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The Next Near Miss  
User currently offlineseb146 From United States of America, joined Nov 1999, 11475 posts, RR: 15
Posted (1 year 5 months 1 day 4 hours ago) and read 1339 times:

Another asteroid is headed toward Earth. It will miss. My question for any rocket scientists: Why don't some of these "near miss" asteroids get sucked into our orbit? If they are passing that close and are relatively light, wouldn't they become a natural sattelite of Earth?


Life in the wall is a drag.
24 replies: All unread, jump to last
 
User currently offlinenazgul From United Kingdom, joined Oct 2012, 46 posts, RR: 0
Reply 1, posted (1 year 5 months 1 day 4 hours ago) and read 1319 times:

You're in luck! I may be an arts student but I am also fairly educated in Physics and Maths. "Near misses' are a relative term and they are actually nowhere near Earth or it's Solar orbit. It's no doubt rouge matter from the Asteroid belt (which as you probably know separates the inner solar system from the outer - the border between Mars and Jupiter). To come into an impact path with Earth it would have to have an incredibly strong metal compound matter to be drawn into our polar magnetic "spin' when it is already on a pre-defined point of destruction. In other words, a near miss is just a term that had been picked up by the media! Having said that, there have been impacts with Earth and will continue to be but hey ho, I would't worry too much  

User currently offlineAesma From France, joined Nov 2009, 6481 posts, RR: 9
Reply 2, posted (1 year 5 months 1 day 3 hours ago) and read 1309 times:

Well recently one passed closer than the Moon is. I'd call that near by any definition. However for it to be "sucked" it would have to be pretty slow. I'd say there is far more chance of a direct hit (and there has been many) than of a "satellization" (there is only one, the Moon, and it is believed to be the result of a hit, so it doesn't even count).


New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
User currently offlinenazgul From United Kingdom, joined Oct 2012, 46 posts, RR: 0
Reply 3, posted (1 year 5 months 1 day 3 hours ago) and read 1287 times:

I don't doubt that one passed closer than the moon. However, if it was of any significance we would have heard about it as it would have posed a threat to population centres (perhaps not in a catastrophic sense). If it was in lunar orbit then it also would pose a threat to us. The satellite that is our moon was, as you rightly pointed out, was caused by ... well, I am a scientist so I have my beliefs and there are others who have theirs.  

User currently offlineseb146 From United States of America, joined Nov 1999, 11475 posts, RR: 15
Reply 4, posted (1 year 5 months 1 day 3 hours ago) and read 1262 times:

Quoting nazgul (Reply 1):
it would have to have an incredibly strong metal compound matter

So, for any asteroid to get sucked into our orbit, it would have to react with Earth's polarity? If/When an asteroid has that, what happens to tides? I guess that would depend on the mass of the object, right? Same with polarity of GPS and cell phone sattelites?



Life in the wall is a drag.
User currently offlineA320ajm From United Kingdom, joined May 2006, 537 posts, RR: 0
Reply 5, posted (1 year 5 months 1 day 2 hours ago) and read 1247 times:

Quoting nazgul (Reply 1):

Earth has a very weak magnetic field. Gravity of the Earth is orders of magnitudes greater. Given the size of an asteroid relative to Earth, I think the Earth's magnetic field would have a negligible effect. If an asteroid was going to hit Earth, it'd be down to gravity.

A320ajm



If the British Empire and its Commonwealth last for a thousand years, men will still say, 'This was their finest hour.'
User currently offlineseb146 From United States of America, joined Nov 1999, 11475 posts, RR: 15
Reply 6, posted (1 year 5 months 1 day 2 hours ago) and read 1232 times:

Quoting A320ajm (Reply 5):
If an asteroid was going to hit Earth, it'd be down to gravity.

So, if Earth's magnetic field is so weak, why do we have a moon? Why are these asteroids not orbiting around Earth? Asteroids are much smaller in mass than our Moon.



