Oh, this is too cool: scientists have found a planet orbiting a binary star (a pair of stars in tight orbit around each other) that is at the right distance to have liquid water! Let me be clear: this planet is much bigger than Earth, and is likely to be a gas giant. So it’s not Earth-like, and probably not itself habitable.

But it might have moons…

[Note: this image is artwork based on the science. Click to tatooineneate.]

OK, first: Kepler is an orbiting telescope that has been staring at one spot in the sky for about three years now. It’s looking at about 100,000 stars. If these stars have planets, and the orbits of these planets are seen edge-on, then they will occasionally pass directly between us and their parent star blocking a little bit of the light. This is called a transit, and if the planet is big enough it can block enough light from the star to be detected by Kepler. So far, 77 planets have been confirmed using Kepler, and over 2000 more have been detected and are awaiting confirmation.

The new discovery deals with a binary star called Kepler-47. It’s about 5000 light years away, which is pretty far for a Kepler system – it’s faint at that distance. Still, the observations look very good, and the conclusions convincing to me.

One of the two stars is very Sun-like, about the same size, temperature, and brightness as our home star. The second is fainter, smaller, and cooler. They comprise an eclipsing binary: their orbit is seen edge-on from Earth, so they pass in front of each other as seen by us as they circle each other. Their orbit is pretty tight: they’re only about 13 million kilometers (8 million miles) from each other, and their orbit is just 7.5 days long.

Two planets were actually found orbiting the stars. Kepler-47b is about 3 times the diameter of the Earth. Its mass isn’t known, but it’s likely 7 – 10 times ours. It’s hot: the orbit is just 50 million km (30 million miles) out, closer than Mercury is to the Sun. It takes about 50 days to orbit.

The second planet, Kepler-47c, is the interesting one. It’s even bigger, 4 – 6 times Earth’s diameter, roughly the size of Uranus, and most likely 20 times our mass. Its orbit is almost exactly the same size as Earth’s, coincidentally, taking 300 days to orbit the binary (its year is shorter than ours because the two stars together have more mass, and therefore more gravity, than the Sun).

Taking into account the orbital size and the physical properties of the stars, the scientists have determined that the planet is at the right distance to be in the stars’ habitable zone: the distance where liquid water could exist on a solid body.

As I pointed out, the planet is probably a gas giant. But it could have moons – in fact, given our own solar system configuration, it seems likely. It’s not crazy to think that these moons, should they exist, might be habitable. That’s *amazing*.

These two new worlds put the roster of confirmed circumbinary planets (that is, planets orbiting binary stars) to six. And we only just started looking a few years ago! Given the number of stars observed and the planets found, and applying a little statistics, it seems entirely possible that there are millions of such planets in our Milky Way galaxy alone.

That’s right: *millions* of possible Tatooines just waiting to be found! And we may yet find them. Finding gas giant planets is far easier than finding their much smaller moons, but one of the goals of exoplanet astronomy is to improve the technology and the techniques to the point where such moons can be detected as well. It may take bigger telescopes and more time, but there is nothing stopping us except our will to do so.

Think of that: *we can detect potential Earths around stars quadrillions of kilometers away!* And all we have to do is want it enough.

*[P.S. If you want to keep up with exoplanet news, there's a wonderful iPhone/iPad app called Exoplanet that has info, diagrams, and updates when new planets are found. I use it myself and really like it.]*

*Image credit: NASA/JPL-Caltech/T. Pyle*

Related Posts:

- Astronomers discover a wretched hive of scum and villainy

- Exoplanet news Part 4: More wretched hives of scum and villany

- No, that’s not a picture of a double sunset on Mars

- New study: 1/3 of Sun-like stars might have terrestrial planets in their habitable zones

*[I'm trying to catch up with all the news that's been released this week while I was off lecturing in Texas. This is Part 2 of a few articles just about exoplanets. Here's Part 1, Part 2, and Part 3.]*

Astronomers have found more Tatooines! Cool.

In September, astronomers announced the discovery of a planet (Kepler-16b) that orbited not one but two stars. The stars orbit each other (in what’s called a binary system) and the planet circles both. This was the first such planet found doing this (out of hundreds of planets orbiting single stars discovered), which opened up the question: how rare is this kind of system? Is Kepler-16b one of a kind?

The answer appears to be no: two more such systems have just been announced! Dubbed Kepler-34b and Kepler-35b, both are gas giants, similar in size to Saturn.

