Getting a Handle on How Much Cosmic Dust Hits Earth

by Nancy Atkinson on March 30, 2012

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A starry sky, with a bright column due to zodiacal light, illuminates the desert landscape around Cerro Paranal, home to ESO's Very Large Telescope (VLT).

Does Earth have a dust build-up problem?

Estimates vary of how much cosmic dust and meteorites enter Earth’s atmosphere each day, but range anywhere from 5 to 300 metric tons, with estimates made from satellite data and extrapolations of meteorite falls. Thing is, no one really knows for sure and so far there hasn’t been any real coordinated efforts to find out. But a new project proposal called Cosmic Dust in the Terrestrial Atmosphere (CODITA) would provide more accurate estimates of how much material hits Earth, as well as how it might affect the atmosphere.

“We have a conundrum – estimates of how much dust comes in vary by a factor of a hundred,” said John Plane from University of Leeds in the UK. “The aim of CODITA is to resolve this huge discrepancy.”

Even though we consider space to be empty, if all the material between the Sun and Jupiter were compressed together it would form a moon 25 km across.

So how much of this stuff – leftovers from the formation of the planets, debris from comets and asteroid collisions, etc. — encounters Earth? Satellite observations suggest that 100-300 metric tons of cosmic dust enter the atmosphere each day. This figure comes from the rate of accumulation in polar ice cores and deep-sea sediments of rare elements linked to cosmic dust, such as iridium and osmium.

But other measurements – which includes meteor radar observations, laser observations and measurements by high altitude aircraft — indicate that the input could be as low as 5 metric ton per day.

Knowing the difference could have a big influence on our understanding of things like climate change and, noctilucent clouds, as well as ozone and ocean chemistry.

“If the dust input is around 200 tons per day, then the particles are being transported down through the middle atmosphere considerably faster than generally believed,” said Plane. “If the 5-tonne figure is correct, we will need to revise substantially our understanding of how dust evolves in the Solar System and is transported from the middle atmosphere to the surface.”

When dust particles approach the Earth they enter the atmosphere at very high speeds, anything from 38,000 to 248,000 km/hour, depending on whether they are orbiting in the same direction or the opposite to the Earth’s motion around the Sun. The particles undergo very rapid heating through collisions with air molecules, reaching temperatures well in excess of 1,600 degrees Celsius. Particles with diameters greater than about 2 millimeters produce visible “shooting stars,” but most of the mass of dust particles entering the atmosphere is estimated to be much smaller than this, so can be detected only using specialized meteor radars.

The metals injected into the atmosphere from evaporating dust particles are involved in a diverse range of phenomena linked to climate change.

“Cosmic dust is associated with the formation of ‘noctilucent’ clouds – the highest clouds in the Earth’s atmosphere. The dust particles provide a surface for the cloud’s ice crystals to form. These clouds develop during summer in the polar regions and they appear to be an indicator of climate change,’ said Plane. “The metals from the dust also affect ozone chemistry in the stratosphere. The amount of dust present will be important for any geo-engineering initiatives to increase sulphate aerosol to offset global warming. Cosmic dust also fertilises the ocean with iron, which has potential climate feedbacks because marine phytoplankton emit climate-related gases.”

The CODITA team will also use laboratory facilities to tackle some of the least well-understood aspects of the problem

“In the lab, we’ll be looking at the nature of cosmic dust evaporation, as well as the formation of meteoric smoke particles, which play a role in ice nucleation and the freezing of polar stratospheric clouds,” said Plane. “The results will be incorporated into a chemistry-climate model of the whole atmosphere. This will make it possible, for the first time, to model the effects of cosmic dust consistently from the outer Solar System to the Earth’s surface.”

CODITA has received a EUR 2.5 million grant from the European Research Council to investigate the dust input over the next 5 years. The international team, led by Plane, is made up of over 20 scientists in the UK, the US and Germany. Plane presented information about the project at the National Astronomy meeting in the UK this week.

Source: Jodrell Bank Centre for Astrophysics

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Shawn March 30, 2012 at 10:44 PM

I would be interested in the results on this, because I have always had the theory that during the age of the giant dinosaurs, the gravitation on earth was somewhat less than what it is now. That could account for the survivability of such large creatures, and be the reason we have none that large today.

Torbjörn Larsson March 31, 2012 at 10:09 AM

We have the largest animals ever, the blue whale, and as for land we have the possibly largest trees, redwoods.

Modeling based on the fossilized bones shows that the dinosaurs labored under the same gravity as we did. They could handle it then, and could do so today if they were still that large.

And really, what we are discussing here are minute changes to the mass (and hence surface gravity) of a planet. Earth masses in at ~ 6*10^24 kg. If we look at these additions and forget atmospheric attrition,* they mean Earth gain at most ~ 300*10^3 kg/day.

In ~ 65 million years, Earth would have gained ~ 65*10^6*400*3*10^5 ~ 8*10^15 kg, or ~ 10^-9 parts more mass. Surface gravity gm = GM/R^2 * m (idealizing Earth as a point mass) would scale as M/R^2 ~ M/(M^1/3)^2 ~ M^1/3, or have been 10^-10 parts larger (using a binomial approximation and order of magnitude).

