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Asteroid Near-Misses (AKA: Holy Shit! We're All Going to Die)

Asteroid to skim past Earth
An asteroid larger than a double-decker bus is to pass within 28,000 miles of Earth on Tuesday, but has no chance of hitting the planet, Nasa has said.
By Nick Collins
Published: 7:00AM BST 12 Oct 2010

The giant rock, which is 20ft (6m) wide, will come its closest shortly before midday, though astronomers are not sure what its exact path will be.

But experts, who named the asteroid 2010 TD54, said that despite passing very close to the planet it would not enter the atmosphere, and that even if it did it would burn up before reaching the ground.

Nasa's Asteroid Watch said on Twitter: "Small space rocks this size would burn up in our atmosphere & pose no ground danger."

The group added that a "moderate telescope" would be required to make out the rock, which will at times be closer to Earth than some satellites, and significantly nearer than the moon.

Emily Baldwin, of Astronomy Now, told The Times: "Fortunately it seems this one will miss us. But it is a reminder that the Earth is still in the middle of a cosmic shooting gallery and we need to keep constant watch for incoming asteroids".

http://www.telegraph.co.uk/science/spac ... Earth.html
 
Asteroid ocean strike 'could strip away ozone layer'
PA
Tuesday, 26 October 2010

A medium-sized asteroid plunging into the ocean would destroy much of the ozone layer, leaving the Earth exposed to dangerous levels of ultraviolet radiation, it was claimed today.

The impact from a space rock 500 metres to one kilometre in diameter would send vast amounts of water into the atmosphere, according to US expert Dr Elisabetta Pierazzo.

Seawater chemicals such as chloride and bromide would strip away significant amounts of ozone, which provides a shield against harmful sun rays.

The result would be a huge spike in ultraviolet (UV) radiation levels at the Earth's surface.

People with fair skins would find their skin burning after just a few minutes of sun exposure.

Farmers would have difficulty growing crops, and rates of skin cancer and cataracts would be likely to rise.

Previous research looking at the effects of an oceanic asteroid impact has focused on the danger of tsunamis.

Dr Pierazzo's new work, published in the journal Earth and Planetary Science Letters, used computer simulations to model the effects on atmospheric ozone.

She tested two impact scenarios, involving a 500 metre and kilometre diameter asteroid.

"The results suggest that mid-latitude oceanic impact of one kilometre asteroids can produce significant global perturbation of upper atmospheric chemistry, including multi-year global ozone depletion comparable to record ozone holes recorded in the mid 1990s," said Dr Pierazzo, from the Planetary Science Institute in Tucson, Arizona.

"The removal of a significant amount of ozone in the upper atmosphere for an extended period of time can have important biological repercussions at the Earth's surface as a consequence of increase in surface UV-B irradiance. These include increased incidence of erythema (skin reddening), cortical cataracts, changes in plant growth and changes in molecular DNA."

People may be forced to avoid direct sunlight to protect themselves against the harmful UV rays, she added.

UV intensity is measured by the ultraviolet index (UVI), with levels of 10 or above assumed to be dangerous.

The highest UVI recorded on Earth so far has been 20, said Dr Pierazzo. But a 500-metre asteroid crashing into an ocean could see UVI jump to values above 20 for several months in the northern subtropics.

A one kilometre impact would see UVI soar to 56, rising above 20 for around two years in both the northern and southern hemispheres.

"A level of 56 has never been recorded before, so we are not sure what it is going to do," said Dr Pierazzo. "It would be producing major sunburn. We could stay inside to protect ourselves, but if you go outside during daylight hours you would burn. You would have to go outside at night, after sunset, to avoid major damage."

Assuming there is enough warning, farmers could reduce the effects of the impact by planting crops with a higher UV tolerance, she said.

Food could also be stored to ensure supplies during a few years of poor productivity.

http://www.independent.co.uk/news/scien ... 17062.html
 
Asteroids: When the time comes to duck
Jonathan Amos | 23:09 UK time, Friday, 29 October 2010

Somewhere out in space there’s a big rock that has our address on it.

