# Math and Science Discover the Unseen Planets of Trappist-1 – Now That’s Cool!

I am sure by now you have heard about NASA’s discovery of 7 – earth-like planets orbiting the star called Trappist-1 by using the Spitzer Space Telescope. And, apparently 3 of them could possibly be habitable for life. All of this is amazing in itself, but, what is even more amazing is they discovered these planets without really even seeing them.

What?!  How is this possible? How do they know then that there are even planets if they can’t see them? It all comes down to some amazing technology, some data collection, a lot of math, science and analysis. If you are looking for ways to get your students excited about math and science and real-world applications to answer questions, you need look no further.

While listening to a story on NPR, as usual, an astronomer came on to discuss how these planets were in fact discovered. In his discussion, I was just floored by all the applications of geometry and statistics used in this discovery. When he said they couldn’t actually ‘see’ any of the planets, but instead, used the dimming light of the star, Trappist-1, that these planets orbit around as an indication that there were in facts objects/planets orbiting about the star. So – basically,  looking at the stars brightness from the Earth, the amount of starlight that is blocked as each planet passes across the view of the star was used to calculate the size of each planet.  Based on the amount of dimming, they were able to determine the size of the planets, relative to Earth, with the dips in the stars light indicating how fast the individual planets were orbitting the star. This video below explains the process really well:

The star, Trappist-1, is what they call an ultra-cool dwarf star, which is about the size of Jupiter and significantly cooler than our own sun, and is only 39 light years away from us.  That seems far to me, but apparently in ‘space units’ that’s really close! (Here’s a great problem for students – how many miles would 39 light years represent?) Each planets mass was determined by the amount of tug of each planet on the other. Then, using the size and mass calculations, they estimated each planets density, which then allowed them to extrapolate that six of the planets are probably rocky. Another really interesting thing about all the planets is they appear to be tidally locked, which means the same side of the planet always faces its sun, so one half of the planet is always dark, the other always light. This is based on the length of each planets day, or its spin on its axis (determined by watching the planets for a period of days and seeing how often they crossed the star). The shortest day (compared to an earth day) is 1.5 days, the longest is about 20 days (they still have to collect more data for this last one). I found this great chart on the NASA Jet Propulsion site that compares each of the seven planets (with an artist’s rendering of what they might look like…remember, no one can actually ‘see’ these planets yet)

This infographic displays some artist’s illustrations of how the seven planets orbiting TRAPPIST-1 might appear — including the possible presence of water oceans — alongside some images of the rocky planets in our Solar System. Information about the size and orbital periods of all the planets is also provided for comparison; the TRAPPIST-1 planets are all approximately Earth-sized.

I find the whole process exciting, interesting, and fascinating. I think students would too and there is so much application of mathematics and science going on here. And, as a certified sci-fi geek, just thinking of the possibilities of other life on those ‘M’ class planets (shout out to my fellow Star Trek groupies) is sparking my imagination. Right now, we don’t have the technology to see these seven planets, but who knows? Maybe a student who explores the math and science behind these now might create that next telescope that lets us see the planets, or the space ship that allows us to travel there? Fun to imagine, and fun for students to explore these ‘brave new worlds where no man has gone before….”.