is also not dependent on latitude. Both of these things have been hypothesized as causative. “… we find no clear relation in timing to the solar cycle, or in amplitude to latitude as has previously been claimed,” the authors write in their conclusion.
When the researchers realized that the events were prolonged rather than acute, they explored the idea that atmospheric mixing could have played a role in extending them by holding the carbon aloft in the upper atmosphere well after the event ended. They also wondered if something about the trees themselves could explain the carbon-14 spike.
But those explanations were unsatisfactory. “They do not show a consistent relationship to the solar cycle,” the paper states, “and several display extended durations that challenge either astrophysical or geophysical models.”
Our Sun is usually well-behaved, allowing our civilization to thrive. But if this study is correct, it has a menacing side that we don’t fully understand. Image: NASA/Solar Dynamics Observatory.
The prolonged nature of the spikes is confounding. “On the other hand,” the authors write in their conclusion, “if the prolonged radionuclide production has an astrophysical origin, this will be hard to reconcile with an impulsive production model of one large energetic particle burst, whether of solar energetic particles or from a stellar remnant.”
So it remains a mystery, for now at least. And an undesirable one. How can we predict one if we don’t know what they are?
“Based on available data, there’s roughly a one percent chance of seeing another one within the next decade,” said Dr. Pope. “But we don’t know how to predict it or what harms it may cause.”
“These odds are quite alarming and lay the foundation for further research.”
One of the great tragedies of the night sky is that we will never travel to much of what we see. We may eventually travel to nearby stars, and even distant reaches of our galaxy, but the limits of light speed and cosmic expansion make it impossible for us to travel beyond our local group. So we can only observe distant galaxies, and we can only observe them from our home in the universe. You might think that means we can only see one face of those galaxies, but thanks to the James Webb Space Telescope that isn’t entirely true.
As light from distant galaxies traverses the cosmos to reach us, its path can be deflected gravitationally along the way, known as gravitational lensing. For very distant galaxies their light is often lensed through galactic clusters closer to us and can produce multiple images. Each of these images comes from a different path of light.
A comparison of galaxies seen from Hubble vs Webb. Credit: NASA, ESA, CSA, Alyssa Pagan (STScI)
You can see this in a recent set of images released by the Space Telescope Science Institute. It shows a comparison of the galactic cluster MACS0647 captured by Hubble in 2012 and as seen by Webb in 2022. In the faint background of this cluster are three images of a more distant galaxy known as MACS0647-JD. It’s the same galaxy, but gravitational lensing lets us see it from slightly different paths. In the Hubble image, the galaxy images are just blurry clusters of pixels, but Webb can resolve these galaxies in some detail. Each image seems to have two smudges of light, and that means JD could be an early colliding galaxy. If it is the merger of two galaxies, it will be the most distant galactic merger we’ve observed.
One of the side effects of gravitational lensing is that it can magnify light from these far galaxies. This means the galaxy appears closer and brighter than it actually is. In the case of MACS0647-JD, the three images are magnified by different amounts. The images known as JD1, JD2, and JD3 are magnified by factors of 8, 5, and 2. Additionally, since the light path of each image is different, we also see the galaxy from three slightly different times.
This image is a great example of the power of JWST. It not only allows us to study the earliest galaxies in detail, but it also allows us to see some galaxies from more than one point of view.
Everybody’s heard of methane. It’s a major part of the atmosphere in places like Uranus and Neptune. On Earth, it’s also part of our atmosphere, where it works to warm things up. Some of it gets there from natural causes. But, a lot of it comes from industrial super-emitters and other human-caused processes. That’s not good because too much methane works, along with other greenhouse gases (like carbon dioxide, or CO2) to “over warm” our atmosphere.
In the right amounts, methane’s role in warming the atmosphere is perfectly normal. For humans, methane has other uses. It’s a big component of natural gas, used for everything from cooking to heating our homes and businesses. But, the releases of methane from big industrial processes, outgassing from landfills, and oil and gas exploration are not normal. They all contribute to climate change.
How to track methane emissions? It turns out this gas can be detected from space and has been for some time. Currently, a satellite called EMIT (for Earth Surface Mineral Dust Source Investigation) is using spectroscopic studies to find big clouds of methane. There are at least 50 “super-emitters” of methane in EMIT’s data, and their existence is cause for concern. Unfortunately, scientists expect to find more as time goes by.
The cube (left) shows methane plumes (purple, orange, yellow) over super-emitters in Turkmenistan. The rainbow colors are the spectral fingerprints from corresponding spots in the front image. The blue line in the graph (right) shows the methane fingerprint EMIT detected; the red line is the expected fingerprint based on an atmospheric simulation. Credit: NASA/JPL-Caltech
Super-emitters deliver methane to the atmosphere at very high rates. How high? “Some of the plumes EMIT detected are among the largest ever seen – unlike anything that has ever been observed from space,” said Andrew Thorpe, a researcher at JPL leading the EMIT methane effort. “What we’ve found in just a short time already exceeds our expectations.”