Throughout geological history, our planet has been hit by a succession of major asteroids and the probabilities suggest further impacts will occur in the future.
No-one can say today when these might happen; we haven’t yet identified an asteroid of sufficient size and on a path that gives us immediate cause for concern.
But the evidence hints strongly that something could find us sooner or later, and we need to be ready.

On average, an object about the size of car will enter the Earth's atmosphere once a year, producing a spectacular fireball in the sky.

About every 2,000 years or so, an object the size of a football field will impact the Earth, causing significant local damage.

And then, every few million years, a rock turns up that has a girth measured in kilometres. An impact from one of these will produce global effects.

We know of some Near-Earth Objects (NEOs) today that are several km wide but fortunately none of them comes close enough to make us sweat.

The important thing is we keep looking. The US space agency’s NEO programme has been running since the late 1990s.
It was tasked with finding 90% of the potentially hazardous objects out there larger than 1km and it’s about 80% through this search. A few years back, the US Congress asked Nasa to extend the survey to include rocks down to about 140m in size.
That requires more and better telescopes and these are coming online. You will hear much more information on NEOs in the coming years because of this finer-scale sweep of the skies.

When a potentially hazardous rock is discovered, one of the best ways to determine its true status is to complete a study using radar, an extremely powerful tool.
Facilities such as the Arecibo Observatory in Puerto Rico or the Goldstone complex in California can pin down a rock’s key properties, determining its velocity to a precision less than 1mm per second, and enabling scientists to compute its orbit hundreds of years into the future.

One of the more interesting factoids that I became aware of recently is just how many of these objects are actually binaries – that’s to say, when the radar observations are done it becomes apparent that the asteroid is really two asteroids, or even a trio.

Some of these are what are termed contact binaries – they touch each other. These are the objects that look like giant peanuts. (My favourite contact binary is the “dog bone” asteroid, 216 Kleopatra, although this is a long way from Earth and no threat to us).
About a quarter of all the objects investigated by radar turn out to be binaries of some kind.

So the inevitable question arises, what do we do if we find that huge rock with our address on it?
The powers that be are on the case. A lot of this work goes under the aegis of the United Nations, and in this context a body called the NEO Mission Planning and Operations Group (MPOG) has been meeting in Germany this week.

This panel of experts – these are astronauts, various space scientists and engineers - is urging the world’s space agencies to improve their search and tracking capabilities, and to start developing concepts to deflect asteroids.

One of the leading figures in this initiative is the Apollo 9 astronaut Rusty Schweickart. He’s the chairman of the B612 Foundation, which campaigns on the NEO topic [PDF], and was one of the attendees at the MPOG meeting. He characterises the threat thus:
“At the upper end, you’re talking about wiping out the dinosaurs and most of life on Earth 65 million years ago; at the smaller end you’re talking about a million objects that hit the Earth last night – we call them shooting stars. It’s the objects in between that occur every few hundred years that we’re concerned with.”

Schweickart is convinced the solutions are within reach to deal with most hazardous asteroids on a collision path with Earth. In the majority of cases, the preferred concept would look much like Nasa’s Deep Impact mission of 2005 which saw a shepherding spacecraft release an impactor to strike a comet.
This gentle nudge, depending when and how it's done, could change the velocity of the rock ever so slightly to make it arrive “at the intersection” sufficiently early or late to miss Earth.

According to Schweickart, rear-ending an asteroid may be the easy part, however. Getting the world’s bureaucracy to act on the threat in a timely fashion may be the bigger challenge, he believes. And here’s why.

Consider the 300m-wide asteroid Apophis. For a while, before the calculations were detailed enough, there was some concern this object might hit Earth in 2036. The odds now are thought to be pretty slim.

But just imagine for a moment that it was headed right for us and we needed to do something about it.
Take a look at the map [at link]. We know enough about the plane of Apophis’s orbit to understand where this rock would intersect the Earth, and it would be somewhere along the red line.

