Earth’s atmosphere vertical electric field and spider

Spiders uses atmosphere electricity to fly through air

Earth's atmosphere maintains a baseline vertical electric field of approximately 120 volts/metre, which tiny spiders detect via specialized sensory hairs on their legs to trigger airborne ballooning behavior.  Even on a clear day, Earth’s atmosphere holds a vertical electric field of about 120 volts/metre; around plants and in unsettled weather it can grow far stronger, and tiny spiders sense it through hairs on their legs to decide when to release silk and fly. Controlled experiments show that atmospheric-strength electric fields move spiders' sensory hairs and can prompt ballooning behavior, although wind remains the dominant force. Sometimes, when it rains or when they feel the urge to migrate, spiders get out their little silk knapsacks, and balloon away. This ballooning behaviour is well understood by spider scientists, but researchers have recently discovered that electric fields can not only trigger the behaviour, but also provide lift, even without the slightest breeze. When one thinks of airborne organisms, spiders do not usually come to mind. Spiders possess delicate tactile and sensory hairs (trichobothria or similar leg hairs) which physically deflect in response to ambient electrostatic charges. They monitor shifts in the local electric potential gradient, which intensifies significantly near plants, trees and during stormy or unsettled weather. Once the electric field surpasses a certain threshold, it signals the spider to release negatively charged silk threads which interact with positively charged environmental objects (like leaves or twigs), creating an upward propulsive force.

However, these wingless arthropods have been found 4 km's [2.5 miles] up in the sky, dispersing hundreds of km's. They travel via the atmospheric potential gradient (APG), an electric circuit between Earth and the ionosphere - the part of Earth's upper atmosphere that's ionised by solar radiation. Thunderstorms act like a giant battery for the APG, charging up and maintaining the electric fields in the atmosphere. The air above a quiet field is electrically different from the ground beneath it. In fair weather, the electric potential typically rises by about 120 volts for every meter of height near a flat surface. That sounds dangerous only because voltage is easy to confuse with current. The fair-weather atmospheric current is extraordinarily small. For a small spider standing on vegetation, however, the field can be useful information. A earlier experiment found that strong, naturally plausible electric fields increased behaviors that precede ballooning, when spiders release silk and let moving air carry them away. Fine hairs on their legs also moved in response to the field. This is one study, not settled consensus. Its spiders were exposed to fields of 1.25 and 6.25 kilovolts/meter, much stronger than the roughly 120 V/m fair-weather field over flat ground but realistic near plants or in disturbed weather. Later work found that electricity assists takeoff while wind remains the stronger influence. Spiders can detect atmospheric-strength electric fields, and those fields can prompt the sequence which leads to flight. The evidence does not show that fair-weather electricity alone launches every ballooning spider.

The repulsion between the charged silk and the surrounding environment can launch a spider upward even in the absence of strong drafts. While electrostatic forces can initiate takeoff and provide lift, physical wind drag remains the primary driver dictating their long-distance travel and horizontal trajectory. A fair-weather reading over level ground is not necessarily the field a spider experiences at the tip of a plant. Vegetation contains water and dissolved ions and is electrically connected to the ground. Narrow stems, leaf edges and branch tips distort the surrounding field, concentrating it around sharp projections. The same geometric principle makes electric fields strongest around the pointed end of a conductor. A plant is not a metal lightning rod, but its shape and conductivity can still create substantial local enhancement. Under a background atmospheric gradient of one kilovolt/meter, the field about ten meters above the canopy of a 35-meter tree could exceed two kilovolts/meter. Near sharp leaves, needles and branches, the modeled values could reach tens of kilovolts/meter. This matters because spiders often prepare to balloon from elevated points such as stems, leaves, fences and branches. The launch site provides clearance for silk and also places the animal in a locally intensified field.