Life in the wall is a drag.
User currently offlineAesma From France, joined Nov 2009, 6481 posts, RR: 9
Reply 7, posted (1 year 5 months 1 day 1 hour ago) and read 1216 times:

Things orbit due to gravitation coupled with speed. The magnetic field has only an effect on energized particles (coming from the sun, mostly, then other stars and similar objects). The Moon is speeding and affected by gravitation, causing an equilibrium of the two, that's what being in orbit means. The Moon is actually slowly escaping Earth's gravity, and one day will be gone. On the other hand the Alpha station (ISS) is orbiting so close that there is still a tiny atmosphere slowing it down, so it is "crashing" and has to be pushed up regularly. For an object to naturally arrive and end up orbiting Earth it has to come at the right speed, the right trajectory, it's a 1 in a billion chance or something like that. With man made objects you have engines to accelerate, change the trajectory, brake, until a stable orbit is obtained.


New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
User currently offlineBEG2IAH From United States of America, joined Apr 2004, 926 posts, RR: 17
Reply 8, posted (1 year 5 months 1 day 1 hour ago) and read 1216 times:
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Quoting seb146 (Reply 6):
So, if Earth's magnetic field is so weak, why do we have a moon? Why are these asteroids not orbiting around Earth? Asteroids are much smaller in mass than our Moon.

I thought our Moon had nothing to do with Earth's magnetic field but gravity of both. Moon was formed after a Mars-sized planet smashed and almost destroyed Earth and our Moon was created from the ejected material that consolidated into a mass. If our planet's magnetic field was so strong to attract asteroids, you wouldn't be able to lift a fork off your table.



FAA killed the purpose of my old signature: Use of approved electronic devices is now permitted.
User currently offlinebueb0g From United Kingdom, joined Jul 2010, 639 posts, RR: 0
Reply 9, posted (1 year 5 months 1 day 1 hour ago) and read 1207 times:

Quoting seb146 (Reply 6):
So, if Earth's magnetic field is so weak, why do we have a moon? Why are these asteroids not orbiting around Earth? Asteroids are much smaller in mass than our Moon.

The moon isn't kept there by magnetism. It's surmised that the moon came into existence when a foreign body, small planet sized, impacted with the Earth billions of years ago, leaving two masses, one smaller, which then subsequently orbited the Earth.

As for asteroids passing through our gravity without being sucked into orbit - it's mostly to do with the trajectory and speed of these objects, and plus, they are often in the grip of a much stronger gravitational field (the sun's.) An object would have to be going relatively slowly, and be on an intercept trajectory to join an orbit around Earth; it's not as simple as "object near planet, object orbits planet". Most of these asteroids will have their trajectory bent slightly by Earth's gravity but will easily escape the gravity field due, mainly, to their high velocities.



Roger roger, what's our vector, victor?
User currently offlinerwessel From United States of America, joined Jan 2007, 2293 posts, RR: 2
Reply 10, posted (1 year 5 months 23 hours ago) and read 1168 times:
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Quoting seb146 (Thread starter):
My question for any rocket scientists: Why don't some of these "near miss" asteroids get sucked into our orbit? If they are passing that close and are relatively light, wouldn't they become a natural sattelite of Earth?

A handful actually do, but the orbits tend not to be all that stable, so the pop out again.

The mass of the asteroid (within reason) has nothing to do with it, it's relative speeds and distances. And in general the amount of speed an asteroid picks up falling towards the earth is just what's needed to escape on the other side, and then you add in any initial velocity that the asteroid had, and most will just zip right by. In some cases the relative motions have things zeroing out in just the right way (consider an asteroid happening to hit the Aphelion of its orbit just as Earth swept past) to effect a capture. If a large third body is involved, certain resonances can occur which can help crate a capture too.

Mind you that these near passages will generate considerable deflection of the asteroid's path (2012 DA14's path, for example, will be deflected about 10 degrees on Friday).

This is the same reason orbital probes to other planets need to slow down in some way when they arrive there, in order to avoid shooting past.


