Monday, April 16, 2012

The hunt for the first exoplanet

The little prince
Today, extrasolar planets, or exoplanets for short, are all over the news. Hundreds are known, and they are cataloged in The Extrasolar Planets Encyclopaedia, accessible for everyone who is interested. Some of these extrasolar planets orbit a star in what is believed to be a habitable zone, fertile ground for the evolution of life. Planetary systems, much like ours, have turned out to be much more common results of stellar formation than had been expected.

But the scientific road to this discovery has been bumpy.

Once one knows that stars on the night sky are suns like our own, it doesn't take a big leap of imagination to think that they might be accompanied by planets. Observational evidence for exoplanets was looked for already in the 19th century, but the field had a bad start.

Beginning in the 1950s, several candidates for exoplanets made it into the popular press, yet they turned out to be data flukes. At that time, the experimental method used relied on detecting minuscule changes in the motion of the star caused by a heavy planet of Jupiter type.

If you recall the two-body problem from 1st semester: It's not that one body orbits the other, but they both orbit around their common center-of-mass, just that, if one body is much heavier than the other, it might almost look like the lighter one is orbiting the heavier one. But if a sufficiently heavy planet orbits a star, one might in principle find out by watching the star very closely because it wobbles around the center-of-mass. In the 50s, watching the star closely meant watching its distance to other stellar objects. The precision which could be achieved this way simply wasn't sufficient to reliably tell the presence of a planet.

In the early 80s, Gordon Walker and his postdoc Bruce Campbell from British Columbia, Canada, pioneered a new technique that improved the possible precision by which the motion of the star could be tracked by two orders of magnitude. Their new technique relied on measuring the star's absorption lines, whose frequency depends on the motion of the star relative to us because of the Doppler effect.

To make that method work, Walker and Campbell had to find a way to precisely compare spectral images taken at different times so they'd know how much the spectrum had shifted. They found an ingenious solution to that: They would used the, very regular and well-known, molecular absorption lines of hydrogen fluoride gas. The comb-like absorption lines of hydrogen fluoride served as a ruler relative to which they could measure the star's spectrum, allowing them to detect even smallest changes. Then, together with astronomer Stephenson Yang, they started looking at candidate stars which might be accompanied by Jupiter-like planets.

To detect the motion of the star due to the planet, they would have to record the system for several completed orbits. Our planet Jupiter needs about 12 years to orbit the sun, so they were in for a long-term project. Unfortunately, they had a hard time finding support for their research.

In his recollection “The First High-Precision Radial Velocity Search for Extra-Solar Planets” (arXiv:0812.3169), Gordon Walker recounts that it was difficult to get time for their project at observatories: “Since extra-solar planets were expected to resemble Jupiter in both mass and orbit, we were awarded only three or four two-night observing runs each year.” And though it is difficult to understand today, back then many of Walker's astronomer colleagues thought the search for exoplanets a waste of time. Walker writes:
“It is quite hard nowadays to realise the atmosphere of skepticism and indifference in the 1980s to proposed searches for extra-solar planets. Some people felt that such an undertaking was not even a legitimate part of astronomy. It was against such a background that we began our precise radial velocity survey of certain bright solar-type stars in 1980 at the Canada France Hawaii 3.6-m Telescope.”

After years of data taking, they had identified several promising candidates, but were too cautious to claim a discovery. At the 1987 meeting of the American Astronomical Society in Vancouver, Campbell announced their preliminary results. The press reported happily yet another discovery of an exoplanet, but the astronomers regarded even Walker and Campbell's cautious interpretation of the data with large skepticism. In his article “Lost world: How Canada missed its moment of glory,” Jacob Berkowitz describes the reaction of Walker and Campbell's colleagues:

“[Campbell]'s professional colleagues weren't as impressed [as the press]. One astronomer told The New York Times he wouldn't call anything a planet until he could walk on it. No one even attempted to confirm the results.”

Walker's gifted postdoc Bruce Campbell suffered most from the slow-going project that lacked appreciation and had difficulties getting continuing funding. In 1991, after more than a decade of data taking, they still had no discovery to show up with. Campbell meanwhile had reached age 42, and was still sitting on a position that was untenured, was not even tenure-track. Campbell's frustration built up to the point where he quit his job. When he left, he erased all the analyzed data in his university account. Luckily, his (both tenured) collaborators Walker and Yang could recover the data. Campbell made a radical career change and became a personal tax consultant.

But in late 1991, Walker and Yang were finally almost certain to have found sufficient evidence of an exoplanet around the star gamma Cephei, whose spectrum showed a consistent 2.5 year wobble. In a fateful coincidence, when Walker just thought they had pinned it down, one of his colleagues, Jaymie Matthews, came by his office, looked at the data and pointed out that the wobble in the data coincided with what appeared to be periods of heightened activity on the star's surface. Walker looked at the data with new eyes and, mistakenly, believed that they had been watching all the time an oscillating star rather than a periodic motion of the star's position.

