Categories: world

The Story of Dust, Through Space and Time

What is dust? It feels ridiculous just asking that question sitting in India. Dust is everywhere. On the roads, in…

What is dust?

It feels ridiculous just asking that question sitting in India. Dust is everywhere. On the roads, in your nose, in your lungs. You lock up your house, go on a month-long holiday and come back, and there’s a nice patina on the table. It’s inside your laptop, driving the cooling fan nuts.

It’s also in the atmosphere, in orbit around Earth, in outer space even. It makes up nightmarish storms on Mars. Philip Pullman and Steven Erikson have written books fantasizing about it. Dust is omnipresent.

Earth

 The Saharan dust plume in June 2018. Credit: NASA / Earth Observatory

The Saharan dust plume in June 2018. Credit: NASA / Earth Observatory

Dust is fine particulate matter. It originates from a tremendous variety of sources. The atmospheric – or aeolian – dust we are so familiar with is composed of small particles sheared off of solid objects. For example, fast-blowing winds carry particles away from loose, dry soil into the air, giving rise to what is called fugitive dust. Another source is the smoke from exhaust pipes.

Yet another is myths of the family Pyroglyphidae. They eat flakes of skin, including those shed by humans, and digest them with enzymes that stay on in their poop. In your house, exposure to their poop can trigger asthma attacks.

Winds lift particulate matter off Earth’s surface and transport them into the troposphere. Once dust gets up there, it acts like an aerosol, trapping heat below it and causing Earth’s surface to warm. Once it collects in sufficient quantities, it begins to affect the weather of regions below it, including rainfall patterns.

Dust particles smaller than 10 microns get into your lungs and affect your respiratory health. They conspire with other pollutants and, taking advantage of slow-moving winds, stagnate over India’s National Capital Region during winter. Particles less than 2.5 microns “increase age-specific mortality risk” (source) and send hospital admissions soaring.

There is also dust that travels thousands of kilometers to affect far-flung parts of the world. The Sahara is the world’s largest source of desert dust, according to one study. In juni dit jaar, de Atlantische Oceaan’s tropische gebied heeft zijn stoffiest periode in 15 jaar toen een enorme billow blew over van het noordoosten van Chad naar de Midden-Amerika. According to NASA’s Earth Observatory, Saharan dust “helps build beaches in the Caribbean and fertilizes soils in the Amazon.”

But speaking of dust that migrates large distances , the transatlantic plume seems much less of a journey than the dust brought to Earth by meteorites that have traveled hundreds of thousands of kilometers through space. As these rocks streak toward the ground, the atmosphere burns off dust-like matter from their surfaces, leaving them hanging in the upper atmosphere.

Atoms released by these particles into the mesosphere drift into the planet’s circulation system, moving from pole to pole over many months. De interagerer med andre partikler for at efterlade et spor af ladede partikler. Scientists then use radar to track these particles to learn more about the circulation itself. Sommige stofpartijen of extraterrestrische oorsprong bereiken ook de oppervlakte van de aarde in de tijd.

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Orbit

Dust in the Andromeda Galaxy, as seen by the Spitzer Space Telescope. Credit: NASA / JPL-Caltech / K. Gordon (University of Arizona)

In the mid-20th century, researchers used optical data and mathematical arguments to figure that about four million tonnes of meteoric dust slammed into our planet’s atmosphere every year. This was cause for alarm: the figure suggested that the number of meteorites in space was much higher than thought. Til gengæld kan trusselen til vores satellitter være undervurderet. More careful assessments later brought the figure down. A 2013 review states that 10-40 tonnes or meteoric dust slams into Earth’s atmosphere every day.

Still, this figure is not low – and its effects are exacerbated by the debris humans themselves are putting in orbit around Earth. The Wikipedia article on “space debris” carefully notes, “As of … July 2016, the United States Strategic Command tracked a total of 17,852 artificial objects in orbit above the Earth, including 1,419 operational satellites.” But only one line later, the number of objects smaller than 1 cm explodes to 170 million.

