Patrick M. Shober, NASA Much of what scientists know about the early solar system comes from meteorites – ancient rocks that travel through space and survive a fiery plunge through Earth’s atmosphere. Among meteorites, one type – called carbonaceous chondrites – stands out as the most primitive and provides a unique glimpse into the solar system’s infancy. The carbonaceous chondrites are rich in water, carbon and organic compounds. They’re “hydrated,” which means they contain water bound within minerals in the rock. The components of the water are locked into crystal structures. Many researchers believe these ancient rocks played a crucial role in delivering water to early Earth. Before hitting the Earth, rocks traveling through space are generally referred to as asteroids, meteoroids or comets, depending on their size and composition. If a piece of one of these objects makes it all the way to Earth, it becomes a “meteorite.” From observing asteroids with telescopes, scientists know that most asteroids have water-rich, carbonaceous compositions. Models predict that most meteorites – over half – should also be carbonaceous. But less than 4% of all the meteorites found on Earth are carbonaceous. So why is there such a mismatch? In a study published in the journal Nature Astronomy on April 14, 2025, my planetary scientist colleagues and I tried to answer an age-old question: Where are all the carbonaceous chondrites?

Sample-return missions

Scientists’ desire to study these ancient rocks has driven recent sample-return space missions. NASA’s OSIRIS‑REx and JAXA’s Hayabusa2 missions have transformed what researchers know about primitive, carbon‑rich asteroids. Meteorites found sitting on the ground are exposed to rain, snow and plants, which can significantly change them and make analysis more difficult. So, the OSIRIS‑REx mission ventured to the asteroid Bennu to retrieve an unaltered sample. Retrieving this sample allowed scientists to examine the asteroid’s composition in detail. Similarly, Hayabusa2’s journey to the asteroid Ryugu provided pristine samples of another, similarly water-rich asteroid. Together these missions have let planetary scientists like me study pristine, fragile carbonaceous material from asteroids. These asteroids are a direct window into the building blocks of our solar system and the origins of life.

The carbonaceous chondrite puzzle

For a long time, scientists assumed that the Earth’s atmosphere filtered out carbonaceous debris. When an object hits Earth’s atmosphere, it has to survive significant pressures and high temperatures. Carbonaceous chondrites tend to be weaker and more crumbly than other meteorites, so these objects just don’t stand as much of a chance. Meteorites usually start their journey when two asteroids collide. These collisions create a bunch of centimeter- to meter-size rock fragments. These cosmic crumbs streak through the solar system and can, eventually, fall to Earth. When they’re smaller than a meter, scientists call them meteoroids. Meteoroids are far too small for researchers to see with a telescope, unless they’re about to hit the Earth, and astronomers get lucky. But there is another way scientists can study this population, and, in turn, understand why meteorites have such different compositions.

Meteor and fireball observation networks

Our research team used the Earth’s atmosphere as our detector. Most of the meteoroids that reach Earth are tiny, sand-sized particles, but occasionally, bodies up to a couple of meters in diameter hit. Researchers estimate that about 5,000 metric tons of micrometeorites land on Earth annually. And, each year, between 4,000 and 10,000 large meteorites – golf ball-sized or larger – land on Earth. That’s more than 20 each day.

Today, digital cameras have rendered round-the-clock observations of the night sky both practical and affordable. Low-cost, high-sensitivity sensors and automated detection software allow researchers to monitor large sections of the night sky for bright flashes, which signal a meteoroid hitting the atmosphere. Research teams can sift through these real-time observations using automated analysis techniques – or a very dedicated Ph.D. student – to find invaluable information. Our team manages two global systems: FRIPON, a French-led network with stations in 15 countries; and the Global Fireball Observatory, a collaboration started by the team behind the Desert Fireball Network in Australia. Together with other open-access datasets, my colleagues and I used the trajectories of nearly 8,000 impacts observed by 19 observation networks spread across 39 countries.

By comparing all meteoroid impacts recorded in Earth’s atmosphere with those that successfully reach the surface as meteorites, we can pinpoint which asteroids produce fragments that are strong enough to survive the journey. Or, conversely, we can also pinpoint which asteroids produce weak material that do not show up as often on Earth as meteorites.

The Sun is baking the rocks too much

Surprisingly, we found that many asteroid pieces don’t even make it to Earth. Something starts removing the weak stuff while the fragment is still in space. The carbonaceous material, which isn’t very durable, likely gets broken down through heat stress when its orbit takes it close to the Sun. As carbonaceous chondrites orbit close, and then away from the Sun, the temperature swings form cracks in their material. This process effectively fragments and removes weak, hydrated boulders from the population of objects near the Earth. Anything left over after this thermal cracking then has to survive the atmosphere. Only 30%-50% of the remaining objects survive the atmospheric passage and become meteorites. The debris pieces whose orbits bring them closer to the Sun tend to be significantly more durable, making them far more likely to survive the difficult passage through Earth’s atmosphere. We call this a survival bias. For decades, scientists have presumed that Earth’s atmosphere alone explains the scarcity of carbonaceous meteorites, but our work indicates that much of the removal occurs beforehand in space. Going forward, new scientific advances can help confirm these findings and better identify meteoroid compositions. Scientists need to get better at using telescopes to detect objects right before they hit the Earth. More detailed modeling of how these objects break up in the atmosphere can also help researchers study them. Lastly, future studies can come up with better methods to identify what these fireballs are made of using the colors of the meteors. Patrick M. Shober, Postdoctoral Fellow in Planetary Sciences, NASA This article is republished from The Conversation under a Creative Commons license. Read the original article.

