You know; that place you go to check out what the weather's gonna do.
Where, before (maybe) getting that info, you have to sit through endless replays of "Storm Stories", "It could happen tomorrow" (or maybe not), and, so help me, "Iceberg Hunters" ...
Aim between the eyes, son. It might charge if it's only wounded.
(Ok. I know! I Know!!! They're shooting off chunks to be recovered and used for extra pure bottled water. But, honestly, could you have resisted? :-)
They have a new series, "Forecasting the End!" and it's to include a piece on rogue planets, probably on the scenario envisioned by Philip Wylie and Edwin Balmer in their 1933 novel, "When Worlds Collide"...
While not the first to venture into this territory (H. G. Wells short story "The Star" (1897) touched on the effects of a close passage), it's easily the most famous (having been adapted into George Pal's 1951 movie).
In 1964, Fritz Leiber published "The Wanderer", also dealing with such a visitor (but he took an approach more metaphysical than scientific. It's been a looong time since I read it, so I could be wrong, but I believe this wandering planet was guided here, in contrast to the random potshots by the others, in which case it's irrelevant to this post.
You see, what I'm concerned with here is the likelihood of such an event involving planetary or stellar size masses colliding or having near misses.
When I was much younger, with much better distance vision, I could take a rifle and put most of my shots (all, if firing from prone or a bench rest) within a 6" (15 cm) bulls eye at 100 yards (or 100 meters), using iron sights. Many people can do better, but that bulls eye is a mighty small target at that range.
It's hard enough to hit with careful aim. If I was to just causally fire the rifle in the general direction, there is an enormous amount of surrounding space into which the bullet is most likely to go. If that bulls eye had thoughts and feelings, I'm sure it would feel pretty safe.
So, just how threatened should a sugar grain (at maybe 0.5 mm diameter) feel about another sugar grain roaming around about 9 miles (15 km) away?
That is the kind of space we are talking about in space.
Trying to get a handle on just how immense the Universe is ain't easy.
The first good attempt I ever came across was ...
It is available for viewing online, at http://www.vendian.org/mncharity/cosmicview/ and at Caltech.
( http://nedwww.ipac.caltech.edu/level5/Boeke/frames.html )
The first has larger pictures, but both are only pale shadows of the original. I hope someone with influence sees this and tries to get this wonderful book back in print.
In 1977, the team of Charles and Ray Eames made a short film ...
Powers of Ten (1977) is available from sellers at Amazon.com (They give a 1968 date, but I believe that is for the initial prototype of the film that was made in 1977) at http://www.amazon.com/The-Films-Charles-Ray-Eames/dp/6305943877/
In one book about creating the movie, "2001: A Space Odyssey", I read that they originally considered a prologue with interviews of various scientists and having a similar "powers of ten" instruction film. But, they decided it was better to just get straight into the story instead.
One of my all time favorite movies Contact (1997) ...
From here, I'm gonna take my shot at giving perspective to the universe, using grains of sugar.
That picture should get you started on that perspective (we'll get to the sugar in a bit).
The Sun is not a large star, nor is it very hot. But it is hot with reference to men, hot enough to strike them down dead if they are careless about tropic noonday ninety-two million miles away from it, hot enough that we who are reared under its rays nevertheless dare not look directly at it.
~Robert A. Heinlein, "Methuselah's Children" (1958 -- or 1941 if that passage is also in the original shorter story from which the novel was later evolved).
Those dark blotches on the Sun are sunspots, storms on the surface that are dark only by comparison with the rest of the surface by being cooler. Actually, they would be blindingly bright, so you can guess what the rest of that surface is really like. They are also large enough to swallow the entire Earth as you can see by the small dot representing us.
Note also, the Lord of our Solar System, Jupiter. Of the approximately 457 Earth-masses of material making up the planets, moons, asteroids, etc., about 318 make up Jupiter and another 100 or so are in Saturn. Isaac Asimov once noted that, to an impartial observer from out there, "our Solar System would consist of Jupiter plus debris".
Now, on to Paul's Sugar Grain Scale of the Universe ...
(NOTE: In the figures below, while I try to give SI (metric) equivalents), I'm following our practice of using the comma to break up large numbers. I am not using it as a decimal marker, as many countries do.)
A long time ago, I came upon a factoid that a pound (454 grams) of table sugar contains around 2,260,000 grains.
Now, the specific gravity of sugar ranges from 0.68 (bagged raw sugar) to 1.5862 (sucrose crystal). (From http://www.sugartech.co.za/density/index.php ).
For our purposes, I'm using bagged table sugar (as it's the most likely type you'll have at home) at 0.7 specific gravity, which works out to 43.7 lbs/cubic foot ( 700 kg/cubic meter). Say, 98,762,000 grains per cubic foot ( 3.488 billion grains/cubic meter)
0.5 mm (500 microns) is a ballpark figure for the average diameter of grain of table sugar. Having this represent our Sun gives us a scale of about 2.782 x 10 to the 12th (or 2.782 trillion) to one.
Diameter of Sun - approx 864,327 miles (1,391,000 kilometers)
Diameter of Earth - approx 7,918 miles (12,742 km)
Earth to Sun - approx 92,960,000 miles (149,600,000 km)
Shrink our Sun to a sugar grain, and the Earth becomes a bacterium about 4.8 microns in diameter (literally microscopic), orbiting about 53.8 mm (about 2.1 inches away).
On this scale, a light year works out to 2.11 miles ( 3.4 km).
Distance to Alpha Centauri = 4.367 light years. The nearest known star (other than the Sun), Proxima Centauri, is about 4.22 light-years away.
So, on this scale, the nearest other sugar grain we might have to worry about a collision with would be about 8.9 miles or 14.32 km away from us. And here, we are speaking of things much larger than planets, making bigger targets.
So, with all due respect to the Global Warming/Climate Change Propaganda Channel (the Weather Channel), of all the things I may lose sleep over, rogue planets just ain't among them.