The Fruitless Search For Solar Systems Like Ours
Scientists have found hundreds of big, gassy planets that orbit close to "their" star, though solar systems with small rocky planets, like ours, have been elusive. This might be because they are hard to detect using existing techniques, but an astronomer says he's getting a bit nervous. He doesn't want to think that we are the exception rather than the rule.
MICHELE NORRIS, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.
ROBERT SIEGEL, host:
I'm Robert Siegel, and now it's time for a puzzle, in this case, a planetary puzzle from NPR science correspondent Robert Krulwich.
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ROBERT KRULWICH: Maybe the first science thing you learn when you're a kid...
Unidentified Child: (Singing) (Unintelligible).
KRULWICH: Is that the sun is surrounded by planets, and you learn their order.
Unidentified Child: (Singing) Mercury, Venus, Earth and Mars...
KRULWICH: And then you learn there's a pattern. First, you get the rocky planets close to the sun, and then the normal progression is after rocky, rocky, rocky, rocky, you get gassy, gassy, gassy, gassy.
Mr. MIKE BROWN (Professor, California Institute of Technology): And then icy, icy, icy, icy, at the end of that. But when you say normal...
KRULWICH: What I mean by normal, I told Caltech astronomy professor Mike Brown is it's, you know, like our solar system.
Mr. BROWN: Exactly. So normal, this is if you had talked to me 20 years ago, I would have said, yes, not only is our planet our solar system that way, but that's the way all planetary systems that we find are going to be, and we understand why.
KRULWICH: Because 20 years ago, we thought there were rules about building solar systems, rules we understood, that you could you know, learn, say, in science films at school.
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KRULWICH: We knew that our solar system began with a cloud.
Mr. BROWN: There's this cloud of gas and dust in space.
KRULWICH: And in that dust, you'd find hydrogen and oxygen.
Mr. BROWN: H2O, water.
KRULWICH: Yeah, and because of gravity, all that water vapor and dust would kind of clump.
Mr. BROWN: So gravity is pulling everything together and pulling everything together.
KRULWICH: Creating in the hot zone near the sun first the rock planets.
Mr. BROWN: Mercury, Venus, Earth, Mars. But as you get out to about where Jupiter is, there's a place that's called, by astronomers it's called the ice line.
KRULWICH: And because the ice line was some distance from the sun, it's kind of cold out there.
Mr. BROWN: At the ice line, it gets to be below the freezing point of water. So all of that gaseous water that's circling the star freezes.
KRULWICH: And produces an orbiting snowball. Actually, it's more like an ice ball that as it gets bigger pulls in more and more water vapor.
Mr. BROWN: So you can start to get big.
KRULWICH: And the bigger it gets, the stronger its gravitational pull.
Mr. BROWN: And makes it go suddenly from being 15 times bigger than the Earth to 300 times bigger than the Earth.
KRULWICH: So the less that we learn from our Jupiter is that to create a big, gassy planet presumably anywhere in the universe, what you need to do is you start far from the sun, where it's cold, you form an ice ball, you grow, that's the theory.
Mr. BROWN: It's a beautifully worked out theory. When I first started teaching classes, this is exactly what I taught because it describes the solar system perfectly. There's beautiful logic to it. It explains all the features that we see.
KRULWICH: And then about 18 years ago, we discovered a planet that was not in our solar system.
Mr. BROWN: The very first planet that was discovered around another star was bigger than Jupiter, which is not surprising, it's easier to discover bigger things, and it was closer to its star than Mercury is to the sun.
KRULWICH: Oh, it's that close?
Mr. BROWN: It's right up next to the star.
KRULWICH: But wait. Didn't you just say that a Jupiter-sized planet forms far from stars, out where it's cold? See, so something's wrong.
Mr. BROWN: Okay, so when you find that first one, you just say, okay, that's weird. I don't know what happened.
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KRULWICH: But then they found a second one.
Mr. BROWN: The second one found, bigger than Jupiter, right next to the star. The third one found, bigger than Jupiter, right next to the star. It's crazy. It's probably two-thirds of them are this way.
KRULWICH: At this point, we have seen more than 400 planets out there in space, most of them big and gassy, and overwhelmingly, they are not where they are supposed to be. Instead of being out in the cold like our Jupiter, scientists now figure they formed in the cold, and then very early on, they pushed through the dust and the other baby planets to move close to their stars.