David Garofalo, Kennesaw State University One of the most powerful objects in the universe is a radio quasar – a spinning black hole spraying out highly energetic particles. Come too close to one, and you’d get sucked in by its gravitational pull, or burn up from the intense heat surrounding it. But ironically, studying black holes and their jets can give researchers insight into where potentially habitable worlds might be in the universe. As an astrophysicist, I’ve spent two decades modeling how black holes spin, how that creates jets, and how they affect the environment of space around them.

What are black holes?

Black holes are massive, astrophysical objects that use gravity to pull surrounding objects into them. Active black holes have a pancake-shaped structure around them called an accretion disk, which contains hot, electrically charged gas. The plasma that makes up the accretion disk comes from farther out in the galaxy. When two galaxies collide and merge, gas is funneled into the central region of that merger. Some of that gas ends up getting close to the newly merged black hole and forms the accretion disk. There is one supermassive black hole at the heart of every massive galaxy. Black holes and their disks can rotate, and when they do, they drag space and time with them – a concept that’s mind-boggling and very hard to grasp conceptually. But black holes are important to study because they produce enormous amounts of energy that can influence galaxies. How energetic a black hole is depends on different factors, such as the mass of the black hole, whether it rotates rapidly, and whether lots of material falls onto it. Mergers fuel the most energetic black holes, but not all black holes are fed by gas from a merger. In spiral galaxies, for example, less gas tends to fall into the center, and the central black hole tends to have less energy. One of the ways they generate energy is through what scientists call “jets” of highly energetic particles. A black hole can pull in magnetic fields and energetic particles surrounding it, and then as the black hole rotates, the magnetic fields twist into a jet that sprays out highly energetic particles. Magnetic fields twist around the black hole as it rotates to store energy – kind of like when you pull and twist a rubber band. When you release the rubber band, it snaps forward. Similarly, the magnetic fields release their energy by producing these jets.

These jets can speed up or suppress the formation of stars in a galaxy, depending on how the energy is released into the black hole’s host galaxy.

Rotating black holes

Some black holes, however, rotate in a different direction than the accretion disk around them. This phenomenon is called counterrotation, and some studies my colleagues and I have conducted suggest that it’s a key feature governing the behavior of one of the most powerful kinds of objects in the universe: the radio quasar. Radio quasars are the subclass of black holes that produce the most powerful energy and jets. You can imagine the black hole as a rotating sphere, and the accretion disk as a disk with a hole in the center. The black hole sits in that center hole and rotates one way, while the accretion disk rotates the other way. This counterrotation forces the black hole to spin down and eventually up again in the other direction, called corotation. Imagine a basketball that spins one way, but you keep tapping it to rotate in the other. The tapping will spin the basketball down. If you continue to tap in the opposite direction, it will eventually spin up and rotate in the other direction. The accretion disk does the same thing. Since the jets tap into the black hole’s rotational energy, they are powerful only when the black hole is spinning rapidly. The change from counterrotation to corotation takes at least 100 million years. Many initially counterrotating black holes take billions of years to become rapidly spinning corotating black holes. So, these black holes would produce powerful jets both early and later in their lifetimes, with an interlude in the middle where the jets are either weak or nonexistent. When the black hole spins in counterrotation with respect to its accretion disk, that motion produces strong jets that push molecules in the surrounding gas close together, which leads to the formation of stars. But later, in corotation, the jet tilts. This tilt makes it so that the jet impinges directly on the gas, heating it up and inhibiting star formation. In addition to that, the jet also sprays X-rays across the galaxy. Cosmic X-rays are bad for life because they can harm organic tissue. For life to thrive, it most likely needs a planet with a habitable ecosystem, and clouds of hot gas saturated with X-rays don’t contain such planets. So, astronomers can instead look for galaxies without a tilted jet coming from its black hole. This idea is key to understanding where intelligence could potentially have emerged and matured in the universe.

Black holes as a guide

By early 2022, I had built a black hole model to use as a guide. It could point out environments with the right kind of black holes to produce the greatest number of planets without spraying them with X-rays. Life in such environments could emerge to its full potential.

Where are such conditions present? The answer is low-density environments where galaxies had merged about 11 billion years ago. These environments had black holes whose powerful jets enhanced the rate of star formation, but they never experienced a bout of tilted jets in corotation. In short, my model suggested that theoretically, the most advanced extraterrestrial civilization would have likely emerged on the cosmic scene far away and billions of years ago. David Garofalo, Professor of Physics, Kennesaw State University This article is republished from The Conversation under a Creative Commons license. Read the original article.