Historically, the quest to detect remote planets, inhabiting the families of alien stars beyond our own Sun, proved to be very difficult. The discovery of the first group of exoplanets more than twenty years ago is certainly one of humanity’s greatest accomplishments. This is because discovering a giant planet, such as our own Jupiter, can be compared to observing light bouncing off a mosquito flying near the 1,000-watt light bulb of a glaring street lamp–when the observer is 10 miles away.
The original successful technique used by astronomers back in 1995, called the Doppler Shift method–sometimes more casually referred to as the “wobble” method–favored the discovery of giant planets circling their parent-stars in roasting, close-in orbits. However, new and improved technologies were soon developed that enabled astronomers to detect ever smaller and smaller exoplanets that resided at greater distances from their stars. Indeed, many astronomers think that exoplanets about the same size as Earth are common denizens in our Galactic neighborhood.
The smaller the exoplanet, the harder it is to discover. For example, if an alien astronomer, belonging to a technologically sophisticated society, went on the hunt for other worlds situated in distant regions of our Milky Way Galaxy, it would have a very difficult time detecting our own tiny, rocky, little blue world. Our Earth would be only a faint speck lost in the powerful glare of the Sun.
The first detection of an exoplanet occurred back in 1988–however, the first confirmed detection came in 1992, with the discovery of some genuinely strange beasts inhabiting the planetary zoo–a batch of bizarre, inhospitable, but completely fascinating worlds in orbit around a dense stellar remnant called a pulsar–the lingering corpse of a massive star that recently ended its hydrogen-burning “life” in the violent, fiery tantrum of an explosive supernova blast, that destroyed the original progenitor star. A team of astronomers detected the first exoplanet in orbit around a still-“living”, hydrogen-burning, Sun-like star in 1995. As of September 2017, there are 3,667 confirmed exoplanets occupying 2,747 systems, with 616 systems containing more than one solitary planet.
Since 2004, the European Southern Observatory’s (ESO’s) High Accuracy Radial velocity Planet Searcher (HARPS) 3.6 meter telescope has successfully discovered about 100 exoplanets, while NASA’s Kepler Space Telescope, since 2009, has found more than two thousand. Kepler has also spotted a few thousand candidate exoplanets still awaiting confirmation. However, it is generally thought that about 11% of these distant worlds may be false-positives. In several instances, multiple planets have been spied circling their parent-star.
Many astronomers think that about 1 in 5 distant Sun-like stars possess an “Earth-sized” planet situated in its habitable zone. The habitable zone surrounding a star is that “Goldilocks” region where the temperatures are not too hot, not too cold, but just right for liquid water to exist. Where liquid water exists, life as we know it could also exist–however, there are other factors to be taken into account, and the location of a planet in its star’s habitable zonedoes not indicate that it is definitely inhabited. In our own Solar System, the planet Venus is situated in the habitable zone of our Star. Alas, Venus is the tragic victim of a runaway greenhouse effect, making it much hotter than it should be. Any water that may once have pooled on the surface of this inhospitable world would have boiled away long ago.
Assuming that there are 200 billion stars inhabiting our Galaxy, scientists can hypothesize that there are 11 billion potentially habitable Earth-sized exoplanets in our Milky Way, rising to about 40 billion if planets orbiting the very numerous red dwarf stars are included in the tally. Smaller than our own small Sun, red dwarfs are both the most numerous, as well as the longest-lived stars in our Milky Way. In fact, red dwarfs go on burning their necessary supply of hydrogen for trillions of years–and the Universe is only about 13.8 billion years old.
The least massive known exoplanet has been dubbed Draugr, and it is approximately twice the mass of Earth’s Moon. In marked contrast, the most massive known exoplanet is DENIS-P J082303.11-491201 b, and it is about 29 times the mass of Jupiter. However, according to some definitions of what constitutes a “planet”, this jumbo distant world is too massive to be designated a “planet”, and it may more precisely be considered a type of failed star called a brown dwarf. Brown dwarfs are objects that are likely born the same way as true stars–as the result of the collapse of a dense pocket embedded within the swirling folds of a cold, dark, giant molecular cloud–but have not attained sufficient mass to light their nuclear-fusing stellar fires.
There are explanets that cling to their parent-star in such close, broiling orbits that they take only a few hours to circle it–and there are others that are so far from their star that it is a challenge for astronomers to determine whether they truly are gravitationally bound to it. Almost all of the distant alien worlds, that belong to the families of stars beyond our own Sun, are inhabitants of our Milky Way Galaxy. However, there have also been discoveries of a few fascinating potential extragalactic exoplanets. The nearest exoplanet to our Earth is Proxima Centauri b, which dances around its star, Proxima Centauri, at “only” 4.2 light-years away from us. Proxima Centauri is the closest stellar inhabitant to our Sun.
Numerous rogue planets also dwell in our Galaxy, and these solitary worlds do not belong to the family of any star at all, but wander through interstellar space without a stellar family to call their own. Alas, these solitary planets probably once belonged to the family of a distant star, but were heartlessly booted out as the result of destructive gravitational interactions with sibling planets, or as the result of a passing star that closely brushed past their own star–with disastrous consequences for the rudely evicted rogue planet.
The discovery of so many faraway exoplanets has stimulated significant scientific interest in the quest to find life beyond Earth–with special attention being paid to planets that orbit their stellar-parent within its habitable zone. Mkv Movies