Probing Pluto’s Paltry Atmosphere Using A Solar Eclipse And Spacecraft

Pluto is so far away from us and so tiny that it’s hard to glean even basic facts about it. What is its tenuous atmosphere made of? And how to observe it during NASA’s New Horizons very brief flyby next July? A recent Johns Hopkins blog post explains how a careful maneuver post-Pluto will let investigators use the Sun to examine the dwarf planet’s true nature.

Investigators will use an instrument called Alice, an ultraviolet spectrometer, to look at the atmosphere around Pluto and its largest moon, Charon. Alice is capable of examining the gases in the atmosphere using a large “airglow” aperture (4 by 4 centimeters) and also using the Sun for observation with a smaller, 1-mm solar occultation channel.

“Once New Horizons flies past Pluto, the trajectory will conveniently (meaning, carefully planned for many years) fly the spacecraft through Pluto’s shadow, creating an effect just like a solar eclipse here on Earth,” wrote Joel Parker, New Horizons co-investigator, in a blog post.

New Horizons
New Horizons spacecraft. Image Credit: NASA

“So we can (and will) just turn the spacecraft around and stare at the Sun, using Alice as it goes behind Pluto to measure how the Sun’s ultraviolet light changes as that light passes through deeper and deeper parts of Pluto’s atmosphere. This technique lets us measure the composition of Pluto‚Äôs atmosphere as a function of altitude.”

And guess where the technique was used not too long ago? Titan! That’s a moon of Saturn full of hydrocarbons and what could be a precursor chemistry to life. The moon is completely socked in with this orange haze that is intriguing. Scientists are still trying to figure out what it is made of — and also, to use our understanding of it to apply to planets outside our solar system.

When a huge exoplanet passes in front of its star, and it’s close enough to Earth, scientists are starting to learn how to ferret out information about its chemistry. This shows them what temperature the atmosphere is like and what it is made of, although it should be emphasized scientists are only starting on this work.

A composite image of Titan's atmosphere, created using blue, green and red spectral filters to create an enhanced-color view.  Image Credit: NASA/JPL/Space Science Institute
A composite image of Titan’s atmosphere, created using blue, green and red spectral filters to create an enhanced-color view. Image Credit: NASA/JPL/Space Science Institute

The goal of performing these transit observations of Titan was to understand how haze on an exoplanet might blur the observations. From four passes with the Cassini spacecraft, the team (led by Tyler Robinson at NASA’s Ames Research Center) found that haze would make it difficult to get information from all but the upper atmosphere.

“An additional finding from the study is that Titan’s hazes more strongly affect shorter wavelengths, or bluer, colors of light,” NASA stated at the time. “Studies of exoplanet spectra have commonly assumed that hazes would affect all colors of light in similar ways. Studying sunsets through Titan’s hazes has revealed that this is not the case.”

The nature of Pluto will better come to light when New Horizons makes its pass by the planet in July 2015. Meanwhile, controllers are counting down the days until the spacecraft emerges from its last hibernation on Saturday (Dec. 6).

Source: Johns Hopkins Applied Physics Laboratory