Briefly after that, in early 1992, Nature reported the first confirmed discovery of an exoplanet by Wolszczan and Frail, based in the USA. Yet, the planet they found orbits a millisecond pulsar (probably a neutron star), so for many the discovery doesn't score highly because the star's collapse would have wiped out all life in that planetary system long ago.

In 1995 then, astronomers Mayor and Queloz of the University of Geneva announced the first definitive observational evidence for an exoplanet orbiting a normal star. The planet has an orbital period of a few days only, no decade long recording was necessary.

It wasn't until 2003 that the planet that Walker, Campbell and Yang had been after was finally confirmed.

There are three messages to take away from this story.

First, Berkowitz in his article points out that Canada failed to have faith in Walker and Campbell's research at the time when just a little more support would have made them first to discover an exoplanet. Funding for long-term projects is difficult to obtain and it's even more difficult if the project doesn't produce results before it's really done. That can be an unfortunate hurdle for discoveries.

Second, it is in hindsight difficult to understand why Walker and Campbell's colleagues were so unsupportive. Nobody ever really doubted that exoplanets exist, and with the precision of measurements in astronomy steadily increasing, sooner or later somebody would be able to find statistically significant evidence. It seems that a few initial false claims had a very unfortunate backlash that did exceed the reasonable.

Third, in the forest of complaints about lacking funding for basic research, especially for long-term projects, every tree is a personal tragedy.

14 comments:

Paul S. said...

Very nice post! Several interesting aspects to the story.

Plato Hagel said...

Yes good article.

It sounds like a typical story of the science world and discoveries?

When pounding new ground there will always be this skepticism without regard for the information being produce and unfortunately the skepticism translates into why there should be any funding.

I could understand the frustration and the shift to a new career.

This would of been the way historically Canada might have been, in terms of it's prior research and developmental attitude....I think some things have changed though.

Politically in economies tight on cash there will be at lot of slashing...to determine where cash should be allotted.

To have acknowledge through confirmation later years may seem a little late and while this frustration had been played out...but imagine, if alive when the confirmation comes....at least you ca say, "I told you so.":)

Uncle Al said...

Terrestrial meteor craters (Nördlingen, Donau-Ries district, Bavaria: town church built of suevite stone blocks), plate tectonics, stomach ulcers' cause and cure. Robert Grubbs denied tenure at Michigan State; now a Nobel Laureate at Caltech. Management sabotages discovery to stabilize its position.

Campbell... became a personal tax consultant. "Póg mo thóin!" Theory postulating massless boson photon vacuum symmetries requires symmetry breakings for massed fermions (leptons, quarks). Bosons and fermions fundamentally diverge. Somebody should look for the vacuum black swan. The worst it can do is succeed.

Adam said...

This way of thinking seems to be playing out in Mars science too. Everyone got so "burned" by the fact that it was a desert instead of a canal-laden paradise that now any evidence of life on Mars is scrutinized past the point of scientific skepticism to a sort of postmodern cynicism; an extreme distrust for anything other than a null result.

Robert L. Oldershaw said...

Although very few seem to have the slightest interest in fractal cosmological models, one called the Self-Similar Cosmological Paradigm (or Discrete Scale Relativity when the self-similarity is exact) actually PREDICTED in 1989 that planets would be found orbiting ultracompact objects.

I know of no other theory that definitively predicted these systems exist and would be observed.

Also, no other theory I know of, except Discrete Scale Relativity, definitively predicted trillions of unbound planetary-mass "nomad" objects decades before they were discovered in 2011.

Interested seekers can find the details of the planet/pulsar prediction in Selected Papers #4 at my website.

Anybody seen any WIMPs in the last 40 years? Sparticles? Extra dimensions? Strings? Multidelusions? ...

Of course not, but they are so fashionable, doncha know.

Robert L. Oldershaw
Discrete Fractal Cosmology

Phil Warnell said...

Hi Bee,

A very nice piece denoting how much research depends on commitment and patients, not just from the researchers themselves but also by those who support them; which in the modern world equates to being us all. The immediate message here was Canada fails as Canada bails, which should serve as a lesson, not only to my fellow citizens, yet more so to all who wish not to have this distinctly human endeavour we call science fail for humanity.

“Are you not ashamed that you give your attention to acquiring as much money as possible, and similarly with honour and reputation, and care so little about wisdom and truth and the greatest improvement of the soul, which you never regard or heed at all?”

-Plato, (Quoting Socrates), “The Apology”

Best,

Phil

Bee said...

Hi Phil,

Yes, it takes commitment and patience. I'm also thinking it's another example that shows that we need more funding of people rather than projects. I just hope we learn from the past. Best,

B.

Arun said...

Dear Bee,

In your awareness, what problems are considered unfashionable today? (i.e., where would one begin the search for today's Campbells?)

-Arun

Bee said...

Dear Arun,

An excellent question.

