The 24th International Conference on Auditory Display (ICAD 2018) June 10-15, 2018, Michigan Technological University PLANETHESIZER: APPROACHING EXOPLANET SONIFICATION Adrián García Riber AGR Image and Sound Art, Music Research and Sound Engineering, Francisco Martí Mora 1-B, 22-3, IB 07011, Spain [email protected] ABSTRACT this field, it seems clear that Pythagoras (6th century B.C.) and his Music of the Spheres as well as Kepler’s Harmonices The creation of simulations, sounds and images based on Mundi (1619), represent the crucial starting point of the information related to an object of investigation is currently a relation between occidental music and astrophysics [1]. real tool used in multiple areas to bring the non-specialized Highly influenced by these fundamental works, the animated public closer to scientific achievements and discoveries. Under sonifications of the solar system from Twyman (2010) [2], and this context of multimodal representations and simulations Mark Ballora’s sonifications for the film Rhythms of the developed for educational and informational purposes, this Universe (2013) [3] (a co-production by the ethno- work intends to build a bridge between virtual musical musicologist and percussionist from the mythical band instruments’ development and physical models, using the Grateful Dead and cosmologist George Smoot III from gravitation laws of the seven planets orbiting around the Lawrence Berkeley Labs), can be found. Quinton, M. et al. [4] Trappist-1 star. The following is a case study of an went a step further with their perceptual research on the solar interdisciplinary conversion algorithm design that relates system’s sonifications created for the planetarium Esplora musical software synthesis to exoplanets’ astronomical data - (2016, island of Malta), proposing a planet properties test measured from the observed flux variations in the light curves through sound recognition, realized on both specialized and of their star- and that tries to suggest a systematic and non-specialized audiences. In this sense of probing the reproducible method, useful for any other planetary system or effectiveness of the astronomical data sonification processes, model-based virtual instrument design. As a result, the Virtual the work of Diaz Merced, W. L. (2013) [5], the Supernova Interactive Synthesizer prototype Planethesizer is presented, Sonification [6] and the xSonify prototype project [7], built in whose default configurations display a multimodal Trappist-1, collaboration with NASA, also stand out. Trying to equilibrate Kepler-444 and K2-72 planetary systems simulation. creative freedom and scientific accuracy to the original data sheet, it’s worth mentioning the solar wind data sonifications 1. INTRODUCTION of Alexander, R. et al. (2010) [8]. In a more creative context, Winton et al. [9] developed the The exponential increase in virtual instruments’ development sonifications of stellar data from the Kepler Telescope (2012), and their popularity and establishment as part of the current using Sonification Sandbox software [10] and Matlab’s workflow on audio productions, both in home studios and interpolation functions to explore the aesthetical possibilities professional environments, creates a new opportunity in of direct unprocessed sonifications. Also interesting are the bringing science to the general public and designing audio orchestral character coding sonifications of Quinn, M. for the tools based on physical or mathematical models of undoubted exoplanets and stars information database of the European creative and artistic utility. There are numerous examples of Southern Observatory [11], and the mapping sonification composers who translate models based on nature or science work of Jamie Ferguson in collaboration with ESA From into musical parameters to give their works a formal and Hipparchus to Hipparcos (2014) [12], that translate several structural solidity transcending their own compositional historic star catalogues to sound in a similar way to John intuition. Their kind of approach, in addition to the publication Cage’s Etudes Australes. Finally, it’s impossible not to of the discovery of the seven Earth-like planets orbiting mention Tim Pyle’s Trappist Transits musical representation around the Trappist-1 star in February 2017, inspired the idea (2017) [13], illustrating data from NASA’s Spitzer Telescope of exploring the creation of a model-based virtual instrument. for informational purposes. Developing an interactive astronomical data sonification tool useful in both creative and educational or informational contexts, this work also tries to suggest a possible line of 3. TRAPPIST-1 SYSTEM interdisciplinary audio tools development. The Trappist-1 system is located 39 light