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
- 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
So Curiosity’s been on the Martian surface for a week, and we’re already seeing faked images touted as being real. The other day it was a more-or-less honest mistake of people spreading around a computer-generated view from Mars – originally meant just to show what the skyline looked like from there – thinking it was real.
Now though, we have what’s clearly an actual fake. Here’s the shot, getting passed around on various Tumblrs:
Now, I’ll note it’s not crazy to think this shot might be real; the Sun is very bright and in many cameras you can get reflections inside the optics, causing this double-Sun effect. It happens all the time. So you wouldn’t really be seeing two suns setting – just one real one and one that’s an internal reflection.
But that’s not what’s going on here, as I knew right away. That’s because I’m familiar with this picture:
That shot is also of the sunset, but it really is from Mars! It was taken by the Spirit rover in May 2005, a spectacular shot of the Sun setting over the Martian landscape.
And that’s where you’ll find the proof of double-sunset-fakery. Compare the double-sunset picture with the real one from Spirit, and you’ll see the profile of the landscape on the horizon is exactly the same. Clearly, the double-sunset pic was faked, adding in the second Sun. In fact, you can see that both images of the "Sun" in the double sunset picture don’t match the real one. In other words, both images of the Sun were faked.
Also, I couldn’t help but think the faked Sun images looked kinda familiar to me as well. Recognize them? Perhaps the picture here will help place them. Clearly, the faker must have come from some wretched hive of scum and villainy.
It may be this picture was created as a joke and got out into the wild, or maybe it was done on purpose to fool people. As usual with things like this, tracing it back to the original is a bit tough (though the Martian skyline picture from earlier was able to be pedigreed). I’ve seen it on several sites now, and I’ve gotten email and tweets about it. It was easy to debunk, so why not?
I don’t know if this image will go viral like the previous unreal one did; this is so obviously hoaxed that it may not have the same sort of traction. Still, it sometimes helps to get ahead of the curve here, and dowse these things with reality before they spread out of hand.
So if you see someone posting that image, send ‘em here. That way, we will crush the hoaxers with one swift stroke.
Image Credits: Mars sunset: NASA/JPL/Texas A&M/Cornell; Tatooine: Uncle Owen’s Wedding Photography Service (now defunct).
[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.]
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!
[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
If there’s a bright center to the Universe, astronomers have found the planet it’s farthest from. Called Kepler-16b, it’s a Saturn-like world which has the distinction of being the first discovered to orbit both Sun-like stars in a binary system.
OK, Star Wars references aside, this is pretty cool. Most of the planets being found around other stars are orbiting single stars. A very few — like a possible planet orbiting Gamma Cephei — orbit one of the stars in a binary system, and some (like NN Serpentis b and c) orbit both stars, but one of them is a dead star like a white dwarf or a neutron star.
Unlike those, Kepler-16 is a binary where both stars, though dinky, are bona-fide stars like the Sun, and the planet orbits both. Actually, how it was found is pretty nifty. The orbiting Kepler observatory is designed to stare at over 100,000 stars and detect the tell-tale drop in light when a planet transits (that is, from our point of view passes directly in front of) its parent star. Kepler has found a lot of planet candidates this way — well over 1200!
Kepler-16 is one (OK, two) of those stars (hence the name), located about 200 light years from Earth. The two stars are eclipsing binaries, meaning that we are viewing them from Earth in the plane of their orbit. Twice every orbital period, one of the stars blocks the light from the other and we see the total light from the system dip a little bit. We know of a lot of eclipsing binaries, and their properties are pretty well understood.
But Kepler-16 is different. Read More