User currently offlineconnies4ever From Canada, joined Feb 2006, 4066 posts, RR: 13
Reply 11, posted (1 year 5 months 14 hours ago) and read 1053 times:

Quoting A320ajm (Reply 5):
Earth has a very weak magnetic field. Gravity of the Earth is orders of magnitudes greater. Given the size of an asteroid relative to Earth, I think the Earth's magnetic field would have a negligible effect. If an asteroid was going to hit Earth, it'd be down to gravity.

Actually, Earth's magnetic field is relatively strong for a planet this size, and indicates decent circulation of molten iron in the core. But it has essentially zero effect on asteroid-type bodies coming fairly close.

NEOs (Near Earth Objects) typically are not co-planar to Earth's orbit, and are moving in a fairly elliptical orbit around the Sun. Because of this, they tend to be moving relatively quickly as they are moving towards perihelion, therefore are in the vicinity a fairly short time, so are usually not terribly influenced bhy our gravitational field. Also bear in mind the field strength is inversely proportional to the square of the distance between primary and secondary. In this case, gthe point of closest approach is about 17,000 miles, i.e., about 4x the radius of the Earth. Therefore 'g' at that point is around 1/16th what it is on Earth. So gravitational effects as well may not be particularly large.

Quoting seb146 (Reply 6):
So, if Earth's magnetic field is so weak, why do we have a moon? Why are these asteroids not orbiting around Earth? Asteroids are much smaller in mass than our Moon.

See above.

Quoting BEG2IAH (Reply 8):
I thought our Moon had nothing to do with Earth's magnetic field but gravity of both.

Quite right. In actual fact, the Moon does not orbit the Earth. Both the Earth and the Moon rotate around a common centre of mass, which is about, IIRC, 1,800 miles below the Earth's surface (might be km's). This partly explains why we can see rather more than 50% of the Moon's surface from Earth.



Nostalgia isn't what it used to be.
User currently offlinen229nw From United States of America, joined Sep 2004, 1925 posts, RR: 32
Reply 12, posted (1 year 5 months 14 hours ago) and read 1036 times:

Quoting nazgul (Reply 1):
rouge matter from the Asteroid belt


Is that like dark matter but redder? Or are you just getting cosmology and cosmetology mixed up?

  

What I really want to know is whether an asteroid could take off on a treadmill though...



It's people like you what cause unrest!
User currently offlineStarAC17 From Canada, joined Aug 2003, 3354 posts, RR: 9
Reply 13, posted (1 year 5 months 14 hours ago) and read 1034 times:

Quoting seb146 (Reply 6):
So, if Earth's magnetic field is so weak, why do we have a moon? Why are these asteroids not orbiting around Earth? Asteroids are much smaller in mass than our Moon.

The magnetic field works to protect us from violent radiation that would come from solar winds that would destroy the ozone layer and leave us exposed to solar radiation that will kill us.

Quoting connies4ever (Reply 11):
This partly explains why we can see rather more than 50% of the Moon's surface from Earth.

Isn't that because the moon completes one revolution in the same amount of time it takes to do one orbit, therefore the same side of the moon is visible from earth.



Engineers Rule The World!!!!!
User currently offlineconnies4ever From Canada, joined Feb 2006, 4066 posts, RR: 13
Reply 14, posted (1 year 5 months 13 hours ago) and read 1017 times:

Quoting StarAC17 (Reply 13):
Quoting connies4ever (Reply 11):
This partly explains why we can see rather more than 50% of the Moon's surface from Earth.

Isn't that because the moon completes one revolution in the same amount of time it takes to do one orbit, therefore the same side of the moon is visible from earth.

Close. The ability to see more than 50% (actually around 59%) of the lunar surface is due to an effect called "libration". This is the sum of three parameters:
- eccentricity of the Moon's orbit; eccentricity defines how elliptical an orbit is (Earth's around the Sun is not circular, for example. We're actually closest to the Sun during Northern winter, farthest during Northern summer);
- inclination of the Moon's orbit w.r.t. Earth's orbit around the Sun;
- what's called diurnal libration, linked to the centre of mass issue.

http://en.wikipedia.org/wiki/Libration

Here's a video showing the effect (speeded up, of course): http://www.youtube.com/watch?v=3f_21N3wcX8

http://www-spof.gsfc.nasa.gov/stargaze/Smoon4.htm

Also, the time it takes for the Moon to go "around the Earth" really depends on definitions:

http://www.sumanasinc.com/webcontent/animations/content/sidereal.html

Astronomy really is the oldest science. As a species we've been looking at the Moon and the stars for 10s of thousands of years. So enjoy.