The researchers explain that the idea of ballooning behaviour being caused by this electric circuit was first floated in the 1800's, but had been dismissed not long after, without being tested. Charles Darwin mused over how thermals might provide the forces required for ballooning as he watched hundreds of spiders alight on the Beagle on a calm day out at sea. Darwin's observation, however, did not provide further evidence in support. It is tempting to retell the story as electricity replacing wind in the explanation of spider flight. Ballooning is an interaction among animal behavior, silk, air movement and electrostatics. A earlier experiment tested three linyphiid species with wind and electric fields. Strong fields elicited pre-dispersal behavior and, when combined with light wind, facilitated takeoff. Yet wind remained the most influential factor, and the authors described electricity’s role as supplementary. Review of ballooning physics likewise treated aerodynamics and the atmospheric field as interacting explanations. Airflow can pull silk from the spinnerets, create drag and carry a spider horizontally. Electrostatic force can assist the initial lift, spread the threads and perhaps help a spider judge when conditions are favorable.

Researchers put forward a theory that electric fields might be at least a part of spiders ballooning strategy, and people were interested to see if the spiders actually responded to the electric fields and their fluctuations. They caught spiders from the genius Erigone from a balloon trap, and set up an experiment without stimuli such as air movement or atmospheric electricity. Then they turned on an artificial electric field and watched what would happen. The team did indeed find that the spiders went ballooning when the field was on, and the field's electrostatic forces alone were enough to power the movement; it's the same force which lifts up your hair if you rub a balloon on your head. When the researchers switched off the electric field, the spiders would glide down; turning the field on made them move upwards. Earth’s surface is normally negative relative to the electrically conducting upper atmosphere. Thunderstorms and electrified clouds help maintain that global difference. Away from storms, ions in the air carry a minute current toward the ground. Electric potential increases with height, producing a field directed downward. A person standing up spans a voltage difference, but the available current is too weak to resemble contact with an electrical outlet. The field is persistent rather than fixed. Charged clouds, rain, fog, airborne particles, humidity and the time of day can change its strength. In unsettled weather, local fields can reach several kilovolts/meter and can sometimes reverse polarity. The variation turns atmospheric electricity into potential weather information. An animal sensitive to the field does not need to understand voltage. It only needs a receptor which moves or changes activity when the local force changes.

The behavioral trials showed that spiders responded to the field, but not how they detected it. Focus was on trichobothria, long, fine mechanosensory hairs on spider legs. These hairs are already known to respond to tiny movements of air and to sound. Using laser Doppler vibrometry, the team measured a trichobothrium on a front leg while exposing it to airflow and changing electric fields. Air moving at 0.5 meters/second pushed the hair aside for the duration of the flow. The electrical response had a different shape. A sudden change in field produced the largest displacement at the transition. The hair then relaxed toward baseline over roughly 30 seconds even while the stimulus continued. Slowly oscillating fields also moved the hair. Because positive-to-negative and negative-to-positive changes bent the hair in the same direction, the authors interpreted the motion as electrostatic induction. A control spine did not move above the instrument’s noise level, making whole-animal motion or stray airflow less likely explanations. The distinction between the airflow and electrical responses is important. It suggests the same hair could carry separable information about wind and field changes rather than reporting both as one undifferentiated push. There is still a gap between mechanical movement and sensory experience. The study did not record the neurons attached to the hairs, disable the hairs and show that detection vanished, or reconstruct the full pathway to behavior. Calling trichobothria electroreceptors is a well-supported proposal, not a finished map of the spider nervous system.

Detecting the field is only half of the physics. Ballooning silk can acquire negative electrical charge. In Earth’s downward fair-weather field, a negative charge experiences an upward force. Like charges on neighboring strands also repel, helping explain why multiple fine threads can spread into a fan instead of tangling together. A Physical Review measured nanocoulomb-scale charges associated with ballooning silk and recorded three launches inside a chamber designed to suppress air movement. The observed motion was consistent with electrostatic lift acting on charged strands. The work did not establish one standard charge carried by every spider. Charge can vary with silk length, surface contact, humidity and other conditions. At the weaker fair-weather field, more charge or more silk is needed to supply the same lift than under the stronger fields used in a chamber. Electricity can therefore play two distinct roles. Before launch, the field provides information through hairs on the spider’s legs. After silk is released, the same field can exert force on the charged threads.

