Asteroid To Pass Within 200k Miles Of Earth This Tuesday

[Zaune]

Guardian

Astronomers around the world have readied their telescopes to catch a glimpse of a speeding ball of rock that will hurtle past the Earth on Tuesday night.

Scientists say the asteroid, which is about a quarter of a mile wide, will pass inside the moon's orbit and come within 198,000 miles (319,000km) of Earth at 23.28GMT. This is the closest a tracked object this size has come to the planet.

Nasa calculates the 400-metre (1,312ft) wide asteroid, known as 2005 YU55, has roughly has a one in 10 million chance of hitting Earth in the next century. Were it to strike, the collision would unleash the equivalent of several thousand megatonnes of TNT.

Even with clear skies the asteroid will not be visible to the naked eye, but professional and amateur astronomers will turn their telescopes on the rock to learn about its surface and chemical composition.

Because the asteroid is approaching from the sun's direction, there will be too much glare to observe the rock with optical or infra-red telescopes until the day of closest approach.

"Most of the asteroids we see are so far out that we only get a small amount of information from the light reflected off them," said Kevin Yates, at the Near Earth Objects Information Centre at the National Space Centre in Leicester. "Because this one is coming in so close we'll be able to get more radar observations, which will give us a detailed surface map, and be able to get more of a chemical signature on the minerals it's made up from."

The Arecibo telescope in Puerto Rico last year revealed the asteroid to be remarkably spherical while its surface is very dark, suggesting it is rich in carbon.

Observatories at Nasa's Goldstone Deep Space Communications Complex, in the Mojave desert of California, and at Green Bank, West Virginia, will join forces with Arecibo to watch the asteroid pass this week. Operators have called on scores of amateur astronomers to help with observations, using 10-12in telescopes with special filters.

A similar flyby will not happen until 2028 when asteroid 2001 WN5 swings past the Earth at a distance of 143,000 miles.

"We are finding a whole variety of unusual shapes out there and this asteroid is particularly spherical. If we can characterise them more and understand them more, then if we ever do have a threat from one, understanding the structure and the materials they're made from would better equip us to divert one. It may be that there are materials on board that could be used as a fuel to drive an engine that would push it into a different orbit over 20 years," Yates added.

The asteroid is among the most ancient objects in the solar system, having formed from the dust and gas disc that surrounded the sun 4.5bn years ago. Though born in the asteroid belt between Mars and Jupiter the rock was pulled by gravity or nudged by collisions on to its new orbital course.

"These are the building blocks left over from when the solar system formed and this particular carbonaceous asteroid is one of the most primitive types," Yates said. "Understanding its chemical composition is like looking into the ingredients book to see how it was put together."

The asteroid will pass close to Venus in 2029, which will disturb its orbit to mean its next passage past Earth, in 2041, could be between 198,000 miles and nearly 30m miles from the planet. The close encounter after that will be with Mars in 2072.

Posted without comment.

[The Romulan Republic]

Another lucky near miss. I wonder how many more of these we'll have before one hits, and weather when that happens we'll have a space program capable of doing anything substantial about it.

[Steel]

To put the distance into perspective, at the earth's orbital speed, this asteroid is only going to be 10 seconds away. If it lies in the same plane as the earth then being 10 seconds ahead (or perhaps behind) in the year would put us under this thing.

[Zaune]

To put the distance into perspective, at the earth's orbital speed, this asteroid is only going to be 10 seconds away. If it lies in the same plane as the earth then being 10 seconds ahead (or perhaps behind) in the year would put us under this thing.

I would honestly have preferred to be made aware of that factoid after it passes us by.

[Dominus Atheos]

Let's put this into perspective here. The 400 meter across asteroid is going pass us at a distance of 319,000,000 meters, or 797,500 asteroid lengths. And even if the asteroid is off course by 319,000,000 meters, space is 3 dimensional; so the chances of it hitting the earth would have to be defined as the surface area of a sphere with that radius, which would be about 1,278,765,359,960,000,000 sq meters. The radius of the earth is 6,378,000 meters so it would occupy about 127,516,010,269,190 sq meters of that sphere, or about 0.01%. And that assumes that the asteroid is exactly 325,000,000 - 313,000,000 (given the diameter of the earth) meters off its projected course, any more or any less and there's no chance of it hitting the earth. I'm not sure what the probability of that is, if they covered that in 8th grade geometry I must have been asleep that day.

TL:DR space if really, really, really big, so don't sweat anything.

