A thoroughly sporadic column from astronomer Mike Brown on space and science, planets and dwarf planets, the sun, the moon, the stars, and the joys and frustrations of search, discovery, and life. With a family in tow. Or towing. Or perhaps in mutual orbit.

Showing posts with label extrasolar planets. Show all posts
Showing posts with label extrasolar planets. Show all posts

Kant's Crowded Universe

I was asked by a magazine to review Alan Boss's new book The Crowded Universe. They asked for a review that was a much an essay on the field as a review of the book itself, which made it a very fun exercise. The following is based on the review that I got to write.

Two hundred fifty years ago, Immanuel Kant, in his Universal Natural History and Theory of the Heavens, laid out a remarkably modern-sounding account of the state of the universe. Moons go around planets. Planets go around stars. Stars go around the Milky Way. The Milky Way and other galaxies (“other Milky Ways,” he called them) go around something even larger. The solar system had an understandable origin, and inevitable consequences:
The planetary structure in which the sun at the centre makes the spheres found in its system orbit in eternal circles by means of its powerful force of attraction is entirely developed, as we have seen, from the originally distributed basic stuff of all planetary material. All the fixed stars which the eye discovers in the high recesses of the heavens and which appear to display a kind of extravagance are suns and central points of similar systems.
To paraphrase: gravity takes stuff and turns it into stars surrounded by planets, and it has done so everywhere you see a star in the sky.
For the first 240 years after the publication of Kant’s assertion, this fact could only be verified for only a single star in the sky: the sun. In 1995 Michel Mayor and Didier Queloz announced the discovery of the first planet orbiting a star other than the sun. Now, fourteen years later, almost 300 stars are known to have planets around them. It is not quite “all of the fixed stars which the eye discovers,” but it’s getting close. Kant was substantially correct. It had been accepted since the 17th century that our sun is not special, but is, instead, but one of many stars in the universe. Now, at the beginning of the 21st century, it is clear that our planets aren’t special either.
Except that some of our planets are still special.
It is tempting to describe the many planetary systems that have been discovered in the past decade and a half as simply weird. Rather than the orderly arrangement of planets that we have here in the solar system, with small planets close, large planets far, and everything going around the sun in satisfyingly circular orbits in a common disk (each one of these properties is “inevitable”, according to Kant, and according to most astronomers up until late 1995), we have instead found planets the size of Jupiter that orbit their stars closer than Mercury, planets with orbits as elliptical as some of the comets in the solar system, and planets with separations from their central star far beyond even the most distant objects detected in our solar system. Weird, indeed. The only type of planetary system that we haven’t found, it seems, is one like our own. Nowhere out there has there been anything quite like the solar system; nowhere out there is another Earth.
But even this special position that our home planet holds is now in jeopardy.
Alan Boss’s new book The Crowded Universe tells the story of the development and launch of NASA’s Kepler spacecraft, which was recently launched from the earth to go into orbit around the sun. Kepler’s 3 1/2 year mission is simple to state: find the Earths. Kepler, along with a similar ESO mission CoRoT, will be the first to finally have a chance to tell us whether planets like the one on which we live are as common as Kant would hope or as rare as some astronomers think.
Boss weaves the story of Kepler (surely a must-read cautionary tale for anyone contemplating a life in NASA mission development) with the larger story of the entire, now booming, field of exo-planets. As someone whose astronomical career has spanned the period Boss discusses, I’m glad someone was taking notes. It is fun to be able to go back to those days when each new planetary discovery was an exciting event with multiple teams struggling to outdo the others with firsts. First planet at the distance of the earth! First transiting planet! First multiple planet system! With the current richness of the exo-planet field it is easy to forget that almost all of this is under a decade old.
Boss gives the insider story not only of the Kepler mission development and the birth and childhood of the entire exo-planet field, but, in a stroke of luck for us all, he got to play a intimate role in the definition of planets in our own solar system, and he gives what I believe is the first account of some of the inner workings of the International Astronomical Union committee that first started trying to figure out what to do with Pluto and Eris and the things that we now call dwarf planets. The demotion of Pluto was unassailably reasonable, but the events leading up to this eventual demotion were some of the more publicly comical occurrences in recent astronomical history. Reliving these moments is an excellent reminder that for all of their command of the physics of the universe around them, astronomers, being human, have the capacity for nearly infinite folly.
But for Boss and The Crowded Universe, Pluto is just a distraction, and rightly so. The meat of his book is the race for finding something like the Earth. Sitting in the middle of the events, it would be easy to get caught up in the day-to-day (or perhaps committee meeting to committee meeting) details. But Boss, while detailing the daily work of himself and other scientists involved in the field, never ceases to forget that we’re privileged to live in such at a time when a nearly-Copernican-magnitude revolution is unfolding.
Yet even if Kepler and CoRoT find an abundance of planets, the 250 year old Kantian revolution will not be complete. The planets that these spacecraft might find could be the precise size of the Earth and could orbit their stars at the exact distance of the Earth, but while an astronomer might be willing to call such a thing Earth-like, most people will still want to know more. Does it have liquid water? Does it have a recognizable atmosphere? And, inevitably, the only thing that really matters, could it – no: does it – support life?
The answer to these questions will take decades or more to answer. Kepler and CoRot are simply first steps along the way. In the meantime, we can perhaps take solace from Kant:
I am of the opinion that it is not particularly necessary to assert that all planets must be inhabited. However, at the same time it would be absurd to deny this claim with respect to all or even to most of them.
It took 240 years to prove him mostly right the first time. With a little bit of luck and a little bit of perseverance and, as Boss shows, a lot of the day-to-day work of astronomers around the world, the final step might come just a little bit faster.

