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How soon could extrasolar planets have been discovered?
Mongo
post Apr 1 2014, 07:02 PM
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Extrasolar pulsar planets were first discovered in 1992, and the first planets around main-sequence stars in 1995. However, it seems clear that main-sequence exoplanets could have been found much earlier, except for the fact that nobody actually looked for them in a way that would have succeeded.

The standard assumption was that all, or almost all, planetary systems followed the architecture of our own system -- a few terrestrial planets at distances ranging from a few tenths of an AU to a few AUs, with larger gas- and ice-giants further out. This would result in systems that are basically impossible to detect with the technology of the time, except perhaps for long-term (years to decades) astrometric studies of nearby dwarf stars. It was known that planetary transits would be easily detectable, but they were thought to be so unlikely due to the geometry, as well as being infrequent in the few existing transiting systems, that they were not worth the resources spent searching for them. Radial velocity searches were considered to be out of the question, with stellar RV shifts ranging up to a few m/s at best, well below the best sensitivity of the spectroscopes of the time.

In fact, "Hot Jupiters" are common, with RV swings measured in the tens or hundreds of m/s, and transiting planets are so common and easy to spot that many current search programs use telescopes no larger than typical amateur telescopes. Today's detectors are better, of course, but that could be compensated for with a slightly larger telescope.

I assume that a planet search program consisting of an all-sky transit search with one or more 30cm-class telescopes would produce several dozen candidates (with at least three observed transits each) orbiting fairly visually bright stars within a few months. Each of those would be examined spectroscopically, and each would be soon found to have RV swings of 50-200 m/s or more. With the existing spectroscopic classification of the primary stars, this would result in fairly accurate masses and radii for each of these planets, as well as expected daytime temperatures. It would be easy to calculate the frequency of "Hot Jupiters" around main-sequence stars (around 1%), and the "inflated Jupiter" effect should be apparent in the data.

So assuming that some astronomer manages to obtain funding and telescope time to conduct such a program, when was the astronomical photometer and spectroscope technology advanced enough for this to have succeeded? The 1960s? 1970s? Surely by the 1980s, at the latest, which seems very late to me.
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algorithm
post Apr 1 2014, 07:55 PM
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I would say that most discoveries could have been made sooner than they were.
Discoveries by there nature tend to be 'ground breaking' often by the fact that it wasn't a 'mainstream' endeavour to look in that direction.
What I am saying is that as in many walks of life things tend to be in vogue.Look at the decades you mention and I'll bet you can think of a major space theme in that particular decade.
At the moment it's exoplanets, the story/history of water, and extraterrestrial life anywhere,past or present.
With the confirmation of ripples in the CMB, we will probably be looking for time zero in the not too distant future.!!??
And as for dark matter/energy..
IMHO it's about time we had boots on the ground.ph34r.gif
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NGC3314
post Apr 2 2014, 03:31 PM
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To my mind, the advantages of CCDs are so great that transit searches wold have a practical chance of succeeding once they were in wide use. Then wide-field searches are enabled, so there are light curves for large numbers of bright stars at once. Plus, compared to photomultipliers, the ability to normalize to the ensemble of stars makes the results much less sensitive to changes in sky conditions than single-channel systems. The breakthrough in detected transiting hot Jupiters would be completely in being able to find them - that transit depth could certainly have been measured with photomultipliers and usual differential techniques (albeit only a handful of amateurs ever got into that technique, but it was the mainstay of observatory gear before CCDs).

Struve famously suggested a radial-velocity search for massive planets (in 1952), and even mentioned the possibility of different system architectures than ours. He notes that the highest-precision measurements at that time had Doppler accuracy 0.2 km/s (so they could have found the signatures of the best hot Jupiters). Once again, though, this was a time-consuming thing, both in exposure and tedious measurement, possible with only a handful of instruments. Once again I see the CCD revolution as key - exposure times dropped so much that serious surveys became feasible, and significantly smaller telescopes could join the party.