The planet Kepler-34b orbits two Sun-like stars once every 289 days. The two stars (Kepler-34A and Kepler-34B; note the capital letter denoting a star versus the lower case letter denoting a planet — which technically should be called Kepler-34(AB)b, but at some point I have to draw the line and simplify) orbit each other every 28 days. The planet Kepler35-b orbits a pair of somewhat lower-mass stars every 131 days (the stars orbit each other every 21 days).

Note that in both cases, the planets orbit their stars at distances much larger than the distances between the two stars themselves. That’s not surprising to me. From far away, a circumbinary planet (literally, "around two stars") feels the combined gravity of the two stars more than either individual star, much like distant headlights on the highway look like a single light. When you’re close, the two lights resolve themselves. Same thing with a planet; if it orbits much closer in the gravity field is a bit more distorted by the individual stars. Too close, and the orbit becomes unstable and the planet can be ejected from the system entirely! But it looks like both Kepler-34b and 35b have nice, stable orbits.

Binary stars are very common in the Milky Way: roughly half of all stars are binary, and now we know that at least three such systems have circumbinary planets. And we’ve only just started looking! Mind you, these planets were found using the transit method, so the orbits have to align just right from our viewpoint or else we don’t see them transit. For every one transiting system we find there are many more that exist but *don’t* transit, so we don’t see them. But they’re out there.

I suspect that the fraction of binary stars with planets is probably lower than for single stars, since planets forming (or moving) closer in to the binary center will get ejected. But still, even with a lower fraction we’re still talking about a pool of hundreds of billions of stars, so it’s likely that there are *millions* of circumbinary planets out there: millions of Tatooines!

And hmmmm. Kepler 34 and 35 are 4900 and 5400 light years away, respectively, making them among the more far-flung planetary systems seen. You might say that if there’s a bright center to the Universe, they’re the planets that it’s farthest from.

I’ve always dreamed of standing on a hill and watching twin suns set in the west. Sadly, the wind won’t blow through my hair like it did Luke Skywalker’s, but that would be a small price to pay. What a view that would be!

http://www.youtube.com/watch?v=305xoy0hKHw

*[UPDATE: Wait a sec! Right after posting, I realized: the two planets are both gas giants, but far enough from their stars that big, terrestrial moons might be possible. So imagine that: a binary sunset with a gigantic planet looming in the sky as well! That would be incredible.]*

*Image credit: Lynette Cook and SDSU*

Geeks across teh intertubez are giddy with delight today. Why? Because it’s November 11, 2011, of course! And if you’re in the US, you’d write this as 11/11/11, so of course this tickles the heart of any true mathematically-inclined nerd such as me. now, in the US we put the month first — MM/DD/YY — which is somewhat silly; in England and other realms they write it more logically with the units getting bigger left-to-right, so for them it’s DD/MM/YY, or, contrary to us yanks, 11/11/11.

OK, so anyway, it’s all ones. Why is that cool?

Well, it just *is*. Duh. But deep down, this goes to the root ("root"! HAHA! Oh man, I’m a math riot) of how we count. And I am *never* one to miss a chance to lecture on nerdalicious topics, so stick with me for a bit.

**The power of ten compels you!**

On the web, which consists of 87% dorks (look it up!), this date is special because it looks binary. For those of you unfamiliar with this, we humans tend to use the number ten as the basis of our counting. Our numbers reflect this: we break things down into powers of ten when we write out a number.

For example, the number 1234 — one thousand, two hundred, thirty-four — has four digits, each representing a power of ten. On the right, we have the "ones" place, where 1 = 10^{0}. For our example, there are four of them.

Next, moving left, is the "tens" place, and 10 = 10^{1}. For 1234, we have three tens, or thirty.

See how this works? Next is the "hundreds" place, and 100 = 10^{2}. Two of those is two hundred.

Last, all the way to the left is the " thousands" place, or 10^{3}. We have one of those, for one thousand.

Add ‘em together, and you get 1 thousand, 2 hundred, thirty four. This is actually a very clever way to write down a number. Compact, efficient, and makes simple arithmetic possible. It’s not that hard to learn how to add fairly large numbers in your head due to this notation. Try that in Roman numerals!

An important note: we use single digits to represent numbers from 0 – 9, then two digits for 10 – 99. Obvious, right? But if you think about it, you’ll see there’s a reason: you don’t need a one digit numeral for "ten", because it has its own column. Counting up from 0, once you reach the base number of ten you just put a 1 in the next column to the left and a 0 in the column on the right. Simple, neat, and efficient.

