Asteroids

Asteroids are small, rocky objects that orbit the Sun, mostly in the region between Mars and Jupiter called the "asteroid belt". Like planets, asteroids do not produce their own light; we detect them from the sunlight that they reflect. There are millions of asteroids, ranging in size from just a few feet for most, to hundreds of miles across for the largest few. In total, the mass of all the asteroids is less than that of Earth's moon. Most asteroids are irregularly shaped or cratered. Asteroids rotate and tumble as they orbit the Sun, which changes the amount of reflected light we observe from Earth, making them a special type of variable object.

Asteroids can be grouped into three main classes by their composition and spectral measurements. These classes are related to how far away from the Sun they formed, and also the fraction of light that they reflect, or their albedo.

433 Eros

433 Eros, or just Eros, became the first near Earth object ever discovered on August 13th, 1898. Over 100 years later, in late 2000, it was the first asteroid ever orbited and landed upon by a spacecraft (NEAR-Shoemaker). Eros is elongated in shape, with an average diameter of 16.4 kilometers. For reference, that diameter is about three-fourths the length of Manhattan Island in New York City (21.6 km), and close to twice the height of Mount Everest (8.85 km). Eros follows an elliptical orbit around the Sun, which it completes in about 643 days. The closest that Eros gets to Earth in its orbit is about 60 million km.

Below is a sonified video of observations of Eros from a single day, August 30th, 2016. The 242 observations played in the video span a time of just under 5 hours. Each interval of time played in the video corresponds to a minute in real-time, resulting in a video that is 32 seconds long. Because of the high resolution of the observations, the brightness varies smoothly. During the video, the reflected brightness of Eros steadily increases, decreases, and increases again, oscillating between H-magnitude 11.85 and H-magnitude 11.5. The video scans over time (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes.

The next video is the phased light curve for Eros. As its irregular figure tumbles through space, Eros completes one rotation in 5.27 hours, and it varies quite smoothly in brightness during each period. We plot two full phases, corresponding to 10.5 hours on Earth. Each period consists of: primary maximum, minimum, secondary maximum, minimum, then back to primary maximum. The difference between the primary and secondary maxima is quite small - only about 0.01 magnitudes - and may be hard to detect. As you take in this video, imagine Eros tumbling. At first, its entire elongated shape is visible, and it is the brightest it can be. As it rotates, less surface area is visible from Earth, and its brightness declines. And so on. The video scans over phase (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes.

Below is the spectrum for Eros. Eros is an S-type asteroid, meaning that its spectrum indicates a silicate-rich, stony surface. The spectrum peaks at about 7400 angstroms, corresponding to a deep red color, and is relatively smooth, having no strong absorption or emission features. This video scans across a plot of brightness measured in flux or intensity of light (y axis) versus wavelength (x axis), moving from blue to red wavelengths from 4350 to 9000 angstroms. Lower pitch represents weaker flux.

The light curve for Eros was found through the Asteroid Lightcurve Photometry Database (ALCDEF), and the data was taken from Warner 2017 (link).
The spectrum for Eros was found through SMASS: the Small Main-Belt Asteroid Spectroscopic Survey, and more specifically from:
Rivkin, A. S., Binzel, R. P., Sunshine, J., Bus, S. J., Burbine, T. H., and Saxena, A. (2004). "Infrared spectroscopic observations of 69230 Hermes (1937 UB): possible unweathered endmember among ordinary chondrite analogs." Icarus 172, 408-414.