Although a belief in other worlds dates back to antiquity, the monk Giordano Bruno became the first person to be executed by the Roman Catholic Church for advocating such views. With the discovery of exoplanets, it became incumbent on the Church to admit its error and apologize for its conduct. That, however, is not likely to happen soon.
The 16th century was a time of strife in Western European Christendom. The Roman Catholic church, in particular, was under siege; not only did it have to deal with the schism known as the Protestant Reformation, but scientific discoveries and theories in astronomy threatened its view that man occupied a privileged place in the cosmos. The Church believed that earth and humanity were special because according to the Bible, man had been created in the image of God. The deity had, moreover, for man’s benefit set the sun, moon and stars in the vault of the sky to help him keep time and provide light during the day and night. (Genesis 1:27 and 14-18. This, by the way, is contradicted in Gen. 1:3 where it is stated that God had earlier created light in the absence of any celestial bodies.) Strangely, no mention is made in the Bible of the creation or the existence of planets. As an omniscient god, Yahweh must, at the very least, have been aware of them yet he didn’t deem it necessary to inform his chosen people of their existence and tell them that they inhabit one.
Their neighbours such as the Babylonians and ancient Greeks, however, weren’t as ignorant as the Jews. They were aware of the existence of a type of celestial body whose movements differed so radically from the seemingly stationary stars that Greek astronomers referred to them as “planetes” or wanderers. Moreover, some of the Greek thinkers of the time realized that they resemble the earth and speculated that our abode is not the only one in the universe. Epicurus (342 – 270 BCE) for instance declared that “There nowhere exists an obstacle to the infinite number of worlds.” (Quoted by Michael Summer and James Trefil in their book Exoplanets P35.) This view was kept alive during the time of the Roman Empire. Around the beginning of our calendar, the Roman poet Lucretius wrote his famous poem De Rerum Natura (On the Nature of Things). In it, he expressed the view that other worlds must of necessity exist since the heavens, according to him, extends into infinity in all directions.
The Church only became aware of the existence of the idea of planets during the Middle Ages when Christian theologians studied the works of the ancient Greeks. They gained first-hand knowledge of the work of the first century Greek astronomer Ptolemy when his book the Almagest fell into their hands after the successful siege of the Moorish citadel of Toledo in Spain in the year 1085. Ptolemy held that the sun and the moon revolved around the earth together with the 5 known planets namely Mercury, Venus, Mars, Jupiter and Saturn. The retrograde motion of the 5 planets he explained in terms of a complicated system of epicycles.
During the Middle Ages, the Church adopted the view of Aristotle that there can only be one world. Catholic philosophers such as Thomas Aquinas declared themselves in agreement with this view and it consequently became dangerous for anyone to express a contrary opinion. Nevertheless, in the year 1584 the monk Giordano Bruno did exactly that. Bruno wasn’t exactly a firebrand atheist or a secularist. On the contrary, he believed in pantheism and rejected some of the Catholic dogmas. Born in the Kingdom of Naples in 1548, he entered a convent as a young seminarian but soon fell afoul of the authorities with his free-thinking views. When the Catholics excommunicated him, he fled Italy and join the Calvinists in Geneva and later the Lutherans in Wittenberg and Helmstedt but they too found his views objectionable and expelled him. Before he went to Germany Bruno resided in England, where he wrote a book that created a furore. It was called De L’infinito Universo e Mondi (Regarding the Infinite Universe and Worlds). Although he agreed with the heliocentric hypothesis of Copernicus, he disagreed with his claim that the sun is the centre of the universe. Following the views of Lucretius, he argued that there are innumerable suns and Earth-like worlds that resemble our solar system. We cannot see these earths, he opined, because they are smaller than their suns and do not emit any light. He also expressed the view that these extrasolar worlds are, like our earth, populated. In light of these considerations, he concluded that the universe has no centre and the theory that the earth is the centre of the universe, in particular, is false.