So many gassy planets formed and then moved next to stars that Mike Brown wonders:
Mr. BROWN: Why didn't Jupiter?
KRULWICH: Yeah, why didn't our Jupiter do what all the other guys did? It's an important question because if our Jupiter had moved in toward our sun, things would be very different today.
Mr. BROWN: If you take Jupiter from where it is now, and you were to move it inward, you will destroy anything that's inside there. There will be no Earth-like planets that are left after you've moved Jupiter in.
KRULWICH: So if our Jupiter had moved in?
Mr. BROWN: We would have never been here.
KRULWICH: Uh-oh. So what if it turns out that most solar systems in the universe have gassy planets that move in? Does that mean we're going to find fewer Earths or different Earths? What do we now think is normal out there?
Mr. BROWN: We have no idea. Every planetary system that we get to see in detail appears different from anything that I would've expected.
KRULWICH: Yeah, but still, there's got to be something you can predict. I mean, you do teach astronomy at Caltech. So...
Mr. BROWN: I've given up. I have no idea what to expect.
KRULWICH: But haven't you told me that other astronomers were searching for solar systems like ours for, I dont know, like five years, 10 years, 12 years?
Mr. BROWN: Fifteen years, probably more than it's probably even 20 years by now, but certainly 15.
KRULWICH: And the method they've been using to search for planets is you have to wait for the possible planet to circle its star.
Mr. BROWN: Yes.
KRULWICH: So for a planet like Jupiter...
Mr. BROWN: You would have to wait 12 years.
KRULWICH: Okay, but since we've been looking for 12 or 15 or 20 years, it's right around now, if there are lots of solar systems like ours out there, we should start to see them, or we should have seen, or we're about to should have seen them?
Mr. BROWN: Or we should have seen a few, and when I look at the list of everything that's been discovered, there is one that maybe fits our picture.
KRULWICH: Okay, so that's a start.
Mr. BROWN: It is a start. It was discovered a couple of years ago, and there's one.
KRULWICH: One, and you're now looking for two.
Mr. BROWN: Two would be good. A few more would be better.
KRULWICH: I should say there are scientists, planet-hunting scientists, who think Mike's a little picky and that actually, there's several solar systems now that look kind of like ours, and they do expect to find more. Well, maybe, says Mike.
Mr. BROWN: But we are at the stage now where we have had that time. We're starting to have enough time to have been able to see these things.
KRULWICH: And now every month it goes by when we don't find solar systems like ours out there in the universe, we have to consider the possibility that what we call home may be a surprisingly uncommon place.
Mr. BROWN: And now I'm wondering if it's going to the point where we're not uncommon, we are a rare exception.
KRULWICH: Well, I think it's a little early to get that worried.
Mr. BROWN: I'm not quite worried yet, but if things don't happen in the next year or so, I think it's time to get very worried.
Unidentified Child: (Singing) Mercury, Venus, Earth and Mars.
KRULWICH: After all, Mike wants to think that what he has taught for years at school is still true, that solar systems like ours are ordinary and everywhere.
Mr. BROWN: You want to be representative of the universe.
KRULWICH: Like the other guys.
Mr. BROWN: Yeah.
KRULWICH: And if it turns out that what we call home, our solar system, is a very rare thing, that's unsettling.
Mr. BROWN: I think that's right, and I would like deep down inside, I think I would like to see other things like this solar system out there, and it would make me feel at home.
KRULWICH: Robert Krulwich, NPR News.
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SIEGEL: Speaking of other solar systems out there, if you go to our Web site, Robert has arranged a trip across the galaxy to see a solar system literally being born. That's at npr.org.
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A Space Voyage To Genesis
This was a first for me. The images in the video below are real. They are images (many from the Hubble telescope) patched into a virtual galaxy so we can click our way across the Milky Way to seek out a very particular, very distant star. "What you see here," says author Michael Benson, "is a Genesis. Not ours, someone else's."
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Michael Benson is a reporter, filmmaker and author of a number of books that feature gorgeous pictures of objects in space. He hangs out with a ragtag community of amateur astronomers including "ugordon" from Croatia, "ngunn" from Wales, "nomisn" from Melbourne, "volcanopele" from Tucson, and "floyd" from Boston. Together, they collect images.