I’d even say it’s a brilliant innovation in notation, and is what allows us to represent huge numbers simply. Roman numerals use symbols for certain numbers, and you just mash them together to represent a bigger number (sometimes subtracting them, too, which is truly awful). Our number 1234 would be MCCXXXIV, which is unwieldy. And adding a number to that is completely nonintuitive. It’s more like a code than a system of notation for numbers. Our current method is way, way better. In fact, I’m not really sure why Roman notation is even taught anymore. Seriously, who needs it? Movie copyrighters and SuperBowl fans. That’s about it.

**All your base are belong 2 us**

But it turns out, you don’t have to use base 10. We have ten fingers, so it’s somewhat natural for us. But in fact other bases are possible, and sometimes even preferred. Like binary.

Binary is the simplest system. It’s base 2. So when you write a number, you use powers of two in the places, not ten. So the columns go from right to left like this:

2^{0} = 1

2^{1} = 2

2^{2} = 4

2^{3} = 8

2^{4} = 16

2^{5} = 32

and so on. You can only use a 0 and 1 in this case, and that makes sense. Why? Because, like base 10, you use a two-digit numeral to represent your base. What we think of as "2" in base ten becomes 10 in binary. It’s the base to the power of 1, just like it is in base 10 (which is called decimal, by the way). I’ll add that when you use the number 10 in decimal you call it "ten", but when you use 10 in binary you call it " one zero" to avoid confusion. If you call it "ten" then all the math people will laugh and make fun of you, and not invite you to their Star Trek marathon^{*}.

In binary, just like in base 10, we add the columns together to make a number. So let’s pick an arbitrary number, like 42^{†}. If we look to the powers of 2, we see it’s 2^{5} (32) + 2^{3} (8) + 2^{1}. So we’d write it in base 2 as 101010. You have to put in the zeroes as place holders, or else you can’t see what power is what. But that makes sense: it’s 1 x 2^{5} + 0 x 2^{4} + 1 x 2^{3} + 0 x 2^{2} + 1 x 2^{1} + 0 x 2^{0}: 101010.

It may seem more cumbersome than base 10, since 42 is only two digits in decimal but 6 in binary. True, but it’s really easy to represent numbers in base 2, since a 0 and 1 can be represented in lots of ways, like an arrow pointing up or down, or a section of a DVD with a tiny laser-burned microscopic pit or no tiny laser-burned microscopic pit, and so on. Anything that exists in two states (on/off, filled/empty) can be used to count in binary. Electric circuits do that, they can be made small and fast, and hey, don’t computers run on electricity?

So yeah. That’s why binary is used in computers.

**Will you still need me, will you still feed me, when I’m sixty-three?**

And finally, that brings us back to the date! November 11, 2011 is 11/11/11 or just 111111. And that looks like a binary number!

So what is binary 111111 in decimal form?

It’s 1 x 2^{0} + 1 x 2^{1} + 1 x 2^{2} + 1 x 2^{3} + 1 x 2^{4} + 1 x 2^{5} = 1 + 2 + 4 + 8 + 16 + 32 = **63**.

That’s just one less than the next higher power of two, 64 (2^{6}). In binary, a number full of 1s is like a decimal number full of 9s. Add one to it, and you bump up to the next power of your base.

And that’s why some ~~dorks~~ people think today is cool. It’s the last binary number this year, and in fact we can’t get another date that looks like a binary number until 01/01/00, or January 1, 2100! That’s the first day of the last year of the 21st century. It’s a long wait.

And? That date will be 010100, or 20 in decimal.

I don’t know if people will hold binary parties tonight (you can either go or not go) or how they will celebrate — one person on Twitter said he’s getting married today, and I have to admire that — but for me, it’s just fun to think about the numbers.

But then, I’m a dork too.

**The Ramans do everything in threes…**

So I’ll leave you with a quiz. Base 3 (called ternary) is fun as well, and I don’t want to leave it out!

In base 3, you can use the numerals 0, 1 and 2. As it happens, today’s date consists of those numerals! So we can write out our entire date in ternary, including the full year: 11/11/2011. I ask you: what’s that in decimal? (Those of you who are in other parts of the world, where you’d say it’s 2011/11/11, you’re invited too). You could cheat and look it up online, but that’s no fun. Being a dork means doing it long hand sometimes!

And fun fun fun, as it happens, that ability to use a 2 means more dates in ternary are coming soon. So here’s a semi-trick question: when’s the next all-*ternary* date?

And, of course: **Happy binary 63 day!**

*Image credits: The Flickr streams of Kichigai Mentat, Joe Shlabotnik, goldberg, and sgilliesm all licensed under Creative Commons.*

^{*} Spare me the nerd rage, please. I’ll be watching Stargate.

^{†} OK, so it’s not arbitrary. It’s a pronic number!

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