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Space News Update — August 11, 2015 —

Contents

In the News

Story 1:

Dawn Spacecraft at Ceres – New Pictures as Investigations Continue

Story 2:

Comet’s Firework Display Ahead of Perihelion

Story 3:

Kick Back, Look Up, We’re in for a GREAT Perseid Meteor Shower

Departments

The Night Sky

ISS Sighting Opportunities

NASA-TV Highlights

Space Calendar

Food for Thought

Space Image of the Week

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1. Dawn Spacecraft at Ceres – New Pictures as Investigations Continue

Scientists have dubbed this brightly streaked, 4-mile-high (6.4 kilometers) mountain on the dwarf planet Ceres "The

Pyramid.” Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/LPI

NASA has released a new Ceres video tour, which was compiled from images gathered by NASA's orbiting

Dawn spacecraft, scopes out the mysterious bright spots at the bottom of the dwarf planet's 2-mile-deep

(3.2 kilometers) Occator crater and a 4-mile-high (6.4 km) mountain scientists are calling "The Pyramid."

"This mountain is among the tallest features we've seen on Ceres to date," Dawn science team member

Paul Schenk, a geologist at the Lunar and Planetary Institute in Houston, said in a statement. "It's unusual

that it's not associated with a crater. Why is it sitting in the middle of nowhere? We don't know yet, but we

may find out with closer observations."

The Pyramid also has unusual bright streaks running down one side, which are not yet understood. Its 4-

mile height is a revision from researchers' previous estimate of 3 miles (4.8 km).

Ceres' more familiar — but perhaps even more mysterious — bright spots reside inside Occator, a 60-mile-

wide (97 km) crater. Occator only recently received an official name, but scientists have been speculating

on the bright spots' nature and origin since they were first glimpsed in January as Dawn approached the

dwarf planet.

Dawn's measurements of the spots — which appear to be subliming gas to create a mini-atmosphere

within the crater — are so far not consistent with the properties of water ice, researchers said.

"The science team is continuing to evaluate the data and discuss theories about these bright spots at

Occator," Dawn principal investigator Chris Russell, of UCLA, said in the statement. "We are now

comparing the spots with the reflective properties of salt, but we are still puzzled by their source. We look

forward to new, higher-resolution data from the mission's next orbital phase."

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The new animation has vertical relief exaggerated by a factor of five to make it easier to examine the

strange topographies and notice subtle changes, NASA officials said. By examining such an animation,

scientists can get a better idea of how particular features of interest fit into the overall structure of the

dwarf planet.

The $466 million Dawn mission launched in September 2007 to study Ceres and Vesta, the two largest

objects in the asteroid belt. The probe orbited Vesta from July 2011 through September 2012, and it

arrived in orbit around the 584-mile-wide (940 km) Ceres this past March.

Dawn is currently spiraling down to its third science orbit around Ceres, which lies about 900 miles (1,500

km) above the dwarf planet's surface. The probe should reach that orbit by mid-August, when it will

resume its observations of Ceres, NASA officials said. (Dawn's previous science orbit featured an altitude of

2,700 miles, or 4,400 km.)

"There are many other features that we are interested in studying further," Dawn science team member

David O'Brien, senior scientist at the Planetary Science Institute in Arizona, said in the statement. "These

include a pair of large impact basins called Urvara and Yalode in the southern hemisphere, which have

numerous cracks extending away from them, and the large impact basin Kerwan, whose center is just

south of the equator."

The intriguing brightest spots on Ceres lie in a crater named Occator, which is about 60 miles (90 kilometers) across and

2 miles (4 kilometers) deep. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/LPI

Link to the NASA video: http://www.nasa.gov/jpl/dawn/cruise-over-ceres-in-new-video

Source: NASA and Space.com Return to Contents

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2. Comet’s Firework Display Ahead of Perihelion

Outburst in action

In the approach to perihelion over the past few weeks, Rosetta has been witnessing growing activity from Comet

67P/Churyumov–Gerasimenko, with one dramatic outburst event proving so powerful that it even pushed away the

incoming solar wind.

The comet reaches perihelion this Thursday, the moment in its 6.5-year orbit when it is closest to the Sun. In recent

months, the increasing solar energy has been warming the comet’s frozen ices, turning them to gas, which pours

out into space, dragging dust along with it.

The period around perihelion is scientifically very important, as the intensity of the sunlight increases and parts of

the comet previously cast in years of darkness are flooded with sunlight. Although the comet’s general activity is

expected to peak in the weeks following perihelion, much as the hottest days of summer usually come after the

longest days, sudden and unpredictable outbursts can occur at any time – as already seen earlier in the mission.

On 29 July, Rosetta observed the most dramatic outburst yet, registered by several of its instruments from their

vantage point 186 km from the comet. They imaged the outburst erupting from the nucleus, witnessed a change in

the structure and composition of the gaseous coma environment surrounding Rosetta, and detected increased levels

of dust impacts.