Bruno realized that his views were unacceptable to the Church but knew that he was safe as long as he did not return to Italy. However, he allowed himself to be persuaded by a certain Giovanni Mocenigo to travel to Venice and teach him memory tricks (for Bruno was also a memory expert). While he was in Venice, Mocenigo betrayed Bruno to the Venetian Inquisition. They arrested him and extradited him to Rome to face trial on several charges including his views on the Cosmos. The trial itself lasted almost 7 years. The Church wanted Bruno to confess to his so-called crimes but he refused and insisted that he had done nothing wrong. The outcome was nevertheless a foregone conclusion – Bruno was convicted on all counts and sentenced to death. The ecclesiastical authorities did not execute him as they sanctimoniously maintained that they will never take a life, but they handed him over to the secular government to do their dirty work for them. On 17 February 1600 Bruno was taken to a square in Rome known as the Campo de’ Fiori where he was hung upside down naked before being burned alive at the stake. If he had confessed his sins, he would have been spared the humiliation but would still have been strangled to death before being incinerated. Bruno’s ashes were thrown into the Tiber river while his books were placed on the Church’s index of prohibited books. The Roman Catholic Church would no doubt like to forget the shameful incident but Freethinkers wouldn’t let them; in 1889 a statue of Bruno was erected in Rome at the very spot where he had been executed.
To salve its conscience and pretend that it has never been opposed to science, the Church now maintains that Bruno was not executed for his views relating to the Cosmos. We are for instance told in the Catholic Encyclopedia that “Bruno was not condemned for his defence of the Copernican system of astronomy, nor for his doctrine of the plurality of inhabited worlds, but for his theological errors.” There is are good reasons for thinking that this claim is false. Although it is in the absence of proper court records and particularly the written judgements concerning both conviction and sentence difficult to establish exactly what happened during the trial, there seems to be widespread agreement that one of the charges on which Bruno was arraigned was his belief in exoplanets. If he was not “condemned” for it, he should have been acquitted on that count. Yet that is apparently not what happened. If he was, on the other hand, convicted for believing in exoplanets, he had to be sentenced for that belief. And the only sentence that was passed in the trial was death by burning. Secondly, one wonders why the Church persecuted and punished Galileo for his defence of the Copernican system of astronomy 35 years later if Bruno had earlier not been “condemned” for holding similar views. The matter was recently investigated by Prof. A. A. Martinez who examined the available documentation relating to Bruno’s trial. He found that despite denials by Church apologists, a belief in multiple worlds had been denounced by Church authorities as heresy as early as 384 C.E. This was reaffirmed by the Pope in his Corpus of Canon Law in 1591 – two years before the trial commenced. Heresy, of course, was a crime for which the death sentence could be imposed. Lastly, according to Martinez the evidence presented in court concerning the charge of believing in exoplanets was not only the strongest but more witnesses testified in relation thereto than any other allegation levelled against Bruno. The inference is accordingly inescapable that Bruno had indeed been executed for his scientific views. See: https://blogs.scientificamerican.com/observations/was-giordano-bruno-burned-at-the-stake-for-believing-in-exoplanets/
Despite these events, science managed to advance and obtain reliable information regarding the universe. Further planets were discovered inside the solar system but the question that remained unanswered was whether planets were orbiting other stars. The problem seemed insoluble since the telescopes used for making such discoveries were too primitive. It was only in the 19th century that an effort was made to answer this question. Hypotheses regarding the origin of the solar system, such as the Nebular Hypothesis of Simon Laplace, gave stimulus to the investigation. Although the technology of the time was still not equal to the task, the astronomers F. W. Bessel and E. C. Pickering developed the astrometric, photometric and spectroscopic methods for detecting exoplanets. But the lack of progress was disheartening. Prof. Robert Ball wrote for instance in his book The Story of Heavens (1900) that “We have already reached a point where man’s intellect begins to fail to yield him any more light, and where his imagination has succumbed in the endeavour to realise even the knowledge he has gained.”
Ball was, however, too pessimistic. A host of discoveries followed in the 20th century. Edwin Hubble, for instance, discovered in 1923 that there are other galaxies outside the Milky Way while the evidence that the universe had its origin during the Big Bang 13.7 billion years ago became overwhelming with the accidental discovery of the cosmic microwave background radiation by Arno Penzias and Robert Wilson in the 1960s. After the discovery of Pluto in 1930, the search for new planets outside our solar system heated up with claims in 1943 that planets had been found circling 61 Cygni, a double star system 11.4 light-years from earth and 70 Ophiuchi, another double star system 16.6 light-years away. Both these claims were, however, rejected by the astronomical community as unfounded. No planets have as yet been detected orbiting either of the star systems.
