Some things just run in families. If you look into the life of Otto Struve, you’ll find that the Russian-born astronomer was the great grandson of Friedrich Georg Wilhelm von Struve, who was himself an astronomer known for his work on binary stars in the 19th Century. Otto’s father was an astronomer as well, as was his grandfather. That’s a lot of familial energy packed into the study of the stars, and the Struve of most recent fame (Otto died in 1963) drew on that energy to produce hundreds of scientific papers. Interestingly, the man who was director at Yerkes and the NRAO observatories was also an early SETI advocate who thought intelligence was rife in the Milky Way.
Of Baltic-German descent, Otto Struve might well have become the first person to discover an exoplanet, and therein hangs a tale. Poking around in the history of these matters, I ran into a paper that ran in 1952 in a publication called The Observatory titled “Proposal for a Project of High-Resolution Stellar Radial Velocity Work.” Then at UC Berkeley, Struve had written his PhD thesis on the spectroscopy of double star systems at the University of Chicago, so his paper might have carried more clout than it did. On the other hand, Struve was truly pushing the limits.
Image: Astronomer Otto Struve (1897-1963). Credit: Institute of Astronomy, Kharkiv National University.
For Struve was arguing that Doppler measurements – measuring the wavelength of light as a star moves toward and then away from the observer – might detect exoplanets, if they existed, a subject that was wildly speculative in that era. He was also saying that the kind of planet that could be detected this way would be as massive as Jupiter but in a tight orbit. I can’t call this a prediction of the existence of ‘hot Jupiters’ as much as a recognition that only that kind of planet would be available to the apparatus of the time. And in 1952, the idea of a Jupiter-class planet in that kind of orbit must have seemed like pure science fiction. And yet here was Struve:
…our hypothetical planet would have a velocity of roughly 200 km/sec. If the mass of this planet were equal to that of Jupiter, it would cause the observed radial velocity of the parent star to oscillate with a range of ± 0.2 km/sec—a quantity that might be just detectable with the most powerful Coudé spectrographs in existence. A planet ten times the mass of Jupiter would be very easy to detect, since it would cause the observed radial velocity of the star to oscillate with ± 2 km/sec. This is correct only for those orbits whose inclinations are 90°. But even for more moderate inclinations it should be possible, without much difficulty, to discover planets of 10 times the mass of Jupiter by the Doppler effect.
Struve suggested that binary stars would be a fertile hunting ground, for the radial velocity of the companion star would provide a “reliable standard of velocity.”
Imagine what would have happened if the discovery of 51 Pegasi (the work of Michel Mayor and Didier Queloz in 1995) had occurred in the early 1960s, when it was surely technically possible. Joshua Winn (Princeton University) speculates about this in his book The Little Book of Exoplanets (Princeton University Press, 2023). And if you start going down that road, you quickly run into another name that I only recently discovered, that of Kaj Aage Gunnar Strand (1907-2000). Working at Sproul Observatory (Swarthmore College) Strand announced that he had actually discovered a planet orbiting 61 Cygni in 1943. Struve considered this a confirmed exoplanet.
Now we’re getting deep into the weeds. Strand was using photometry, as reported in his paper “61 Cygni as a Triple System.” In other words, he was comparing the positions of the stars in the 61 Cygni binary system to demonstrate that they were changing over time in a cycle that showed the presence of an unseen companion. Here I’m dipping into the excellent Pipettepen site at the University of North Carolina, where Mackenna Wood has written up Strand’s work. And as Wood notes, Strand was limited to using glass photographic plates and a ruler to make measurements between the stars. Here’s the illustration Wood ran showing how tricky this would have been:
Image: An example of a photographic plate from one of the telescopes used in the 1943 61 Cygni study. The plate is a negative, showing stars as black dots, and empty space in white. Brighter stars appear as larger dots. Written at the bottom of the plate are notes indicating when the image was taken (Nov. 10, 1963), and what part of the sky it shows. Credit: Mackenna Wood.
Strand’s detection is no longer considered valid because more recent papers using more precise astrometry have found no evidence for a companion in this system. And that was a disappointment for readers of Arthur C. Clarke, who in his hugely exciting The Challenge of the Spaceship (1946) had made this statement in reference to Strand: “The first discovery of planets revolving around other suns, which was made in the United States in 1942, has changed all ideas of the plurality of worlds.”
