October 20, 2019

Astronomy Video of the Week: Alice Sees Pluto Occult the Sun

Welcome to Pluto!

Image credit: NASA/JHU APL/SwRI

It was a crazy wild ride last week, as NASA’s New Horizons spacecraft whizzed through the Pluto system in a historic encounter. We did’t get much work done last Tuesday, that’s for sure. But among the stunning images of Pluto and its moons and amazing close-up flyby sequences, another fascinating observation was made, that we feel is worth mentioning here today.

After the flyby, New Horizons passed briefly through the shadows of both Pluto and its large moon, Charon. This sort of trajectory needle-threading from 32 Astronomical Units (A.U.s) away is amazing enough.

As it did so, New Horizons turned back facing Pluto and recorded the most distant solar eclipse ever:

The eclipse/occultation was ‘observed’ by New Horizons’ Alice ultraviolet imaging spectrometer. What you’re seeing in the short video above is a simulation on the left, versus the drop in the count rate observed by Alice on the right. The measurements were conducted to probe the tenuous atmosphere of Pluto, which is thought to extend and merge with that of nearby Charon at 12,160 miles (19,570 kilometres) distant.

Alice also listened for radio signals sent to it from Earth via the Deep Space Network to carrying out a similar radio occultation experiment. The results from this and the Charon occultation are forthcoming.

The model seen for Pluto’s atmosphere by Alice sits somewhere between the ‘turbulent’ and ‘stagnant’ scenarios, though closer to the stagnant end of the spectrum.

An amazing observation by an amazing mission!

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