On the other hand, the announcement in 1963 by the Dutch astronomer Peter van de Kamp that he had discovered two planets around Barnard’s Star, a red dwarf star approximately 6 light-years from the sun couldn’t be dismissed out of hand. Van de Kamp meticulously observed the star for 25 years and employed the astrometric method (according to which one infers from the perturbations or “wobbles” in the star that it has an invisible companion) in concluding that the 2 planets orbit the star. He also took numerous photographs at the Sproul Observatory in the USA in support of his claim. Although it was accepted by some astronomers that the existence of these two exoplanets had been proven, problems started mounting when others unsuccessfully tried to replicate Van de Kamp’s findings. They blamed the refracting telescope that he had used for his erroneous claims. Not only are these types of telescopes not ideally suited for observations of this nature, but Van de Kamp’s had a change in its lens cell in 1947 and it was found to have caused jumps in the data. Van de Kamp, of course, did not take kindly to the criticism of his work. An article that he wrote in rebuttal in 1977 concluded with a Rembrandt etching of the appearance of Jesus to the doubting Thomas and a quote from John 20:29 – “Blessed are they that have not seen, and yet have believed.” I suspect this invocation of religious faith in settling a scientific dispute did not sit well with Van de Kamp’s fellow astronomers and didn’t help his cause much. At any rate, by the time he died in 1995, the consensus was that he had been mistaken.
In 2018, however, it was announced that at least one planet had been discovered orbiting Barnard’s star, while the possibility of a second one was also mooted. See https://earthsky.org/space/astronomers-discover-cold-super-earth-in-second-closest-star-system-barnards-star. That is of course what Van de Kamp had also claimed. The other interesting thing is that in both instances the discoveries were made by employing the astrometric method of detecting exoplanets. My initial reaction was that Van de Kamp had been vindicated and that this constituted confirmation of his discovery. If so, then he was the first person to discover an exoplanet. On further reflection, however, I concluded that that is not so. Van de Kamp claimed at the time that he had discovered two gas giants orbiting Barnard’s star with periods of 13.5 and 19 years respectively. This is at odds with the latest findings. The planet that has now been discovered is rocky and 3.2 times the mass of the earth with an orbital period of 233 days.
Shortly before Van de Kamp’s death, the field of exoplanet detection experienced its first real progress. In 1989 David Lantham and his co-workers from Harvard discovered that a celestial body orbits the star HD114762 at a distance of 90 light-years from earth. Their speculation in the article that they wrote for the scientific magazine Nature namely that it is in all probability a Brown Dwarf was confirmed in 1992. The problem is that a Brown Dwarf is not a planet; it is a failed star and regarded as a hybrid – something between a star and a planet. Incidentally, subsequent discoveries have revealed that Brown Dwarfs do not only orbit stars, they sometimes have a retinue of planets of their own.
The revolution in the discovery of extrasolar planets started in 1992. On 9 January of that year, an article appeared in Nature written by Alex Wolszczan and Dale Frail. They reported that they had discovered two planets circling Pulsar PSR1257+12 in the constellation Virgo approximately 2300 light-years from earth. The announcement created a stir in the astronomy community. Apart from being the first discovery of exoplanets, it also overturned the widespread belief that only main-sequence stars can have planets. According to current theory, the particular Pulsar was formed when two White Dwarfs ( former sun-like stars that are at the end of their lives) collided with each other, resulting in their wholesale destruction and the birth of a fast-spinning and super heavy star composed almost entirely of neutrons called a Pulsar. The planets that orbit the Pulsar were likewise formed from the debris after the collision. It is generally accepted that with the incredibly high electromagnetic radiation from the Pulsar life on the planets is out of the question. Not everyone agrees with this assessment though. Some even contend that life can exist on a Neutron star itself. Gerald Feinberg and Robert Shapiro, for instance, argue in their book Life Beyond Earth that life consisting of magnetic atom polymers can occur on the surface while Robert L. Forward wrote a science fiction novel called Dragon’s Egg in which microscopic quasi-crystalline beings with a life expectancy of 37 minutes known as the Cheela live on the Neutron star.
Pulsars are extraordinary objects; the fact that they revolve in milliseconds around their axes and emit electromagnetic radiation with great regularity caused Jocelyn Bell Burnell and Anthony Hewish who had discovered them in 1967 to think that they were signals that had been sent by an extra-terrestrial civilization. They accordingly called the signals LGM (Little Green Men). These unique properties of a Pulsar make it easier to detect planets orbiting it. The regularity of its radio pulses can be used to track its motion while mutual gravitational perturbations of the various celestial bodies in such a system often reveal further information about the existence of planets. This is known as the Pulsar Timing method of discovering exoplanets. Its reliability enabled Wolszczan and Frail to calculate that the two planets in question are four times more massive than the earth and that they orbit the Pulsar in 66 and 98 days respectively. (A third planet, twice the mass of our Moon, was discovered in 1994.) These extraordinary planets are, however, not as common as one would like to think. To date, only two more Pulsars with planets have been discovered. They have nevertheless proved to be exceptionally interesting. In 2009 Pulsar planet PSR B1620-26b was discovered 12,400 light-years from earth. It completes one circumbinary orbit of a White Dwarf star and a Pulsar every 100 years. What is, however, mind-boggling is the age of the planet. At 12.7 billion years it is almost three times older than the earth and a mere billion years younger than the universe. As a result, it was dubbed the “Methuselah” planet in the popular press. Equally astonishing is the 2011 discovery of Pulsar planet PSR J1719-1438b which is 4,000 light-years from earth. It circles its Pulsar in 2.177 hours at a distance less than our sun’s radius. What caused a flutter, however, was the composition of the planet. It turned out to be extremely dense and made of crystalline carbon. In other words, the planet orbiting the Pulsar is actually a gargantuan diamond.
