It has been an exciting time for space fans lately, because the study of exoplanets has just taken one giant leap forward. A group of Portuguese researchers announced back in 2015 that by carefully looking for patterns in the light from a star called 51-Pegasi, they were able to detect the light from one of its planets called 51-Pegasi-B.
We’re talking about honest-to-goodness hit the planet and bounced off kind of light, the first direct light we've ever observed from a planet outside the Solar System.
This planet is no stranger to fame. Way back in 1995, it was the first exoplanet found orbiting a Sun-like star.
51-Pegasi-B is fifty-one light-years away in the constellation Pegasus, hence the name. But its yellow G-type main sequence star is just like ours, and yet, it is nothing like Earth. It’s what scientists call a “hot Jupiter” - huge and gaseous, but orbiting really close to its host star.
Discovering exoplanets like this in the first place is tricky business, because stars are so bright that they tend to outshine any objects around them.
We’ve found all of the planets that we know of so far without seeing them directly. Instead, we've used other methods, like watching how the planets’ gravity tugs on its star, causing a shift in the wavelengths of its light. Looking for these shifts is called the Radial Velocity Method, and it’s helped us detect hundreds of exoplanets.
The other main way to find exoplanets is by checking to see if a star's light fluctuates in a predictable way; this might mean that a planet is passing in front of it.
Although these methods have been incredibly useful, they are limited. If we were able to directly measure the light coming off an exoplanet, it would be much better, because the planet wouldn’t need to pass right in front of its star in order for us to know it's there, which is actually pretty rare.
Plus, its reflected light could actually tell us about the planet. We could tell just by looking if it had an atmosphere, and if it did, if it was packed with elements like nitrogen or methane. We could even conceivably see what color it is, which is why these new findings are so exciting.
Astronomers collected data over seven different nights, and put together ninety different signatures of light, aka spectra. 51-Pegasi’s light-spectra had most of the usual predictable patterns you'd expect from such a star, created by fluctuations in its brightness.
However, the researchers knew that 51-Pegasi-B had to be in there as well, creating its own tiny fluctuations. Separating that tiny pattern out had never been done successfully, but the team believed that they could do better. They knew that the light patterns they'd collected were combinations of three different things: the light emitted by the star, the light from the planet, and some random noise.
If they could get rid of the star’s contribution to that light, then the remaining data would be of just the planet’s light.
What they did was put together a sort of template for all of 51-Pegasi’s as-usual spectrum, and then just subtracted those points from the data overall. The spectrum that was left fit the pattern of a planetary signal, and the astronomers were able to conclude their results as 99.7% accurate.
Now, what scientists are wanting to prove is that the technique works with more modern, sensitive instruments, like the James Webb Space Telescope just around the corner. Eventually, we should be able to use this method, and it just might be the way we discover which planets harbor life.
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Sources: This story was originally published on SciShow Space. I am republishing a lightly edited version on SkyFeed in light of interest in the subject. Green, Hank. "A New Way To Find Planets!" SciShow Space, YouTube. 30 April 2015. Web video.
Citation: Rovira, Lia N. "We've Devised A New Way To Discover Planets By Accidentally Finding One." SkyFeed. 25 June 2018. Web article.