Can you imagine the thrill that would have run up the spine of a science fiction fan in the late 1940s when he or she read that? Someone steeped in Heinlein, Asimov and van Vogt, with copies of Astounding available every month on the newsstand and the great 1950s era of science fiction about to begin, now reading about an actual planet around another star? I have a lot of issues of Astounding from the late 1930s in my collection though few from the late ‘40s, but I plan to check on Strand’s work to see if it appeared in any fashion in John Campbell’s great magazine in the following decade. Surely there would have been a buzz at least in the letter columns.
Image: Kaj Aage Gunnar Strand (1907-2000) was director of the U.S. Naval Observatory from 1963 to 1977. He specialized in astrometry, especially work on double stars and stellar distances. Credit: Wikimedia Commons / US Navy.
We’re not through with early exoplanet detection yet, though, and we’re staying at the same Sproul Observatory where Strand did the 61 Cygni work. It was in 1960 that another Sproul astronomer, Sarah Lippincott, published work arguing that Lalande 21185 (Gliese 411) had an unseen companion, a gas giant of ten Jupiter masses. A red dwarf at 8.3 light years out, this star is actually bright enough to be seen with even a small telescope. And in fact it does have two known planets and another candidate world, the innermost orbiting in a scant twelve days with a mass close to three times that of Earth, and the second on a 2800-day orbit and a mass fourteen times that of Earth. The candidate planet, if confirmed, would orbit between these two.
Image: Swarthmore College’s Sarah Lippincott, whose work on astrometry is highly regarded, although her exoplanet finds were compromised by faulty equipment. Credit: Swarthmore College.
The work on Lalande 21185 in exoplanet terms goes back to Peter van de Kamp, who proposed a massive gas giant there in 1945. Lippincott was actually one of van de Kamp’s students, and the duo used astrometrical techniques to study photographic plates taken at Sproul. It turns out that Sproul photographic plates taken at the same time as those Lippincott used in her later paper on the star were later used by van de Kamp in his claim of a planetary system at Barnard’s Star. It was demonstrated later that the photographic plates deployed in both studies were flawed. Systematic errors in the calibration of the telescope were the culprit in the mistaken identifications.
Image: Astronomer Peter van de Kamp (1901-1995). Credit: Rochester Institute of Technology newsletter.
We always knew that exoplanet hunting would push us to the limits, and today’s bounty of thousands of new worlds should remind us of how the landscape looked 75 years ago when Otto Struve delved into detection techniques using the Doppler method. At that time, as far as he knew, there was only one detected exoplanet, and that was Strand’s detection, which as we saw turned out to be false. But Struve had the method down if hot Jupiters existed, and of course they do. He also reminded us of something else, that a large enough planet seen at the right angle to its star should throw a signal:
There would, of course, also be eclipses. Assuming that the mean density of the planet is five times that of the star (which may be optimistic for such a large planet) the projected eclipsed area is about 1/50th of that of the star, and the loss of light in stellar magnitudes is about 0.02. This, too, should be ascertainable by modern photoelectric methods, though the spectrographic test would probably be more accurate. The advantage of the photometric procedure would be its fainter limiting magnitude compared to that of the high-dispersion spectrographic technique.
There, of course, is the transit method which has proven so critical in fleshing out our catalogs of exoplanets. Both radial velocity and transit techniques would prove far more amenable to early exoplanet detection than astrometry of the sort that van de Kamp and Lippincott used, though astrometry definitely has its place in the modern pantheon of detection methods. Back in 1963, when van de Kamp announced the discovery of what he thought were planets at Barnard’s Star, he relied on almost half a century of telescope observations to build his case. No one could fault his effort, and what a shame it is that the astronomer died just months before the discovery of 51 Pegasi b. It would be fascinating to have his take on all that has happened since.
It occasionally bugs me that I had a lot of observing time on the 24″ coude auxilliary telescope coupled to the high dispersion spectrograph at the Lick 120″ from 1969 to 1974, working on doctoral thesis topics, was blessed with repeatedly getting excellent weather for my observing runs, and never considered that by improving the comparison spectrum to see down to tenths of a kilometer per second I could look for planets. I was looking at stars and interstellar material. My weather was so good, by luck, that there was whispering about whether others should get my run times..And Struve’s articles and book were one of my inspirations for becoming an astronomer.
