By Dr. Gary Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
The first of three articles on advances in the study of the Solar System.
We humans have long suspected that we are not alone; that the circumstances of our planet and our solar system are perhaps more ordinary than they might appear from our view of the night sky. For most of recorded history, humankind believed that the Earth was the sole oasis for life in an otherwise barren universe and center stage in the design of the cosmos.
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Today, of course, we know this not to be true. Most astronomers credit Nicolaus Copernicus and Galileo Galilei with the discovery of the heliocentric model — that the Earth and all the other planets revolve around the Sun. And to be fair, these gentlemen were both largely instrumental in championing this idea until it was taken seriously by the mainstream scientific community.
But the first documented record of someone pondering the notion of the heliocentric model was actually Aristarchus of Samos in 270 BCE, almost 2,300 years ago and more than 700 years before the time of Copernicus or Galileo.
We Wondered about the Existence of Exoplanets Long before any Actual Discoveries
Similarly, we wondered about the existence of exoplanets long before any actual discoveries were made. An exoplanet is defined as any planet outside our own solar system, which would include planets within the Milky Way galaxy and planets in other galaxies. Giordano Bruno, a 16th-century philosopher and mathematician, was one of the first to openly discuss the possibility of the existence of these far-off worlds.
Bruno hypothesized that the stars we see in the night sky might actually be suns with their own planets orbiting around them. Like Copernicus and Galilei, Bruno was persecuted by the Catholic Church for his heretical views.
However, he did not let the charges of blasphemy stop him from speaking his mind. In 1584, Bruno asserted that “the space we declare to be infinite…in it are an infinity of worlds of the same kind as our own.” Bruno stuck his neck out to defend his idea, but it would not be long before he’d be joined by one of the true titans of astronomical discovery, Sir Isaac Newton.
If the Laws of Physics Are Consistent across the Universe Other Stars Ought to Have Planets Too
Newton was a mathematician and physicist. Principia, his seminal work, defined the laws of motion in the universe. From Newton’s enlightened perspective, he argued that if the laws of physics are consistent across the universe, as indeed they appear to be, then other stars ought to have planets just as ours does.
Notwithstanding these bold claims, it would be nearly 300 years before the first evidence of exoplanets would inadvertently be discovered. In 1917, Dutch-American astronomer Adrian van Maanen discovered a white dwarf star about 14 light-years from Earth. It is cataloged today as van Maanen 2 in honor of its discoverer.
When van Maanen used light spectroscopy to analyze the white dwarf, he observed the presence of heavy elements, but he could not deduce the reason for this unusual characteristic. More than a hundred years later, we now know that van Maanen was seeing evidence of exoplanets that had been destroyed by their former star as it transitioned through the red giant phase before it finally became a white dwarf star.
Canadian Trio Announces the Discovery of Exoplanets around Gamma Cephei Star
It would be another 70 or so years before the first deliberate searches and suspected discoveries of exoplanets would take place. In 1988, three Canadian astronomers observed the star Gamma Cephei and announced a discovery of exoplanets around it. However, the discovery was unconfirmed at the time due to limitations in observation technology and data analysis tools.
In 1992, two radio astronomers observed the pulsar PSR 1257+12 (now known as PSR B1257+12) and found what they believed to be two exoplanets orbiting the strange object. This led astronomers to question whether exoplanets were commonplace only around pulsars.
However, in 1995 astronomers Michel Mayor and Didier Queloz announced the confirmed discovery of an exoplanet orbiting the main sequence star 51 Pegasi. Mayor and Queloz would later be awarded the 2019 Nobel Prize in Physics for their discovery. Their find gave astronomers hope that exoplanets were fairly common because main sequence stars are the most common stars in the galaxy.
NASA Launches Kepler Space Telescope in 2009
In response to these encouraging discoveries, the National Aeronautics and Space Administration (NASA) launched the Kepler Space Telescope on March 7, 2009. The space telescope was named after famed astronomer Johannes Kepler. Its primary mission was to search for exoplanets throughout the Milky Way galaxy.
Kepler was launched into an Earth-trailing heliocentric orbit of approximately 372 days. The spacecraft’s only onboard instrument was a photometer that continually monitored the brightness of about 150,000 main sequence stars at a time. Whenever an exoplanet orbiting a distant star passes or “transits” between the space telescope and the star, it blocks a little bit of the light coming from the star.
By analogy, imagine an ant walking across the lens of a flashlight and blocking a little bit of the beam with its body. These kinds of tiny changes from such enormous distances are imperceptible to the naked eye. But Kepler’s photometer was extremely sensitive, so the telescope was able to pick up even the most subtle changes in emitted light.
Kepler would stare at the same set of stars week after week, month after month, and wait to detect changes in light emitted from them. Whenever a dip in light was observed from one of the stars, this was a preliminary indication that an exoplanet was transiting in front of the star.
The Kepler mission was originally planned to last about three and a half years, but Kepler pushed on to more than nine and a half years before being decommissioned. That is funding for the Kepler was discontinued and NASA stopped operating it.
How did Kepler fair at exoplanet hunting? In the second part of this series, we’ll see what Kepler found, and what astronomers have been able to glean from Kepler’s observations.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.