Huge asteroid headed for close encounter with Earth

[klr]

http://www.reuters.com/article/2011/11/ ... FN20111104

(Reuters) - A huge asteroid will pass closer to Earth than the moon on Tuesday, giving scientists a rare chance for study without having to go through the time and expense of launching a probe, officials said.

Earth's close encounter with Asteroid 2005 YU 55 will occur at 6:28 p.m. EST on Tuesday, as the space rock sails about 201,000 miles from the planet.

"It is the first time since 1976 that an object of this size has passed this closely to the Earth. It gives us a great -- and rare -- chance to study a near-Earth object like this," astronomer Scott Fisher, a program director with the National Science Foundation, said on Friday during a Web chat with reporters.

The orbit and position of the asteroid, which is about 1,312 feet in diameter, is well known, added senior research scientist Don Yeomans, with NASA's Jet Propulsion Laboratory in Pasadena, California.

"There is no chance that this object will collide with the Earth or moon," Yeomans said.

Thousands of amateur and professional astronomers are expected to track YU 55's approach, which will be visible from the planet's northern hemisphere. It will be too dim to be seen with the naked eye, however, and it will be moving too fast for viewing by the Hubble Space Telescope.

"The best time to observe it would be in the early evening on November 8 from the East Coast of the United States," Yeomans said. "It is going to be very faint, even at its closest approach. You will need a decent-sized telescope to be able to actually see the object as it flies by."

Scientists suspect YU 55 has been visiting Earth for thousands of years, but because gravitational tugs from the planets occasionally tweak its path, they cannot tell for sure how long the asteroid has been in its present orbit.

"These sorts of events have been happening for most of the lifetime of the Earth, about 4.5 billion years," Fisher said.

Computer models showing the asteroid's path for the next 100 years show there is no chance it will hit Earth during that time, added Yeomans.

"We do not think that it will ever impact the Earth or moon (but) we only have its orbit calculated for the next 100 years," he said.

Previous studies show the asteroid, which is blacker than charcoal, is what is called a C-type asteroid that is likely made of carbon-based materials and some silicate rock.

More information about its composition and structure are expected from radar images and chemical studies of its light as the asteroid passes by the planet.

"I've read that we will be able to see details down to a size of about 15 feet across on the surface of the asteroid," Fisher said.

NASA is working on a mission to return soil samples from an asteroid known as 1999 RQ36 in 2020, followed by a human mission to another asteroid in the mid-2020s.

Japan also plans to launch an asteroid sample return mission in 2018.

[Pensioner]

The dinos thought that fooker will miss us.

[klr]

The dinos thought that fooker will miss us.

Well, if this one is "huge", then the dino-killer was ginormous altogether.

Hopefully this one will do something useful. Any suggestions as to where it should hit?

[Atheist-Lite]

Test run before the big hammer next year.

[Schneibster]

It's only 300m across. It would take out the core of a city if it hit one, which is highly unlikely. The strike would be on the close order of a kiloton; not even 1/20 of a Hiroshima.

A dino-killer is more like 30km across. If one of those comes down it's a gigaton or five, and expect the weather to be very cold for a couple decades. It probably wouldn't kill off the human race, but billions would die, many quite promptly of breathing rock vapor, earthquakes, tsunami, and of secondary impacts from debris from the primary strike.

[Atheist-Lite]

It's only 300m across. It would take out the core of a city if it hit one, which is highly unlikely. The strike would be on the close order of a kiloton; not even 1/20 of a Hiroshima.

A dino-killer is more like 30km across. If one of those comes down it's a gigaton or five, and expect the weather to be very cold for a couple decades. It probably wouldn't kill off the human race, but billions would die, many quite promptly of breathing rock vapor, earthquakes, tsunami, and of secondary impacts from debris from the primary strike.

That rock vapour is nasty stuff. People should be made more aware of it. Always wear a scarf near anything being demolished, no matter how it happens.

[Schneibster]

I'm talking about thousand-degree vaporized mixed silicates and ferric oxides that fry your lungs, not to mention your eyes. Not dust.

[FBM]

"There is no chance that this object will collide with the Earth or moon," Yeomans said.

Always the bridesmaid, never the bride.