Nostalgia isn't what it used to be.
User currently offlineA320ajm From United Kingdom, joined May 2006, 537 posts, RR: 0
Reply 15, posted (1 year 5 months 12 hours ago) and read 998 times:

Quoting connies4ever (Reply 11):
Actually, Earth's magnetic field is relatively strong for a planet this size, and indicates decent circulation of molten iron in the core. But it has essentially zero effect on asteroid-type bodies coming fairly close.

The dynamo is strong, you are correct   The point I was making was that relatively the magnetic field is weak - compared to say, gravity. We make magnets on Earth many orders of magnitude greater e.g. LHC etc.



If the British Empire and its Commonwealth last for a thousand years, men will still say, 'This was their finest hour.'
User currently offlineKlaus From Germany, joined Jul 2001, 21391 posts, RR: 54
Reply 16, posted (1 year 5 months 1 hour ago) and read 926 times:

Entering an orbit around a planet is actually not that trivial to do for planetary survey probes.

When they're approaching the planet, they convert potential energy (their mass being "high up" relative to the planet) into kinetic energy (they're accelerating while their mass mostly stays the same).

The problem is that fundamentally there are two main outcomes to this:

• crashing directly into the planet if the course was set towards it or

• flying by and after that converting the kinetic energy they just gained in equal measure back into potential energy (converting the speed they had just gained on approach back into distance from the planet), meaning they will completely escape the planet's pull again

Actually entering an orbit means that some of the kinetic energy must be "thrown overboard" before the probe escapes the planet again; And that can be done by firing its engine to "brake" (effectively expelling some of the kinetic energy via the exhaust of the engine) or if the planet has an atmosphere by grazing it just by the right amount so friction will take some of the kinetic energy away, and after still climbing out of the atmosphere due to the remaining kinetic energy, again firing the engine to redirect from a strongly elliptic course (which would lead into the atmosphere again, ultimately causing a crash to the surface) into a less elliptical or even circular stable orbit.

A stable orbit has the orbiting body with just the right amount of kinetic energy and a properly adjusted course that it cannot escape the planet (too little kinetic + potential energy) but also doesn't come close enough for atmospheric braking to take effect (too much kinetic + potential energy and the lowest point of the orbit being still well above the atmosphere).

The same applies to asteroids – they just don't have any braking engines (fortunately!), so only very, very few of the big ones come close enough and are already slow enough to experience atmospheric braking to a sufficient degree that they don't simply escape earth's gravity again or even hit the earth head-on.

Given the scale of the solar system and the relatively tiny size of the earth, it's actually pretty difficult to hit it from afar by throwing asteroids at it.


User currently offlineStarAC17 From Canada, joined Aug 2003, 3354 posts, RR: 9
Reply 17, posted (1 year 4 months 4 weeks 1 day 13 hours ago) and read 879 times:

Quoting Klaus (Reply 16):
Given the scale of the solar system and the relatively tiny size of the earth, it's actually pretty difficult to hit it from afar by throwing asteroids at it.

You're right but look at the moon, there are heaps of very large craters on it from asteroid impacts in the past so while the chances are low compared to many things the earth is in a shooting gallery.

Earth has been hit just as much but we have a planet that destroys the evidence.



Engineers Rule The World!!!!!
User currently offlineKlaus From Germany, joined Jul 2001, 21391 posts, RR: 54
Reply 18, posted (1 year 4 months 4 weeks 1 day 12 hours ago) and read 877 times:

Quoting StarAC17 (Reply 17):
Earth has been hit just as much but we have a planet that destroys the evidence.

The moon has preserved craters accumulated over billions of years – and it has no atmosphere for protection against the smaller ones which burn up harmlessly, never reaching th e earth in one piece.


