The most likely way we will discover life on a distant exoplanet is by discovering a biosignature. This can be done by looking at the atmospheric spectra of a world to discover the spectral pattern of a molecule that can only be created through biological processes. While it sounds straightforward it isn’t. The presence of simple molecules such as water and oxygen don’t prove life exists on a planet. It’s true that Earth’s atmosphere is oxygen rich thanks to life, but geological activity can also produce large quantities of oxygen. And as a new study shows, some molecules we’ve long thought to be biological in origin may not be.
Ideally astronomers would love to find evidence of a really complex molecule such as chlorophyll. But there isn’t likely to be tons of chlorophyll in an atmosphere, so the spectral pattern would be faint, and even if it were clear the pattern is complex and hard to distinguish. So astronomers generally focus on simpler but unique molecules. One of these molecules is dimethyl sulfide, (CH3)2S or DMS for short. It is only produced by phytoplankton on Earth, so it would be a strong indicator of life. Or so we thought.
In this new work the team was able to synthesize DMS and other sulfur-based molecules in the lab abiotically. While that doesn’t prove the same process can happen in the wild, the team went on to show how DMS could be formed on a world with a thick organic haze. We know such planets exist because Saturn’s moon Titan is just such a world. If, for example, Titan happened to be closer to the Sun, the ultraviolet radiation would be significant enough to trigger the chemical reactions necessary to create DMS. If Titan were in Earth’s orbit, a distant alien race would detect DMS in the atmosphere of a planet in the Sun’s habitable zone. It would look like a slam dunk, but Titan would still be toxic to life as we know it.
How a biosignature molecule might form naturally. Credit: Reed, et al
But Titan might have some presence of exotic life, which is another conclusion to this study. While the authors show that the presence of DMS or similar molecules wouldn’t prove life exists on a world, they argue that it would indicate a strong potential for life. Basically, a warm planet with the kind of rich organic haze in its atmosphere would necessarily have the kind of complex organic molecules life needs to evolve. If DMS exists on a world, then the potential for life exists at the very least.
While this study shows we will need to be careful about treating particular molecules as biosignatures, it also supports what exo-biologists have known for some time. The discovery of life on another world isn’t likely going to happen as a single great eureka moment. What is more likely is that a handful of planets will have chemical markers that support the possibility of life. Over time as we find more candidate biomarkers in their atmospheres we will be ever more confident that life exists.
When a massive star explodes as a supernova, it does more than release an extraordinary amount of energy. Supernovae explosions are responsible for creating some of the heavy elements, including iron, which is blasted out into space by the explosion. On Earth, there are two accumulations of the iron isotope Fe60 in sea-floor sediments that scientists trace back about two or three million years ago and about five to six million years ago.
The explosions that created the iron also dosed Earth with cosmic radiation.
“Life on Earth is constantly evolving under continuous exposure to ionizing radiation from both terrestrial and cosmic origin,” the authors write. Terrestrial radiation slowly decreases over billions of years. But not cosmic radiation. The amount of cosmic radiation that Earth is exposed to varies as our Solar System moves through the galaxy. “Nearby supernova (SN) activity has the potential to raise the radiation levels at the surface of the Earth by several orders of magnitude, which is expected to have a profound impact on the evolution of life,” they write.
The authors explain that the two million-year-old accumulation is directly from a supernova explosion, and the older accumulation is from when Earth passed through a bubble.
The bubble in the study’s title comes from a particular type of star called OB stars. OB stars are massive, hot, and short-lived stars that usually form in groups. These stars emit powerful outflowing winds that create “bubbles” of hot gas in the interstellar medium. Our Solar System is inside one of these bubbles, called the Local Bubble, which is almost 1,000 light-years wide and was created several million years ago.
An artist’s conception of the hot local bubble. Image Credit: NASA
The Earth entered the Local Bubble about five or six million years ago, which explains the older Fe60 accumulation. According to the authors, the younger Fe60 accumulation from two or three million years ago is directly from a supernova.
“It is likely that the 60Fe peak at about 2-3 Myr originated from a supernova occurring in the Upper Centaurus Lupus association in Scorpius Centaurus (~140 pc) or the Tucana Horologium association (~70 pc). Whereas the ~ 5-6 Myr peak is likely attributed to the Solar System’s entrance into the bubble,” the authors write.
The left panel shows the Local Bubble and nearby stellar associations, while the right panel shows their galactic coordinates. The right panel also shows a new Galactic bubble discovered in 2018. It’s likely the remnant of an SN that exploded in Upper Centaurus Lupus. Image Credit: Nojiri et al. 2024.