Infamous Super-emitters
EMIT has been busy. For example, it detected a plume about 3.3 kilometers long southeast of Carlsbad, New Mexico. It’s smack dab over the Permian Basin, one of the largest oilfields in the world. EMIT also found 12 plumes from oil and gas infrastructure in Turkmenistan, some stretching over 32 kilometers. In Iran, near Tehran, there’s a plume at least 4.8 kilometers long. It’s blowing out from a waste-processing plant. These are all known super-emitters.
The flow rates of gas into the atmosphere from these sites are dismaying. In the Permian basin, the flow rate is 18,300 kilograms per hour. The Turkmenistan plumes are sending 50,400 kilograms per hour in total into the atmosphere. That’s roughly similar to a gas leak in the 2015 Aliso Canyon event in California. It sent 50,000 kilograms per hour into the air at various times and was among the largest methane releases in U.S. history.
Curtailing Methane Gas Emissions
The fight to reduce greenhouse gases is an important one in the effort to slow global warming. Scientists do use ground-based methods to find methane emissions. However, space-based detectors deliver clearer looks at where it and other gases are polluting the atmosphere.
“Reining in methane emissions is key to limiting global warming. This exciting new development will not only help researchers better pinpoint where methane leaks are coming from, but also provide insight on how they can be addressed – quickly,” said NASA Administrator Bill Nelson. “The International Space Station and NASA’s more than two dozen satellites and instruments in space have long been invaluable in determining changes to the Earth’s climate. EMIT is proving to be a critical tool in our toolbox to measure this potent greenhouse gas – and stop it at the source.”
While CO2 is the prime greenhouse gas in the news most of the time, methane is critically important to regulate, too. It makes up a smaller fraction of human-caused greenhouse-gas emissions than CO2. However, methane is roughly 80 times more effective at trapping heat in the atmosphere for 20 years after it is released. It also stays in the atmosphere over shorter time periods, compared to CO2. Its short lifetime in our air does have an upside. If we can curtail methane emissions, the atmosphere will see improvement more quickly. That leads to a slower warming cycle in the short term.
Finding More Methane Super-emitters
EMIT will likely find many more super-emitters. “As it continues to survey the planet, EMIT will observe places in which no one thought to look for greenhouse-gas emitters before, and it will find plumes that no one expects,” said Robert Green, EMIT’s principal investigator at JPL. The mission is the first of a new class of spaceborne imaging spectrometers to study Earth. Another is the Carbon Plume Mapper (CPM), designed to detect methane and CO2. JPL is working with a nonprofit, Carbon Mapper, along with other partners, to launch two satellites equipped with CPM in late 2023.
Identifying methane point sources is a huge step in the process of reducing greenhouse gases. EMIT supplies knowledge of the locations of big emitters, and that gives operators of the super-emitter facilities the chance to take quick action. The ultimate goal is to reduce or even eliminate the release of methane into our already warming atmosphere.
The EMIT observations aren’t the first ones to detect methane emissions on Earth. GHGSat, which is a private company that monitors such emissions from space spotted leaks from the Nordstream pipeline between Denmark and Sweden. The pipeline was sabotaged and emitted methane at 79,000 kg per hour.
Less than a year after it went to space, the James Webb Space Telescope (JWST) has already demonstrated its worth many times over. The images it has acquired of distant galaxies, nebulae, exoplanet atmospheres, and deep fields are the most detailed and sensitive ever taken. And yet, one of the most exciting aspects of its mission is just getting started: the search for evidence of life beyond Earth. This will consist of Webb using its powerful infrared instruments to look for chemical signatures associated with life and biological processes (aka. biosignatures).
The chemical signatures vary, each representing a different pathway toward the potential discovery of life. According to The Conversation’s Joanna Barstow, a planetary scientist and an Ernest Rutherford Fellow at The Open University specializing in the study of exoplanet atmospheres, there are four ways that Webb could do this. These include looking for chemicals that lifeforms depend on, chemical byproducts produced by living organisms, chemicals essential to maintaining a stable climate, and chemicals that shouldn’t coexist.
In their search for life beyond Earth, astrobiologists have been restricted to the “low-hanging fruit” approach. This consists of searching for terrestrial (or rocky) planets that orbit within their parent stars’ circumsolar habitable zones (HZs) or the distance where planets will be warm enough to maintain liquid water on their surfaces. With next-generation telescopes like Webb, which combine sensitive optics, coronographs, and spectrometers with near- and mid-infrared imaging capability, the field of exoplanet study is transitioning from discovery to characterization.