[Simon_Jester]

Let's put this into perspective here. The 400 meter across asteroid is going pass us at a distance of 319,000,000 meters, or 797,500 asteroid lengths. And even if the asteroid is off course by 319,000,000 meters, space is 3 dimensional; so the chances of it hitting the earth would have to be defined as the surface area of a sphere with that radius, which would be about 1,278,765,359,960,000,000 sq meters. The radius of the earth is 6,378,000 meters so it would occupy about 127,516,010,269,190 sq meters of that sphere, or about 0.01%. And that assumes that the asteroid is exactly 325,000,000 - 313,000,000 (given the diameter of the earth) meters off its projected course, any more or any less and there's no chance of it hitting the earth. I'm not sure what the probability of that is, if they covered that in 8th grade geometry I must have been asleep that day.

Your calculations are off a bit.

From the point of view of the asteroid, the Earth can be viewed as a fixed target 'downrange' at some distance- as the asteroid moves along, it will either strike the place the Earth occupies, or it won't. But for these purposes, on any given close pass space might as well be two-dimensional. The third dimension doesn't matter because the asteroid traces a line through the volume the Earth occupies; it can't miss by getting the 'depth' wrong, only by being off 'sideways' from a course that would strike the Earth.

The easy way to visualize it: the asteroid is being thrown at a very small bullseye (the Earth) in a large, flat target.

However, your basic result is substantially right- if a random meteor is guaranteed to pass somewhere within 300000 kilometers of the Earth, then it 'hits' a random point on a circle 600 thousand kilometers wide, with the Earth at the center. The Earth itself makes up only 2% of the width of the circle, and 0.04% of its area- again, very small bullseye, very large target.

Of course, since the asteroid in question would impact like a nuclear bomb so big, not even the Russians were crazy enough to build one... a 0.04% chance of a direct hit is not entirely happy-making.

However, on this pass the asteroid's position is not random- we've been observing it for a long time, and know its course to a certain precision, and can predict with much better than 99.96% confidence that it will miss. The real catch is that it will pass Earth at an imperfectly-predictable distance (plus or minus a few thousand kilometers, say), which means that the Earth's gravity will bend it through a slightly-unpredictable angle, which combined with the same thing happening at Venus later on, means we can't say with such confidence where it's going to pass us the next time it comes by in 2041.

On the other hand, even if it's lobbed at us completely at random it will still miss with practically 100% certainty, and even if it was headed right for us we would have enough time to mount a deflection mission because we'd have twelve years to figure out where it was going, go "oh shit" and respond. I would recommend, tentatively, nuking it from a standoff distance- think improvised Orion drive, not Armageddon.

But that's me.

[Steel]

Let's put this into perspective here. The 400 meter across asteroid is going pass us at a distance of 319,000,000 meters, or 797,500 asteroid lengths.

I'm not sure how the number of asteroid lengths is relevant, the thing is point sized compared to the earth anyway. Certainly wouldn't just laugh off being missed by 50 bullet widths, when that only amounts to only one body width for me.

And even if the asteroid is off course by 319,000,000 meters, space is 3 dimensional; so the chances of it hitting the earth would have to be defined as the surface area of a sphere with that radius, which would be about 1,278,765,359,960,000,000 sq meters. The radius of the earth is 6,378,000 meters so it would occupy about 127,516,010,269,190 sq meters of that sphere, or about 0.01%. And that assumes that the asteroid is exactly 325,000,000 - 313,000,000 (given the diameter of the earth) meters off its projected course, any more or any less and there's no chance of it hitting the earth. I'm not sure what the probability of that is, if they covered that in 8th grade geometry I must have been asleep that day.

TL:DR space if really, really, really big, so don't sweat anything.

We aren't trying to teleport the asteroid into the centre of the earth, it is tracing out a line that we need to intersect with the cross section of the earth. Indeed, more than that even, although space is 3d, a lot more stuff is in the same plane as all the planets* than isn't due to everything forming from an accretion disc. So actually, the chances of an object hitting us aren't the same as if we just treat everything as having an unconstrained random position, velocity pairing.

If the orbits are truly coplanar (worst case, we have a 1-d system here essentially) then it does just boil down to where we lie on the orbital path when the other object passes (both on the way in and out), i.e.:

p(collision) = 2*Earth diameter/total length of earth orbit = 4*REarth/2*pi*AU

= 2*REarth/pi*AU

*well one of the planets has an inclined orbital plane...

[Simon_Jester]

Orbital inclinations vary by enough that on the scale of near-Earth asteroids and the question "will they collide with us or not?" it's a 2-D problem; it's totally possible for an asteroid to soar past Earth 'above' or 'below' the plane of the Earth's orbit by several hundred thousand kilometers. So, no, simplifying to a 1-D problem is going to greatly overestimate the danger.