The images aren't theirs. They are mostly images taken by government space telescopes and posted on public Web sites. Benson and the others download the raw digital data, render them into black and white, then edit, colorize, and sometimes animate them. Then they swap what they've done at UnmannedSpaceflight.com and wonder at the amazing things they see.
Benson is really good at this. For example, here's his rendering of the Crab Nebula, which is about 6,500 light-years away. The image came from a space telescope; the color is Bensonl's: a baby blue cloud of gas left over from an exploding star that erupted in A.D. 1054 Earth time.
That rich aquamarine is Benson's approximation of what helium, ionized hydrogen plus a dash of carbon, oxygen and nitrogen might look like to a visiting human with slightly larger-than-life eyes.
Here's an amazing one: two galaxies, called "The Antennae," colliding. This image, says Benson, is "a preview of what will happen when the Milky Way meets Andromeda in about 2.5 billion years."
The coolest thing about these images is that they are new. As soon as governments post the data on their sites (Hubble for deep space; Magellan for Venus; Galileo and Voyager for Jupiter; NASA/ESA Hubble for Saturn; NICMOS for Titan; NASA's HiRISE for Mars), this gang of amateur astronomers grabs the images and starts trading, looking, hunting.
While it can take thousands of years for light from distant stars to reach Earth, light from Saturn and Mars gets here in minutes. Which is why solar system pictures have the immediacy of local news coverage. For example, here's a shot from Mars taken by the HiRISE on Feb. 19, 2008, that amazingly captured an avalanche on Mars as it happened!
The white stuff on the left is dry ice (CO2 ice) on a Martian ridge. Where the white ends and the rocks turn red, that's actually a steep slope plunging down 2,300 feet, and the dust flying around on the right is rock literally crashing onto a canyon floor. This picture arrived on Earth just after the dust settled.
If you're having trouble figuring this image out, check out this just-released reconstruction from Bernhard Braun, one of the UmmannedSpaceflight.com regulars, who, using HiRISE data, gives you a more recognizable view from across the canyon.
The folks at UnmannedSpaceflight.com are a self-appointed, adventurous, often highly talented bunch of colorists, editors, animators, stargazers and photographers — most of them, it seems, aren't scientists — who together have become an unofficial news site, hijacking pictures so the rest of us can see beautiful or dramatic images without getting permission from the governments that took those pictures. They don't need permission. These images are for everyone to see and use as they wish, and there are lots of them. The Mars Rovers alone sent 200,000 images to Earth.
Meanwhile, some of those amateurs have become increasingly famous for their ability to turn the government's data in objects of great beauty. Michael Benson, for example, is about to exhibit some of his photographs at the Smithsonian Institution's National Air and Space Museum in Washington. The picture you see above is a star in our Milky Way, Eta Carinae, that exploded about 150 years ago, but somehow wasn't destroyed. Instead it survives as two lobes of gas precariously appearing to pull in opposite directions.
The lines are created by Hubble's lens. This picture appears in Benson's new book, Far Out (Abrams, 2009), a volume rich with spectacularly shaped galaxies, stars poised to explode and jets of gas shooting across deep space. His last one, Beyond, featured intimate close-ups of loops of flame leaping across the Sun's surface, strange dunes on Mars, and volcanoes sending plumes 86 miles into space near Jupiter.
There are, of course, people who can look at a volcano near Jupiter or a rockslide on Mars and remain, well, unmoved. Why get all excited about rocks falling down a cliff? But when that cliff is 34 million miles away and the image jumps onto your computer so quickly it feels like this happened down the block, suddenly the solar system feels more like a neighborhood. And for a lot of folks, that is a very new, very special, very good feeling.
(If you are a self-styled space adventurer or just curious, you might want to click on the All Things Considered radio story above. It explores the newest quandary in local astronomy: How come the new solar systems we are discovering don't look like they're supposed to? It's a puzzler from CalTech astronomer Mike Brown.)
Special thanks to John Pavlus for the video, Danny Madorsky for his musical score, and to young Brian for his performance of "The planets, the planets..." on the radio broadcast.