Ballistic experiments show that tardigrades are unlikely to be an alien species

Tardigrades have not been shown to survive all space conditions at once

A 2007 mission launched several species into low-Earth orbit, exposing them to microgravity in temperature-controlled modules. Survivability rates were high for microgravity exposure alone, but plummeted when combined with exposure to the full UV spectrum and the vacuum of space.

Extreme temperature resilience appears to be temporary for tardigrades

Although often considered indestructible, scientists observed these creatures could endure temperatures near 150°C for only a few minutes in their tun state. Outside this state, only half the samples in a Danish study survived 37.1 degrees Celsius (98 degrees Fahrenheit) for 24 hours, making tardigrades extremotolerant rather than extremophiles.

Tardigrades can survive in a dehydrated state for decades

Despite being known as water bears, these microscopic creatures can shut down their metabolism when entering cryptobiosis, squeezing more than 95% of the water from their bodies. In this tun state, tardigrades can even survive the vacuum of space.

Why tardigrades are a model extremotolerant species rather than an extremophile

By expelling most of the water from their bodies, water bears assume a state resembling a dried-up cyst and can withstand extreme environments, such as arid deserts. But in this state and these environments, tardigrades cannot grow, reproduce, or perform other functions associated with life, unlike extremophiles like dry-loving xerophiles.

Tardigrades average about half a millimeter in size, with rear legs used for grasping

Their physiology and size, which is even smaller in the tun state, allow them to be carried by the wind and latch onto moist surfaces. They have been found in ocean trenches approximately 5 kilometers deep and at altitudes of six kilometers in the Himalayas.

Experiments suggest nuking a metal-rich asteroid may strengthen it

Scientists exposed meteorite samples to proton irradiation at CERN to mimic the effects of a nuclear detonation. The material exhibited greater resistance to breaking after the exposure, suggesting nuclear weapons may better serve to deflect asteroids, not break them.

A lunar probe’s crash landing may have spilled tardigrades onto the moon

In 2019, Israel’s Beresheet probe, which contained tardigrades in a cryptobiotic state, underwent a gyroscopic failure when attempting to land. If they survived the crash, the tardigrades may have spread across the lunar surface, raising ethical concerns about planetary contamination.

Fossils suggest tardigrades developed cryptobiosis more than 180 million years ago

As of 2024, three tardigrade fossils have been discovered, all preserved in amber. Analysis suggests different species of the organism existed over 500 million years ago, when marine heterotardigrades and freshwater terrestrial eutardigrades diverged. (Some readers may experience a paywall.)

Tardigrades typically live between 3 and 30 months

While avoiding predators, including other tardigrades, nematodes, snails, mites and some fungi, these organisms feed on decaying plant matter and cellular fluid, which they access by puncturing cell walls with their stylets—spear-like structures within their mouths.

Earth is constantly bombarded by material from space

Most of this matter is composed of small particles, with any smaller than 33 feet in diameter burning up in the atmosphere. Larger asteroids can reach the ground, and those larger than several thousand feet cause global damage, including earthquakes and tsunamis.

Tardigrades’ intrinsically disordered proteins may help preserve biological matter

Researchers have attempted to create more drought-resistant crops by introducing proteins that help protect tardigrades in their dehydrated tun state. The proteins’ ability to stabilize molecular degradation may allow scientists to develop refrigeration-free storage for vaccines, insulin, and blood.

See how distant aliens could preemptively strike humanity

Could aliens destroy us from light-years away? The team at Kurzgesagt imagines the impact of a highly sophisticated alien civilization setting out to crush humanity and considers the real-world logistics for warfare conducted across the Universe.

Studies show the asteroid that killed the dinosaurs was from the outer asteroid belt

Isotopic evidence confirms the rock was a carbon-rich asteroid, likely born beyond Jupiter and later knocked into Earth's path after billions of years of orbital drift and gravitational nudges. Its path spanned over 4 billion years and ended in the extinction of 75% of life, including all nonavian dinosaurs.

Jupiter may have affected the trajectory of the asteroid that wiped out the dinosaurs

Despite its reputation as Earth’s cosmic shield, Jupiter’s gravity pulls more asteroids into Earth-crossing orbits. Simulations show that Earth experiences over three times more asteroid impacts because of Jupiter’s influence than if Jupiter didn’t exist.

What would happen if a massive asteroid struck Earth?

While NASA states that no known asteroid currently threatens Earth, past impacts demonstrate that the risk is real. The agency has tested deflection technology to alter an asteroid's path, as this visualization imagines a worst-case collision scenario.

Mold growth in space raises the hypothesis of life being brought to Earth

Panspermia suggests that life could be carried throughout the cosmos by asteroids, comets, and other objects, but it requires organisms that can withstand the extreme cold of space travel, stellar radiation, lack of water, and intense heat of planetary impacts. The discovery of mold on the International Space Station and experiments showing it can withstand radiation in outer space-like conditions increase the plausibility of the hypothesis.

