Hello,

Time for yet another dose of 'Science' straight from Tyler's keyboard directly to your Optic Nerves! (And from there, hopefully to your information retention system...)

This time I will be discussing the methods that astronomers use to detect Exo-Planets. The article that follows this one will go one step further to explain how scientists can also detect if these Exo-planets have the correct factors to possibly harbor life on those detected planets.
 
We've come a long way since the first optical telescope first patented in 1608. Galileo hearing about this invention, built his own in 1609 and made his first celestial object observations, namely that the Earth revolved around the Sun, not the Sun revolving around the Earth as previously thought.

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This discovery was the first of many that lead to a Scientific revolution in the field of Astronomy. Fast forward to the present and we are starting to explore distant Star systems for Exoplanets with ever more sensitive instruments and detection methods.

What exactly is an "Exoplanet" is probably a good place to start this discussion. Wikipedia defines it as the following: "An exoplanet or extrasolar planet is a planet outside of our solar system that orbits a star." So simply put, any massive body detectable from Earth that orbits a star other than our own sun, can be defined as an exoplanet. Great, so that's pretty easy to follow so far. As for the detection of such exoplanets, now that's where it starts to get a little to a lot more complicated. So, lets dive right in to this rabbit hole!

There are a large number of detection methods which have proved successful and I will discuss a few of these below.


1. Transit Photometry: This method uses the minute dimming of a star's apparent light as a planet body "transits" a star from a face on perspective from an observer on Earth. This example is pretty easy to put into a tangible experiment we can perform here on Earth. Let's take an example with my stickman friend "Booooob" or we can call him Bob for short. (Hats off to those that pick up the sci-fi literature reference):

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Bob's flashlight in this example is an analog for a distant star's light. This light could be visible light, x-ray, infrared, etc. During a planetary transit, a tennis ball or other round type planetary object in the second frame transit's directly in front of the light source between the source of light and the sensor at the other side and a difference in light intensity is observed.

I took this analogy one step further and performed the same experiment in the real world with the help of my co-worker Curtis "C-Note" Cottom (thank you for the assistance) using a projector and a glass Earth marble analog attached to a headphone cable using an alligator clip. It was a clunky experiment, but gets the point across pretty well to prove the theory.

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In this example, you can see an actual drop of 20 lux (the SI unit of illuminance, equal to one lumen per square meter) during the analog planet transit across my phone's camera sensor. Astronomers will photograph a star over time each night and will look for drops in light intensity compared to previous observations. Once a drop is detected during a an observation, astronomers will continue taking a picture of that particular star looking for the same dip in intensity again. This will tell the astronomer 2 things and this is where physic's comes in handy. Using the time between similar light intensity dips can tell them the time it takes this particular planet to orbit the parent star. Using that and knowing the star's relative mass based on a separate method of observation, the planet's relative mass can then be determined and from this it's radius can be inferred.

Side note and trivia question: If I place my phone on my desk I read 558 Lux from the same camera sensor feeding into the app. This is under indirect fluorescent recessed ceiling lighting commonly found in office buildings. So why is the projector so much less intense even when that light is directional and focused more directly at the camera sensor on my phone??? Hint, think about the color. The first correct answer will receive mention in my next Science article as a matter of pride. 

So, let's put this into an astronomical perspective which will really blow your mind. As of 11/17/17 there are 3,558 confirmed Exo-planets, of which 2,771 have been discovered using the direct Transit Photometry method. And of that number only 374 are the relative radius of Earth. Using only our Sun's size (remember that our Sun is a little smaller than a White Dwarf which is the most common type of star in the Universe as far as we can tell) here is a pictorial showing our Solar system objects compared to our own Sun:

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So imagine if you will you were an observer on the surface of Pluto exactly when Earth is directly between the line of sight of the Sun and Pluto. How small would the Earth Transit be then? Now move the observer to the nearest neighboring star, Alpha Centauri A, at an average of 4.3 light years from Earth. How small would our Earth look transiting across our Sun from that distance? Now you can see how sensitive the telescope sensors have to be for the light intensity drop at that distance to be detecable. And the furthest detected Exo-planet confirmed using the transit method is roughly ~27,700 light years away from Earth and is close to the radius of a Jupiter sized planet and the Star is about 1.5 times that of our Sun. That's like finding a single atom on the tip of a needle inside a haystack the size of Texas for scale.


2. Radial Velocity: The second detection method I want to discuss is the Radial Velocity detection method. This uses the apparent wobble of the observed star resulting from the tidal tug of a massive orbiting body around itself. 

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If the ball in the picture was massive enough (imagine it was a spherical ball of solid lead for example) then the stick figures lighter body would appear to wobble to correct for the shift in balance. This can be detected with today's powerful telescope. This method is more difficult than Transit Photometry, but is far more sensitive in detecting orbits of massive planetary objects that are closer to the parent star.


3. Microlensing: And the last detection method I want to discuss is microlensing. 

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So this concept can be somewhat confusing, but in the diagram you have two stars. They can be from the same system or a separate star system entirely. For this detection method to work a large number of background stars are tracked. Astronomers can then plot the position each star should have travelled over time and can detect any difference from what is observed and conclude a gravitational microlensing effect caused by a planets mass on the light bending around its gravity well. More than 1000 events of microlensing around stars has been observed over the past 10 years. And to date as of 11/17/17, 51 planets have been detected with this method out of the 3558 total Exo-planets discovered.


I hope I didn't lose anyone in those explanations, but I think I may have raised some eyebrows hopefully. As a reminder, for the next article, I will cover how we detect if an Exoplanet has the factors that could harbor life as we know it. Even as far as to what the types of elements are present in the Planets Atmosphere and how scientists can detect this to within a high level amount of certainty. 

Don't forget to reply back with your guess to my trivia question in Italics under Transit Photometry for a chance to be mentioned in the next article for bragging rights.

Thanks again everyone,
Tyler Waldrop