Land ho!

If you pay any attention to space news, or even just to the front page of the LA Times you will know that this week brought reports of the first-ever pictures of planets beyond our solar system.
I had no inside scoop on this one, so I learned it the hard way: a reporter called me up to ask for commentary. My immediate comment: “uhhhh…. Can I go and read the scientific paper first?” A good reporter will say “of course” but many less good ones will say “well I just want a quick quote; can you give me a reaction?” Luckily, this one said “of course.” I read the paper. Papers, actually. Two groups of astronomers had taken pictures of planets around other stars at about the same time. I went into reading-a-scientific-paper mode and started asking the standard questions that I ask whenever a read a scientific paper:
· Do I believe the results? I tend to be quite skeptical of results, whether they are mine or anyone else’s. Cutting edge science is hard, or someone would have done it already. There are many ways to make mistakes and to misinterpret data, particularly when you desperately want a certain result to occur. These astronomers clearly want their results to tell them there are planets. Did they take any shortcuts that could have led them astray? Did they stray into wishful thinking? I read carefully looking for sloppiness, as I would do when reading any other scientific paper.
In this case there appeared to be no sloppiness, and no wishful thinking. The observations were quite meticulous. The analysis solid. I don’t see any reason not to believe that they had indeed seen something. So far so good.
· Do I believe the interpretation? At this point, I believed that, yes, indeed, the thing that had caught their attention in their data was probably real. I d something. But what was it? Was it really a planet, like they claimed? Many scientific papers can be meticulous about discovery and then sloppy about interpretation. The reason for the sloppiness is often, again, wishful thinking. The astronomers here saw something, and they really wanted that something to be a planet. That desire for discovery can lead to data cherry picking just like that that has often been discussed about the intelligence community interpretation that there were weapons of mass destruction in Iraq. You pay close attention to the data that supports what you want to be true, you discount data which is less supportive. Scientists are supposed to be driven purely by facts and immune to such thinking, right? Well, no. Science is supposed to be driven by facts, but scientists are just people who can’t help but be influenced by many outside things.
Did it happen here? I kept reading. I couldn’t find any flaws in their interpretation. They did all of the things that they needed to do to really prove that what they were seeing was a planet going around a distant star. They didn’t ignore any of the counter evidence. The news was good. I believed the results and the interpretation. Only one question more to go!
· Do I buy the spin? Any paper that is being covered by the press is being spun, whether the authors intend for it to be or not. Sometimes the spin is fair, sometimes it is a bit oversold, and sometimes the spin can be so off that it takes an accurate scientific paper and turns the public interpretation into bad science. These papers about imaging planets around other stars were, in my opinion, a bit oversold. These pictures of planets around stars were more of a long-expected technical milestone than astounding discovery.
OK! I was ready to talk to the reporter. What to say? I thought through my reactions: yes, these really were the first images of planets outside of the solar system; yes, the scientists are good and credible; yes, people have been working for a long time to achieve this thing. But how was I going to deal with the other thoughts that I had? No, this was not nearly as exciting as people were making it out to be. We have known about planets around other stars for more than a decade now, and taking a few pictures adds very little to our scientific understanding of them. There was a race to see who could take these pictures first, not because anyone really had many questions about what the planets would look like, but simply so that someone could be declared the winner and put the feather in his cap.
That’s not a very kind thing to say about work by a colleague who has worked hard to achieve this result. And it’s not really what a reporter – searching for the breathless quote – wants to hear. Yet that was my initial reaction.

