Barnard's Star Planet by Don Dixon
Ask an astronomer why he or she has devoted their lives to the study of the cosmos, and you’re likely to hear about a lifelong romance with the sky, a connection with the deep vastness of space, and a drive and a desire to explore what’s out there. Astronomers are in the discovery business, and they want to add to the richness of the Universe.
Dr. Mike Brown, Pluto Killer
But many times the act of revealing something new can actually have unintended, destructive consequences, as the changing science literally reshapes the world around us. One first hand insight can be read as Caltech astronomer and Kuiper belt explorer Mike Brown reflected on his 2005 discovery of Eris, the larger-than-Pluto object which led to the eventual demotion everyone’s favorite spheroid. This “destroyed” the old solar system, leaving our neighborhood with a mere 8 “real” official planets in the eyes of astronomers. This caused a gigantic public backlash, with everyone from schoolchildren to grandmas writing astronomers and planetarium directors nasty letters that ended with lots of exclamation points. Mike Brown seemingly accepted his public role as a sort of astronomical bad guy when he picked his Twitter name @plutokiller. In fact, a quick check on my Twitter account just now revelas Dr. Brown jokingly tweeting:
“I just persuaded a group doing a solar system scale model to not include Pluto as the 9th planet. My work is never done.”
So, perhaps to make an astronomical omelet, you have to break a few Kuiper eggs? Pluto’s predicament may just be a semantic battle between astronomers over what a planet is, but astronomers sometimes find themselves with the strange task of actually trying to”un-discover” something, proving that something we thought was real is only a numerical illusion.
Much of what we know about the Universe comes from teasing an incredible amount of information out of the faint light we see from a galaxy, a star, planet, or even specks of dust. Like any scientific data, these fingerprints of light can be interpreted in different ways, and subject to many different factors affecting them, so eliminating alternative explanations for something before announcing a major discovery becomes especially important.
When the first planet found around another star was announced, our imaginations solidified our new sister solar system for us by visualizing this new world whirling around its star. We made this planet as real as anything else in the Universe (I mean, have you ever been to Pluto?). But what would be our reaction if this planet suddenly blinked out of existence, and yanked from our reality? Can astronomers recall an entire world? As it turns out that’s exactly what happened, and it was decades before the extrasolar planets around 51 Pegasai or PSR-1257+12. The astronomer who gave us the first extrasolar worlds was Peter van de Kamp, and the man who took them away was the University of Pittsburgh’s George Gatewood.
Peter van de Kamp
Peter van de Kamp was born in the Netherlands in 1901, and by many accounts, was an endearing child who liked to play tricks on other children and adults. He received his doctorate in physics at the University of Utrecht in 1922, and then traveled to Berkeley. It was there he made his mark on astronomy with his award-winning work with statistical astronomy and later astrometry, the study of the precise positions of stars. Van de Kamp focused on precisely measuring the visible wobble of binary star systems. By taking successive snapshots of the stars over a period of years, he could meticulously trace out the orbits of the two stars around each other, working out their masses and orbital separation. This works even if one of the objects is too dim to see – the wobble from one star gives away the mass the position of the other star. Van de Kamp then surmised that if he looked at a star that was close enough to the earth, the wobble of even a low mass object around that star would show up on his photographic plates. A low mass object… like a planet.
It didn’t’ take long for Van de Kamp to find his best candidate: Barnard’s Star. It’s the fourth closest star to us at only 6 light-years from earth, and it’s a red dwarf, which meant its mass was a seventh that of the sun, making any planet’s pull that much more obvious. If there were planets invisibly orbiting Barnard’s Star, he was convinced he could see it happening in slow motion over the course of many years.
24 inch (61 cm) refractor at Sproul Observatory
So beginning in 1938, Van de Kamp began taking pictures of Barnard’s Star with the 24 inch refracting telescope at Sproul Observatory at Swarthmore College, where he had been named Director the year before. Almost every night the observatory was open and the skies were clear, the light from Barnard’s Star’s small dot and the other stars that happend to be in the camera’s field were chemically imprinted on the emulsion of large photographic plates. Van de Kamp and his assistants developed the plates, and Barnard’s Star’s position was painstakingly measured with respect to the stars around it. But the motions of the rotation of the earth as it orbited the sun had to be accounted for, and removed from the calculations. And what was left over would be the wobble due to any unseen companion. But this leftover motion was extremely small – at the limit of detection of Van de Kamp’s Philadelphia-area based telescope; this was at the cutting edge of astrometry.
Six years of almost daily images and measurements piled up, and in 1944, Van de Kamp surprised the world by announcing that Barnard’s Star indeed had a substellar companion a whopping 60 times the mass of Jupiter. Van de Kemp kept observing the star after the announcement at a pace of about 100 images a year. By the time of the 1963 meeting of the American Astronomical Society meeting in Tucson, Arizona, Van der Kamp was armed with more than 2400 images, and new wobble calculations based on them. Van De Kamp’s object went from 60 Jupiter masses to just 1.6 Jupiter masses, orbiting Barnard’s Star in 24 years. A true planet!
Van de Kamp's 1969 planet's wobble (note the big jump at ~1950) From Richard Nugent's website.
But astronomers at the meeting were skeptical. According to Van De Kamp’s observations, the planet had a very elliptical orbit, something very different than the nearly circular orbits of the planets in our own solar system. As the years and observations and measurements piled up, the planet’s orbit became even more elliptical, worrying even Van de Kamp. In 1969, Van de Kamp announced that he has solved the problem of the highly elliptical orbit – by removing the planet entirely, and replacing it with two planets, approximately a Jupiter mass each, orbiting Barnard’s Star once very 12 and 26 years. These two planets interacting with the star together would reproduce the wobble Van De Kamp had observed. We suddenly now had two extrasolar planets joining the 9 of our own solar system, and man was only just landing on the moon.