It is never easy being a true pioneer. Had astronomers been bold enough back in the day, they might have detected the numerous volcanic eruptions on Io from Earth, well before the Voyagers came through in 1979:
https://www.planetary.org/articles/looking-at-ios-volcanoes
I recall how Carl Sagan mentioned the huge sodium cloud surrounding Io in the 1978 book Murmurs of Earth. He postulated that perhaps Jupiter was somehow disrupting regions of surface salts on the moon. Active volcanoes were just too wild, even though we knew about Mars’ volcanoes since Mariner 9.
When Voyager 1 was approaching Io, the mission team thought the Galilean moon would serve as a Rosetta Stone of cosmic activity in the Jupiter system. Instead, they couldn’t find a single identifiable impact crater, and soon after that came the volcano discoveries. I think Callisto ended up getting that job.
As for Europa possessing a global ocean of liquid water, there were proposals earlier in the 1970s, but again, most astronomers thought that was just too out there to be possible.
Surprise.
Paul,
The Internet Archive has scanned copies of most of the early pulps in their pulp magazine archive:
https://archive.org/details/pulpmagazinearchive?sort=title&tab=collection
You can search for the magazine titles or even for text within the magazines. I searched for 61 Cygni and got many hits. These two are interesting:
Astounding Science Fiction April 1948 (Bonestell cover):
https://archive.org/details/AstoundingScienceFictionv41n2/page/n87/mode/2up?q=61+cygni
Astounding Science Fiction September 1944: “Extra-Solar Planets by R. S. RICHARDSON”. Robert S. Richardson was both an astronomer and a Science Fiction writer, publishing under the pseudonym Philip Latham :
https://archive.org/details/Astounding_v34n01_1944-09/page/n105/mode/2up?q=61+cygni
Really useful references, Frank. Many thanks!
I did not know Richarson wrote SciFi as Philip Latham. I have 2 of Richardson’s popular astronomy books: “Man and the Moon” (1961) (illustrated by Bonestell) [The jacket and blurb on my copy is not the one shown on web searches. It is just a crude drawing of a rocket heading towards the Moon.] and Exploring Mars (1954).
His non-fiction books seem to be rare. “Mars” (1964) Richardson and Bonestell don’t seem to be available with a dust jacket, and even the jacketless ones are rather pricey.
As it turns out, it was August 1941 that science fiction writer Isaac Azimov proposed a series of stories to Astounding magazine editor John Campbell, the Foundation series. It was to be an analog to Gibbon’s history, The Decline and Fall of the Roman Empire, only played out over the planets of the Milky Way galaxy.
Beside such a vast stage, this was quite a leap of faith – since even tentative exoplanet identifications were still a long ways away. Robert Heinlein, for example
wrote many stories set on or headed to exoplanets, but the first of such was in also in 1941 “Methuselah’s Children”. Space Opera took these matters more lightly, of course. The “hard science fiction” writers acknowledged that the technology was hard, but the issue of having any real destinations was not necessarily addressed.
Though in coming to that point, noting the work of Struve and other pioneers were probably faced with a lot of heat and skepticism from their star and galaxy oriented colleagues. And I suspect that it was also reflected in the imaginations even of science fiction writers. Logically enough, when transit to the solar system planets took a leap of imagination, interstellar travel must have struck many as simply beyond bounds. After all, Stapledon stopped off at Neptune with his “First and Last Men” even after eons and the separations involved in Star Maker, I hesitate to guess. If Mars was far enough to wander to imagine hostile, friendly or superior aliens, then concocting stories about inhabitants of planets of Sirius or Alpha Centauri would be an extravagance… Or else an idea that was less founded in the prevailing science.
Owing to have studied in a “star oriented” astronomy department in the 70s as well, and one that had quite a line up of distinguished observers and analysts, I came away with a notion that the case for anything not self luminous was not very good. But I had hopes something might develop.
Perhaps at that time there was more evidence presented for dark matter than exoplanets and more adherents to the latter at the time. And owing to the rigor that observations and analysis was conducted or passed on to students, it all made sense of a sort. Planetary system formation theory varied between interactions between passing stars producing a stream of matter like that between colliding galaxies – or else later, a rare window for formation in a dispersing circumstellar disk. Ten million years and you were “out”. And analyses of stars through the 19th and 20th century moved more in parallel with the accomplishments of “modern physics”. Planets were modest laboratory elements by comparison.