o o o o o o o
Five years ago today I discovered Sedna. Sedna is an unexpected oddity in the outer solar system. It is on a looping 12,000 year long (!) orbit around the sun that carries it as far away as 1000 times the distance from the earth to the sun and as close as 76 times the earth-sun distance. Nothing else known has such an orbit, and no one really knows how Sedna got there. For five years we’ve been searching hard for something else like Sedna, and, so far, we’ve come up blank.
Four and a half years ago, we had a big press conference to announce the discovery. As usual, the reports called up other astronomers around the world for comment. Some were indeed quite excited by the discovery, but more than a few told the reporter some version of “well, it’s true, but it’s really no big deal. We’ve know to expect things like this for a long time so it is not surprising that someone found one.”
Most scientists don’t talk to the press that much, and, when they do, they talk to them like they would talk to another scientist. When talking to a fellow astronomer, for example, I am able to step back and freely say that the discovery of Eris was not particularly a big deal. It was simply an object slightly larger than Pluto with very few intrinsic scientific implications (Sedna, in contrast is a big deal and has huge implications, but that discussion will have to wait). It became a big deal culturally, as it precipitated the long-discussed downfall of Pluto, but, scientifically, it really didn’t change much of the way that we view the solar system.
When reacting to scientific papers, scientists are more used to the idea of peer review (more on this next week!), where you are supposed to be detached and point out the good and the bad and the utterly mistaken parts of a paper. You are certainly not supposed to be excited.
But commenting to the public on scientific papers is not peer review. Reporters are not scientists. They are not reporting to scientists. They are reporting to people who have a million other bits of news coming in and may or may not pay attention to this one. But if they do pay attention to this one, they will actually think about and learn a little bit about science that day. Any scientist should be happy when that happens. The role of the commenting scientist in this case is not to downplay the significance of some other scientist’s result, but to explain the excitement.
After the experience with Sedna (and, later, Eris and Haumea and Makemake, which all went through the same process) I thought hard about the right way to interact with scientific news. These days, I try to keep in mind my:
Five Rules for a Scientist Talking to the Press about Someone Else’s Result
1. Momentarily forget scientific detachment: If the result is exciting, allow yourself to be excited. Explain why you’re excited.
2. Re-explain the science. More often than not, the person talking to you has heard more of the spin than the science. The science is actually the cool part. Emphasize it.
3. Resist the cliché. In commentary about exo-planets, someone will invariably say “and this will help us discovery earth-like planets.” For Mars the cliché is “and we can look here for life.” For Titan: “and no we will better understand the origin of life.” Clichés are nice things to say, since you don’t have to think much to say them, but, as a consequence, they don’t actually mean much, either. And, since they are clichés which can be used for almost anything, they don’t do much to actually explain the science. The real science is probably much more interesting than the cliché.
4. Never ever hesitate to point out bad science. Bad science is worse than no science. Never hold your nose and pretend to be excited when things smell funny. In many circumstances, explaining why something is bad science provides an excellent education as to what good science should be. If the science is good but the spin makes it bad, unspin. Talk about what the science really says.
5. Congratulate and thank your colleagues. Someone did something good that allowed you to have a chance to do a little public scientific education. Send him or her a quick email and say thanks and job well done.
The reporter called back to talk about planets. I was excited. I re-explained the science and why it mattered. I talked about how interesting it is to me to start to see the architecture of other planetary systems and what this will tell us about planets near and far. At the end of the interview I summed up my thoughts in a way that, in retrospect, I like enough to repeat here:
I can’t say the pictures are surprising. We have known for a long time that these planets are out there and that someone someday would take pictures of them. But that doesn’t take away from the exciting fact that we are seeing planets around other stars for the first time. When you start to sail across the ocean you know that you are finally going to reach shore, but, still, when you see land for the first time it is the most beautiful and exciting thing in your universe. “Land ho!” is never said in a quiet voice.
And then I hung up the phone and sent congratulations to my colleagues for their exciting discoveries.