[timschmidt]

> SpaceX is deorbiting about one or two satellites daily, and that number is only going to grow.

> What that means for our planet isn't entirely clear

100 tons of meteors hit Earth every day[1], so it seems fairly clear the 800kg Starlink v2 mini satellites[2] don't amount to much. Maybe once a dozen providers are deorbiting a similar amount of mass daily, we might notice. But even then I'm not sure there would be any negative effects. This seems like clickbait scare mongering at the moment.

1: https://pressbooks.online.ucf.edu/astronomybc/chapter/14-1-m...

2: https://dishycentral.com/how-big-are-starlink-satellites

[throwup238]

It’s closer to 43+-14 tons and most of that is cosmic dust [1] and most of that is under a millimeter in size [2].

[1] https://en.wikipedia.org/wiki/Cosmic_dust

[2] https://www.sciencedirect.com/science/article/pii/S0012821X2...

[mrtksn]

I think probably means SpaceX will need to keep sending rockets at rate of 1 or 2 satellites per day to replenish the infra. How much impact sending 800kg satellite into low orbit has?

(in batches, obviously)

[fumblertzu]

but those 100 tons do not contain that much aluminum. I remember a story where the aluminum aerosols may have a strong effect https://cires.colorado.edu/news/within-15-years-plummeting-s...

[timschmidt]

At least 1.4% of Earth is aluminum. Meteors will have similar composition on average. Aluminum smelting likely vaporizes a much larger volume of material.

[eesmith]

That aluminum is not in the upper atmosphere. Quoting https://www.nature.com/articles/s41598-021-89909-7.pdf

> ... the satellites are mostly aluminum; most meteoroids, in contrast, contain less than 1% Al by mass 25 . Thus, depending on the atmospheric residence time of material from reentered satellites, each mega-constellation will produce fine particulates that could greatly exceed natural forms of high-altitude atmospheric aluminum deposition, particularly if the full numbers of envisaged satellites are launched. Anthropogenic deposition of aluminum in the atmosphere has long been proposed in the context of geoengineering as a way to alter Earth’s albedo 26 . These proposals have been scientifically controversial and controlled experiments encountered substantial opposition 27 . Mega-constellations will begin this process as an uncontrolled experiment 28 .

Or from https://www.science.org/doi/pdf/10.1126/science.adr9689

> Concerns are mostly focused on aluminum, the most common component in satellites. If the disintegrated metal ends up as aluminum oxide or hydroxide, it can react with hydrogen chloride — the main reservoir of chlorine in the stratosphere, a hangover from the days of chlorofluorocarbons — to produce aluminum chloride. Hydrogen chloride is a relatively safe repository for chlorine, but aluminum chloride is easily split apart by light, freeing the chlorine to destroy ozone. Metal aerosols could also seed the creation of more polar stratospheric clouds, which catalyze reactions that liberate destructive forms of chlorine. “One can speculate, but without critical laboratory measurements of the chemistry, it’s very hard to know [the effects],” says John Plane, an atmospheric chemist at the University of Leeds. ... “You have to wonder whether [SpaceX] is creating a major problem 30 years from now,” Lionnet says.

[timschmidt]

It's tough to find figures, but the amount of aluminum lost during smelting not accounted for in dross is as much as half a percent. World smelting capacity is 113 million tons per year. Which maths to as much as 565,000 tons of vaporized aluminum per year.

You're right that it's released into the lower atmosphere, though I'm sure smoke stacks loft that significantly in many cases. And it's difficult for me to believe that a few hundred kg per day, even if all of it ended up in the upper atmosphere, is anything more than a blip in comparison to what lofts up from industry.

The difference would have to be many thousands of times worse for upper atmosphere releases for it to even register.

[eesmith]

> though I'm sure smoke stacks loft that significantly in many cases

It must be nice believing that your personal views are always correct.