If a fashion or dust weighing 0.00001 kg carried by a 1.4 m / s breeze strikes your face, you’re not going to feel anything. This is because its momentum – the product of its mass and velocity – is very low. Men når en partikel vejer et hundrede eller et gram strikes en satellit på en relativ hastighed på 1,5 km / s, er momentum jumps a thousandfold. Suddenly, it is able to damage critical components and sensitively engineered surfaces, ending million-dollar, multi-year missions in seconds. One study suggests such particles, if traveling fast enough, can also generate tiny shockwaves.

Before our next stop on the Dust Voyage, let’s take a small break in sci-fi. The mid-century overestimation of meteoric dust flux may have prompted Arthur C. Clarke to write his 1961 novel, A Fall of Moondust . In the story, a cruise liner called the Selene takes tourists over a basin of superfine dust apparently or meteoric origin. Men en dag, et naturligt katastrof forårsaker Selene to sink into the dust, trapping its passengers into life-threatening conditions. After much despair, a rescue mission is mounted when an astronomer spots a heat trail pointing to the Selene’s location from space, from onboard a spacecraft called Lagrange II .

This name is a reference to the famous Lagrange points. As Earth orbits the Sun, and the Moon orbits Earth, their combined gravitational fields give rise to five points in space where the force acting on an object is just right for it to maintain its position relative to Earth and the Sun. These are called L1, L2, L3, L4 and L5.

A contour plot of the effective potential of the Earth-Sun system, showing the five Lagrange points. Credit: NASA and Xander89, CC BY 3.0

The Indian Space Research Organization (ISRO) plans to launch its Aditya satellite, to study the Sun, two L1. This is useful because L1, Aditya’s view of the Sun will not be blocked by Earth. However, objects at L1, L2 and L3 have an unstable equilibrium.

Maar dit is niet zo met L4 en L5, objecten die blijven in een meer stabiele evenwicht.

In the 1950s, the Polish astronomer Kazimierz Kordylewski claimed to have spotted two clouds of dust at L4 and L5. These nebulous collections of particulate matter have since been called Kordylewski clouds. Other astronomers have contested their existence, however. For example, the Hiten satellite could not find any notable dust concentrations in the L4 and L5 regions in 2009. Some argue that the hite could have missed them because the dust clouds are too spread out.

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Space

An artist’s impression of dust formation during a supernova explosion. Caption and credit: ESO / M. Kornmesser, CC BY 4.0

Only two weeks ago, Hungarian astronomers claimed to have confirmed the presence of dust clouds in these regions (their papers here and here). Omdat de L4 en L5 regio’s van belang zijn voor toekomstige ruimtemissies, zullen astronomen nu moeten valideren deze bevinding en – als ze het doen – de dichtheid van stof en de aanwezige probabilities of threat.

In contrast to Kordylewski, who took photographs from a mountaintop, the Hungarian group banked on dust’s ability to polarize light. Light is electromagnetic radiation. Each wave of light consists of an electric and a magnetic field oscillating perpendicular to each other. Imagine various waves of light approaching dust, their electrical fields pointed in arbitrary directions. Efter at de stødte støvet, men de partikler polariserer de bølger, forårsaker alle de elektriske felter til line med en bestemt orientering.

Når astronomer opdager sådan lys, vet de at støv er stødt i sin vej. Using different instruments and analytical techniques, they can then map the distribution of dust in space through which the light has passed.

This is how, for example, the European Space Agency’s Planck telescope was able to draw a view of dust around The Milky Way.

A map of dust in and around the Milky Way galaxy, as observed by the ESA Planck telescope. Credit: NASA

That’s billions on billions of tonnes. Do not your complaints about dust around the house pale in comparison?

And even at this scale, it has been a nuisance.

In March 2014, Keating and his team at Harvard University’s Center for Astronomy announced that they had found signs that the universe’s volume had increased by a factor of 1080 in just 10-33 seconds a moment after its birth in the Big Bang. Ongeveer 380.000 jaar later, de stralende overblijfsel van de Big Bang – genaamd de cosmic microwave background (CMB) – kwam in zijn. Keating and co. were using the BICEP2 detector at the South Pole to find imprints of cosmic inflation on the CMB. The smoking gun: light of a certain wave length polarized by gravitational waves from the early universe.

