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OUT OF THIS WORLD | Science Pics of the Week

Science Pics of the Week: The hazy blue sunsets of Pluto


Scott Sutherland
Meteorologist/Science Writer

Friday, October 9, 2015, 2:05 PM -

Lightning flashes under an airglow sky, mysterious ripples speed through an infant star system and New Horizons shows us the hazy blue sunsets of Pluto. It's Science Pics of the Week!

A flash of lightning under a glowing sky

Spend enough time watching the planet as you circle high above it at over 27,000 kph and you see some pretty amazing stuff.

Here's one of the latest views that NASA astronaut Scott Kelly captured as he was pointing his camera out the cupola of the International Space Station on Thursday night.

That vibrant green/orange glow along the horizon is what's known as airglow. It's related to the aurora borealis, in that it's partly caused by charged particles from space striking the upper atmosphere. However, unlike the auroras, which are usually seen closer to the poles and typically only when there's some kind of solar activity happening, airglow occurs on a much more regular basis, it's seen at pretty much any place on Earth to some degree, and it's really only visible when you look at the atmosphere edge-on.

At the same time, though, he snapped his picture at just the right time to also catch a brilliant flash of lightning at the top of a thunderstorm beneath him!

Wow!

Mystery ripples sweep through an infant star system

Speaking of amazing things you can see if you spend enough time looking at space, astronomers used a combination of images from the Hubble Space Telescope and the Very Large Telescope at the European Southern Observatory to watch as giant ripples sped through the planet-forming disk of an infant star system.

What's remarkable about this? It's apparently the very first time they've ever seen anything like it.

WATCH BELOW: Sara Mendes da Costa narrates the account of this incredible new discovery by Hubble and the European Southern Observatory.

What's causing these ripples around AU Microscopii? Are the flares from this young star blasting out immense coronal mass ejections, stirring up the planet-forming disk? Is stellar activity interacting with planets that may be hidden in the disk, stripping off atmosphere and causing these effects?

AU Microscopii is sure to be the focus of many hours of observation moving forward, to dig deeper for clues about this cosmic mystery.

The hazy blue sunsets of Pluto

As NASA's New Horizons spacecraft flew past Pluto in July, it turned its camera back towards the Sun, and snapped back-lit images of the dwarf planet. Sliding various filters in front of the lens, the probe stored images in blue, red and near-infrared light, which were then combined by the team back here on Earth to produce this incredible image:


Colour image of back-lit Pluto. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

"Who would have expected a blue sky in the Kuiper Belt? It's gorgeous," Alan Stern, the New Horizons principal investigator from Southwest Research Institute (SwRI), said in a statement.

Technically, what we're seeing here isn't really a blue sky. Pluto's atmosphere is so thin that if you were standing on the surface looking up, you'd just see the blackness of space above your head. However, just as someone standing on the Moon during a lunar eclipse would see all of Earth's sunsets at once, creating a red glow around the planet, New Horizons is capturing all of Pluto's sunsets at once.

The difference here is that, due to the thin, hazy atmosphere, all of Pluto's sunsets happen to be blue!

According to the John Hopkins University Applied Physics Laboratory:

The haze particles themselves are likely gray or red, but the way they scatter blue light has gotten the attention of the New Horizons science team. “That striking blue tint tells us about the size and composition of the haze particles,” said science team researcher Carly Howett, also of SwRI. “A blue sky often results from scattering of sunlight by very small particles. On Earth, those particles are very tiny nitrogen molecules. On Pluto they appear to be larger — but still relatively small — soot-like particles we call tholins.”
Scientists believe the tholin particles form high in the atmosphere, where ultraviolet sunlight breaks apart and ionizes nitrogen and methane molecules and allows them to react with each other to form more and more complex negatively and positively charged ions. When they recombine, they form very complex macromolecules, a process first found to occur in the upper atmosphere of Saturn’s moon Titan. The more complex molecules continue to combine and grow until they become small particles; volatile gases condense and coat their surfaces with ice frost before they have time to fall through the atmosphere to the surface, where they add to Pluto’s red coloring.

In another discovery announced this week, also involving tholins, scientists with the New Horizons team have located patches of exposed water ice on Pluto's surface.


Patches of water ice spotted by New Horizon's Linear Etalon Imaging Spectral Array (LEISA) instrument. Credit: NASA/JHUAPL/SwRI

The blue in the above image isn't true colour, though. It's a simple highlighting to show where infrared spectroscopy picked up the signal for water ice.

Whereas the tholins in the atmosphere produce the intense blue sunsets around the edges of Pluto's disk, they actually turn these water ice deposits bright red on the surface, as seen in the colour-enhanced view of the same region, below.


A portion of the colour-enhanced Pluto image released on Sept 24, 2015. The regions of brightest red - in crevasses and craters throughout the region - correspond to the locations of water ice, highlighted in blue in the previous image. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

"I’m surprised that this water ice is so red," said Silvia Protopapa, a member of the New Horizons science team from the University of Maryland, College Park. "We don’t yet understand the relationship between water ice and the reddish tholin colourants on Pluto's surface."

Sources: NASA/Scott Kelly | Hubble/ESA/ESO | NASA/JHUAPL

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