Small Asteroid To Buzz Earth 171
ddelmonte writes in to tell us about a small near-earth object, discovered just 2 days ago, that is expected to pass within 64,000 km of our planet on March 2, 13:44 UT. NEO 2009 DD45 will be well inside the Moon's orbit and just under twice the altitude of geosynchronous satellites. According to Sky and Telescope, 2009 DD45's closest approach will be over the Pacific west of Tahiti, so observers in Australia, Japan, and perhaps Hawaii will have the best chance of spotting it with, say, an 8-in. telescope. Here's where you can generate an ephemeris of the object for your location. At closest approach NEO 2009 DD45 will be moving half a degree per minute and peaking around magnitude 10.5. It will be brighter than 13th magnitude for only a few hours.
Impossible in this timespan (Score:5, Informative)
Another perspective (Score:1, Informative)
Re:Piggy ride! (Score:5, Informative)
If we have the deltaV to land on the rock, then we have the deltaV to match its orbit without bothering to land on it. So why waste time with the landing?
Or were you thinking that little or no deltaV would be required because the rock was passing close by?
Well, no, a quick guesstimate based on the limited information in the article has it passing at about 9km/s relative to Earth, at 64000km altitude. Which is rather more than escape speed. About 8500 m/s over Earth escape speed, in fact. We've sent probes out faster than that a few times. The stuff that goes out past Jupiter, for instance. But it's a non-trivial exercise.
Buzz vs. Non-buzz (Score:5, Informative)
Three days notice. 20 to 50 meter diameter. Assume it's dense rock and a vertical impact trajectory into the ocean (avg. 1000 m depth).
Impact energy 116 kT to 1.8 MT. Very near the lowest energy potential impact of the known NEOs, actually. Not relevant here since the object quite clearly misses. But if and when one doesn't miss, someplace is going to catch a small to medium nuke sized blast, and there won't be time to do squat about it.
My money says we'll have the capability to defend ourselves against such an impact. The second time.
Re:Piggy ride! (Score:5, Informative)
IF you land on it, it will continue to travel without fuel for propulsion for a VERY long time... that could be rather useful
It you match speeds with it you will continue to travel without fuel for propulsion indefinitely. Being docked to a rock will make no difference. The advantage of having the rock there is that you can mine it for resources and use it as a radiation shield. You could also push transfer momentum to it if you want to change your velocity.
Re:Thirty metres (Score:3, Informative)
Re:Piggy ride! (Score:5, Informative)
Physics doesn't work that way.
You seem to think it's like hopping on the back of an old London bus: grab it as it passes and jump up onto the step. But speeds in space are far greater than that. If you try to catch an asteroid as it passes, words like 'splat' or 'crunch' are appropriate. You need to match the asteroid's velocity very closely in order to land on it without being destroyed - and if you can do that, then you're on the same orbit as the asteroid anyway, and you'll go where it goes whether you land or not. So you don't actually need the asteroid to be there.
I suppose you might arrange something cunning with a big net and a lot of bungee rope, if you can pull off an incredibly accurate flight plan, but even so it's unlikely that the asteroid is going to be near any other targets of interest in the near future; it's more worth your while to load up the extra fuel needed to fly direct to the planet or moon you want to study.
Re:Another perspective (Score:5, Informative)
1 km/s is EXACTLY 3,600 km/h. Not roughly 30,000 km/h as you suggest.
Parent links to malicious site (Score:3, Informative)
Looking at the source of the page, it attempts to download a movie on eDonkey, change your AIM name, send off spam emails, open up lots more windows, and probably much more. It also moves the window around so you can't close it, and pops up messages when you try to alt+f4.
In short; DO NOT CLICK THE LINK.
Re:Small english/metric error, I believe (Score:3, Informative)
> Geosynchronous orbit is 32,000 miles...
Geosynchronous orbit is 22,236 miles.
Re:Piggy ride! (Score:5, Informative)
Re:This is ghostwriter asking for Permission to Bu (Score:1, Informative)
I think it was supposed to be Ghostrider. As in, from "Ghostriders in the sky."
Negative Ghostrider, pattern is full. .....
GODDAMMIT!
So, I used a calc on the impact (Score:5, Informative)
http://www.lpl.arizona.edu/impacteffects/ [arizona.edu]
And the results are (assumed that you are 2000km from impact - if it hit it would be in the ocean...)
Your Inputs: Distance from Impact: 2000.00 km = 1242.00 miles
Projectile Diameter: 30.00 m = 98.40 ft = 0.02 miles
Projectile Density: 8000 kg/m3
Impact Velocity: 17.00 km/s = 10.56 miles/s
Impact Angle: 90 degrees
Target Density: 1000 kg/m3
Target Type: Liquid Water of depth 100.00
meters, over typical rock.
Energy: Energy before atmospheric entry: 1.63 x 1016 Joules = 3.90 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 314.0 years
Atmospheric Entry: The projectile begins to breakup at an altitude of 14100 meters = 46100 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 10.8 km/s = 6.7 miles/s The impact energy is 6.58 x 1015 Joules = 1.57 MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 0.151 km by 0.151 km
Major Global Changes: The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
What does this mean?