Erica Morley and Daniel Robert at the University of Bristol studied 36 adult sheet-web spiders in the genus Erigone, including 20 males and 16 females. The animals had been collected with balloon traps near the university’s veterinary school. Each spider stood on a narrow vertical cardboard strip inside a transparent box measuring 0.9 meters on each side. Aluminum plates above and below the arena turned the box into a parallel-plate capacitor. The complete setup sat on an anti-vibration table inside an acoustically isolated Faraday-cage room. The plates created fields of zero, 1.25 or 6.25 kilovolts/meter. Those two active treatments were chosen to represent values found in overcast, misty or stormy weather and around grounded vegetation. They were not meant to reproduce an ordinary 120 V/m flat-field day. Every spider experienced all three treatments in randomized order, with one condition tested/day. After a five-minute settling period, the field was applied for two minutes. The researchers cleaned and electrically neutralized the launch strip between trials, then scored the videos without knowing which treatment was shown. They counted two established signs of imminent aerial dispersal. In a tiptoe, a spider raises its abdomen and extrudes silk. A spider can also drop on a dragline and then release ballooning silk. Both behaviors became significantly more frequent when an electric field was present. The clearest visual result came after takeoff. In the still chamber, turning the field on made an airborne spider rise; switching it off let the spider descend. The observation showed that electrostatic force could support motion under the experimental conditions.

Ecology has traditionally foregrounded light, sound, chemicals, temperature and airflow. The atmospheric electric field is less obvious to human senses, but it is no less present. Terrestrial organisms have always lived inside it. Other work has found that bees can detect flower-associated electric fields and that caterpillar sensory hairs respond to electrostatic cues from approaching predators. Those cases do not prove every arthropod has an electrical sense, but they make the spider result less isolated. For a ballooning spider, a plant tip is simultaneously a physical launch tower and an electrical field concentrator. The hairs on its legs can sample both wind and voltage, while its silk becomes part sail and part charged lifting surface. The familiar image of a spider waiting for a breeze is therefore incomplete. It may also be standing inside an electrical weather map, feeling the atmosphere move before its silk ever leaves the plant. Spiders have sensory hairs called trichobothria which would move in response to the electric field, which the researchers believe is what the spiders use to detect the APG. Although science has taught us so much, these sorts of studies show just how much there is left to learn about the tricks spiders have up their eight little sleeves.

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How our solar system was born?

Process of birth of our solar system 

The solar system as we know it began life as a vast, swirling cloud of gas and dust, twisting through the universe without direction or form. About 4.6 billion years ago, this gigantic cloud was transformed into our Sun. The processes that followed gave rise to the solar system, complete with eight planets, 181 moons, and countless asteroids. The solar system's earliest outer bodies were built from 83% to 92% heat-forged chondrules (dry rock) with very little ice, revealing that early planet assembly chose fire over ice. Millimeter-sized molten droplets of silicate minerals formed by extreme heat in the solar nebula. Studies of ancient iron meteorites show that volatile-rich, icy dust was muscled out or scarce in the first generation of outer planetesimals. This surprising dry-rock assembly took place within the first million years of the solar system's history (about 4.56 billion years ago), with water and ice arriving in significant amounts much later. During the Solar System’s first million years, its earliest outer worlds formed from material that was up to 92% heat-forged rock, while gas flowing through the young system filtered out much of the surrounding ice-rich dust. Chemical tracers in carbonaceous iron meteorites indicate that the earliest outer Solar System planetesimals contained only 8 to 17% fine matrix, extending aerodynamic sorting to the opening era of planet formation.