The Local Bubble is not a quiet place. It took multiple supernovae to create it. The authors write that it took 15 SN explosions over the last 15 million years to create the LB. “We know from the reconstruction of the LB history that at least 9 SN exploded during the past 6 Myrs,” they write.
The researchers took all the data and calculated the amount of radiation from multiple SNe in the LB. “It is not clear what would the biological effects of such radiation doses be,” they write, but they do discuss some possibilities.
This figure shows the average dose rate experienced at ground level as a function of the distance to the nearby SN. The average dose is calculated over the first 10 kyr (solid line) and over the first 100 kyr (dashed line) after the SN explosion. It’s not enough to trigger an extinction, but it could’ve driven species diversification. Image Credit: Nojiri et al. 2024.
The radiation dosage may have been strong enough to create double-strand breaks in DNA. This is severe damage and can lead to chromosomal changes and even cell death. But there are other effects in terms of the development of life on Earth.
“Double-strand breaks in DNA can potentially lead to mutations and jump in the diversification of species,” the researchers write. A 2024 paper showed that “the rate of virus diversification in the African Tanganyika lake accelerated 2-3 Myr ago.” Could this be connected to SN radiation?
“It would be appealing to better understand whether this can be attributed to the increase in cosmic-radiation dose we predict to have taking place during that period,” the authors tease.
The SN radiation wasn’t powerful enough to trigger an extinction. But it could’ve been powerful enough to trigger more mutations, which could lead to more species diversification.
Radiation is always part of the environment. It rises and falls as events unfold and as Earth moves through the galaxy. Somehow, it must be part of the equation that created the diversity of life on our planet.
“It is, therefore, certain that cosmic radiation is a key environmental factor when assessing the viability and evolution of life on Earth, and the key question pertains to the threshold for radiation to be a favourable or harmful trigger when considering the evolution of species,” the authors write in their conclusion.
Unfortunately, we don’t clearly understand exactly how radiation affects biology, what thresholds might be in place, and how they might change over time. “The exact threshold can only be established with a clear understanding of the biological effects of cosmic radiation (especially muons that dominate at ground level), which remains highly unexplored,” Nojiri and her co-authors write.
The study shows that, whether we can see it in everyday life or not, or even if we’re aware of it or not, our space environment exerts a powerful force on Earth’s life. SN radiation could’ve influenced the mutation rate at critical times during Earth’s history, helping shape evolution.
Without supernova explosions, life on Earth could look very different. Many things had to go just right for us to be here. Maybe in the distant past, supernova explosions played a role in the evolutionary chain that leads to us.
On June 6th, 2024, the fourth orbital test flight of the Starship successfully lifted off at 07:50 a.m. CT (08:50 a.m. EDT; 06:50 PDT) from SpaceX’s Starbase in Texas. This test was the first time the Starship (SN29) and Super Heavy (BN11) prototypes reentered Earth’s atmosphere and landed successfully. While the SN29 conducted a powered vertical landing before splashing down in the Indian Ocean, the BN11 executed a similar powered landing before splashing down in the Gulf of Mexico. In a recent tweet, Elon Musk shared a photo of the BN11 booster being pulled out of the sea.
News of the retrieval was posted via Elon Musk’s X account, where he hinted at the possibility of refurbishment and reuse, writing, “Fixer upper.” In addition to being the first flight test in which both vehicles made it back in one piece, this flight was also the first time that a Super Heavy booster simulated a landing at a “virtual tower.” In the future, SpaceX intends to retrieve its boosters by “catching” them with the Orbital Launch Mount tower at their Starbase facility. This is expected to occur for the first time during the fifth integrated flight test, scheduled for no earlier than late November 2024.
The flight test was originally scheduled for September but was delayed by the Federal Aviation Administration (FAA) until November due to environmental complaints and the licensing process. According to statements by the FAA and SpaceX, the company was already authorized to conduct multiple flights using the same mission profile they followed for the fourth flight test. However, adding an attempted “catch” has led the FAA to conduct a more thorough review of the flight and the launch facility.
Researchers have developed a set of hexagon-shaped robotic components that can be snapped together into larger and larger structures. Each one of the component hexagons is made of rigid plates that serve as its exoskeleton. Driven by electricity, the plates can change their shape, shifting from long and narrow to wide and flat at high speed. The combined structures are capable of jumping four times their own body height, then can shape-shift to roll extremely fast, or use multimodal actuation to crawl through confined spaces.