To know that those geoengineers who want to disperse aluminum oxide to reduce the Earth's albedo clearly don't know how insignificant those aircraft deployed aerosols are compared to the byproducts of aluminum smelting.

To understand that conclusions like 'We find that the population of reentering satellites in 2022 caused a 29.5% increase of aluminum in the atmosphere above the natural level, resulting in around 17 metric tons of aluminum oxides injected into the mesosphere' can be ignored because 17 metric tons should be a blip compared to what lofts up from industry. (Quoting https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.102... )

That statements like "The natural entry of aluminum (Al) into Earth's atmosphere, primarily from meteoroids, is estimated at 141.1 metric tons (Mg) per year" is a deliberate obfuscation because it doesn't include antropogenic ground contributions. (Quoting https://www.viasat.com/content/dam/us-site/corporate/documen... )

That people looking into wood-composite alternatives to aluminum, due to concerns about "increased metallic aerosols in the stratosphere" (https://conference.sdo.esoc.esa.int/proceedings/sdc9/paper/8... ) are wasting their time.

[timschmidt]

> It must be nice believing that your personal views are always correct.

Well that's needlessly confrontational.

> That statements like "The natural entry of aluminum (Al) into Earth's atmosphere, primarily from meteoroids, is estimated at 141.1 metric tons (Mg) per year" is a deliberate obfuscation because it doesn't include antropogenic ground contributions.

Completely baffled as to who said this, and who you're accusing of deliberate obfuscation. The quote certainly wasn't pulled from any of my comments.

> That people looking into wood-composite alternatives to aluminum, due to concerns about "increased metallic aerosols in the stratosphere" (https://conference.sdo.esoc.esa.int/proceedings/sdc9/paper/8... ) are wasting their time.

And you seem to have assumed a position here which I haven't taken. I have made no statements positive or negative about whether or not aluminum aerosols are harmful. Only that industry dwarfs satellite re-entry. And only after looking up stats.

I hope you're able to have a less angry day! Maybe take a walk?

[SeanAnderson]

I had no idea 100 tons of external material was entering our atmosphere each day. Fascinating.

[timschmidt]

An additional tidbit: this is not enough mass to offset the amount of helium and hydrogen which escapes Earth's atmosphere daily. Earth is on net losing mass. Eventually, Earth will lose all the hydrogen locked in it's oceans via this process. Not sure if that's destined to happen before or after we're engulfed by the expanding sun though.

[khuey]

At the current rate of loss Earth has 150 billion years worth of hydrogen.

[rkomorn]

Well that's bad news for all the infrastructure projects in my current city and country. They're gonna run out of hydrogen before our subway extension is finished.

[thayne]

The composition is different though. In particular, these satellites probably have more heavy elements for things like batteries and electronics

[andsoitis]

Meteors contain various heavy metals, primarily iron and nickel, which form metallic cores of asteroids and make up the bulk of many meteorites.

They also contain other siderophilic metals, including cobalt, chromium, gold, platinum, iridium, and tungsten. The high concentration of these metals, especially precious metals like gold and platinum, is due to their affinity for sinking to the core of early planets and asteroids, which are remnants of the primordial solar system.

[timschmidt]

Further, satellites like Starlink's are engineered to burn up on re-entry. Meaning that they are manufactured of materials known to combust at re-entry velocities in thicknesses and shapes appropriate to that end.

[eesmith]

One key difference is the satellites have a lot of aluminum - a light element - while meteors do not.

Estimates I've seen are that the amount of Al in the upper atmosphere will be dominated by satellite demise. And we don't know how that will affect things.

The history of CFC and the ozone layer suggests caution.

[goopypoop]

> The typical meteor is produced by a particle with a mass of less than 1 gram—no larger than a pea

> The total mass of meteoric material entering Earth’s atmosphere is estimated to be about 100 tons per day

[timschmidt]

... yes? Does the mass of individual meteors or satellites matter if they both burn up on [re]entry?

On average, something like 17 meteors large enough to strike the ground hit earth daily.