How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

Also the difference between a 187 foot wide rock entering at a shallow angle and a 427 foot wide rock entering at 90 degrees is the first breaks up high in the atmosphere and probably ends up not being that much more destructive on the ground as compared to the Chelyabinsk event, vs the second case it starts to break up, but most of the fragments punch straight through to the ground still going 7 km/sec and you get a 250 megaton ground blast and 4 mile diameter crater.

thankfully even in the worst case, latter case the chances of it happening over a heavily populated area are less than 1%

The Chelyabinsk asteroid was a 10 year average asteroid, besides that one and Tunguska, since the invention of motion picture recording technology, probably another dozen have come in like that one and hit the deep ocean or exploded over a totally unpopulated area and nobody noticed.

It took a while to get "lucky" and have one explode over an area populated enough and with enough modern motion picture recording devices for lots of documentation of it. Chelyabinsk could have gotten real unlucky and had a somewhat larger asteroid come in at a somewhat steeper angle and it wouldn't have been the end of the world, but a really, really bad day for poor Chelyabinsk.

Some animation claim that the flyby occurred when the asteroid was flying towards perihelion, i.e. it would come from the night side of Earth and it should be easier to detect earlier.

However, if it had already passed perihelion and be on the way out it would have approached the Earth from the day side of earth, making it very hard to detect with ground based optical telescopes. A space telescope at L1 Lagrange point would be needed to detect asteroids approaching from the day side.

How much warning time would we be talking?

the headline says "massive" but asteroids at the lower end of that range are small enough that if you could intercept exoatmospherically with a ten, 20 megaton nuclear weapon at a couple hundred meters would vaporize the bulk of it.

An Earth crossing asteroid is less than a year within Earth's orbit and hence on the day side as seen from the Earth. During this time, it would only be visible with a space telescope.

How long the asteroid stays within Earth's orbit depends on the orbital eccentricity, i.e. how deep into the solar system it will fly, does it cross the orbit of Venus or even the orbit of Mercury. Thus the time can be just a month or two. Worst of all, in the shortest case, the asteroid will approach nearly from the direction of he Sun.

Using the SOHO solar observatory (located at L1) has a camera pointing towards the Sun, but blanking out the actual disk of the Sun. It has detected a lot of small Sun gracing comets just prior to flying on to the back side of the Sun. If they survive the encounter with the Sun, they will move very fast away from the Sun, possibly crossing the orbit of and potentially colliding with Earth.

The SOHO camera field of view is only a few degrees just showing the immediate vicinity of the Sun. The asteroid hunter at L1 would have to have a much wider field of view (up to 180 degrees) but blank out the sun from the view.

One (and basically the only) use for the ISS would be as a staging/launch point for asteroid deflection missiles.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

The big ones that sneak up on us are typically either very dark covered in carbon soot like dust or coming from the direction of the sun so that they are in the twilight sky until the last possible moment or both. I am a bit surprised that the automatic searchers didn't get it a bit sooner (so will they be). There is a protocol for Earth crossers with suspected close approach or collision risk at the minor planets centre.

They need a series of at least three good observations separated by a few hours to get an initial orbital solution that can then be refined as more widely spaced observations become available.

The survey instruments are pretty good now.

It has been quite a while since a human comet searcher beat one of the automated systems. Hence the comets and asteroids they find just have name of detection system a year and a designation code. A lot used to be called Levy or Tanaka in the good old days of dedicated experts.

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Regards, 
Martin Brown

A very dark carbon asteroid inside the orbit of the Earth will get

*hot* and radiate a lot in the 8-15 um thermal-IR range but very little in the near-IR or visible range. Thus comparing ThIR and NIR pictures should help identifying such objects.

Since the hot object is tumbling around it will also radiate ThIR on the "night" side of the object, while a very reflective object nearly on the line between Sun and Earth, will have a very small reflective area for visible light and NIR.

Warm certainly enough to maybe melt water depending on how slowly it spins - that is why comets develop tails as they near the sun.