Now imagine the UN meeting convened to discuss whether the mission sent up to deflect the asteroid should try to slow or accelerate the rock. The choice is important because it would determine where on the line the rock would hit if the mission is not entirely successful in getting the asteroid to pass by the Earth.
In other words, one strategy chosen over the other would lessen the risks for some while increasing them for others.

So, you can bet Russia, Venezuela and Senegal would have very different views on which mission profile should be chosen.
That’s why Schweickart believes the geopolitical obstacles need to be tackled now and the mechanisms put in place to deal with thorny issues like the one I’ve just described:
“If we can get past that bureaucratic challenge, we can in fact prevent [large] asteroid impacts from hitting again in our future. This is an amazing and rather audacious statement to make, but if we really do our job right, we should never be hit again by an asteroid that can do serious damage to life on Earth.”

http://www.bbc.co.uk/blogs/thereporters ... duck.shtml
 
I was thinking the other day about various methods of stopping, obliterating or diverting asteroids away from Earth, and it seems that the biggest issue faced by scientists is how to keep the asteroid together (i.e. stopping it from fragmenting).

I thought about this for some time.

My solution would be to land various nuclear power plants and magnetic induction coils and induce a very strong magnetic field. As most asteroids are composed mostly of iron, this would have the effect of locking all the parts together.
Then, astronauts on the surface could gradually power up some rocket thrusters to push the asteroid into a new orbit.
If the magnetic field is correctly shaped and poled, even ion engines could be used as the thrusters.

Logistically, this would be a huge enterprise, I know - but what is the price of saving the planet?
 
Provided the fragments are small enough, I see no problem with fragmentation - fragments would burn up in the atmosphere, while a whole asteroid might not.

Even if a few fragments did make it to the surface, a few small impacts would, I feel, be less destructive overall than one huge one.

But perhaps someone's done the maths that says otherwise..?
 
The problem is the size of some of these fragments.
Quite a few asteroids seem to be made of 2 or more large lumps bashed together. Each of those bits, separated, could still do a lot of damage.
If an asteroid breaks apart, everything becomes a lot less predictable (i.e. more variables).
 
Two widely separated 50 megaton explosions could easily be more dangerous than one 100 megaton explosions: there is more chance one of them will hit the atmosphere. To remove all danger of impact the asteroid would need to be pulverised into ten-metre segments, which would burn up in the atmosphere. Note that the energy of impact would still be the same, so there would be an almighty flash in the atmosphere, which could easily cause severe problems on the surface- blindness, flash-burns and so on. But the energy would be more evenly spread.

Magnetising the asteroid would only work for metal asteroids, and more than 80% of asteroids are stony rather than iron, if I recall correctly.
 
In what follows, I'm assuming that the framentation takes place at some distance from Earth, giving the fragments some time to disperse:

The energy delivered by a pulverised asteroid would be less than that delivered by the complete one, because some of the fragments would miss earth altogether.

Of those that don't, many will burn up in the atmosphere. But they won't all arrive at once, and the burn-ups would not be instantaneous anyway, so I doubt there'd be any danger of flash-burns. Anyhow, a lot of the energy is dispersed fairly gradually in the atmosphere.

And a few modest surface impacts would be more survivable than one huge one.
 
eburacum said:
Magnetising the asteroid would only work for metal asteroids, and more than 80% of asteroids are stony rather than iron, if I recall correctly.
Click to expand...

After millions or billions of years even the stony asteroids have accumulated a large amount of ferrous material, which may be enough to bind it all together.
You are right, however - there is just the possibility that the asteroid of doom heading our way has no iron in it all, in which case we need to choose some other strategy...
 
Horizon: Asteroids

Today on BBC2 from 9:00pm to 10:00pm

Famed for their ability to inflict Armageddon from outer space, asteroids are now revealing the secrets of how they are responsible for both life and death on our planet. Armed with an array of powerful telescopes, scientists are finding up to 3000 new asteroids every night. And some are heading our way. But astronomers have discovered that it's not the giant rocks that are the greatest danger - it's the small asteroids that pose a more immediate threat to Earth. Researchers have explained the photon propulsion that propels these rocks across space, and have discovered that some asteroids are carrying a mysterious cargo of frost and ice across the solar system that could have helped start life on earth.
 