The crater opened in the water has a diameter of 1.4 km = 0.866 miles
For the crater formed in the seafloor: Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
Transient Crater Diameter: 670 m = 2200 ft
Transient Crater Depth: 237 m = 777 ft
Final Crater Diameter: 837 m = 2750 ft
Final Crater Depth: 179 m = 586 ft
The crater formed is a simple crater
The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 82.8 m = 272 ft.
At this impact velocity ( Thermal Radiation: What does this mean?
At this impact velocity ( Seismic Effects: What does this mean?
The major seismic shaking will arrive at approximately 400 seconds.
Richter Scale Magnitude: 4.4
Mercalli Scale Intensity at a distance of 2000 km:
Nothing would be felt. However, seismic equipment may still detect the shaking.
Re:Piggy ride! (Score:4, Informative)
Yeah. No friction or air resistance in space, that's what you're missing. Oh, and all of physics since Galileo, you're missing that too.
The brick has less mass than the iron lump, true - and so it has proportionately less inertia. But the gravitational force on the brick is also less than that of the iron lump, by the same proportion. The two cancel out. If they have the same velocity, then if one escapes, so does the other. It's the same principle as how a brick will fall at the same speed as a feather, if dropped in a vacuum.
Similarly, if a spaceprobe and an asteroid fly away from the Earth at the same velocity, it doesn't matter whether they're attached or separate: both will follow the same path.
Re:Piggy ride! (Score:4, Informative)
Have you read anything by this guy Newton? Fig, or Isaac, one of the two. He pretty much explained (about 300 years ago) how this whole "gravity" thing works.
And, for what's it's worth, 5 miles/second (I shudder to think you might have meant metres/second) is below escape velocity. It's barely above orbital velocity. So not even your lump of iron would escape. Even if gravity worked they way you think it does, as opposed to the way it really does.
Re:Piggy ride! (Score:2, Informative)
Yeah. No friction or air resistance in space, that's what you're missing. Oh, and all of physics since Galileo, you're missing that too.
That's not true. There is a very small amount of air resistance in space (interstellar hydrogen.) In theory, stuff released out into space won't coast forever relative to the origin - just damned near it. Also, two items released into "empty" space on a parallel course will NOT continue on a parallel course. They will gravitationally attract one another. Who's missing what, now? :)
Re:Impossible in this timespan (Score:4, Informative)
From TFA:
"This little cosmic surprise, designated 2009 DD45, turned up two days ago as a 19th-magnitude blip in images taken by Rob McNaught at Siding Spring Observatory in Australia. It was already within 1.5 million miles of Earth and closing fast."
So no, they had no prior info about this asteroid. And yes, this fact concerns me as well, but this is the problem with asteroids / comets having a low albedo - they're difficult to observe with the usual instruments.
Re:Piggy ride! (Score:3, Informative)
OK, OK. Looks like a made mistake on that one. Although, I did phrase my point as a question, as I'm no expert on space science. My mistake.
I understood where you were coming from. These are common beginners' misconceptions.
Here's how it works (you confused a few things). We have things like mass, cross-sectional area (important in slowing things down), density, etc.
For starters, let's use your ping pong ball, brick, and iron. Furthermore, let's assume a perfect vacuum. If I fire them all at velocity v, they'll continue forever at velocity v. Mass doesn't make them slow down (but it does affect how much energy I have to expend to make them go velocity v).
Now, let's get a little deeper as to why this is. All objects have mass (pretty much every non-quantum mechanical object in existence), which is a measure of what we call inertia. Inertia is just a fancy word that basically states that an object with mass resists changes to its motion (Newton's eponymous first law). This means point masses tend to travel in straight lines if they were already doing that. Or it could simply be stopped (it won't just spontaneously start moving for no reason). What all this means is that a ton of iron is a hell of a lot harder to stop than a 1/4oz ping pong ball. (Newton's 2nd law: force required to change something is proportional to its mass, i.e. the heavier it is, the more ass you have to put into it to move, the "more mass, more ass" principle) This is where your slowing down question comes in.
Now, let's assume that our thought-experiment space is actually filled with something like air or water. If you've ever been in a swimming pool, river, or gale, you know that both air and water can definitely slow you down or move you about. This is called "resistance", and it's basically a form of Newton's 3rd law (every action has an equal and opposite reacion). Now, let's assume two objects of equal mass, but one is a really large sheet while the other is compact like a bullet. Moving through the water/air/solar wind/intergalactic hydrogen medium, this stuff exerts force on our objects as they pass through. However, the sheet interacts with a lot more of the medium, since it has a larger cross-sectional area per unit mass, so it slows down more quickly than our compact bullet. This is why a feather floats to the ground slowly, while a rock simply falls. On a more significant scale, at sufficient speeds, lots of heat gets generated by friction. This is pretty good for us, since the atmosphere protects us from debris from space.
Hopefully that helps you.