In the 17th century the nature of stars as suns seemed to slink in surreptitiously with Copernicus and Kepler for a number of reasons. A principal reason was the inability to do any parallax measure – and for a while even having a notion that there was one possible, what with Earth-centered vs. heliocentric frame controversies. Galileo and Kepler were contemporaries and correspondents who actually deliberated about Kepler’s theory and Galileo’s results. In an English translation of Sidereus Nuncius ( by the former in1610) Albert Van Heldon wrote an extensive introduction to an English translation published in 1989. It also drew on earlier studies such as Edwin Rosen’s in the 50s and 60s, including “Kepler’s Conversations with Galileo”. Correspondence, it would appear. But amid this dialog between theorist and observer, there was a discussion about the nature not only of planets, but stars – and then the ghost of Giordano Bruno who was burned at the stake. The last of the three believed stars were suns. Galileo, practically in passing observing the planets and moon, noted as well that the stars were like dust. And Kepler himself, beside sorting out planetary orbital motion, was willing to believe that solar system planets were inhabited – with all types of implications. Nonetheless, when Galileo reported that Jupiter had four moons…
Well, according to Van Helden in a concluding chapter connected to his translation:
“Kepler reserved his greatest praise for the discovery of Jupiter’s satellites. When he had first heard the rumor of the existence of four new planets (before reading Sidereus Nuncius), he had feared that perhaps Galileo had found planets around a fixed star. This would have supported the doctrine of Giordano Bruno, that Kepler dreaded so much. Having read the book, he was not reassured, he was overjoyed. Here were four planets the existence of which no one had suspected.”
Skipping some of Kepler’s observances on religious and political controversies, I note in a following quote attributed to his correspondence:
” (For example, there was a period when the distinction between the planets and the fixed stars were unknown; it was quite some time before Pythagoras or Parmenides perceived that evening star and morning star are the same body…”
Van Helden reflects on Kepler’s argument that objects in the heavens or cosmos should have some utilitarian purpose and that on account of its moons, Jupiter is likely inhabited. And in the written dialog, Van Helden argues that while Kepler let his imagination extrapolate to great lengths on developments, Galileo held the reins more tightly, speaking mainly in terms of observations. These “Conversations” evidently were also published in 1610 at Florence.
Bruno, executed in 1600, did not have an opportunity to participate in these conversations, though his extrapolations extended much farther, either based on intuitions or readings from classical Roman works, perhaps singularly stemming from the Latin poet Lucretius (95-44 BCE), a summary of the epicurean view of the cosmos in verse ( De rerum natura, On the nature of things). Unfortunately, the reconciliation of western European beliefs with classical sources had concentrated on Aristotle’s conclusions (e.g., Thomas Aquinas) – which featured an Earth centered cosmos. Presumed strict reasoning, strictly enforced.
In the present day, astronomical debates seem to drop into similar categories. But at the very least we have much better instruments, methodologies, scientific models and data to address the basic issues. Still, we don’t know whether anything in the distant sky above us is an abode for life – though in the last few decades we have cracked the problem of detecting and describing exoplanets in a rudimentary fashion. At this point when the naked eye number of the stars might have been five or six thousand, we have about that number of detected exoplanets.
I am going on memory here but I recall that in this book:
https://www.rarebookcellar.com/pages/books/113796/mark-littmann/planets-beyond-discovering-the-outer-solar-system
… the author mentioned he found an exoplanet in the late 1980s. The “problem” was that it was a giant Jupiter type world and it was very close to its star. Other astronomers rejected it because everyone knew that Jovian planets are far from their suns.
I may have the source wrong but I am correct about this story. I just wish I could remember which star and planet he was referring to and if it were confirmed later.
Here is a piece on exoplanets that were recorded way back in the day but not recognized until much later:
https://www.jpl.nasa.gov/news/overlooked-treasure-the-first-evidence-of-exoplanets
Pluto was recorded on photographic plates back to 1915 without anyone noticing it. Uranus and Neptune also had earlier records of their existence before their official discoveries in 1781 and 1846, respectively.