Impact 'catastrophe calculator' updated
By Jonathan Amos, Science correspondent, BBC News

Want to know what would happen if a 10km-wide asteroid came out of the sky and slammed down on your city?

Scientists at Purdue University and Imperial College London have updated their popular impact effects calculator first produced in 2004.

Users dial in details about the hypothetical impactor, like its diameter and density.

The web program then estimates the scale of the ensuing disaster, such as the size of the crater left behind.

It will also tell you how far away you need to be to avoid being buried by all the material thrown out by the blast, or set on fire.

The original calculator was a "big hit" when it was released, not just within the research community but with a curious public, also. Devised by Purdue's Professor Jay Melosh and colleagues, it is underpinned by scientifically accurate equations.

Many government organisations and scientific institutions regularly link to the calculator as an education tool.

The updated program, known as Impact: Earth! incorporates some additional impact effects, such as the tsunami wave height from an ocean collision. But the key difference those familiar with the old tool will notice is the much more visual and user-friendly interface.

"We've had to update things as knowledge has improved," said Imperial's Dr Gareth Collins.

"One of the major new additions is the estimates for tsunami wave height at a given distance away from an ocean impact. This had been a popular request, but we didn't put it in the original calculator because there simply wasn't consensus back then on what the hazard was. There's since been some good research and we now have a better understanding of the issue," he told BBC News.

On average, an object about the size of car will enter the Earth's atmosphere once a year, producing a spectacular fireball in the sky.

About every 2,000 years or so, an object the size of a football field will impact the Earth, causing significant local damage.

And then, every few million years, a rock turns up that has a girth measured in kilometres. An impact from one of these can produce global effects.

"The site is intended for a broad global audience because an impact is an inevitable aspect of life on this planet and literally everyone on Earth should be interested," said Dr Melosh.

"There have been big impacts in the past, and we expect big impacts in the future. This site gives the lowdown on what happens when such an impact occurs."

Purdue servers host the new calculator; Imperial will continue to host the old web program. This is being retained for those internet users who do not have fast connections.

The Imperial site is also trialling a tool that will enable users to map the impact effects on to the virtual globe software Google Earth.

"When we first launched the calculator, we hoped it would be a useful tool for scientists working in the field and for those people who were simply keen to find out more when a new crater was discovered and they wanted to understand the consequences if that event had happened yesterday," recalled Dr Collins.

"So we thought there would be some curiosity, but we were simply blown away by the interest."

http://www.bbc.co.uk/news/science-environment-11685803

http://www.purdue.edu/impactearth
 
yes, I watched that episode of Horizon. Excellent stuff. There is something incredibly fascinating about these huge rocks floating through space like deserted ships in an endless ocean. I was amazed by how accurately we are able to plot the courses and positions of these elephantine chondrites though millions of miles of space and how the sun fuels their acceleration.
It's hard to explain but there is something so romantically lonely about them as they pilot blindly on their endless odyessy.
 
Shining light on asteroid deflection
http://www.physorg.com/news/2011-02-ast ... ction.html
February 2nd, 2011 in Space & Earth / Space Exploration

Asteroid Apophis was discovered on June 19, 2004. Credit: UH/IA

(PhysOrg.com) -- So you think global warming is a big problem? What could happen if a 25-million-ton chunk of rock slammed into Earth? When something similar happened 65 million years ago, the dinosaurs and other forms of life were wiped out.

“A collision with an object of this size traveling at an estimated 30,000 to 40,000 mile per hour would be catastrophic,” according to NASA researcher and New York City College of Technology (City Tech) Associate Professor of Physics Gregory L. Matloff. His recommendation? “Either destroy the object or alter its trajectory.”