For obvious reasons I can't but mention the phenomenology of quantum gravity here. It is an underfunded area that suffers, much like the hunt for exoplanets, from claims of near-discoveries that turned out to be data flukes (think noise in grav wave interferometers, time delay in gamma-ray bursts).

People are rightfully skeptic about what's going on there. But, and that's a big but, all investment into quantum gravity is wasted without phenomenology. There's no way around it. Eventually, we have to find something, or quantum gravity will forever remain philosophy. Investment in qg pheno is in my opinion vastly less risky and more promising than investing in studying the details of any one particular approach to a theory of quantum gravity. So why are there so few jobs, so little grants, so limited interest? I believe that's a big mistake, and in a few decades that will be obvious in hindsight.

But of course I'm biased on that.

There is one other example that comes to my mind which isn't quite so self-centered, which is what Stockwell elaborates on in his book The Quest for the Cure: Drugging proteins with large molecules. Apparently that's considered not so promising by many, because large molecules tend to be unstable or don't easily enter cells, but Stockwell argues there are ways to work on that. Basically his whole book is making a case that the research field needs continued funding and commitment to pay off.

Did you have a specific topic on your mind? Best,

B.

Shantanu said...

Bee, what do you think of Peter's list
here
http://www.math.columbia.edu/~woit/wordpress/?p=2876
on topics where not much attention is given

I would add some more examples in specific topics
on which not much is done

o Magnetic monopoles
o Koide mass formula
o Einstein-Kibble-Sciama gravity

Uncle Al said...

Large molecules are injected and expensive to assemble. 2 g aspirin/70 kg human is 28.6 mg/kg with MW = 180.2. Vancomycin is MW=1485.7. Aspirin potency is a 16 gram dose, the pill bottle being a bucket. Remarkably active vanco is 20 mg/12 hr intravenous.

Einstein-Cartan-Kibble-Sciama gravitation has chiral spacetime torsion. Existing apparatus can validate ECKS. Somebody should look, for quantum gravitations (triangle-like anomalies, arxiv:0811.0181) require parity-breaking Chern-Simons correction to Einstein-Hilbert action. Physics paints black swans white with symmetry breakings, obtaining cygnets that become black swans.

Bee said...

Hi Shantanu,

That there isn't much done on a topic doesn't mean more should be done... The question you're asking is difficult to answer, and though I can't give you a list, I have written on this blog many times how to address the question:

In the scientific community there are scientists and there are problems and every scientist chooses some topic (or several) to spend their time on. The question you are asking then takes the form: does the amount of work done on a topic accurately reflect the actual promise of a topic? That brings up the question how you figure out how promising a topic is. The only people whose opinions matter are the ones who know enough to actually work on it. So in the end, we have only ourselves to judge each other. The answer to your question then lays at hand: The number of people who invest time in a topic reflects the promise.

That however works only if scientists are free to chose the topic that they work on. Unfortunately, this is presently not the case, not even remotely. Scientists have to take into account all sorts of considerations that have nothing to do with their own scientific judgement, for example if they are likely to get a grant on some topic. As a result, presently the number of people that work on some topic does not accurately reflect scientific promise. In fact, I think we have a rich-get-richer effect, because it's much easier to work in a field that already many work on.

Now I can't tell you what would happen if we were to remove all pressures that skew scientists interests. I guess we'd see a big flow of people away from overpopulated topics towards smaller niches. Best,

B.

Shantanu said...

Bee,
What I was getting at is people work work on "paths
where no one has gone before" should be encouraged.
Although this is not saying anything new (Smolin and Loeb have written about it), at the end of the day no one wants to practice what they preach.


to give an example, I know someone who has been working single-handedly on one of the topics for the past seven or so years and has papers accepted in journals and all this he has done without a cent of funding or mentoring. But despite this (almost) no one even invites him for seminars and he was refused invitations to one aspen conference he tried to go. But despite all this discouragement, he continues to tirelessly work on this.
Probably there are more such cases like him. OTOH I have lost count of the large # of talks on string theory landscape, brane worlds and many other ideas for which there is no evidence.

Bee said...

Hi Shantanu,

What I am trying to say is what reason do you have to believe that they "should" do that? You have some opinion and I have some opinion, and Lee and Peter have some opinion, but there are also all the people who "vote with their feet" and place themselves in string theory groups, who evidently don't share your opinion. What makes you think you know better than they do?

What I have explained you above is that the system presently isn't aggregating information well, so there is good reason to believe that in fact the present distribution of researchers on topics is not accurately reflecting promise. That doesn't make you or Peter the person to say what fields should more work be done on, but it says we gotta fix that problem and then we'll probably see a lot of change.

And, yes, I know too several people who have made their life very hard just by working on their own ideas. Even if they get published and cited, they'll have a very hard time getting a job anywhere. It is an unfortunate truth that the climate in physics is presently so that you better do what many other people are doing too, or you risk being unemployed. I also know, sad but true, a steadily increasing number of skilled and gifted physicists who have left academia because they got seriously fed up with the status quo and lack of future perspective. Best,

B.