(Example - now wondering whether the new echelle spectrographs on our consortium remote 0.6-1m telescopes are stable enough for hot Jupiters...)
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Hungry4info
post Apr 2 2014, 05:06 PM
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Stebbins (1910) was able to get photometric errors on the order of ± 0.006 mag, detecting the secondary eclipse of Algol for the first time. HD 189733 b has a 0.03 magnitude transit depth. So I suspect we've had the technology to detect transiting hot Jupiters for around a hundred years now. Getting a mass estimate would have been much harder. NGC3314's great post covers that part well enough.


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J.J.
post Apr 2 2014, 06:04 PM
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^
Ditto. Transit discoveries have probably been possible for a long time, but they were contingent on preceding RV discoveries.


--------------------
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Master Betty: Nyah. Haha. It is EVIL, it is so EVIL. It is a bad, bad plan, which will hurt many... people... who are good. I think it's great that it's so bad.

-Kung Pow: Enter the Fist
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JCG
post Apr 9 2014, 07:44 AM
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I'm one of the old-timers who was involved in several surveys looking for extrasolar planets in the 1980s and 90s. Hindsight is always 20/20 in any prospect as it is here, no offense intended, it's a fact I deal with, too. There are couple of factors you need to consider when speculating on why didn't "they" just (fill in the blank) back the day. In the case of extrasolar planets, there are a couple of practical factors to consider: CCDs were not as sensitive and low-noise as they are today and were nowhere near as easy to use. The first forays into extrasolar planets using CCDs used a 512x512 device (the so-called Galileo CCD, the offspring of the CCD developed at JPL for use on the imaging system for the Galileo spacecraft) that was one-of-a-kind and jealously fought over by any and all astronomers for their special subject whether planetary astronomy was used for multiband imaging, spectroscopy, planetary, stellar, galactic, you name it research. No telescope committee would have ever considered using that or any existing CCD for looking for planetary transits, even though the technique was being studied theoretically at the time. Remember also that the frequency of extrasolar planets was "0" so no seriously-believed calculation could be performed to argue for using a precious science-grade CCD for planet searches as opposed to quasar studies, galaxy studies, supernova searches, etc. That calculation got pulled up by its bootstraps, finally (the comment about RV observations is correct).

Another reason is "telescope" time. Back in the day there were not a lot of 1-meter class telescopes to be handed out. And, there was very little money to build and support them (operationally). And each telescope got caught in the same problem of what is the best use of the resource, i.e., what are the most pressing scientific problems that have a high probability of being answered in a minimal amount of telescope time.

The first searches for extrasolar planets using CCDs starting with the imaging of the circumstellar disk of Beta Pictoris by Smith & Terille using a stellar coronograph and the Galileo CCD (there was only one of these state-of-the-art devices at the time). I and a few others confirmed their results by building stellar coronographs from spare parts and other existing intruments. Although simple in concept, the coronograph is a difficult beast to use if one wants quantitative results - there is much, much more to an observation than just theoretical SNR. We were allowed only a few hours on a 2.2-m telescope (UH/Mauna Kea) with the Galileo CCD hoping it would not be cloudy. Fortunately, we were successful. Subsequent dedicated searches for "really hot Jupiters"around red dwarves using the CCD/coronograph technique (imaging near 900 nm where CCD sensitivity starts falling off and "really hot Jupiters" might show some detectable emission in the NIR) were allocated time because we were able to show quantitatively how much time we needed to reach scientifically useful results. Even so, we had to fight ferociously for just a few nights of time. There are just too many other really neat scientific problems to address given the number of telescopes, the number of CCDs available and the chances of cloudy nights. We found a few red dwarf binaries but no Jupiters.

Another issue that limited observations at the time is that of the software and algorithms needed to rapidly process the data (along with all the calibration, quality control, etc., that goes along with processing). No one ever looked forward to reading hundreds of 9-track tapes into the communal computer system for rudimentary image processing algorithms.

That said, one type of search that was very successful was the search for the Kuiper Belt objects and beyond by Dave Jewett. That's because he could calculate the expected discovery rate in quantitative terms and the telescope time needed for even a null result (which was scientifically interesting) was acceptable. So lots of telescope time was dedicated to that search to the consternation of the galactic astronomers but the great joy of the planetary astronomers.

