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Does the Oort Cloud protect us?

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Ever since I heard that our solar system is hypothesized to be surrounded by a massive spherical cloud of trillions of comets extending a good way to our nearest star (if that was exaggerated, let me know), I've been wondering whether or not this Oort Cloud may provide us 'some' protection from gamma ray bursts? My reasoning is simply that the beams of gamma ray bursts are typically, if I'm not mistaken, relatively 'narrow' (using the term 'narrow' loosely, of course), and thus might have 'some' difficulty making it through such a cloud without losing some of its energy striking the comets of the cloud.

 

In other words, could the Oort Cloud help to, for lack of a better term, weaken any potentially life-ending gamma ray bursts that unfortunately are aimed straight for us? I'm just talking in principle here; obviously there would have to be multiple comets in the path of the beam for this to be even remotely helpful, but given the supposed size of the cloud, it seems plausible that it could dampen it somewhat.

 

Anyone have any opinions?

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Ever since I heard that our solar system is hypothesized to be surrounded by a massive spherical cloud of trillions of comets extending a good way to our nearest star (if that was exaggerated, let me know), I've been wondering whether or not this Oort Cloud may provide us 'some' protection from gamma ray bursts? My reasoning is simply that the beams of gamma ray bursts are typically, if I'm not mistaken, relatively 'narrow' (using the term 'narrow' loosely, of course), and thus might have 'some' difficulty making it through such a cloud without losing some of its energy striking the comets of the cloud.

 

In other words, could the Oort Cloud help to, for lack of a better term, weaken any potentially life-ending gamma ray bursts that unfortunately are aimed straight for us? I'm just talking in principle here; obviously there would have to be multiple comets in the path of the beam for this to be even remotely helpful, but given the supposed size of the cloud, it seems plausible that it could dampen it somewhat.

 

Anyone have any opinions?

I’m certainly no expert but it seems to me if the ort cloud had enough material to protect us from gamma ray bursts then we’d have difficulty in seeing the cosmos in any great detail, as for the size this will help.

 

http://www.scienceforums.net/topic/65024-interactive-scale-of-the-universe/page__p__664954__fromsearch__1#entry664954

 

 

Edited by dimreepr

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Exactly. We see stars.

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If the gamma ray burst happened to be aligned with a giant comet in the Oort, the comet might block the GRB, but only for a fraction of a second, not long enough to save Earth from a direct hit.

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If the gamma ray burst happened to be aligned with a giant comet in the Oort, the comet might block the GRB, but only for a fraction of a second, not long enough to save Earth from a direct hit.

Only if the giant comet was much larger than the Earth. A comet the size of the Earth is extremely dubious. A comet the size of Pluto would be a giant comet.

 

A comet, even a giant one, would transit the GRB rather than eclipse it.

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gamma ray bursts are only 'narrow' in a cosmic sense. by the time the beam gets to us it could be as narrow as a few tens of thousands of light years across assuming it was from a nearby galaxy. larger if it was further away.

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Only if the giant comet was much larger than the Earth. A comet the size of the Earth is extremely dubious. A comet the size of Pluto would be a giant comet.

 

A comet, even a giant one, would transit the GRB rather than eclipse it.

 

So it is safe to say that the Oort cloud does not protect us, at all, from a GRB. No more than a fly in the sky will protect you from sunburn.

Edited by Airbrush

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Yeah I'd say so, also there is an extremely large amount of comets an meteors there, but the space is so vast, they are so spread out, the probability of a GRB hitting one is extremely low. Take the asteroid belt, it is much denser than the Oort cloud (AFAIK) but even there the asteroids are really spread out, if you flew through if, the chance of hitting an asteroid is extremely low.

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Yeah I'd say so, also there is an extremely large amount of comets an meteors there, but the space is so vast, they are so spread out, the probability of a GRB hitting one is extremely low. Take the asteroid belt, it is much denser than the Oort cloud (AFAIK) but even there the asteroids are really spread out, if you flew through if, the chance of hitting an asteroid is extremely low.

 

The gamma ray burst will hit ALL of them if it is observable from earth. the only problem is it will also hit all the space in between them as well.

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The Sun or the Moon might protect us IF they happened to be perfectly aligned with the GRB and Earth, which is a one in a Million chance. GRBs come from all angles, not necessarily from the plane of the solar system.

Edited by Airbrush

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The Sun or the Moon might protect us IF they happened to be perfectly aligned with the GRB and Earth, which is a one in a Million chance. GRBs come from all angles, not necessarily from the plane of the solar system.

 

Wouldn't the beams of light be as close as makes no difference to parallel (like the sun's) and thus the moon would only provide as much protection as it does shadow in a solar eclipse ie not much

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The Sun or the Moon might protect us IF they happened to be perfectly aligned with the GRB and Earth, which is a one in a Million chance. GRBs come from all angles, not necessarily from the plane of the solar system.