Dr. Matloff, whose research includes the best means to avert such a disaster, believes that diverting such objects is the wisest course of action. In 2029 and 2036, the asteroid Apophis (named after the Egyptian god of darkness and the void), at least 1,100 feet in diameter, 90 stories tall, and weighing an estimated 25 million tons, will make two close passes by Earth at a distance of about 22,600 miles.

“We don’t always know this far ahead of time that they’re coming,” Dr. Matloff says, “but an Apophis impact is very unlikely.” If the asteroid did hit Earth, NASA estimates, it would strike with 68,000 times the force of the atom bomb that leveled Hiroshima. A possibility also exists that when Apophis passes in 2029, heating as it approaches the sun, it could fragment or emit a tail, which would act like a rocket, unpredictably changing its course. If Apophis or its remnants enter one of two “keyholes” in space, impact might happen when it returns in 2036.

Large chunks of space debris whizzing by the planet, called Near-Earth Objects (NEOs), are of real concern. NASA defines NEOs as comets and asteroids that enter Earth’s neighborhood because the gravitational attraction of nearby planets affects their orbits. Dr. Matloff favors diverting rather than exploding them because the latter could create another problem — debris might bathe Earth in a radioactive shower.

Dr. Matloff’s research indicates that an asteroid could be diverted by heating its surface to create a jet stream, which would alter its trajectory, causing it to veer off course. In 2007, with a team at the NASA Marshall Space Flight Center in Huntsville, Alabama, he investigated methods of deflecting NEOs. The team theorized that a solar collector (SC), which is a two-sail solar sail configured to perform as a concentrator of sunlight, could do the trick. Constructed of sheets of reflective metal less than one-tenth the thickness of a human hair, an SC traveling alongside an NEO for a year would concentrate the sun’s rays on the asteroid, burn off part of the surface, and create the jet stream.

To do that, it is necessary to know how deeply the light would need to penetrate the NEO’s surface. “A beam that penetrates too deeply would simply heat an asteroid,” explains Dr. Matloff, “but a beam that penetrates just the right amount — perhaps about a tenth of a millimeter — would create a steerable jet and achieve the purpose of deflecting the asteroid.”

For the past year, Dr. Matloff and a team of City Tech scientists have been experimenting with red and green lasers to see how deeply they penetrate asteroidal rock, using solid and powdered (regolith) samples from the Allende meteorite that fell in Chihuahua, Mexico in 1969. Dr. Denton Ebel, meteorite curator at the American Museum of Natural History in New York City, provided the samples.

Assistant Professor of Physics Lufeng Leng, a photonics and fiber optics researcher, along with student Thinh Lê, an applied mathematics senior, used lasers to obtain optical transmission measurements (the fraction of light passing through the asteroidal material). Their research was supported by a Professional Staff Congress-City University of New York research grant.

“To my knowledge,” says Dr. Matloff, “this is the first experimental measurement of the optical transmission of asteroid samples. Dr. Ebel is encouraging other researchers to repeat and expand on this work.”

In a related study, Dr. Leng and her student (whose research was partially supported by City Tech’s Emerging Scholars Program) narrowed the red laser beam and scanned the surface of a thin-section Allende sample, discovering that differences in the depth of transmitted light exist, depending on the composition of the material through which the beam passes. From their results, they concluded that lasers aimed from a space probe positioned near an NEO could help determine its surface composition. Using that information, solar sail technology could more accurately focus the sun’s rays to penetrate the asteroid’s surface to the proper depth, heating it to the correct degree for generating a jet stream that would re-direct the asteroid.

“For certain types of NEOs, by Newton’s Third Law, the jet stream created would alter the object’s solar orbit, hopefully converting an Earth impact to a near miss,” Dr. Matloff states. However, he cautions, “Before concluding that the SC will work as predicted on an actual NEO, samples from other extraterrestrial sources must be analyzed.”

Dr. Matloff presented a paper on the results of the City Tech team’s optical transmission experiments, “Optical Transmission of an Allende Meteorite Thin Section and Simulated Regolith,” at the 73rd Annual Meeting of the international Meteoritical Society, held at the American Museum of Natural History and the Park Central Hotel in New York City.