The advent of relatively inexpensive highly, sensitive, large format scientific grade CCDs (and fast computers) has changed the whole search strategy for a number of problems. I remember when Gene and Carolyn Shoemaker (and Glo Helin) performed their NEO asteroid searches with film(!). And when Tom Gehrels started using a CCD with TDI to look for them his discovery numbers were far too low at first because the CCD he was using was very small (miniscule!) in format when compared with what we have today, but the best he could get. A modern cell phone camera (CMOS) array could do better! Consider what the PanSTARRS 1.4 Gpixel (yes, gigapixel) camera can do compared to the original Shoemaker searches. And the new ATLAS system will have 8 cameras of 100s Mpx on 8 small (0.5-m) telescopes to do automatic and autonomous searches for "city-busters" among the NEOs. All of this could be done with Schmidt cameras, film plates, and lots of graduate students, but nowhere(!!!) near as efficiently.

The history of looking for transits of planets is analogous. It wasn't done in the past because the time to do it had not yet come. It had to be pulled up by its bootstraps with every other aspect of observational astronomy (with really good arguments for "me first") trying to cut the straps for the available resources. Fortunately, the pioneers never gave up and their arguments eventually won the day.

P.S. I visit this site every so often and don't comment much, but this particular conversation caught my eye and I thought I could help with some perspective. Keep up the good work. JCG
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Mongo
post Apr 9 2014, 01:25 PM
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Welcome aboard, JCG! Thank you for that very informative and detailed post. It confirms what I had originally suspected, that given the limited resources of the time, there were too many demands upon them for a long-shot like a search for extrasolar planets via transits to be allocated significant telescope time. Radial velocity searches could have found many planets, but the prevailing paradigm of planetary systems meant that high-cadence RV measurements (needed to find Hot Jupiters) were not considered. Plus as you said, the CCD technology of the day, while theoretically being capable of discovering Hot Jupiters, was still too inefficient (in terms of its ratio of time spent to results) to have a real chance of positive results.
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belleraphon1
post Apr 10 2014, 12:08 PM
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Interesting thought that if most other solar systems followed our systems architecture, RV searches would only just now be finding the Jupiters. In that case I suspect we would still just have a few RV searches ongoing. And transit searches might still be waiting in the wings. But nature gifted us with this wonderful array close in planets and planetary systems. Success means more resources. And those applied resources have opened the flood gates of discovery.

Craig
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JCG
post Apr 10 2014, 08:05 PM
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Thank you for the welcome, Mongo. The frustration with progress from both professional and layman's perspective is the inability to do everything at once. Ah! If we could! For the professional the last 50 years of astronomy is like being at Disneyland (dates me!) with only enough money for a ticket or two and only one short visit per year. What rides to chose and in what order for the next decade or so? Very frustrating but calls for calm planning; sometimes projects just have to wait.
The advent of the inexpensive professional quality CCD and large high-quality telescope (~< 1 m) has allowed many amateur astronomers to become productive members of the space exploration community providing high quality results. Something I find amazing and gratifying since these able souls have taken on some of the burden on astronomers decades ago. An anecdote in that regard: I started with visual observations for the AAVSO when I was kid in the late 60s. In the early 70s I worked with an engineer at LPL to make a single channel photometer with Si-photodiodes to make an inexpensive photometer for amateurs who could not afford expensive 1P21 phototube-based systems (even home-built) - I never trusted my visual observations of magnitude. The sensitivity was not very good in those devices, but would be better than an inexperienced eye alone. The project got displaced by graduate studies (priorities!) and I never went back to the project. Now it is a moot point.
Another anecdote from that time period concerning priorities and prevalence of instrumentation to perform state-of-the-art observations: In the mid-70s I was fortunate enough to be able to use Frank Low's Ge (germanium) bolometer (at LPL/UA) for thermal measurements (10 and 20 micron bands) of asteroids. I had access to the world's state-of-the-art detector system, which was state-of-the-art because it was for all practical purposes one of the only such bolometers around. So, I was able to make measurements no one else could, but I also took time away from every other astronomer who wanted to use that system for any other type of observation. Remember this was when quasars were little understood as were any other number of now commonly understood, post-Hubble, IRAS, etc., phenomena - there were lots of "hot topics" to go after besides asteroids. Anyway, every observing program can get preempted. One early morning (I mean about 5 am, just before dawn) in August 1975, Frank (and a colleague) burst onto the observing floor (after having driven 30 miles to the Mt Lemmon Observatory) stating excitedly, "I need the bolometer!" It was his device so what could I say? He ran onto the observing platform and slew the telescope around to Nova Cyg which had just gone off and was still increasing in magnitude. In a few minutes he made enough measurements of the thermal profile to reach quantitative conclusions for (at the time crude) time-phased modeling of the shock and dust cloud expansion still in the expansion stage, "packed his bags" and left. I was more than happy to oblige Frank, not just because it was his instrument, but because I understood the priorities of the moment. Now there are dedicated searches and automatic measurements of energetic events from thermal to gamma rays. Back then such measurements could be done but only by chance circumstances - the Ge just happened to be at a telescope ready to go.
In a very general sense we all understand why it takes so long to move forward in discovery, especially in "search" programs. That does not relieve the frustration. However, this thread does bring to mind that the details of why science lurches forward are filled with human experience, discovery and disappointment, fun and misery, perseverance and ... retirement ... which can avert that frustration with amusement.
So, Mongo, me go eat beans and watch more Mel Brooks!