The robotic components were developed at the Max-Planck-Institute for Intelligent Systems (MPI-IS). The modules are made of six lightweight rigid plates made from glass fiber that form a hexagon. Magnets embedded into the plates allows for quick connection to other components as well as providing a shared electrical ground between the modules.
Individual HEXEL modules combine soft artificial muscles with rigid components for fast and large motions. Credit: Zachary Yoder / MPI-IS Ellen Rumley / MPI-IS
The design team integrated artificial “muscles” into the inner joints of the hexagons, called hydraulically amplified self-healing electrostatic (HASEL) muscles. Applying a high voltage to the module causes the muscle to activate, rotating the joints of the hexagon and changing its shape from long and narrow to wide and flat.
“Combining soft and rigid components in this way enables high strokes and high speeds. By connecting several modules, we can create new robot geometries and repurpose them for changing needs,” said Ellen Rumley, a visiting researcher from the University of Colorado Boulder, in a press release from MPI-IS. Rumley and Zachary Yoder, who are both Ph.D. students working in the Robotic Materials Department, are co-first authors of a new paper, “Hexagonal electrohydraulic modules for rapidly reconfigurable high-speed robots,” published in Science Robotics.
The modules are reconfigurable, with an easy process of attaching or detaching the modules. Chains of modules can be rapidly connected and can operate from one voltage source. The modules can each have their own behaviors, which allows for various operations.
The team created a video to show the various configurations and behaviors that can be created with HEXEL modules. The modules can be seen rolling, dancing, jumping, crawling, and many other motions.
“In general, it makes a lot of sense to develop robots with reconfigurable capabilities,” said Yoder. “It’s a sustainable design option – instead of buying five different robots for five different purposes, we can build many different robots by using the same components. Robots made from reconfigurable modules could be rearranged on demand to provide more versatility than specialized systems, which could be beneficial in resource-limited environments.”
Noctilucent clouds were once thought to be a fairly modern phenomenon. A team of researcher have recently calculated that Earth and the entire Solar System may well have passed through two dense interstellar clouds causing global noctilucent clouds that may have driven an ice age. The event is thought to have happened 7 million years ago and would have compressed the heliosphere, exposing Earth to the interstellar medium.
Interstellar clouds are vast regions of gas and dust that flat between the stars inside galaxies. They are mostly made up of hydrogen along with a little helium and trace elements of heavier elements. They are a key part of the life circle of stars providing the materials for new stars to be formed and are seeded with elements after stars die. The clouds vary significantly in size, density and location and are an important part of the evolution of the Galaxy.
An annotated illustration of the interstellar medium. The solar gravity lens marks the point where a conceptual spacecraft in interstellar space could use our sun as a gigantic lens, allowing zoomed-in close-ups of planets orbiting other stars. Credits: Charles Carter/Keck Institute for Space Studies
Earth’s journey around the Galaxy is not for the impatient for it takes about 250 million years to complete one full orbit at a speed of 828,000 kilometres per hour. Currently the Solar System is located in the Orion Arm, one of the spiral arms of our Galaxy. During the journey, Earth travels through different regions, encountering stars and different densities of the interstellar medium. It experiences gravitational interactions with nearby stars and nebula sometimes exerting subtle interactions. Regardless of the immense journey, the stars of our Galaxy remain relatively unchanged over a human lifetime.
The Milky Way is a spiral galaxy with several prominent arms containing stellar nurseries swathed in pink clouds of hydrogen gas. The sun is shown near the bottom in the Orion Spur. Credit: NASA
A team of astronomers let by Jess A. Miller from the Department of Astronomy of Boston University have traced the path of the Sun back through time. In doing so, they have identified two occasions when the Earth and Solar System passed through two dense interstellar clouds. One of the crossings occurred 2 million years ago, the other 7 million years ago. Exploring the properties of the clouds, the team assert that the clouds are dense enough that they could compress the solar wind to inside the orbit of Earth.
The Solar Wind is a constant stream of charged particles, mostly electrons and protons that are emitted from the upper layer of the Sun’s atmosphere, the corona. The particles travel through the Solar System at speeds between 400 and 800 kilometres per second. The edge of our Solar System is defined as the point where the solar wind merges with the interstellar medium.
A composite image comprised of the Sun’s surface, corona, and digitally-added coronal loops rendered by Andrew McCarthy. (Credit: Andrew McCarthy)
Previous teams have analysed climate change events due to these interstellar medium interactions with similar findings. Global cooling has been the result with an ice age being triggered. The study by Miller and team have readdressed this very topic using modern technology and processes.