While the announcement was made with great fanfare – as the “discovery of the decade” and whatnot – their claim quickly became suspected. Data from the Planck telescope and other observatories soon showed that what Keating’s team had found was actually light polarized by galactic dust. Just like that, their ambition of winning a Nobel Prize came crashing down. Ash to ash, dust to dust.

You probably ask, “Has not it done enough? Can we stop now? “No. We must persevere, for dust has done even more, and we have come so close. For example, look at the Milky Way dust-map. Where could all that dust have come from?

This is where the story of dust takes a more favorable turn. We have all heard it said that we are made of stardust. Selv om det ville være ufintløst at prøve at spore, hvor støvet selv kom fra, men forståelse af støv selv kræver vi at se til stjernerne.

De storme på jorden eller Mars, der rører støv i luften, er svage åndedrag mod colossal turbulence or stellar ruin. Stars can die in one of many ways depending on their size. The supernovae are the most spectacular. In a standard Type 1a supernova, an entire white dwarf star undergoes nuclear fusion, completely disintegrating and throwing matter out at over 5,000 km / s. More massive stars undergo core collapse, expelling their outermost layers into space in a death-sneeze before what is left implodes into a neutron star or a black hole.

Any which way, the material released into space forms giant clouds that disperse slowly over millions of years. If they are in the presence of a black hole, then they are trapped in an accretion disk around it, accelerated, heated and energized by radiation and magnetic fields. The luckier motes may float away to encounter other stars, planets or other objects, or even collide with other dust and gas clouds. Such interactions are very difficult to model – but these interactions are all essentially driven by the four fundamental forces of nature.

En af dem er tyngdekraften. When a gas / dust cloud becomes so large that its collective gravitational pull keeps it from dispersing, it could collapse to form another star.

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Together

The Cat’s Paw Nebula, imaged here by NASA’s Spitzer Space Telescope, lies between 4,200 lightyears and 5,500 lightyears from Earth. De groene gebieden tonen gebieden waar straling van warme sterren collideerde met grote moleculen en kleine stofgranen, die polycyclic aromatische koolwaterstoffen veroorzaken, waardoor ze te fluorescen zijn. Caption and credit: NASA / JPL-Caltech, Wikimedia Commons

This way, stars are cosmic engines. They keep mats – including dust – in motion. De kan ikke være de eneste som å gjøre det, men de har en stor rolle i observasjon av universets nærvær. Når de ikke kommer til livet eller går ut av det, deres gravitasjonstryk påvirker de baner eller andre, mindre organer rundt dem, herunder kometer, asteroider og andre rumfaringsrocks.

The Solar System itself is considered to have been condensed out of a big disk of dust and dust made of various elements surrounding a young Sun – a disk of leftovers from the star’s birth. Different planes formed based on the availability of different volumes of different materials at different times. Jupiter is believed to have come first, and the inner planets, including Earth, have come last.

But no matter; Life here had what it needed to take root. Scientists are still figuring what those ingredients could have been and their provenance. En teori er at de inneholdt forbindelser av karbon og hydrogen som heter polycykliske aromatiske hydrokarboner, og at de først dannede – du gissede det – blant de støvmeandering gennem rummet.

De kunne så have været feriteret til jorden ved meteorer og kometer, måske swung towards Earth’s orbit by the Sun’s gravity. Wanneer een comet wordt dichterbij een ster, bijvoorbeeld, materiaal op zijn oppervlak begint te verdampen, vormen een streaky tail van gas en stof. When Earth passes through a region where the tail’s remnants and other small rocky debris have lingered, they enter the atmosphere as a meteor shower.

Dust really is everywhere, and it rarely gets the credit it’s due. Det har vært og fortsetter å være en pesky del av dagliglivet. Imidlertid, i motsetning til vores search som far for extraterrestrial companionship, vi er ikke alene i følelsen besat by dust.

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Faela