“At present,” he adds, “a debate is underway between American and Russian space agencies regarding Apophis. The Russians believe that we should schedule a mission to this object probably before the first bypass because Earth-produced gravitational effects during that initial pass could conceivably alter the trajectory and properties of the object. On the other hand, Americans generally believe that while an Apophis impact is very unlikely on either pass, we should conduct experiments on an asteroid that runs no risk of ever threatening our home planet.”

Provided by New York City College of Technology
Click to expand...
 
“A collision with an object of this size traveling at an estimated 30,000 to 40,000 mile per hour would be catastrophic,”

No sh*t, Sherlock!

I wonder how much they pay people to state the bleedin' obvious these days?
 
Asteroid makes sharpest turn yet seen in solar system
http://www.newscientist.com/blogs/short ... urn-y.html
23:25 9 February 2011
Jeff Hecht, contributor


(Image: NASA)

On Friday, a metre-sized asteroid called 2011 CQ1 was spotted zipping only 5480 kilometres above the Earth's surface. That is the closest near miss on record, beating the previous record holder, a rock that buzzed Earth in 2004 called 2004 FU162, by a few hundred kilometres.

When something that small comes close to our planet, Earth's gravity is sure to bend its orbit. In this case, the approach was so close that the little asteroid's path bent by 60 degrees, reports Don Yeomans of NASA's Jet Propulsion Laboratory in Pasadena, California.

Short of collisions with a planet, that's the biggest orbital change ever recorded by observers. It was large enough to shift the asteroid from one category of objects into another. As Yeomans and his JPL colleague Paul Chodas explain in an online update:

Prior to the Earth close approach, this object was in a so-called Apollo-class orbit that was mostly outside the Earth's orbit. Following the close approach, the Earth's gravitational attraction modified the object's orbit to an Aten-class orbit where the asteroid spends almost all of its time inside the Earth's orbit.
Gravitational encounters between objects large and small have been rearranging the solar system since it formed some 4.56 billion years ago. We now believe even planets have been shuffled in their orbits. In this case, we had the good fortune to spot a very large change in the orbit of one very small object around the sun.

But now that 2011 CQ1 has had its 15 minutes of fame, we are unlikely to spot the small, dim object again, says Emily Lakdawalla of the Planetary Society, a space advocacy group in California: "We'll probably never be close enough to it again to be able to pick its dim light out from the background of stars."
Click to expand...
 
Giant asteroid heading close to Earth
A giant asteroid weighing 55 million tonnes will just miss the Earth later this year, Nasa experts have predicted.
By Martin Evans 7:02AM BST 05 May 2011

The rock, which is quarter of a mile across, will pass between our planet and the moon in November and will be visible with small telescopes.
Robin Scagell of the Society for Popular Astronomy said: “It’s rare we get the chance to see an asteroid up close.”

If it were to hit the earth, the asteroid, named YU55, would have an impact equivalent to 65,000 atom bombs and would leave a crater more than six miles wide and 2,000ft deep.

Passing by at a distance of just 201,000 miles, the asteroid will be the largest object ever to approach the earth so close.
Nasa has officially labelled it a Potentially Hazardous Object, but have stressed there is no danger of impact while on its current course.
YU55 orbits the sun every 14 years and last passed the earth in April 2010 at a distance of 1.5 million years [?!].

There are currently 874 near earth asteroids which are considered to be potentially dangerous.
They are closely monitored and the list is being constantly added to as astronomers discover new objects in near space.

Scientists estimate that there is usually one large collision with earth every few hundred thousand years.

http://www.telegraph.co.uk/science/spac ... Earth.html
 
rynner2 said:
Passing by at a distance of just 201,000 miles, the asteroid will be the largest object ever to approach the earth so close.
Nasa has officially labelled it a Potentially Hazardous Object, but have stressed there is no danger of impact while on its current course.
YU55 orbits the sun every 14 years and last passed the earth in April 2010 at a distance of 1.5 million years [?!].
Click to expand...