The Sun, yes, the Moon, no.

 

Assuming that a GRB can come from anywhere in the sky with equal probability, the odds the Moon or Sun would be in the way are one in 185,000 or so due to the ~32 arc minute angular diameter of the Moon and the Sun as seen from the Earth. That is where the similarities end. You have to consider the size of the shadow. The Sun would shadow a chunk of the sky that is 10,000 times the size (cross-sectional area) of the Earth. The Moon's shadow would be tiny, about 7.5% of the Earth's cross-sectional area.

 

That 7.5% protection: It's nothing. With one exception, the gamma rays from a GRB won't hit the Earth's surface. That one exception is a GRB that is so close that it blows away more than half the Earth's atmosphere. A more remote GRB will "only" dissociate the oxygen and nitrogen in the upper atmosphere. We'd say good bye to the ozone layer and hello to long-lasting stratospheric smog of nitrogen dioxide. Whether the Moon is between the GRB and the Earth would make essentially no difference on the outcome.

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Good answer D H, that's what I wanted to know. The Moon's shadow would be only 7.5% of Earth's surface. The Moon is 1/4 the diameter of the Earth, or 2,000 miles, or approx 1/16 the area. So the shadow on Earth would be approximately the same as it's size, a circle of radius 1,000 miles.

 

Does anyone know about how wide the beam of a GRB is?

Edited by Airbrush

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Does anyone know about how wide the beam of a GRB is?

It depends on how far away the GRB is. There's a mistaken conception that laser beams are parallel (and GRBs aren't as good as laser beams). They aren't. The best one can do is a Gaussian beam, which lasers come very close to being. There's still going to be divergence. The only way to avoid divergence is to have an infinitely-wide source. A commercial grade laser has a beam divergence of about 0.05 degrees, and some used for long range communication reduce this by a factor of ten.

 

Gamma ray bursts have a beam dispersion between 1 and 20 degrees, depending on the type and depending on whose article you read. If Alpha Centauri emitted a GRB (which it can't, so don't worry) aimed at the Earth, the beam would be over 10,000 AU across by the time it reached the Earth.

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What if it protects us but not in the way that people here are talking about. What if it protects us from being noticed by aliens civilizations. Airplane radar often return false readings when encountering ice so why wouldn’t alien technology also?

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51 minutes ago, AshwinCampbell said:

What if it protects us but not in the way that people here are talking about. What if it protects us from being noticed by aliens civilizations. Airplane radar often return false readings when encountering ice so why wouldn’t alien technology also?

The laws of physics are the same for them as they are for us, their technology may be more advanced/refined than ours but essentially the same (in terms of detection), so I very much doubt they'd be using radar for interstellar distances (besides all they'd detect is a planet, not us), therefore the above is just as valid for the aliens as it is for GRB.

Edited by dimreepr

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In a slightly related query, I was wondering whether Oort Cloud objects could possibly interfere with planet hunting telescopes that focus on objects orbiting distant stars. Obviously these telescopes work so I thought that these Oort Cloud objects must be really small so as to not interfere. 

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27 minutes ago, AshwinCampbell said:

What if it protects us from being noticed by aliens civilizations. Airplane radar often return false readings when encountering ice so why wouldn’t alien technology also?

The first radio transmission made by human was just a bit more than one hundred years ago. So the signal arrived at most ~124 light years from the Earth (ignoring fact of losing power (inverse-square law) and/or absorbing part of it by particles, interstellar molecules etc.)

 

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10 minutes ago, Scott of the Antares said:

In a slightly related query, I was wondering whether Oort Cloud objects could possibly interfere with planet hunting telescopes that focus on objects orbiting distant stars. Obviously these telescopes work so I thought that these Oort Cloud objects must be really small so as to not interfere. 

They're relatively small, with a lot of space between, a long way from us and moving.

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I didn’t do any sums but I wondered how big they would appear on the telescope compared to how small exoplanets appear on the telescope. I thought there would be some algorithm for determining one or the other.

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1 minute ago, Scott of the Antares said:

I didn’t do any sums but I wondered how big they would appear on the telescope compared to how small exoplanets appear on the telescope. I thought there would be some algorithm for determining one or the other.

I wouldn't know how, but the major variable is the distance to the planet. 

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5 hours ago, Scott of the Antares said:

In a slightly related query, I was wondering whether Oort Cloud objects could possibly interfere with planet hunting telescopes that focus on objects orbiting distant stars. Obviously these telescopes work so I thought that these Oort Cloud objects must be really small so as to not interfere. 

Oort Cloud objects are so rarified that a brief random blocking of light would be ignored, it could even be a rogue planet.  Astronomers only pay attention to transits caused by constant periodic dimming from exoplanets.

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I'm only aware of one celestial body that protects the Earth, namely Jupiter. It acts like a bouncer. Without Jupiter's gravity, comets (such as Shoemaker-Levy 9) would collide with our planet much more frequently.

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