The search for alien... planets

David Benford
Feb 5, 2016
4 min read

An artist's depiction of a sunflower-shaped starshade that could help space telescopes find and characterize alien planets. Credit: NASA/JPL/Caltech

The search for life outside our solar system has been an ongoing endeavor for decades. In order to find life, we have to find planets. To find planets, we need ground based observatories, space telescopes, and a whole lot of luck. Finding an object in the pitch blackness of space is not easy. Finding an object, the size of a pin prick at distances that are quite unimaginable is even harder. Today's technology and methods are on a far greater scale then they were in the past, and while astronomers today have found hundreds upon hundreds of planets outside our solar system, there are still techniques to do so more efficiently still being discovered.

Planets cannot be observed directly - they can only reflect light, not create it - thus, astronomers must turn to their parent star. In doing so, there are three typical techniques that are commonly used today: Radial Velocity, Transit Photometry, and Microlensing.

Radial velocity is the process in measuring a stars ever so slightly movement as a planet orbits it. When a star is being orbited by a planet, the pull from the planet gives the star a slight wiggle, which in case, ends up shifting the star’s light spectrum, or color change. Depending on which direction the star moves - towards us or away from us - the light of that star shifts a little blue, or, shifts a little red. This shift in light spectrum is known as the Doppler Effect. This method of searching for planets, up until 2009 with the launch of the Kepler Space Telescope, was the most effective way in searching for planets outside our solar system.

Transit Photometry is the method which astronomers observe the slight dimming in light from the star as a planet passes in front of it while facing Earth's direction. If such a dimming is detected at regular intervals that we can predict and lasting over a certain amount of time, then there is probably a planet that’s in orbit around its parent star.

The third method is called 'Microlensing' and probably one of the more difficult observing techniques to explain. Microlensing is based off Albert Einstein's prediction in his General Theory of Relativity. Taken from the planetary.org website, it states, “when the light emanating from a star passes very close to another star on its way to an observer on Earth, the gravity of the intermediary star will slightly bend the light rays from the source star, causing the two stars to appear farther apart than they normally would." In other words, as light travels from one star and passes by another star, the gravity of that star will bend the previous star’s light. What this does is lead to that star becoming even brighter than it previously was and lasting several weeks. Now, when a star has a planet orbiting it, the gravity from that planet will also bend the light, causing a third image and another spike in brightness that subsides after a few hours or days. Furthermore, from this reading, astronomers can assume there is a body in orbit around such star, so long as this happens on a regular interval.

OGLE Planet Detection through Microlensing The microlensing process in stages, from right to left. The lensing star (white) moves in front of the source star (yellow) magnifying its image and creating a microlensing event. In the fourth image from the right the planet adds its own microlensing effect, creating the two characteristic spikes in the light curve.

Each method has their advantages and disadvantages when it comes to the search for alien planets. However, there is a new technique which is currently in development and probably the one I am most excited about.

It is currently in development by Northrop Grumman, and as the photo above depicts, is shaped like a set of flower pedals. The creation of these pedals have to be exact, and by exact, I am talking about it being within 10ths of a millimeter exact!! The concept is for there to be two sections - the star shade, which would be taller than a 15-story building, and a space telescope that would be flying tens of thousands of miles behind it. When you are looking at a star to find a planet, you are receiving a ton of light interference, therefore making the planet extremely difficult to observe directly. Up to this point, every planet has been observed, indirectly. What the star shade would allow us to do, is observe planets orbiting a star, in a habitable zone, directly! A common analogy used - take your thumb or hand, and hold it up towards the sun, blocking the majority of the light. With that complete, you can visually see everything around your thumb with a lot more ease.

It is going to take many years to completely ground test, engineer, and gather the funding needed to make this concept a reality and blasted off to space. But this - the ingenuity, the concept, and the idea to dream big and build big, is what makes astronomy the most exciting field in science.

"Flower Power: Giant 'Starshades' Prepped for Exoplanet Hunting." Space.com. N.p., n.d. Web. 04 Feb. 2016.

"Microlensing." The Planetary Society Blog. N.p., n.d. Web. 04 Feb. 2016.

"Radial Velocity." The Planetary Society Blog. N.p., n.d. Web. 04 Feb. 2016.

"Starshade." Northrop Grumman. N.p., n.d. Web. 04 Feb. 2016.

"Transit Photometry." The Planetary Society Blog. N.p., n.d. Web. 04 Feb. 2016