If it orbits the Sun every 14 years, how is it managing to pass the Earth every year or so?
Also, it's gone from 1.5 million miles to 201,000 miles away...that is more than just a bit worrying, isn't it?
 
Mythopoeika said:
rynner2 said:
Passing by at a distance of just 201,000 miles, the asteroid will be the largest object ever to approach the earth so close.
Nasa has officially labelled it a Potentially Hazardous Object, but have stressed there is no danger of impact while on its current course.
YU55 orbits the sun every 14 years and last passed the earth in April 2010 at a distance of 1.5 million years [?!].
Click to expand...
If it orbits the Sun every 14 years, how is it managing to pass the Earth every year or so?
Also, it's gone from 1.5 million miles to 201,000 miles away...that is more than just a bit worrying, isn't it?
Click to expand...
You're getting the cart before the horse! It's the Earth that passes the asteroid every year or so. If the asteroid orbits the sun in the same direction as the earth, the actual time between conjunctions would be more than a year. (If I were sober, I'd be able to calculate the time more accurately!)

The fact that it can come so close shows that its orbit crosses that of the Earth, but only rarely do such crossings happen when the Earth is actually nearby.
 
rynner2 said:
You're getting the cart before the horse! It's the Earth that passes the asteroid every year or so. If the asteroid orbits the sun in the same direction as the earth, the actual time between conjunctions would be more than a year. (If I were sober, I'd be able to calculate the time more accurately!)

The fact that it can come so close shows that its orbit crosses that of the Earth, but only rarely do such crossings happen when the Earth is actually nearby.
Click to expand...

Aah, right...yeah, I forgot about that. :)
 
When it returns next year, isn't the April date a bit close to the supposed 2012 'End Times/Armageddon/etc etc' date...?
 
Mythopoeika said:
rynner2 said:
You're getting the cart before the horse! It's the Earth that passes the asteroid every year or so. If the asteroid orbits the sun in the same direction as the earth, the actual time between conjunctions would be more than a year. (If I were sober, I'd be able to calculate the time more accurately!)

The fact that it can come so close shows that its orbit crosses that of the Earth, but only rarely do such crossings happen when the Earth is actually nearby.
Click to expand...

Aah, right...yeah, I forgot about that. :)
Click to expand...

Well, Myth would have been right if it wasnt for that Galileo geezer.
 
If the asteroid and Earth were both in circular orbits, then the Earth would pass the asteroid every year and 25.7 days.

But the asteroid's orbit is highly elliptical (and Earth's isn't exactly circular either!), which complicates things. When the asteroid is at aphelion, it will be moving much slower than average, so the Earth will overtake it more quickly. But there are people out there with better data and computer programs, so I'll leave the detailed calculations to them!
 
It's the earth-crossing asteroids of sufficient size that we don't know about that are the real worry. As boxers say, it's the punch you don't see that knocks you out!
 
I'm more confused that the asteroid went from being 1.5 million years away to just over 200,000 miles away.
 
Cultjunky said:
I'm more confused that the asteroid went from being 1.5 million years away to just over 200,000 miles away.
Click to expand...
I covered that earlier:

"The fact that it can come so close shows that its orbit crosses that of the Earth, but only rarely do such crossings happen when the Earth is actually nearby."

If objects are in different size orbits (which implies different periods of revolution), then the distance of closest approach will vary widely from year to year. (It's easier to see on a diagram, or an animated graphic.) The Earth's orbit is nearly circular, that of the asteroid is highly elliptical.
 
But how does it change from years to miles? Or did they mean light years?
 
Cultjunky said:
But how does it change from years to miles? Or did they mean light years?
Click to expand...

Bad journalism, of course.
 
Cultjunky said:
But how does it change from years to miles? Or did they mean light years?
Click to expand...
Ah! I think that was probably a typo.
 
I thought I was missing some Astro 101 module :lol:

Y'no...Holy $&*£ that's moving fast type of thing.
 
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