Probably Not An Alien Megastructure

One way to look for planets in distant solar systems is look at stars long enough to notice if there are any periodic dips in its brightness levels. These dips are very subtle drops in brightness when the planet passes in front of the star, blocking some of the light from the star.

image This image from NASA shows light curve of a Planet transiting its star.

Transit data are rich with information. By measuring the depth of the dip in brightness and knowing the size of the star, scientists can determine the size or radius of the planet. The orbital period of the planet can be determined by measuring the elapsed time between transits. Once the orbital period is known, Kepler’s Third Law of Planetary Motion can be applied to determine the average distance of the planet from its stars. The changes are often very minute and rarely in the reach of pattern recognition algorithms. To solve this problem, Yale researchers crowd sourced it. The initiative is called Planet Hunters. Hundreds of people from around the world help analyze the data from Kepler Space Mission. And once in a blue moon, a planet is found.

So far, over 12 million observations have been analyzed. Out of those, 34 candidate planets had been found as of July 2012. However, in October 2012 it was announced that two volunteers from the Planet Hunters initiative had discovered a novel Neptune-like planet which is part of a four star double binary system, orbiting one of the pairs of stars while the other pair of stars orbits at a distance of around 1000 AU. This is the first planet discovered to have a stable orbit in such a complex stellar environment. The system is located just under 5000 light years away, and the new planet has been designated PH1, short for Planet Hunters 1. From Wikipedia, Planet Hunters

How much light does a planet like Earth block from a star like Sun?

For an observer at a distance, both bodies are essentially circles. We’ll compare their areas,

\[\frac{\text{Area of Earth}}{\text{Area of Sun}} = \frac{\pi r_{earth}^2}{\pi r_{sun}^2} = \left ( \frac{r_{earth}}{r_{sun}} \right )^2\]

Radius of Sun is about 110 times the radius of Earth.

\[\left ( \frac{r_{earth}}{r_{sun}} \right )^2 = \left ( \frac{1}{110} \right )^2 = 0.01\%\]

So, an earth-like planet will block about 0.01% of light coming from its parent star. This is what a 0.01% dip looks like on a chart.

[show the goddamn dip]

The largest planet in our solar system, Jupiter, has a radius 1/10th of Sun. Its transit will block about 1% of light. This is what a 1% dip looks like on a chart.

[show it another time]

In Comes WTF Star

WTF Star is also known as KIC 8462852. Some 1500 light years away, it is the most interesting star in the night sky which cannot be seen by the naked eye.

The light curves of KIC 8462852 look like,

image Source: AstroWright http://sites.psu.edu/astrowright/2015/10/15/kic-8462852wheres-the-flux/

The first dip brings the readings from 1 to 0.85. A massive 15% dip. Second dip is a gigantic 22% dip.

\[\left ( \frac{r_{x}}{r_{star}} \right )^2 = 22\%\] \[r_x \approx \frac{r_{star}}{2}\]

If the charts are to be believed, there is probably a planet around WTF Star that is half as huge as the star itself. A crazy size for a planet.

WTF Star has a radius about 1.5 times the radius of Sun. Half of which will be 0.75 times Solar Radius. In terms of planets, that is 7 times the radius of Jupiter.

But, It Can’t Be A Planet!

Phil Plait isn’t a fan of the definitions of Planet and Stars.

Open Questions from This

References

Transit Photometry, Methods of Detecting Exoplanets - Wikipedia https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets#Transit_photometry Transit light curve - NASA Mission Pages http://www.nasa.gov/mission_pages/kepler/multimedia/images/transit-light-curve.html Astronomers may have found giant alien ‘megastructures’ orbiting star near the Milky Way - Independent.co.uk http://www.independent.co.uk/news/world/forget-water-on-mars-astronomers-may-have-just-found-giant-alien-megastructures-orbiting-a-star-near-a6693886.html No, we haven’t discovered alien megastructures around a distant star - The Washington Post https://www.washingtonpost.com/news/speaking-of-science/wp/2015/10/15/no-we-havent-discovered-alien-megastructures-around-a-distant-star/ Citizen scientists catch cloud of comets orbiting distant star - New Scientist https://www.newscientist.com/article/dn28191-citizen-scientists-catch-cloud-of-comets-orbiting-distant-star/ Where’s the Flux? - AstroWright http://sites.psu.edu/astrowright/2015/10/15/kic-8462852wheres-the-flux/ Upper Limit to a Planet - Bad Astronomy http://blogs.discovermagazine.com/badastronomy/2006/09/07/the-upper-limit-to-a-planet/#.VieFMPkrKUk