The team find that the interactions have indeed played a part in changes to the atmosphere of Earth. They find that levels of hydrogen in the upper atmosphere would have increased substantially. The newly acquired hydrogen would be converted to water molecules in the lower atmosphere and it would also have led to a reduction in mesospheric levels of ozone. These processes would have led to the appearance of global noctilucent clouds in the mesosphere. They would not have been permanent but may have blocked 7% of sunlight from reaching Earth, plunging our planet into an ice age.
Earth’s last half-billion years were action-packed. During that time, the climate underwent many changes. There have been changes in ocean levels and ice sheets, changes in the atmosphere’s composition, changes in ocean chemistry, and ongoing biological evolution punctuated with extinction events.
A record of Earth’s temperature over the last 485 million years is helping scientists understand how it all played out and illustrating what could happen if we continue to enrich the atmosphere with carbon.
The new temperature record is presented in research titled “A 485-million-year history of Earth’s surface temperature.” It’s published in Science, and the lead author is Emily Judd. Judd is from the Department of Paleobiology at the Smithsonian National Museum of Natural History.
“This research illustrates clearly that carbon dioxide is the dominant control on global temperatures across geological time.”
Jessica Tierney, University of Arizona
The new historical temperature comes from an effort named PhanDA, which stands for Phanerozoic Data Assimilation. PhanDA combined data from climate models with data from geology to determine how the climate has changed over the last nearly 500 million years. The Phanerozoic is Earth’s current geological eon, and it started 538.8 million years ago. It’s known for the proliferation of life, and its beginning is marked by the appearance of the hard shells of animals in the fossil record.
PhanDA is a mix of data and prior simulations by the scientific community. “This approach leverages the strengths of both proxies and models as sources of information, providing an innovative way to explore the temporal and spatial patterns in Earth’s climate across the Phanerozoic,” the researchers write in their paper. It allowed the researchers to reconstruct the climate more thoroughly.
This figure illustrates the data used to create PhanDA. A shows the temporal distribution of proxy data used in PhanDA. B shows the spatial distribution. C shows the range (gray band) and median (black line) of GMSTs within the prior model ensemble for each assimilated stage. Image Credit: Judd et al. 2024.
“This method was originally developed for weather forecasting,” said Judd. “Instead of using it to forecast future weather, here we’re using it to hindcast ancient climates.”
We’re blowing by atmospheric carbon benchmarks, and the Earth is warming. We’re now at over 420 ppm of CO2. The best way to understand what’s coming our way is by looking at the past.
“If you’re studying the past couple of million years, you won’t find anything that looks like what we expect in 2100 or 2500,” said co-author Scott Wing, the curator of paleobotany at the National Museum of Natural History. Wing’s research focuses on the Paleocene–Eocene Thermal Maximum, a period of dramatic global warming 55 million years ago. “You need to go back even further to periods when the Earth was really warm, because that’s the only way we’re going to get a better understanding of how the climate might change in the future.”
During the Paleocene-Eocene Thermal Maximum (PETM), a massive amount of carbon was emitted into the atmosphere and the oceans. The Earth’s temperature reacted swiftly, warming by between five and eight degrees Celsius in only a few thousand years. While a few thousand years might seem long compared to a human lifetime, it’s nearly instantaneous for the climate of an entire planet. It likely triggered the massive extinction of between 35% to 50% of benthic life. Fossils show that during this time, sub-tropical planets grew in the polar regions.
Many scientists think the PETM is the best analogue for what we’re facing today. No matter what we do with our emissions in the next several decades, much of the carbon humanity has released into the atmosphere since the Industrial Revolution will persist in the atmosphere for thousands of years.
Earth’s reconstructed Global Mean Surface Temperature for the past 485 million years. Blue rectangles show the maximum latitudinal ice extent, and orange dashed lines show the timing of the five major mass extinctions of the Phanerozoic. The five orange fishbone symbols mark mass extinctions. Image Credit: Judd et al. 2024.
PhanDA illustrates the unbreakable link between carbon and global warming. According to co-author Jessica Tierney, a paleoclimatologist at the University of Arizona, the link between the climate and carbon is undeniable. “This research illustrates clearly that carbon dioxide is the dominant control on global temperatures across geological time,” said Tierney. “When CO2 is low, the temperature is cold; when CO2 is high, the temperature is warm.”
While proof of the link between climate and carbon isn’t new, this long timeframe drives it home. “The consistency of this relationship is surprising because, on this timescale, we expect solar luminosity to influence climate,” the authors write. “We hypothesize that changes in planetary albedo and other greenhouse gases (e.g., methane) helped compensate for the increasing solar luminosity through time.”