About 66 million years ago, an asteroid larger than Mount Everest struck Earth off the coast of the Yucatán Peninsula and wiped out at least 75% of all species, including nearly all dinosaurs.

Defending Earth against asteroids

This three-minute video overview explains NASA's ambitious test to slightly alter the course of an asteroid by slamming a fast-moving space probe into its surface. Scientists hope to one day, if needed, use the technique to protect Earth from an asteroid impact.

A scientist debunks theories for why aliens might invade Earth

While TV and films offer common tropes for why aliens would invade Earth, many of those reasons aren't actually feasible. For example, a species with technology advanced enough to allow it to travel between planets likely doesn't need to enslave flawed humans to carry out its labor.

A modern-day version of the dinosaur-killing asteroid would kill billions of people

Such an asteroid would level Central America, trigger tsunamis, spark global fires, and plunge the planet into an artificial winter lasting over a decade. Bunkers would be insufficient for survival without years of provisions.

Ticks are extremely hard to kill

These arachnids can transmit more than a dozen diseases to humans, and they're very resilient: Some can survive extreme heat and cold, live for years without a blood meal, and even survive multiple days underwater.

Dinosaurs would likely still roam Earth if the Chicxulub asteroid had hit elsewhere

Some scientists argue that the asteroid's impact would have been less severe if it had struck the ocean instead of shallow seas. In this scenario, small dinosaurs might have become urban survivors, living in cities alongside humans, much like pigeons or rats do today.

The Cybertruck's custom alloy exoskeleton withstood gunfire

Although the Cybertruck was not designed to be bulletproof, ballistics tests with Glock, MP5, shotgun, and Tommy gun rounds showed the vehicle sustained only minor damage, such as impact craters and cracks in the glass, without fully penetrating the structure.

If aliens visited Earth, it seems unlikely they'd be evolved biological creatures like us

The writer behind Mindless Algorithm, George McGowan, challenges various assumptions about aliens depicted in science fiction. One of those is that aliens are, like humans, individual entities that live, age, and die. McGowan suggests that the difficulty of intergalactic travel and the aliens' technological advancements make it more likely that they'd be an advanced form of AI or digital copies of biological entities.

Research suggests a 95-kilometer-wide (59-mile-wide) asteroid impact could boil the Earth's oceans

Even a 1-kilometer-wide (0.62-mile-wide) asteroid can trigger earthquakes and tsunamis on impact with oceans. The overwhelming majority of asteroids that reach Earth are much smaller and burn up in the atmosphere before reaching the ground.

Craters found on the moon and the calculated dates of these impacts, based on rocks returned by the Apollo missions, suggest that Earth was pummeled by asteroids for millions of years—a period known as the Late Heavy Bombardment.

Simulations suggest that a paper airplane launched from the International Space Station would maintain its orientation and gradually descend for 3.5 days before chaotically tumbling down and burning up.

About 1,500 species of tardigrades have been identified by their unique physiology

Freshwater-bound eutardigrades live on mosses and lichens and are distinguished by variations in the shape and number of claws at the end of their legs. Marine heterotardigrades, which live on algae and deep-sea sediments, have been observed to possess feathers, inflatable appendages, and flagpole-like tails.

Simulate asteroid impact, mitigation, and defense scenarios

Tens of thousands of asteroids are in orbit in our solar system, and only a fraction come close enough to concern humanity. This simulator allows you to see the big picture scenarios of an asteroid impact, strategies to mitigate its destruction, and how Earth could defend itself.

If the Earth stopped spinning, 85% of the world's population would experience supersonic winds

The planet's equator moves about 470 meters per second—over 1,000 miles per hour—and air there would continue moving at this speed for several minutes if the ground stopped rotating. These conditions would cause tsunamis, global storms, and fling debris fast enough to destroy nearly all human-made structures.

You are 65,000 times more likely to be struck by lightning than to be hit by space trash

In 2023, about 1,500 pieces of space junk fell to Earth, with most consisting of payload fragmentation debris. The vast majority that falls back to Earth burns up before reaching the surface, making it three times less likely to be struck by space trash than by a meteorite.

NASA's DART mission successfully deflected an asteroid

The Double Asteroid Redirection Test crashed into asteroid moonlet Dimorphos in 2022, altering its orbital radius. The project required precise astrodynamics to strike the moonlet from 11 million kilometers away while traveling 22,530 kilometers per hour.

The hypothetical particle that travels faster than light

Astrophysicists inspired by science fiction developed the theory of the tachyon—a Greek word for "fast"—which is a field or particle hypothetically able to travel faster than light. Although no experiments have confirmed any part of it, it's a fun theory to consider.