P.S. Remind me to tell the story of how, in 1976, a Jesuit priest parted the clouds for 30 minutes one night at Kitt Peak allowing two critical (polarimetric) measurements that helped alter our understanding of quasars and NEOs. The bit about the Jesuit priest, the parting of the clouds, the importance of the observations, etc., is true but whether due to chance circumstance or divine intervention makes for amusing discussion. Another beer, please. JCG
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JCG
post Apr 10 2014, 08:39 PM
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QUOTE (belleraphon1 @ Apr 10 2014, 02:08 AM) *
Interesting thought that if most other solar systems followed our systems architecture, RV searches would only just now be finding the Jupiters. In that case I suspect we would still just have a few RV searches ongoing. And transit searches might still be waiting in the wings. But nature gifted us with this wonderful array close in planets and planetary systems. Success means more resources. And those applied resources have opened the flood gates of discovery.

Craig


Transit searches have a great advantage over RV searches.
RV searches observe one target star at a time, although many stars can be done per night they are done in sequence. Also, RV searches need bright objects or very large telescopes because of the great dispersion of the spectrum needed to observe the RV-induced spectral shift. So the going is slow, one-at-a-time so to speak. RV searches are limited to close by (brighter) stars, but can be very sensitive. Also, the cos(i) - detectability relationship of the alignment of the orbital plane (inclination, i) of the target system allows for a greater chance of discovery of something compared to transit searches where alignment is critical and probability of detecting a planet for any given star is proportional to ~ "2*R/a" where "a" is semi-major axis of planet in units of R, the radius of the star. So, transit searches are (like RV searches) more sensitive to large objects orbiting very close to the star.
Transit searches can use large format CCDs to observe (image the brightness of) thousands, if not millions, of stars at the same time (in dense stellar areas) and use broadband so that the number of photons collected, hence signal-to-noise, is greatly increased. Transit search, concentrating on sequences of small patches of sky, can search quite a ways into the galaxy so are good for statistical purposes (needed!!) but not necessarily to find the Earth-like planet closest to the Sun.
BTW, remember when the Drake equation factor for the number of stars with planets was ... unknown. That was just a few years ago! Now speculators (I say that fondly) can concentrate on the other factors which are closer to home, like how long does a high-tech civilization last ... independent of nuclear war. That limiting factor is probably closer to zero than we would like or even anticipate. Read the HANDY1 model at http://www.atmos.umd.edu/~ekalnay/pubs/201...ivas-kalnay.pdf . You don't need to be adept at coupled differential equations to make sense of it.

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belleraphon1
post Apr 11 2014, 01:55 PM
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Great to have your insight JCG!
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