Songs of Exoplanets

Earlier this week University of Arizona student Allie Mousseau and graduate student Ben Rackham, members of the EDEN team, welcomed a group of 12 students at the UA SkyCenter atop Mt. Lemmon and introduced them to the methods we are using to find exoplanets. The activity was a collaboration between our EDEN team and Project POEM, which aims to foster interest in STEM careers among visually impaired middle and high school students. Since the Project POEM students have different levels of visual impairment, the traditional data visualization tools were not suitable for demonstrating the concepts to the students. We wanted to find a way that allowed them to get an intuitive sense of the exoplanet transit data – to bring the abstract concept closer to the students’ everyday experiences. Steward Observatory graduate students Alex Bixel and Ben Rackham and University of Arizona professor Daniel Apai came up with an innovative method to demonstrate exoplanet transits: by translating stellar lightcurves (brightness variations) into piano tunes, all students could easily pick up the events when planets pass in front of their host stars – the sort of transits Project EDEN is searching for.

The students heard examples of models of exoplanet transits to learn about how we can tell the size and orbital period of an exoplanet from its light curve.  Here, for example, is a visual comparison of the transit depths for three planet-sun combinations:  a Jupiter-like planet orbiting a Sun-like star, an Earth-like planet orbiting a Sun-like star, and an Earth-like planet orbiting an M-dwarf star:

And here are how those same model lightcurves sound when converted to pitches:

Jupiter-Sun:

Earth-Sun:

Earth-M dwarf:

As you can hear, it’s much easier to detect an Earth-sized planet around a small M-dwarf star than around a Sun-like star–the transit depth is almost as deep as a Jupiter-sized planet transiting the Sun!

Of course, real measurements always have noise as well, and the students got to experience this first-hand by analyzing a transit light/soundcurve of the sub-Neptune GJ 1214b that we recently observed with the Kuiper 61″ telescope on Mt. Bigelow:

Finally, the students listened to segments of a 20-day, nearly continuous lightcurve of TRAPPIST-1 taken with the Spitzer Space Telescope.  This amazing dataset, which was published in Nature last year, contains transits of seven Earth-sized transiting exoplanets, three of which have surface temperatures that could allow for liquid water!

This artist’s concept allows us to imagine what it would be like to stand on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius.

The students listened to segments of this lightcurve and worked together to identify transits, breaks for data downlinking from the telescope, stellar flares, and even a simultaneous double-transit of two planets.  They used the open-source Aria Maestosa program to change the tempo and instrument used to represent the data in order to best analyze the data. As you can hear, the similarities of the transit depths between the planets and the practice of compressing many days of data into a few tens of seconds make this no easy task!

Samples of TRAPPIST-1 Spitzer Light Curve:

It was great to see the excitement of the students as they have explored worlds beyond the solar system through “interstellar songs”!

Listening to the melodies of exoplanet transits.