The first solid worlds assembled in the outer Solar System did not simply collect a representative scoop of everything around them. A new analysis of carbonaceous iron meteorites indicates that their parent planetesimals contained only 8 to 17% fine, volatile-rich matrix. The rest, as much as 92% by mass, was dominated by millimetre-scale rocky particles called chondrules that had been intensely heated before they cooled. The result pushes evidence for selective planet building into roughly the Solar System’s first million years. Previous meteorite work had documented a related trend in carbonaceous bodies which formed about two to four million years after the first dated solids. “Worlds” needs a precise meaning here. These were planetesimals, the asteroid-scale predecessors from which planets and moons grew, rather than completed outer planets. No intact example from this earliest generation survives. Their lost composition has instead been reconstructed from the metallic cores that reached Earth as iron meteorites. The finding also does not mean that the outer disk lacked ice. The surrounding material was rich in cold dust, water ice and organics. The surprise is that so little of that fine-grained component entered the first known bodies.

Before it was molded into a neat set of planets, every scrap of matter in the solar system was part of a gigantic nebula, a floating interstellar cloud. This giant cloud was made up of dust, hydrogen, and other gases. It began to collapse in on itself after becoming gravitationally unstable. This was possibly because of a nearby supernova, an exploding star, sending shock waves rippling through space. Gravity then caused dust and gas to be continually tugged to the center of the cloud, making its core very hot and dense. Primitive carbonaceous meteorites preserve two visibly different ingredients. Chondrules are compact, usually rounded silicate particles made when dust or earlier solids experienced short bursts of high temperature. Some were melted into droplets; others were thermally sintered. They later cooled into the small rocky beads found throughout many meteorites. Matrix is the material between them. It consists of much finer dust which largely avoided comparable heating and retained more volatile elements, carbon-rich compounds and water-bearing material. A chondrite’s matrix fraction is therefore more than a description of its texture. It records how much cold, chemically rich dust accompanied the heat-processed rock into a parent body. The new study inferred matrix fractions of 0.08 to 0.17 for the earliest carbonaceous iron-meteorite parent bodies. Subtracting those numbers from the whole gives chondrule fractions of about 83 to 92%. The title’s “heat-forged rock” refers to that upper-end chondrule share, not to a direct measurement of a surviving miniature planet. The distinction matters because the meteorites being analyzed are metal, not pristine conglomerates in which the original chondrules can still be counted. The conclusion depends on chemical reconstruction.

There are the expanding remains of a massive supernova, known as the Veil Nebula. It became a snowball effect. As more matter got pulled in, the center got denser, increasing the gravity and pulling even more dust inwards. About 99.9% of the material fell into the middle of the cloud and became the Sun. Once the center became hot and dense enough it triggered nuclear fusion. Then visible light flooded the solar system for the first time. The 0.1% of matter which remained orbited around the Sun, causing this randomly shaped gas cloud to form a flat disc shape. This flat disc, called the protoplanetary disc, was where the planets formed. Planetesimals assembled during the Solar System’s opening epoch inherited abundant aluminium-26. This radioactive isotope had a half-life of about 717,000 years, so its decay supplied a powerful but rapidly fading source of internal heat. Bodies which formed early received enough aluminium-26 to melt extensively. Metal separated from silicate and descended into their interiors, forming cores. The process erased the starting mixture’s visible texture: chondrules dissolved into magma, ice reacted or escaped, and fine matrix ceased to exist as a recognizable component. Later collisions broke some of those differentiated worlds apart. Pieces of their metal cores became the carbonaceous iron meteorites available today. They no longer look like the original planetesimals, but some elements and oxidation relationships survived well enough to carry a record of what went into them. This creates an unusual investigation. There is no primordial rock to inspect under a microscope and no direct count of beads and dust. The researchers instead asked what starting mixture could produce the chemistry retained by cores after melting and differentiation. As NASA’s overview of early planetary systems notes, planetesimals began appearing extraordinarily quickly in the outer nebula. The timing explains both why this first generation is scientifically valuable and why its original fabric was so thoroughly destroyed.