As we explored in previous articles, this involves direct imaging studies of exoplanets and obtaining spectroscopic data from their atmospheres. Since the early 19th century, scientists have known that certain chemical elements absorb light at certain wavelengths and radiate it in others. By performing a “chemical inventory” of exoplanet atmospheres, astrobiologists will be able to place much tighter constraints on exoplanet habitability. In other words, they will be able to say with much greater confidence if a planet is habitable (and not just “potentially habitable”).
That being said, the chemical indicators that Webb could look for (as Barstow explains) can be broken down into four groups: Oxygen and Ozone, Phosphine and Ammonia, Methane and Carbon Dioxide, and Chemical Imbalances. Oxygen is an obvious biosignature because of its importance to the emergence and maintenance of life here on Earth. In Earth’s early history, our atmosphere was largely composed of carbon dioxide, and oxidization was prevented by removing oxygen (aka. a “reducing” atmosphere).
Over time, cyanobacteria and other photosynthetic organisms converted atmospheric CO2 into oxygen gas. This culminated in the “Great Oxygenation Event” (GOE) roughly 2.4 to 2.0 billion years ago, when Earth’s atmosphere went from a “reducing” to an “oxidizing” atmosphere. This allowed more complex organisms like insects, birds, mammals, and (eventually) hominids to evolve and flourish. Then there’s Ozone, which formed in Earth’s upper atmosphere from the interaction of oxygen gas and ultraviolet (UV) radiation.
This led to the creation of the Ozone Layer, which today protects life on Earth from the majority of the Sun’s UV radiation. However, finding these molecules in an exoplanet’s atmosphere does not necessarily mean we’ve found evidence of life. As multiple studies have shown, there are numerous ways that a planet’s atmosphere can become oxidizing through the creation of “abiotic oxygen” (aka. not the result of biological processes). As Barstow indicated, another scenario involves a “runaway greenhouse effect,” where evaporating surface water leads to more heating and evaporation in a feedback loop.
The presence of so much water vapor in the planet’s atmosphere will lead to photolysis, where exposure to solar radiation causes water to break down into hydrogen and oxygen gas (the former of which is lost to space while the latter is retained). In another scenario, tidally-locked planets that orbit within a star’s HZ are exposed to considerable radiation on their sun-facing side, which can also lead to photolysis and an atmosphere dominated by abiotic oxygen. Since oxygen gas is toxic to photosynthetic life forms (such as those that existed in Earth’s early history), it could prevent the emergence of life.
Next up, there’s Ammonia and Phosphine, which are naturally occurring in the atmospheres of gas giants (and icy moons that orbit them) but are also produced by life here on Earth. Phosphine as a potential biosignature has been a hot topic of late, given that planetary scientists detected it not long ago in Venus’ atmosphere. However, both occur in minute quantities here on Earth, making them rather difficult to detect in the atmospheres of distant exoplanets.
Methane and Carbon Dioxide are also considered potential biosignatures (especially in combination, according to Barstow) because of their association with biological processes here on Earth. Both are produced as byproducts by animals, methane resulting from organic decay and digestion, and carbon dioxide as the exhalations of oxygen-consuming animals. The presence of enough CO2 in an atmosphere is also essential to maintaining stable temperatures over time. Too much or too little can lead to a runaway greenhouse effect or glaciation.
Last, according to Barstow, there is the possibility that chemical imbalances could point the way toward life. This is because chemical equilibrium does not exist in a system where life is present since life constantly consumes certain chemicals, producing energy and other chemicals as a byproduct. This echoes what planetary scientists James Lovelock (co-founder of the Gaia Hypothesis) argued in his famous book, the Greening of Mars. “Stability,” he argued, is only present in systems or planets that are lifeless (in this case, he was referring to Mars).
Artist’s impression of the “Earth-like” exoplanet Kepler 62f. Credit: NASA Ames/JPL-Caltech/T. Pyle
Another possible biosignature that Barstow does not mention is hydrogen. In recent years, researchers from Cornell University showed how the presence of volcanic hydrogen in an exoplanet atmosphere could extend the habitable zones of stars. Not only is hydrogen gas (H2) a natural greenhouse gas, but the presence of volcanic activity is also considered important to the emergence of life. Other research from the University of Cambridge showed how ocean planets with hydrogen-dominated atmospheres (“Hycean” planets) could be the best place to search for life.
However, in all these cases, the presence of these chemicals in an exoplanet’s atmosphere should not be treated as definitive proof that life exists there. As Barstow reminds readers, it is easy to get caught up in the excitement of exoplanet research and forget that the process is long and painstaking. As she summarizes:
“[W]e still have to measure how much of these gases are present to draw meaningful conclusions. This isn’t straightforward as the signals can overlap and need to be carefully disentangled… JWST is only just opening up a new, rich laboratory of planetary atmospheres, and as we explore no doubt we will find many of our previous assumptions are proven wrong.”