But the case for Van de Kamp’s planets soon started to show serious cracks. John Hershey, a colleague at Sproul Observatory, started looking for wobbles in another low-mass candidate, Gliese 793, whose images were obtained for the past few decades alongside Barnard’s Star. Amazingly enough, he found the exact same wobble that Van De Kamp found in Barnard’s Star. Surely, Gliese didn’t have the exact same planetary system pas Barnard’s Star! The only reasonable explanation was some previously unseen effect of the telescope. Key events in the wobble both stars detected correlated with two key dates: 1949 and 1957, and sure enough, both were dates when the telescope was undergoing maintenance, and the main lenses in the telescope had been removed and replaced, respectively. The image of Van de Kamp’s planets dimmed.
Pittsburgh's Allegheny Observatory by Jim Fotia
In the early 70s, George Gatewood was a was a young researcher at the University of Pittsburgh’s Allegheny Observatory located among the steep hills near downtown Pittsburgh. Gatewood was interested in characterizing the unique instrumental errors in the various telescopes in the world who carried out astrometric observations, so that photographs between telescopes could be shared between studies. So he and his advisor from The University of South Florida, Heinrich Eichhorn, happened to have more than 200 photograph of Barnard’s Star from Allegheny Observatory from 1916 to 1971. In addition, the Observatory’s Director Nicholas Wagman had confided in Gatewood that his own data suggested that the Barnard’s Star planets were instrumental phantoms. But Wagman refused to publish his data, and suggested Gatewood collect new observations.
Dr. George Gatewood
Gatewood initially had no interest in disproving the existence of Van de Kamp’s planets. In fact, Gatewood actually met the renown astronomer at a conference in 1966, and expressed his admiration for Van de Kamp’s work. But after two strong requests from Wagman, the graduate student and his advisor took up the task of independently verifying the nearby world. They had less images than Van de Kamp, but they had a better technique for reducing the star’s natural motion through the sky, and used eleven reference stars to pinpoint Barnard’s Star’s exact location on the photograph, compared to Van de Kamp’s three. The project became Gatewood’s 1972 PhD. dissertation, and the title says it all: “An Unsuccessful Search for a Planetary Companion around Barnard’s Star BD +4°3561″ The only two planets outside our solar system suddenly vanished for everyone.
Gatewood and Eichhorn's motion of Barnard's star is plotted as points, with the size of the points weighted. The dashed line represents van de Kamps' claimed orbit, while the straight line is the motion of a star with no planet. Thanks to Richard Nugent's great website.
That is, for all except Van de Kamp. He defiantly continued to believe in his planets even in the face of the slam-dunk evidence against them. That year, Peter van de Kamp retired from Swarthmore, and returned to the Netherlands. He later claimed to have found more planets, this time around the nearby sun-like star Epsilon Eridani, but that claim was likewise disproven over time as well (but other planets were “refound” just a few years ago by radial velocity! I haven’t read yet if there is any correlation between these radial velocities and vdK’s residuals. Probably a coincidence?). There are indications that Van de Kamp felt persecuted by the astronomical community. The determined astronomer held on to his worlds all the way until his death in 1995 at the age of 93.
George Gatewood met with Van de Kamp again shortly before his death, where the elder astronomer continued to insist that his planets were indeed real. He then suggested that Gatewood should stop looking for errors in other peoples data, and take the risk of making some observations of his own.
Peter van de Kamp
Gatewood must have taken the advice to heart. Just a year after Van de Kamp’s death, Gatewood announced that one of the stars he had previously cleared of planets in 1972, Lalande 21185, which he then restudied in 1992 with the aid of lasers (no planets again), but now upon a third look, had the signature of two planets. Gatewood knew all to well what kind of scrutiny such an announcement would be subjected to, so was extra careful in eliminating all other possible measurement and instrument errors in his calculations. Gatewood might never have publicly made his planetary birth announcement if it were not for the excitement that was flowing through the astronomical community at the time. The first extrasolar planets had been confirmed around the sun-like star 51 Pegasai by using a method of detecting wobbles using the spectrum of the star, making it much more sensitive to massive planets that go around their sun very quickly. It seems that the golden age of new world discovery was really here.
So Gatewood unleashed his planets out onto a world much friendlier to exoplanets. One of the first tests for Gatewood’s progeny came when Dr. Geoff Marcy and his team used their proven planet-finding radial velocity technique to observe Lanane 21185. Not only did Marcy not find any planets, he held up the spectra of Gatewood’s star as a perfect example of a normal M-dwarf star with no wobbling! The new science essentially eliminating the possibility of Gatewood’s planets.
Although Gatewood’s Planets joined Van De Kamp’s planets in being incinerated by the scientific crucible, the radial velocity method finally satisfied our desire to truly know that the planets were out there. Peter Van De Kamp predicted that the Universe was teeming with other worlds, something that the radial velocity planet hunters proved decades later.
The extrasolar planet count is currently at 424, and set to go into the thousands over the next 10 years. The few original worlds given to us seem now like long exorcised astronomical ghosts. But for so long, they were all we had, birthed after long, laborious, manual work over decades. At least for some who lived through that era, and the champions who held on to them with such passion, Barnard’s Star’s planets are even more real than the dozens discovered since.