Not long after the discovery of Wolszczan and Frail, Michel Mayor and Didier Queloz of the University of Genève announced in October 1995 that they had discovered the first planet of a main-sequence star, 51 Pegasi. A massive gaseous planet, named 51 Pegasi b, had been found orbiting very close to it. As might be expected, the planet was promptly called a “hot Jupiter” by journalists. A torrent of discoveries followed. Most of these were initially made by teams of planet hunters but as technology improved, their function was taken over by space telescopes. The latter has been extremely successful. For instance, the Kepler space telescope discovered 2668 exoplanets between the date of its launch on 7 March 2009 and 12 January 2017. According to the latest statistics published on the NASA web site, 4013 exoplanets have been discovered as of 14 August 2019 with 3949 more awaiting confirmation. The properties of these celestial bodies differ vastly. They come in a wide range of masses, compositions, ages, temperatures, densities and distances from their central stars. Not all of the planets that have been discovered, I must point out, orbit stars. These rogue planets, as they are called, are often expelled from their solar systems through gravity and drift around aimlessly in space. According to Elizabeth Tasker (The Planet Factory P.217) there may be an astounding 400 billion of these orphans in the Milky Way, a figure twice that of the number of stars.
The direct observation of planets outside our solar system have not been possible and astronomers have to use other methods to obtain evidence of the existence of exoplanets. A non-technical description of these can be found on Wikipedia. See https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets. The space telescopes are also designed to employ certain of these methods. Kepler, for example, uses the transit technique, while the Spitzer Space Telescope finds planets by detecting their infrared heat. And the Wide Field Infrared Survey Telescope (WFIRST) that NASA plans to launch during the 2020s, will locate planets through gravitational microlensing and direct imaging.
Of course, the ultimate purpose of the search for exoplanets is to find extra-terrestrial life. To do that, astronomers concentrate on finding exoplanets within the habitable zones of stars. Unfortunately, however, such a find does not guarantee success. In August 2016, for instance, it was announced with great fanfare that an exoplanet had been discovered within the habitable zone of our closest star, Proxima Centauri – a red dwarf star approximately 4.37 light-years from earth. (The star, by the way, is part of a triple star system of which Alpha Centauri A and B are the other two members.) Although the exoplanet, known as Proxima Centauri b is very close to its star at one-twentieth of the earth’s distance to the sun or 0.05 astronomical units, Proxima Centauri is very dim and has only 0.17% of the sun’s absolute visibility. It was accordingly assumed that the latter fact compensates for the proximity of the exoplanet to its star and that it has much the same climate as the earth. Subsequent studies, however, showed that that is not so and that Proxima Centauri b is in all probability a lifeless desert. See https://www.skyandtelescope.com/astronomy-news/proxima-centauri-b-likely-a-desert-world/
Although no extraterrestrial life has been discovered to date, it is hardly likely that it does not exist anywhere in the universe. The number of stars and planets simply militates against such a view. More problematic, however, is the existence of complex life elsewhere and in particular the incidence of advanced extraterrestrial civilizations who will be able to communicate with us. Much has been written on the subject, but it is not something that needs to be discussed now.
That, nevertheless, brings us back to Giordano Bruno. When Galileo was convicted for his defence of the Copernican system by the Inquisition, he was, unlike Bruno, merely sentenced to house arrest. It took the Roman Catholic Church 357 years to acknowledge that they had erred in finding Galileo guilty, but in 1992, Pope John Paul the 2nd eventually apologized. Given the facts that have come to light since the execution of Bruno, one would think that an apology is imperative in his case. But with the attitude of the Church that I have referred to, that is unlikely to happen soon. What is happening instead, is that the Christians, true to form, exploit the latest discoveries of science to their advantage and tell us that the existence of exoplanets demonstrates the greatness of God.