[Schneibster]

Well, for the next several thousand years, yes. I haven't checked how far they have projected orbits, but it's far enough out to not even be a consideration for doing anything in our lifetimes for anything bigger than a city-killer, and even that's astronomically unlikely simply because not much of the Earth's surface is city.

[FBM]

Damned dinosaurs used up all the good asteroids and left us with nothing but pebbles.

[Schneibster]

Life without skyfall works for me. Maybe I'm a pussy.

"May you live in interesting times" is said to be a curse in various Asian languages. I never thought the qualification of Asian was required; it didn't sound good the first time I heard it. I've also heard it said that it's accompanied in full form by the additional, "...and come to the attention of important people."

[hackenslash]

A dino-killer is more like 30km across.

10 km (about 6 miles), if memory serves. More critical than the size is the mass, which can vary quite considerably based on its composition.

[Schneibster]

Chicxulub? We're talking opposite ends of the same order of magnitude. I ain't gonna argue about that.

A man's got to know his limitations.

ETA: Wow, I went and looked it up, they're now estimating the impact effects at 96 Tt, that is, 96 thousand gigatons, four orders of magnitude more than I recalled.

Guess my forgettery is operating full-time.

[hackenslash]

Indeed. There was a fun discussion that arose out of somebody asking 'what evolutionary trait would be the most useful in the event of four (count them) bolides the size of Texas impacting Earth?' When we'd all finished pissing ourselves at the utter ignorance of the question, I asked The Blue Flutterby to do a back-of-an-envelope calculation for just one:

The volume of a bolide the size of Texas is given by:

V = (4/3)πr3 where r = 622,000 m

This gives us a value for the volume of our bolide of 1.008 × 1018 m3.

Now, to make life simpler, let's assume that we're dealing with an iron meteorite. Iron has a density of 7,873 Kg m-3 (Source: the properties of the elements table from Kaye & Laby's Tables of Physical & Chemical Constants), therefore an iron meteorite will have a mass of 7.936 × 1021 Kg, to a reasonable level of approximation. A more precise calculation would take into account that an iron meteorite actually contains around 6.7% nickel (source: the abundances of the elements table from the same source as above), and since nickel is denser than iron, leaving it out means that we're underestimating the mass, and erring on the conservative side again. By comparison, the mass of the Earth is 5.9736 × 1024 Kg, so we're dealing with a body that is 0.13% the mass of the Earth, which means that already, it's a significant mass.

Bolides typically move through space at speeds of around 20 Km s-1, and so, we can calculate the kinetic energy of such a bolide once we know its mass, courtesy of E = ½mv2. Feeding m = 7.936 × 1021 Kg and v = 20,000 m s-1 into this formula, we arrive at a value for the kinetic energy of 1.587 × 1030 Joules.

Now, if a bolide of this mass impacted the Earth at that speed, and atmospheric braking wouldn't do much to slow it down, a significant fraction of that energy would be converted to heat upon being brought to a halt in an inelastic collision. Even if we assume conservatively that only 50% of that energy is converted to heat as it impacts the Earth and comes to a halt, that still leaves us with 7.935 × 1029 Joules to play with. By comparison, the Tsar Bomba, the largest thermonuclear weapon ever tested in the atmosphere by humans, was puny - it had a yield of 50 megatons, or 2.1 × 1017 Joules. Therefore, if a bolide the size of Texas impacts the Earth, it will yield as much heat energy as 3.779 trillion Tsar Bomba H-bombs.

That amount of heat energy is going to have some significant effects to put it mildly. Let's assume for the sake of argument, again a radical simplification, that all the heat energy is dumped into the bolide mass itself, prior to transfer to the surroundings. Iron has a specific heat capacity by mass of 442 J Kg-1 K1-, which is the amount of heat energy required to raise the temperature of 1 Kg of iron by 1 Kelvin. So, to derive the temperature change T, given a specific heat capacity C, a mass m and an energy input E, we have:

T = E/Cm

Feeding our data into the formula above, we have that the temperature change of the bolide will be approximately 225,000 kelvins.[11]

Apologies if I've missed any superscript tags. This was copied from RDF, and all formatting is lost and has to be done manually since the forum was shut down.

[Schneibster]

Sure is lucky we got a Jupiter.