years (12 parsecs) 2. ASTRONOMICAL DATA SONIFICATION away from the solar system within the constellation of REFERENCE WORKS Aquarius. It’s formed by a red dwarf star, Trappist-1A, and seven planets named from Trappist-1b to Trappist-1h, as function of their radial distance to the star. In 2015 the In an attempt to make a state-of-the-art review in terms of Transiting Planets and Planetesimals Small Telescope astronomical data sonification and to analyze the technology, (TRAPPIST) monitored the brightness of the star for 245 processes, tools and techniques that are currently involved in hours over 62 nights, from September 17th to December 28th, showing clear transit-like signatures later confirmed as planets This work is licensed under Creative Commons b, c and d [14]. The system was completely identified using Attribution – Non Commercial 4.0 International License. the Trappist telescope, the Spitzer Space Telescope, the Very The full terms of the License are available at Large Telescope, the UKIRT, the Liverpool Telescope and the http://creativecommons.org/licenses/by-nc/4.0/ http://doi.org/10.21785/icad2018.008 219 The 24th International Conference on Auditory Display (ICAD 2018) June 10-15, 2018, Michigan Technological University William Herschel Telescope [15]. The complete system musical interaction. Csound [20] was used in combination discovery was finally published in February 2017 [16]. with Cabbage front end [21] to implement a VST (Virtual Studio Technology) plugin and maximize compatibility with 4. PHOTOMETRIC TRANSIT DETECTION any DAW (Digital Audio Workstation), both on Mac and PC computers. Blender software [22] was used for the graphic The photometric transit detection technique is based on the design of the star. observation of the light flux variations of celestial objects. It The prototype can be downloaded for testing from: basically consists of pointing a telescope at the star and obtaining its light curve, a graphic representation of brightness https://archive.org/details/@agriber flux variations along time. When a planet passes in front of a star, it produces a partial eclipse and the consequent loss of flux perceived can be measured in terms of time and depth. As illustrated in Figure 1, the duration of total eclipse has a direct correspondence with the decrease of energy observed in the light curve and, according to (1), the transit depth is proportional to the surface ratios of the planet and the star, Rp/R*. Figure 2: Planethesizer interface illustrating the axes used in the simulation’s graphic display. Figure 2 shows the prototype interface that allows end- users to control sound properties as a function of the radius, semi-axis, inclination, period and impact factor for the orbit of each planet or synthesizer in astronomical units. To reproduce the eclipse sequence cadence, each planet can be initially Figure 1: Measure of flux variations over a generic delayed introducing time differences expressed in days. Level light curve. Seager & Mallén-Ornelas, 2003. [17] control is allowed for master output, the keyboard’s synthesizer as well as for every planet’s module. The Restart !" button initializes the eclipse sequence and the Init. Delay Off = √∆�, (1) !∗ button deactivates initial delay, allowing the synchronization of the planets for creative purposes. The prototype also Equation (2) gives the orbital inclination of the planet, includes a global tempo, global zoom control and one on/off where a is the orbital radius (assuming circular orbit, Kepler’s button for each planet. Instrument default configuration rd 3 law), and b is the impact parameter which represents the represents a multimodal simulation of the Trappist-1 system. increase of total eclipse duration for orbits close to the star’s Saving and recalling presets is also allowed. equator. It can also be calculated from the light curve using (3). According to the research agenda proposed by Kramer et � = ���,- � !∗ , (2) al. [23], the plugin’s requirements relay on three main axes: / adaptation to the language and needs of the research field, end- user control or interaction and prototype integrability. As 78 5 (-,√∆3)5,6 : (-;√∆3)5 described below, several targets were defined for the prototype: � = 79 , (3) 1 78 -,< 79 • Provide a synchronized multimodal simulation for planetary systems The orbital period of each planet can be calculated • Provide an effective and interactive control for every measuring the time interval between transits. At least three sound parameter expressed in astronomical units transits are needed to obtain conclusive results [18]. • Provide end-users a flexible control of the simulation including global tempo and single planet, keyboard and 5. PLANETHESIZER VST PLUGIN DESIGN master level controls