Extremophiles were likely to have been Earth's first, and are expected to be its last, organisms

Their ability to survive in an enormous range of environmental conditions, including some resembling what has been modeled to have existed relatively shortly after Earth's formation, makes them the leading candidates for enduring the increasing solar intensity and the subsequent effects (e.g., zero-oxygen atmosphere, evaporated oceans) expected in the coming billions of years.

The name ‘tardigrades’ comes from the Latin word for ‘slow walkers’

Before being renamed for their movements, German pastor Johann August Ephraim Goeze called them Kleiner Wasserbär—little water bears—in the first published observations of the creatures in 1773. He noted their voracious appetite made them seem like bears under a microscope.

Explore a gallery of tardigrades

Although sometimes called moss piglets, tardigrades are most often white or clear with some dark pigments. Tardigrades only move by crawling, not swimming, and depictions of organisms with caved-in heads or other coloration result from sample preparation for microscopes.

Critical organic molecules have been found on an asteroid

NASA's OSIRIS-REx mission returned samples containing amino acids and nucleobases from asteroid Bennu. Without Bennu having been destroyed—as is common for asteroids that enter Earth's atmosphere—its samples serve as a time capsule of the solar system's early chemistry.

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

T. rex didn't stomp, it walked on tiptoes like a bird

A new biomechanical study analyzing four T. rex specimens, including the famous "Sue" at Chicago's Field Museum, found the dinosaur used a "distal-first" foot strike, described as landing on its toes before its heel, similar to a modern ostrich. The technique improved stride efficiency and shock absorption, letting adults reach speeds up to 14 mph, while younger, lighter T. rexes could sprint closer to 25 mph.

Only 40% of city-destroying asteroids have been detected

Statistical modeling shows that while we have identified the majority of extinction-level asteroids, smaller asteroids that can cause significant damage remain elusive. Some asteroids, like the one that exploded over Chelyabinsk in 2013, can't be detected ahead of time since they come from the sun's direction.

Shooting stars are streaks of light produced by meteoroids

As these rocks enter Earth's atmosphere at high speeds, friction causes them to burn up, briefly leaving streaks of light. The color of these fireballs can be used to determine the composition of the meteoroid, if it does not reach the ground and become a meteorite for analysis.

Scientists have tested atmospheric models by firing rockets into the aurora borealis

Functioning like components of a CT scan, the missiles transmit signals that can be used to identify charged particles and electromagnetic currents in slices. The slices are then combined to construct a computer-based model of Earth's atmospheric structure, which is used to compare the accuracy of physics-based models.

Watch visualization of different-sized asteroid impacts

The animations range from a 4-meter-wide asteroid that would burn up in the atmosphere with the impact of 0.6 Hiroshima nuclear bombs to a 940-kilometer asteroid the size of the dwarf planet Ceres, which would produce a mass extinction event.

Protecting astronauts against space radiation

Outside the protective atmosphere of Earth, astronauts are constantly bombarded by radiation, which, among other dangers, increases the risk cancer. While those of us on Earth can mitigate the effects of similar radiation by limiting exposure,...

Microgravity can alter the evolution of viruses and bacteria

Experiments conducted on the International Space Station have shown that microgravity environments can delay viral and bacterial infections and induce mutations not seen on Earth. These mutations could have implications for long-term space missions and human health and suggest space can serve as a testing ground for developing new therapeutic approaches.

A four-billion-year-old meteorite reignited the debate about life on Mars

Recovered from Antarctica in 1984, ALH84001 contained organic compounds, magnetite and iron sulfide grains of potential biological origin, and features that resembled fossilized bacteria. With technological advancements, scientists found abiotic origins for these features in the following decades.

Watch tardigrade samples under an optical microscope

Tardigrade samples can be collected by gathering moss and submerging it in tap water for 24 hours. The moss should then be cut and drained with a mesh sieve, and the water should be collected. Samples are observable in the water between 10x and 40x magnifications.

Aliens may be closer to Earth than scientists have previously assumed

The hunt for extraterrestrial life is often associated with traveling far into the depths of space for clues. But answers could be closer than we think. Modern space missions have demonstrated our capability of sending probes beyond the solar system, making it plausible that other civilizations could do the same.

Why the existence of extremophiles greatly improves the odds of life beyond Earth

The conditions for life have long been thought to include liquid water, an energy source, and the essential elements for organic molecules within environments on or near Earth's surface. However, because extremophiles thrive in far more inhospitable environments, astronomers now analyze exoplanets whose characteristics indicate environments that fall within a broader range of possibilities when searching for signs of extraterrestrial life.

About 10% of the radiation people are exposed to each year comes from outer space, with higher percentages for those living at higher elevations or who fly often.