Titan and Saturn Moving Through a Technicolor Sky

Back in December of 2016, NASA’s Kepler Space Telescope observed Titan and Saturn moving through its field of view. Over 3.7 days, Kepler watched the system, unblinking, imaging nearly constantly with 30 minute exposures for the entire time.

Compared to most of the targets that Kepler was designed to observe, Saturn and Titan are both pretty bright. Because of this, they saturated the pixels of the camera that they fell on, resulting in bleeding of the charge accumulated by those pixels into their neighbors.

A small team (Sarah Horst, Erin Ryan, and Carly Howett) and I took this data set and endeavored to dig Titan out of the glare of Saturn. No one had observed Titan with this kind of observatory on this kind of timeline before, and we could learn new things about the dynamics of Titan’s extremely complex atmosphere by seeing how much its reflectivity changed over time. We had to invent some new techniques to do this, and they are the subject of a paper we have submitted for peer review.

As part of this process, we had to break down each black-and-white image into where we thought each detected photon came from. Did this one come from Titan, Saturn, the empty sky, or a background star? The methods we put together let us do this surprisingly accurately (we were able to measure Titan’s brightness to a precision of 0.19%, even though up to 60% of the photons striking the camera at Titan’s location actually came from Saturn).

With this kind of photon-tagging, we could now colorize the images depending on where each photon came from. We colored saturated pixels white — they are just blown out and kind of a mess. Unsaturated counts that we ascribe to Titan we color yellow, Saturn we color magenta, and the background stars we color cyan. We mix these layers and produce a false color image highlighting these three components.

This is the result:

Image credit: NASA / A. Parker, 2019.

The images show the slice of sky that the Kepler K2 team recorded in anticipation that Titan and Saturn would move through them. The strip seems to wobble slightly because we have added a slight correction to each frame to track the motion of the spacecraft. Toward the end of the animation, Enceladus peaks out of the saturated light around Saturn for a few frames.

I will post further updates as the status of our submitted paper progresses.