However a perfect black body at the Earth's orbit without an atmosphere their peak sun side temperature is likely to be more like 5C peaking at around 12um. Enough that the more sensitive far IR systems might see it. How bright the side facing Earth is depends on its actual temperature which could be quite a bit cooler.

There was never enough military demand to see objects cooler than 37C so the sensitivity is not so good at these longer thermal wavelengths.

I think most of the survey instruments are wide field big sensor devices on fast Schmidt scopes mostly in the visible or near IR backed with computer programs to spot anything that moves.

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Regards, 
Martin Brown

That is more about sublimation (going directly from solid to gas).

The average full sphere temperature would be close to -15 C. However, for "equatorial" regions the variation can be quite large. Look at the day time surface temperatures of the Moon, it can be uncomfortably high. Admittedly the sun has been shining for up to two weeks. Anyway for faster rotating bodies the warm equatorial regions going from late "evening" to early "night" is still quite warm and radiates ThIR quite well.

The most sensitive IR detectors are cooled by letting helium evaporate at 4 K. This unfortunately means that the detector is usable only as long as there is some liquid helium left in the tanks.

On Wednesday, July 31, 2019 at 9:30:44 AM UTC-4, snipped-for-privacy@downunder.com wro te:

Earth

red

hat

I

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Isn't the temperature of space below that? So a shielded radiator should b e able to dissipate the heat absorbed by the satellite and condense the hel ium. The helium would then be essentially a heat pipe. This may be too la rge to be practically launched.

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  Rick C. 

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It is very difficult to do that. The standard tricks get you a heat shadow. The Hubble ran into a bunch of related problems with thermal effects known to the spook bird manufacturers but highly classified. They had to reinvent the wheel (and theirs was a bit rounder too).

Sticking a mirror or maybe two in the path between the sun and the sensor is about as good as you can get. Biggest problem is that for a wide angle survey instrument you want a very large number of pixels.

So instead of 0.01 radian diameter source at 5800K and the rest at 4K you trade that for 0.05 radian occulting disk at 280K emitting maybe

5-10% and the rest at 4K with one good mirror interposed. Two is about where the law of diminishing returns sets in.

In low Earth orbit you also have a hefty chunk of 300K emission very nearby and subtending a much larger solid angle than the sun.

--
Regards, 
Martin Brown

Temperature is a property of matter.

Hrmmm, Looks like we're spending all those trillions on the "wrong" type of defense industry LOL ;-)

Let's see if we can get the elevators working on the "Gerald".

[...]

You're a good deal more likely to be killed in a war than by a falling asteroid.

Jeroen Belleman

Problem: Huge-ass asteroid on collision course with Earth

Solution: Nuke it

Problem: 12 medium-sized radioactive asteroids on collision course with Earth

-- john, KE5FX

If you use a big enough nuke, the fragments will all have been moved onto slightly different orbits - if they are all moving apart, none of them are on the original orbit.

Even if you don't blast it into separate bits, what you do blast off will have momentum in a different direction to what's left of the asteroid, and the residue will have an equal and opposite change of momentum.

It's all calculable - more accurately after the blast - and if a first blast didn't do all that was needed, you'll probably have time for another.

--
Bill Sloman, Sydney

How about detonating far enough away so as not likely to break it into pieces, just cause a slight change in course so it misses Earth? If you do that far enough out, only a small change in it's arc at that point, would cause a big change in distance later.

I thought there were other options,

"John Miles, KE5FX" wrote in news: snipped-for-privacy@googlegroups.com:

Problem: Folks unable to analyze a problem, leading to not needed non solutions.

Solution: Ignore them.

Here... they would use a FUSION type nuclear device, not one that radiates or contaminates.

Obliteration does not work, because that turns a "bullet" type projectile into a "shotgun blast" type projectile.

Deflection would be the only usable choice.

IOW, we are all doomed, essentially, but not because of radiated meteorites.