User currently offlineStarAC17 From Canada, joined Aug 2003, 3354 posts, RR: 9
Reply 19, posted (1 year 4 months 4 weeks 1 day 12 hours ago) and read 869 times:

Quoting Klaus (Reply 18):
The moon has preserved craters accumulated over billions of years – and it has no atmosphere for protection against the smaller ones which burn up harmlessly, never reaching th e earth in one piece.

Oh I know this, but some of those craters are the size of cities or larger. Many of those asteroids that hit the moon could have done some serious damage on earth.

Good thing the Moon is there also as it is a nice shield  .



Engineers Rule The World!!!!!
User currently offlineAR385 From Mexico, joined Nov 2003, 6099 posts, RR: 31
Reply 20, posted (1 year 4 months 4 weeks 1 day 5 hours ago) and read 830 times:
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According to what I´ve read, an asteroid this size crashes against the Earth once every 1,200 years. This one would cause damage similar to what the Tunguska object caused back in 1908. Of course, that was in the middle of the woods, nowadays if it hit a city it would be bad.


MGGS
User currently offlineStarAC17 From Canada, joined Aug 2003, 3354 posts, RR: 9
Reply 21, posted (1 year 4 months 4 weeks 1 day 5 hours ago) and read 826 times:

Quoting AR385 (Reply 20):
According to what I´ve read, an asteroid this size crashes against the Earth once every 1,200 years. This one would cause damage similar to what the Tunguska object caused back in 1908. Of course, that was in the middle of the woods, nowadays if it hit a city it would be bad.

There weren't cities in 1908, news to me  .



Engineers Rule The World!!!!!
User currently offlineconnies4ever From Canada, joined Feb 2006, 4066 posts, RR: 13
Reply 22, posted (1 year 4 months 4 weeks 15 hours ago) and read 773 times:

Quoting AR385 (Reply 20):
According to what I´ve read, an asteroid this size crashes against the Earth once every 1,200 years. This one would cause damage similar to what the Tunguska object caused back in 1908. Of course, that was in the middle of the woods, nowadays if it hit a city it would be bad.
http://en.wikipedia.org/wiki/Impact_event

http://impact.arc.nasa.gov/

http://neo.jpl.nasa.gov/risk/

If something this big were impacting every 1,200 years or so, I think we'd be a little further back on the technology scale. Tunguska in 1908 was a low-level air burst, perhaps 30,000 ft or so, that flattened everything from the hypocenter in a radius of 20-30 km. If it had been near a populated area, there would have been a large body count.

The asteroid in question, 2012 DA14 seems to be in the 50m range. Tunguska may have been nearer 100m. Here's a scenario of what could happen in 2012 DA14 actually impacted a populated area:

http://www.cbc.ca/hamilton/news/stor...02/14/hamilton-asteriod-earth.html

But, as has been reported by many science commentators in the media, we rally don't know what's out there, we can only estimate from what we've historically observed, or seen in the geological record. But bear in mind there can always be "outliers" that we might miss until the last moment.



Nostalgia isn't what it used to be.
User currently offlineAR385 From Mexico, joined Nov 2003, 6099 posts, RR: 31
Reply 23, posted (1 year 4 months 4 weeks 12 hours ago) and read 741 times:
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Quoting connies4ever (Reply 22):
If something this big were impacting every 1,200 years or so, I think we'd be a little further back on the technology scale.

From your link

http://www.cbc.ca/hamilton/news/stor...02/14/hamilton-asteriod-earth.html

"NASA estimates that asteroids this size fly this close to the Earth about once every 40 years and hit the planet roughly once every 1,200 years. The last time it happened was on June 30, 1908, when a meteorite crashed in Tunguska, Russia."



MGGS
User currently offlineMadameConcorde From San Marino, joined Feb 2007, 10864 posts, RR: 38
Reply 24, posted (1 year 4 months 4 weeks 12 hours ago) and read 730 times:

They say this asteroid came historically close to Earth. It sailed harmlessly past its closest approach point and is now gone bye bye.

  



There was a better way to fly it was called Concorde
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