As this rotating disc span around the Sun, it began to cool and form different types of solid material. Near to the Sun, the temperature was very high, so minerals and metals formed. And on the edge of the disc, far away from the heat of the Sun, less volatile solids like ice and ammonia formed. As the disc continued to cool down, these whirling solids stuck together to form big clusters of mass. Gradually they got larger and larger, sweeping up all the leftover dust, until they grew into the planets we recognize today. Another proxy was the valence state of iron outside sulfides. In simple terms, it measures how oxidized the iron was before the parent body differentiated. Fine matrix carried water ice and oxidized silicate precursors. A planetesimal which accumulated more matrix therefore gained more material capable of oxidizing iron. Chondrule-rich starting material should leave a more reduced signature. The researchers used core-mantle mass balance to work backwards from meteorite measurements to that original state. The iron calculation returned matrix fractions in the same 8 to 17% interval as the sulfur calculation. Sulfur abundance and iron oxidation respond to different aspects of matrix and require different calculations. Their convergence makes it harder to explain the result as a quirk of one element’s behavior during melting. It does not remove every assumption. The reconstruction uses the compositions of chondrules and matrix in younger surviving chondrites as end members for material that no longer exists intact. Estimates of original core size and sulfur distribution also carry uncertainty. The range is a defensible population estimate, not a recipe precise to the last percentage point for every early body.

Part of a chondrite found in the Sahara desert, showing the formation of chondrules. Chondrites are the most common type of meteorite to fall to Earth. The hot, rocky material near the center of the solar system was sculpted into terrestrial planets with metal cores, Mercury, Venus, Earth and Mars. On the cool edges, the gas and ice giants were born, Saturn, Jupiter, Neptune and Uranus. Damanveer Grewal of Yale University, Zhongtian Zhang of Princeton University and Joanna Drążkowska of the Max Planck Institute for Solar System Research used two independent chemical proxies. The first was bulk sulfur. In carbonaceous material, sulfur is much more concentrated in fine matrix than in chondrules. If an original planetesimal incorporated a large matrix fraction, the body’s total sulfur inventory should have been correspondingly high. Some of that sulfur would subsequently follow metal into the core, where iron meteorites could preserve evidence of it. The team reconstructed the total sulfur content of each parent body from core chemistry and estimates of the core’s share of the body. The resulting inventories were too low for matrix-rich starting material. Across the sampled carbonaceous iron-meteorite groups, sulfur pointed to an original mixture overwhelmingly dominated by chondrules. Yale’s account of the research explains why the oldest material had to be approached through these residual signatures: the aluminium-26-rich parent bodies melted completely, destroying the textures which would otherwise reveal their ingredients directly. There is no direct observation of an ancient gas stream “rejecting” an icy grain. The filtering language describes the process inferred from the composition pattern. Sulfur supplies a quantitative estimate of the result after that process had finished.

Rocks that escaped the pull of planets were left as asteroids, scattered through the solar system without a permanent home. Many of these rocks orbit the Sun in an area between Mars and Jupiter known as the asteroid belt. They can be very large, the biggest, Ceres, has a diameter of nearly 600 miles. The asteroids are rocky debris left over from the era of planet formation, 4.5 billion years ago. They’re very valuable to us as scientists, because they contain material that Earth and the other planets were originally made from, frozen in time. The study of these rocks can tell us a lot about what conditions were like in the disc, when planets were still forming. Tiny matrix grains were strongly coupled to the nebular gas. As gas moved through the disk, these particles tended to travel with it. Millimetre-scale chondrules had greater inertia and responded differently. They could drift, settle toward the disk’s midplane or become concentrated in pressure maxima while finer dust remained suspended and was carried onward. A review of planetesimal formation describes how pressure bumps and related structures can trap larger solids while very small grains remain coupled to gas. When particle concentrations become high enough, processes such as streaming instability can help collapse the solids into planetesimals. The gas was therefore not a literal sieve and did not distinguish hot rock from icy dust by temperature or chemistry. It separated particles because size, density and porosity determined their aerodynamic response. The hot and cold components happened to occupy different parts of the physical spectrum. "Filtered out” is also relative rather than absolute. Even the earliest reconstructed bodies retained 8 to 17% matrix. They were strongly depleted in fine ice-rich dust, not perfectly free of it.