Near-earth asteroid passes happen every decade or so, maybe more; actual impacts by rocks this size are much, much rarer, i.e. none in the past million years or so.

As to DA's mention of asteroid diameters, I think it's useful because it conveys the scale- in relative terms, the asteroid is a bacteria-sized object trying to hit a man-sized target while flying helplessly on a more or less random course through an area the size of several city blocks.

[Skgoa]

Simon, what you are forgetting is that both objects are moving. I.e.
1) Since gravity between two objects changes their movement, the asteroid's velocity is actually a big factor in the question of whether it will be pulled to Earth in a significant way.
2) It's not just a question of the asteroid's orbit crossing ours exactly, but it also has to do it in a rather tiny time-frame.

So, while for this asteroid that doesn't change the situation, it means that the actual chance of being hit by any asteroid in general is reduced quite a bit from what we would get, if we treated it inly as a 2d problem.

[Simon_Jester]

Simon, what you are forgetting is that both objects are moving. I.e.
1) Since gravity between two objects changes their movement, the asteroid's velocity is actually a big factor in the question of whether it will be pulled to Earth in a significant way.
2) It's not just a question of the asteroid's orbit crossing ours exactly, but it also has to do it in a rather tiny time-frame.

So, while for this asteroid that doesn't change the situation, it means that the actual chance of being hit by any asteroid in general is reduced quite a bit from what we would get, if we treated it inly as a 2d problem.

Well. Given that we know the approximate speed the asteroid is traveling in, and given that it's going to pass somewhere in the general vicinity of Earth...

You can draw, at any given time, a plane perpendicular to the asteroid's line of flight. At some specific moment, that plane will contain the Earth. If the asteroid happens to pass through the bit of that plane which the Earth is actually in, it hits the Earth.

It doesn't matter what the timing is- either the Earth will be there when the asteroid arrives, or it won't. The definition of "there" may be a patch which doesn't exactly correspond to the size of the Earth, due to the effects of deflection from the Earth and the moon's gravity. But on a given close pass, there's a specific bundle of trajectories the asteroid can have, which occupy a tube with cross-section roughly 10-15000 km across, that result in the asteroid striking the Earth on that pass. If we draw a flat plane containing the asteroid, and perpendicular to its trajectory, and the asteroid is not located in the cross section of that tube, it will miss the Earth.

Hence, 2D problem, at least as far as computing the odds on a given pass goes.

[Skgoa]

Yes, on a given pass. I just wanted to point out that we aren't likely to get a close encounter with anything at all, much less actually being hit by it.

[Tolya]

That is interesting news.

Im wondering, what would be the closest safe proximity in this case? How close would the orbits have to be to intersection for the asteroid to be pulled in by Earth's gravity field?

I remember the nonsensical ending of Armageddon, where the asteroid would still hit the Earth, only in two parts.

[Eternal_Freedom]

If it's flying past us pretty much any proximity is safe. There was an incidentin the 70's where an asteroid came within 57km of the Earth's surface and skipped off the atmosphere.

It depends on angle. Shallow angles mean the object is likely to skip off the atmosphere, whereas a steeper angle will allow an impact, if it doesn't burn up on re-entry.

[Tolya]

If it's flying past us pretty much any proximity is safe. There was an incidentin the 70's where an asteroid came within 57km of the Earth's surface and skipped off the atmosphere.

It depends on angle. Shallow angles mean the object is likely to skip off the atmosphere, whereas a steeper angle will allow an impact, if it doesn't burn up on re-entry.

The angle also does depend on how close the trajectories intersect. So, is it safe to assume that if it doesn't hit us directly, we're good?

[Eternal_Freedom]

Yeah, I woudl say so. It either hits us or it doesn't. A very close approach might drastically alter the asteroid's path but it won't spiral in and hit us. Primarily because a typical asteroids velocity is far in excess of Earth orbital velocity, so it will just fly past us.

[Skgoa]

And now you guys are once again forgetting that we are talking about orbital mechanics. The actual velocity or vector of the asteroid in relation to the sun doesn't matter. We only care about it's movement relative to us. I can very easily concieve of cases were an object would be going very fast and have an orbit around the sun that does ordinarily stay rather far from ours, yet it crashes into us. E.g. us slowly "overtaking" an asteroid on a slightly wider orbit. On the other hand, it's equally as easy to devise a case where an object is relatively slow and crosses our path very very closely, yet misses us completely. E.g. a comet that is crossing our orbit right "behind" us.
So, aside from very crude generalizations, there is no way to solve the two-body-problem without crunching the numbers.