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Astronomers spot closest Earth-buzzing asteroid ever recorded :
Astronomers have identified an asteroid that's just made the closest pass to Earth ever recorded – and it was only spotted after it had passed. The object skimmed Earth's atmosphere over the weekend, close enough to have its orbit changed by the planet's gravity.
On August 16, an asteroid designated 2020 QG whizzed past our planet at a distance of only 2,950 km (1,830 mi) above the surface. That's well within the altitude of many satellites, and almost twice as close as the previous record-holder, an asteroid called 2011 CQ1. Of course, this record is about the closest pass to Earth, and doesn't include objects that have impacted the planet.
That said, even if it had hit, asteroid 2020 QG wouldn't have caused any damage. It measures about 3 to 6 m (10 to 20 ft) wide, meaning it would have just burned up in the atmosphere.
Perhaps the Monolith was doing a fly-by.
(Score: 2) by deadstick on Friday August 21 2020, @12:06PM (4 children)
Of course it's an arbitrary boundary, and a very practical one. Yes, you could say the Moon is within the Earth's atmosphere, or Betelgeuse for that matter. But would you take that into account to analyze their motion?
The Karman Line is a very useful criterion for predicting whether an object is measurably affected by the Earth's atmosphere.
There's an analogous procedure with regard to gravity. In the Apollo days, the Earth and Moon were assigned "spheres of influence". I forget their relative sizes, but when a spacecraft was in the Earth's sphere, lunar gravity was disregarded; when it crossed into the Moon's sphere, Earth gravity was disregarded. Saved a lot of cycles on those horse-drawn computers.
On one of the missions, there was a routine announcement that the spacecraft had moved into the lunar sphere, and the mission commander said "Yeah, we felt a little jerk there." Walter Cronkite didn't get the joke, and joyously announced that Apollo had "surged ahead" into the Moon's gravity. NASA loved Cronkite and wasn't about to embarrass him, so the word went out to STFU about it.
(Score: 2) by Immerman on Friday August 21 2020, @01:59PM (3 children)
A fair definition of atmosphere is probably "air molecules traveling on sub-orbital trajectories", so that they will return to Earth (collisions with other molecules notwithstanding), unlike a cloud or ring of gas which remains in orbit. And as an upper limit you have the Earth's Hill Sphere (a.k.a. Roche Sphere, and quite likely the "sphere of influence" you mention) - the boundary at which gravitational influence of the body you're orbiting is balanced by the gravity from its primary - leave the sphere and you'll go into orbit around the primary instead of the original body. (.e.g. when leaving the moon, once you get outside the Moon's sphere you'll be orbiting the Earth, and if you kept going until you were outside the Earth's sphere you'd start orbiting the sun)
> predicting whether an object is measurably affected by the Earth's atmosphere
Define "measurably"
The ISS is nominally at ~354km, deep within the Earth's thermosphere, and needs regular boosts to counteract the drag from air resistance. That's pretty darn measurable.
(Score: 2) by FatPhil on Saturday August 22 2020, @09:20AM (2 children)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by Immerman on Saturday August 22 2020, @02:25PM
I'm glad you agree. Reread my post and convince yourself that's what I said.
(Score: 2) by Immerman on Saturday August 22 2020, @02:39PM
To be extra clear, I suppose I said something slightly different than you -
I said: A molecule on a sub-orbital trajectory is part of the atmosphere
You said: a molecule that's part of the atmosphere is on a sub-orbital trajectory
Those aren't logically equivalent, but they have a pretty heavy amount of overlap.
My statement claims that a molecule out beyond the moon, but still on a sub-orbital trajectory that will return it to Earth, is part of the far reaches of the Earth's atmosphere.
Your statement leaves open the possibility of additional restrictions that would mean it's NOT part of the atmosphere.
Either way, if it leaves the Earth's Hill Sphere and begins orbitting the sun, I think we can both agree that it's definitely not part of the Earth's atmosphere any longer.
Though I suppose technically my first statement alone, without the rest of the post, would leave open the possibility of alternative qualifications that might still allow it to be considered part of the atmosphere. But I think the rest of my post proves that wasn't my intent.