Many of the asteroids in the solar system melted early on in their history to form an iron core and rocky mantle. During melting the heavier material, metal, sinks to the center while the lighter rock floats up to form a crust. The bodies that didn’t melt are a type of meteorite known as chondrites, sedimentary rocks which formed in the early solar nebula. Because they didn’t melt, they’re pristine samples of the original solids that formed in the cooling protoplanetary disc. For scientists they’re some of the most valuable leftover materials we have. They’re also the most common type of meteorite that falls to Earth. Carbonaceous chondrite parent bodies which formed two to four million years after the first calcium-aluminum-rich inclusions generally contain more matrix. Across much of the record, the fraction rises with accretion time, from roughly 30% in some groups to nearly the whole rock in the most matrix-rich examples. The new iron-meteorite points extend that relationship into an earlier interval which previously lacked intact evidence. Aerodynamic sorting did not begin only after the disk had been evolving for several million years. It appears to have influenced composition from the onset of outer planetesimal formation. The pattern also offers an explanation for the scarcity of the oldest chondrules in unmelted meteorites. Many early chondrules may not be missing because few were made. They may have been captured efficiently by the first aluminium-26-rich bodies and then destroyed when those bodies melted. One group cautions against turning the general trend into a universal clock. CR chondrites formed comparatively late, around 3.7 million years after the first solids, yet contain only about 17% matrix. Different rings, dust traps or local histories could produce exceptions inside a changing disk."

It was previously reported meteorite evidence that the young Solar System contained a gap separating inner and outer reservoirs. Isotopic differences indicate that material on the two sides did not mix freely. The new work addresses a second kind of selection within the outer reservoir. Chondrules and matrix could originate in the same broad region yet enter planetesimals at different rates because gas drag treated them differently. The disk could be divided geographically by rings and gaps while also sorting particles locally by their motion through gas. The finding also bears on when chondrules existed. Earlier examined model in which Jupiter-driven collisions generated chondrules about 1.8 million years after Solar System formation. This may describe one later production route. The present inventory does not identify the event or events which heated the earliest grains. It does require chondrule production to have been widespread from the beginning, before the oldest differentiated outer bodies assembled. Several heating mechanisms or several generations of chondrules may therefore be needed. The standard broad picture still holds: the outer Solar System offered colder, more volatile-rich material than the inner region. What changes is the assumption that location alone determined the composition of its first bodies.

Available ingredients and incorporated ingredients were not the same thing. Before gravity locked solids into planetesimals, gas motion had already changed which particles could gather together. The earliest bodies sampled by carbonaceous iron meteorites were consequently much rockier and more matrix-poor than their cold surroundings might suggest. The inference rests on a small and indirect archive. Accretion ages are relative to the first solids rather than exact calendar dates. The study reconstructs parent populations, not named planets, and it cannot yet show whether the inner Solar System followed the same chondrule-to-matrix sequence. Even with those boundaries, two independent tracers connect vanished early bodies to a longer trend preserved in younger meteorites. During the first million years, outer Solar System construction was already selective: compact, heat-processed beads gathered efficiently, while much of the finest ice-rich dust stayed with the flowing gas. Chondrites contain the first solids that formed in the solar system. By analyzing them we can figure out how old the solar system is. We can unpick the 4.5 billion year journey from the solar nebula, to the protoplanetary disc, to the solar system we see today. Earth formed from this nebula, so our journey to understand it is also a journey of self-discovery. It lets us understand our own home in universe.

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