For some reason that continues to elude me, the general public always loves a good space story. Or, at least, the mass media seems to think they do. And seeing as how the media can easily keep track of which of their stories are viewed the most times, I tend to trust their analytics.
Whether it be a newly discovered planet that orbits a binary star system like Anakin Skywalker’s home planet of Tatooine, or the millionth artist’s rendition of what a cosmic meltdown might or might not look like, it seems people just can’t get enough of the great beyond. I suppose it shouldn’t be that surprising. After all, people have always gazed up at the stars and wondered what was out there. It has only been recently, however, that enormous telescopes have allowed us to actually find out.
But of all the senseless attention-grabbing headlines out there, the most sensationalist has to be the discovery of every new planet orbiting a star that is not our own. There are countless numbers of exoplanets out there, and even if we can determine that they’re close enough to their star to maintain liquid water, there’s no way we can tell whether or not it has the potential for life.
So what’s the big fuss?
What’s more interesting than the planets themselves, I think, are the methods by which they are detected. It takes quite the trick of mathematics to be able to deduce the existence of a tiny planet orbiting a comparatively giant star a mind-boggling distance away from our own eyes.
As it is, there are several ways in which we detect new planets. The first would be the same way in which classical astronomers deduced the planets on the fringes of our own solar system – by their gravitational influences. But rather than tugging at other known planets, the sought-after exoplanets are tugging on their own stars.
If we were to gaze at a solar system from a birds-eye view with the planets moving around like a record player, we should be able to detect faint wobbles of the star about a central point caused by the constantly moving tugs of gravity from its planets. This is nice in theory, but for now it remains no more than an idea, much like a “Diving with the Stars” television show. Oh wait, shit, nevermind. Stars are so far away and their potential wobbles so minimal (unlike Kristy Alley’s, zing!) that current techniques aren’t sensitive enough to measure the movements.
What we can do, however, is measure such a star’s Doppler shift. If we were to look at that same solar system from its edge, the star’s wobble would be moving away from us, then parallel to us, and then towards us, depending on the point of its wobble. If that seems confusing, imagine watching a kid on a merry-go-round. If you stay in the same spot, the kid will be moving towards you or away from you at different times, depending on where he is on the ride. When moving toward us, its light would be detected slightly bluer. When moving away, it would be shifted red.
You’re already familiar with this idea, but with sound waves instead of light waves. As a douchebag in a muffler-less Camry with a spoiler comes racing toward you, the sound his POS makes gets higher in pitch. Then, after he crawls past you at the speed of smell, the sound gets lower in pitch.
Similarly, as a star’s wobble moves toward us, the frequency gets higher, making it bluer. As it moves away, the frequency gets lower, and thus redder. This effect is not too small for our instruments to pick up. In fact, there have been 31 confirmed exoplanets discovered with this method and 323 more potential candidates.
The next method of discovering potential planet Vulcans is called the transit method. This one again requires that we be looking at a distant solar system from its edge. Then, any planet revolving around it would pass between Earth and its planet star at regular intervals. By picking up on this minute, periodic dimming, we can deduce the presence of planets. This method has confirmed a whopping 231 exoplanets.
Third on the list is gravitational lensing. You might recall at some point having heard that space is curved due to gravity. Well, it’s true, and when light gets close to a massive object like a star, it will bend right along with the curved space around that object. This effect causes objects behind massive objects to become magnified – a phenomenon called gravitational lensing.
Now, this magnification allows researchers to measure a star’s brightness with even more precision. Those stars with planets, as it turns out, appear brighter than similar stars without planets. This is because those planets reflect light, causing tiny changes in total brightness. This form of detection has managed to bag 15 exoplanets.
Moving on, we come to a slightly rarer form of star called a pulsar, which give off radio waves in flashes that occur more regularly and precisely than an atomic clock. Any disturbance in those radio waves indicates a planet. This form of detection – which also happens to have been around the longest – has netted 16 confirmed exoplanets.
Last but not least, there’s good old direct observation. Our telescopes have become so advanced, that for some of the closer and dimmer stars, we can blot out the glare of the parent star enough to detect planets in a distant orbit. So far, we’ve managed to find 13 using this method.
As of March 1 of this year, there have been 861 planets not orbiting Sol to have had their existence confirmed. But we’re not nearly done there. The Kepler Space Observatory was launched in March of 2009 with the express intent of discovering Earth-like exoplanets, and it’s managed to glimpse an additional 18,000 candidates.
If you’re a PhD student in the field of astronomy, there is no shortage of projects for you to work on or data to get your hands on.
But what makes a planet potentially Earth-like? Currently, scientists point to its size, the distance from the parent star that it orbits, and what type of star is hosting its presence. In short, they’re looking for conditions for planets that would have gravity similar to Earth’s and the ability to have liquid water.
There are seven different types of stars out there, and of them, Class Ms are both the dimmest and most common. They also just happen to be our best chance at discovering a suitable planet for life. First of all, as previously mentioned, they’re the most common, so that raises the odds right there. But also, being the dimmest, they’re some of the easiest to look for planets.
A recent study by researchers at Harvard University and the Smithsonian Center for Astrophysics analyzed 3,987 M-dwarf stars and calculated the frequency of planets in their potentially habitable zone. However, they were using old models for said habitable zone; models that were, in fact, written by a Penn State professor more than 20 years ago.
An even more recent study from that same Penn State professor updated the estimates of a habitable zone by taking into account more accurate information on how water and carbon dioxide absorb light and heat. The new numbers allow planets to be further away from their stars and maintain the possibility of liquid water.
After applying the new habitable zone calculations to the Harvard study, researchers report that of the eight M-dwarf stars within 10 light years, we should expect to find 3 Earth-like planets. Extrapolating, that indicates that 4 out of every 10 M-dwarf stars should also have one across the entire universe. In the Harvard study alone, that’s almost 1,600 potentially habitable planets.
And the closest should be no more than a mere seven light years away. Perhaps finding Vulcan or Frogstar World A isn’t that far off after all.
The paper, “A Revised Estimate of the Occurrence Rate of Terrestrial Planets in the Habitable Zones Around Kepler M-Dwarfs,” was published on the Arxiv by Ravi kumar Kopparapu, professor at the Penn State Astrobiology Research Center.