The most famous is probably Galileo recording Neptune in 1612; he even mentioned it moving but did not put two and two together:
https://www.astronomy.com/science/who-discovered-neptune/
Makes one wonder what else is being overlooked because contemporary astronomers are situated (I am not going to say stuck or mired, really) in certain paradigm, such as once declaring that exoplanets cannot remain stable orbits in a binary star system.
Now we have planets in triple star systems:
https://theconversation.com/previously-thought-to-be-science-fiction-a-planet-in-a-triple-star-system-has-been-discovered-153524
https://exoplanets.nasa.gov/news/1667/discovery-alert-a-forgotten-planet-found-in-a-triple-star-system/
This includes my wondering if we are staring astroengineering projects in the face and not recognizing them. Or not wanting to.
Perhaps this?
Will the real ‘first exoplanet’ please stand up?
Yes that is it, thank you!
Quoting from the piece you found:
And an important historical footnote raises yet another claim to the real “first,” though one largely dismissed at the time. In the late 1980s, astronomer Dave Latham of Harvard experimented with the same technique that the Mayor and Marcy teams later used: measuring subtle stellar wobbles.
Latham saw something remarkable. A very large object was orbiting a star about 128 light years away. But while he thought it might be a planet, he and other astronomers believed that a small star or even a brown dwarf—a kind of failed star—seemed more likely. Latham’s team said so in their 1989 paper announcing the discovery; the object just seemed too big and too close to its star to be anything else.
In the years that followed, however, discoveries of gigantic, star-hugging planets, now known as “hot Jupiters,” began to pile up. Latham’s object eventually was accepted as a planet, making it a true, if unsung, “first.”
But 51 Peg still manages to retain its first-ever status, and it’s all about the timing. The 1989 announcement suggested a possible planet, though its discoverers lacked enough data to be sure. Confirmation would not come until long after 51 Peg made its big splash in 1995 as the first exoplanet to be reliably identified in orbit around a normal star.
Hi Larry
The putative exoplanet discovery was mentioned at the end of Matloff & Mallove’s “The Starflight Handbook” – the star was HD 114762. However its unseen companion has since then had its estimated mass rise into the red-dwarf range, so it’s no longer a planet.
The reference…
A Search for Substellar Companions to Solar-type Stars
Campbell, Bruce ; Walker, G. A. H. ; Yang, S.
Publication: Astrophysical Journal v.331, p.902
Pub Date: August 1988
Publisher: The Astrophysical Journal
DOI: 10.1086/166608
A Search for Substellar Companions to Solar-type Stars
Unfortunately, the names of these astronomers have not gone down in history, even though they contributed enormously to the progress of astronomy. It’s a bit like the place of women in this science, too often Jocelyn BELL or Margaret BURBIDGE are famous, but how many others have contributed their little stone to the edifice: who knows Emilie du Chatelet or Gabrielle Flammarion? Look them up, you’ll be surprised! What fascinates me in the article is: “a photo plate; a ruler and a pencil ;)
Speaking of whom, was there no picture of Dr Lippincott?
Nothing intentional, but I’ve added Lippincott’s image to the article to correct the omission.
Paul,
the photo plate was registered on December 11, 1963 under no. 2170 (today 29759) Look here : https://public.aip.de/historical-sky/en/
I also found a certain Peter Van de Kamp & Sarah Lee Lippincott who worked with Strand: it seems that the first “intuitions” about exoplanets were made in …1937 !
https://www.daviddarling.info/encyclopedia/V/vanderKamp.html
https://www.daviddarling.info/encyclopedia/L/Lippincott.html
Fred
1937! Interesting.
To my knowledge, the first who showed , as soon as 1938, how to detect transiting exo-Jupoter was D. Belorizky who demonstrated that at that time it was realistic to search for transiting Jupiter by photometry with photo-electric cells:
https://ui.adsabs.harvard.edu/abs/1938LAstr..52..359B/abstract
Now, the first known indication of a possible detection of exoplanets by transit was predicted by
Dionysius Lardner (1793–1859) in a book of popular science:
Lardner D (1853) Hand-book of natural philosophy and astronomy. Walton and Maberly, London, p. 771
These are wonderful references to have, Jean. I was unaware of both! I see a follow-up post coming some time soon.