Overall, Earth’s global mean surface temperature (GMST) ranged from 11° to 36°C during the Phanerozoic, a larger range than previously thought. It also shows that greenhouse climates were hotter than thought. The largest temperature swings were in the high latitudes, but tropical temperatures ranged from 22 C to 42 C. This goes against the idea that the tropics have a fixed upper limit and shows that life must have evolved to survive in those higher temperatures.
The research also shows that our current climate is actually cooler than the climate through most of the Phanerozoic. Technically, Earth is in an ice age right now, though the ice is receding and has been for thousands of years. Earth’s current GMST is 15 Celsius, lower than during most of the Phanerozoic.
But while that may sound comforting, it’s not. It’s the rate of change in the GMST that’s dangerous. Our GHG emissions are warming the planet faster than at any time during the Phanerozoic.
“Humans, and the species we share the planet with, are adapted to a cold climate,” Tierney said. “Rapidly putting us all into a warmer climate is a dangerous thing to do.”
This figure from the published research shows the climate states through the Phanerozoic. D shows the latitudinal surface air temperature gradient associated with each of the climate states. Coloured bands show the 16th to 84th percentiles, and coloured lines show the median value. Image Credit: Judd et al. 2024.
While PhanDA is generally in agreement with previous climate reconstructions, it deviates in some ways. For example, cold climate periods don’t always coincide with glaciation and ice ages. Earth’s surface is ever-changing, and that can make some conclusions difficult to reach. “Many of the traditional glacial indicators can have nonglacial origins, complicating the interpretation of the rock record, and limited outcrop of older rocks and poor age control can make it difficult to discern between isolated alpine glaciers and widespread ice sheets,” the authors explain.
But that doesn’t take much away from PhanDA. It strengthens our understanding of climate and carbon.
This figure illustrates the undeniable relationship between atmospheric carbon and a warming climate. B shows PhanDA GMST versus CO2, colour-coded by geologic era. The black dashed line shows the York regression, a statistical method used to draw a straight line between data points with some uncertainties. C shows the CO2 ranges for each of the defined climate states. Image Credit: Judd et al. 024.
Shockingly, the work suggests that Earth’s climate is even more sensitive to CO2 than some current models show.
“PhanDA GMST exhibits a strong relationship with atmospheric CO2 concentrations, demonstrating that CO2 has been the dominant force controlling global climate variations across the Phanerozoic,” the authors write in their conclusion.
If there really are advanced alien civilizations out there, you’d think they’d be easy to find. A truly powerful alien race would stride like gods among the cosmos, creating star-sized or galaxy-sized feats of engineering. So rather than analyzing exoplanet spectra or listening for faint radio messages, why not look for the remnants of celestial builds, something too large and unusual to occur naturally?
The most common idea is that aliens might build something akin to a Dyson sphere. In their need for more powerful energy sources, an advanced civilization might harness the entire output of a star. They wrap a star within a sphere to capture every last photon of stellar energy. Such an object would have a strange infrared or radio spectrum. An alien glow that is faint and unique. So astronomers have searched for Dyson spheres in the Milky Way, and have found some interesting candidates.
One major search was known as Project Hephaistos, which used data from Gaia, 2MASS, and WISE to look at five million candidate objects. From this they found seven unusual objects. They appear to be M-type red dwarfs at first glance, but have spectra that don’t resemble simple stars. This kind of star-like infrared object is exactly what you’d expect from a Dyson sphere. But of course extraordinary claims require extraordinary evidence, and that’s where things get fuzzy.
Almost immediately after the paper was published, other astronomers noted that the seven objects could also be hot Dust-Obscured Galaxies, or hotDOGs. These are quasars, so they appear star-like, but are obscured by such a tremendous amount of dust that they mostly emit in the infrared. And their spectra can be quite different from a M-type star. So the challenge is to distinguish between a hotDOG and a Dyson sphere. Which is where a new paper on the arXiv comes in.
Rather than trying to specifically distinguish between the two, the authors instead look at the distribution of known hotDOGS. They found that statistically about 1 in 3,000 quasars are of the hotDOG type, so that a broad search for Dyson spheres would likely include some dusty quasars. The authors go on to note that any civilization powerful enough to build star-scale structures would also have the ability to obscure their infrared signal. We can’t simply assume that aliens would build a Dyson sphere in such an obvious way. Overall, the authors argue, the seven candidate superstructures can be accounted for by hotDOGs and other phenomena, thus there is currently no clear evidence for alien superstructures.