As a comparison, a 10^-10 part of a year is ~10^-10*400*20*60*60 ~ 3*10^-3 s. I don’t think 3 milliseconds more on a year would made the dinosaurs die of old age. Nor do I think the ~ 10^10*100*10^3 ~ 10 mg more weight we are discussing here would make their survivability as a species less. Really, the sheer number of different giant species under an immense time period implies survivability was never an issue.

Biologists tell us traits are mostly unique one offs. The remaining like body mass isn’t, witness the blue whales and redwoods, but ecological trends are ruling them instead.

Pastoral humans were much less environmental knowledgeable and caring than todays society (yay us!) , and killed off most of the new megafauna that arose under the ice ages. That is why there are so few large animals left, even though their extinction rate has gone down considerably with the advent of modern society.

—————-
* According to this, Earth loose ~ 3 kg/s of hydrogen and little else. This is ~ 3*60*60*24 or ~ 260 metric tons each day.

The odds are, the dinosaurs were ~ 10 mg _heavier_ than they would have been today. Oh noes, think of the magnificently sized dinosaurs we could have had!

Skipdallas1 March 31, 2012 at 11:59 AM

Like the article says: 5-200 metric tons per day entering the atmosphere, some of this material eventually makes its way to the surface. With this in mind, I would think that the earth is gaining mass. A very small amount to be sure compared to the total mass of the earth. I have no idea about any loss of atmosphere to solar wind or other mechanisms but our magnetic field keeps this to a negligible figure I would think. And any losses should be countered by the out-gassing of volcanoes, cow farts etc. :-)

Duncan Ivry April 1, 2012 at 12:10 AM

I’m not quite with you. The losses you mention are not countered by the out-gassing, because this is created by processes on earth or inside the earth (well, regarding the cows, not completely, but for the most part, because the cows consume grass, and the grass consumes sunlight).

As far as I can see, the article above just tells, that we *still* don’t know how much dust enters our atmosphere, but we will “investigate the dust input over the next 5 years”. With this in mind, I would think — ;-) sorry — we should restrain from statements about the mass of the earth starting with the words “I would think”.

Torbjörn Larsson April 1, 2012 at 10:35 AM

As a problem, it sure has collected a lot of dust through the years. “Only” 5 years more to go…

Skipdallas1 April 1, 2012 at 11:17 AM

I promise to restrain myself from thinking in the future! Not! :-) Also with more thought: Would not volcanic out-gassing just be changing the properties of mass already here from a solid, or liquid to a gaseous form? The same for cow-toots! So the overall mass really stays the same, just in a different form. In addition, I will refrain from making statements prefaced with; “I would think.” :-)

Torbjörn Larsson April 1, 2012 at 10:30 AM

So what you are saying is tl;dr. If the SciAm article is correct, easily checked, and the incoming mass is in the lower region of the mentioned range, Earth may loose mass. As for outgassing (I nearly wrote “farts”), see Duncan Ivry’s comment.

In any case it is a wondrous near balance, a coincidence on the same order as the size and orbital mechanics of the Moon giving us neat solar eclipses. If Earth was much smaller or larger, or the system impactor distribution would be different at this age of the system, we wouldn’t observe this close match between incoming and outgoing mass.

Coming back to the original plight of the dinosaurs, I saw this after posting. It shows how the mass standard has drifted, because even with a set of standards most have gained mass in a round of comparisons.

From the figure, on average the kilogram prototypes have gained ~ 30 μg over a century, or ~ 0.3 *10^-9 kg/year. A 100 ton specimen then would now weigh in, by comparison with the mass prototype, with an additional 100*10^3*0.3*10^-9*65*10^6 ~ 2*10^3 kg or ~ 2 % more in mass.

The drift in mass measurements is a much larger problem than the drift in Earth gravity. Maybe that dinosaur needed to lay off the weekend hamburger. =D

Speaking of gravity changes, local surface gravity varies between ~ 0.5 % between the equator and the poles, ~ 0.3 % between sea level and Mount Everest, and including local mass concentrations between 9.78 and 9.82 m/s^2 or ~ 0.4 % between various cities. Gravity RMS variety can hence top at ~ 0.7 %.

These metric ton scale problems (well, maybe not seriously the first) are surely more problematic, for a huge enough organism, than the mg scale problem of Earth’s changing mass.

Sam April 1, 2012 at 2:55 PM

Can they find a method to try to detect evidence of panspermia from alien bacteria, spores, or viruses that was frozen in outer space and came back to the living state when warmed by earth?
http://holographicgalaxy.blogspot.com

Aqua4U April 1, 2012 at 11:40 PM

Difficult to estimate dust rates from anything less than 360* 24/7 observations lasting decades? Meteor shower and storm variability may be key here as intensity(s) are difficult to predict?

Short story subject: Observers on Earth note a steady increase in visible comet populations. More comets are seen in a single year than in all the past one hundred years. New/unpredicted meteor showers and storms are noted. Solar radiance drops a minor but significant percentage. Fantastic sunrises and sunsets are noted around the globe. Then the BIG comet comes in and swings around the sun leaving an immense trail of dust and an ion tail stretching all the way to Mars at closest passage to Sol = 45 million km!

Aqua4U April 1, 2012 at 11:46 PM

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