What if the Earth had rings?


Short answer: Bad news for space travel. And this isn't just idle speculation for boozy astrophysicist parties. Space junk—spent rockets, lost astro-screwdrivers, satellite parts—could form rings around our planet as surely as water, ice and dust encircle Saturn. Scientists have been especially concerned about satellite collisions, where debris from one wreck could trigger a futuristic 12-car pileup.

On 10 February 2009 it started to happen. In the first collision between two intact satellites, the defunct Russian craft Kosmos-2251 struck communications satellite Iridium 33 at a speed of 42,100 kilometres per hour. The impact shattered one of Iridium 33's solar panels and sent the satellite into a helpless tumble. Kosmos-2251 was utterly destroyed. The two orbits are now home to clouds of debris that, according to the US military's Space Surveillance Network (SSN), contain more than 2000 fragments larger than 10 centimetres. The collision may also have produced hundreds of thousands of smaller fragments, which cannot currently be tracked from Earth.

Such debris is a serious worry. With satellites travelling at tens of thousands of kilometres per hour, any encounter with debris could be lethal. "Being hit by a 1-centimetre object at orbital velocity is the equivalent of exploding a hand grenade next to a satellite," says Heiner Klinkrad, head of the space debris office at the European Space Agency in Darmstadt, Germany.

New Scientist: Space Junk—Hunting Zombies in Outer Space

Image: Some rights reserved by NASA Goddard Photo and Video



  1. My imagination says there is more potential energy in a piece of cm sized space junk at orbital speeds then in a hand grenade.

    Is there a physicist in the house?

    1. wgmleslie, you beat me to it. Planetes was a whole series premised on space junk. One of the most clever titles ever (ancient greek for wanderers, which became our word for planets, but the title also refers to the characters). The intro alone packs more space history than your average documentary.


  2. it’s the relative speed that matters, not the overall speed of an object. If I’m moving 16999 mph and something moving 17000 mph in the same direction hits me, i won’t even feel it unless it’s a large object. It certainly won’t puncture anything durable. Anything going significantly slower or faster will find itself in a different orbit fairly quickly, and as far as I know, all that garbage is orbiting the earth in the same direction.

    in short; it’s not quite as bad as they make it sound.

  3. The bad news is, it will once the moon enters the Roche limit and gets torn apart. The good news is that this won’t happen before Xmas.

  4. The moon will never enter the Roche limit. The moon’s orbit actually is getting farther away from the Earth at 4 centimeters per year.

  5. Weren’t both satelites traveling at 42,100 kilometres per hour?

    Wouldn’t the collision just be the difference in their vectors? maybe a few 1,000 kph?

    1. The writer Junot Diaz has often said that pollution makes New Jersey’s sunsets some of the most striking around. By extension, a planetary ring made out of pollution and garbage should be quite stunning. At least from the ground.

  6. If someone comes up with a viable way to clean out space junk from valuable orbital real estate, I’m investing!

  7. There is a physicist in the house, and it isn’t the speed that is important, it is the relative speed. Two objects in nearly the same orbit have nearly the same speed so the relative speed is nearly zero and the collision is not nearly so catastrophic.

    The issue comes in when an object is in an elliptical orbit that intersects another orbit. Then, when they meet, they aren’t travelling at anything close to the same speed and collisions can be quite violent.

    The question about the energy content compared to a hand grenade therefore has no real meaning since the absolute velocity of the projectile is irrelevant to computing the energy of the collision. Unless you know the absolute velocity of both object, or their relative velocity, you can’t say.

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