Perhaps most surprisingly, Rosetta found that the outburst had pushed away the solar wind magnetic field from

around the nucleus.

A sequence of images taken by Rosetta’s scientific camera OSIRIS show the sudden onset of a well-defined jet-like

feature emerging from the side of the comet’s neck, in the Anuket region. It was first seen in an image taken at

13:24 GMT, but not in an image taken 18 minutes earlier, and has faded significantly in an image captured 18

minutes later. The camera team estimates the material in the jet to be travelling at 10 m/s at least, and perhaps

much faster.

“This is the brightest jet we’ve seen so far,” comments Carsten Güttler, OSIRIS team member at the Max Planck

Institute for Solar System Research in Göttingen, Germany. “Usually, the jets are quite faint compared to the

nucleus and we need to stretch the contrast of the images to make them visible – but this one is brighter than the

nucleus.”

Soon afterwards, the comet pressure sensor of ROSINA detected clear indications of changes in the structure of the

coma, while its mass spectrometer recorded changes in the composition of outpouring gases. For example,

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compared to measurements made two days earlier, the amount of carbon dioxide increased by a factor of two,

methane by four, and hydrogen sulphide by seven, while the amount of water stayed almost constant.

“This first ‘quick look’ at our measurements after the outburst is fascinating,” says Kathrin Altwegg, ROSINA

principal investigator at the University of Bern. “We also see hints of heavy organic material after the outburst that

might be related to the ejected dust. But while it is tempting to think that we are detecting material that may have

been freed from beneath the comet's surface, it is too early to say for certain that this is the case.”

Meanwhile, about 14 hours after the outburst, GIADA was detecting dust hits at rates of 30 per day, compared with

just 1–3 per day earlier in July. A peak of 70 hits was recorded in one 4-hour period on 1 August, indicating that the

outburst continued to have a significant effect on the dust environment for the following few days.

“It was not only the abundance of the particles, but also their speeds measured by GIADA that told us something

‘different’ was happening: the average particle speed increased from 8 m/s to about 20 m/s, with peaks at 30 m/s –

it was quite a dust party!” says Alessandra Rotundi, principal investigator at the ‘Parthenope’ University of Naples,

Italy.

Perhaps the most striking result is that the outburst was so intense that it actually managed to push the solar wind

away from the nucleus for a few minutes – a unique observation made by the Rosetta Plasma Consortium’s

magnetometer.

The solar wind is the constant stream of electrically charged particles that flows out from the Sun, carrying its

magnetic field out into the Solar System. Earlier measurements made by Rosetta and Philae had already shown that

the comet is not magnetized, so the only source for the magnetic field measured around it is the solar wind. But it

doesn’t flow past unimpeded. Because the comet is spewing out gas, the incoming solar wind is slowed to a

standstill where it encounters that gas and a pressure balance is reached.

“The solar wind magnetic field starts to pile up, like a traffic jam, and eventually stops moving towards the comet

nucleus, creating a magnetic field-free region on the Sun-facing side of the comet called a ‘diamagnetic cavity’,”

explains Charlotte Götz, magnetometer team member at the Institute for Geophysics and extraterrestrial Physics in

Braunschweig, Germany.

Diamagnetic cavities provide fundamental information on how a comet interacts with the solar wind, but the only

previous detection of one associated with a comet was made at about 4000 km from Comet Halley as ESA’s Giotto

flew past in 1986.

Rosetta’s comet is much less active than Halley, so scientists expected to find a much smaller cavity around it, up to

a few tens of kilometres at most, and prior to 29 July, had not observed any sign of one.

But, following the outburst on that day, the magnetometer detected a diamagnetic cavity extending out at least 186

km from the nucleus. This was likely created by the outburst of gas, which increased the neutral gas flux in the

comet’s coma, forcing the solar wind to ‘stop’ further away from the comet and thus pushing the cavity boundary

outwards beyond where Rosetta was flying at the time.

"Finding a magnetic field-free region anyway in the Solar System is really hard, but here we've had it served to us

on a silver platter – this is a really exciting result for us," adds Charlotte.

“We’ve been moving Rosetta out to distances of up to 300 km in recent weeks to avoid problems with navigation

caused by dust, and we had considered that the diamagnetic cavity was out of our grasp for the time being. But it

seems that the comet has helped us by bringing the cavity to Rosetta,” says Matt Taylor, Rosetta Project Scientist.

Source: ESA Return to Contents

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3. Kick Back, Look Up, We’re in for a GREAT Perseid Meteor Shower

The Perseids appear to radiate from spot below the W of Cassiopeia in the constellation Perseus, hence the shower’s

name. This map shows the sky facing northeast around 12:30 a.m. local time August 13. Source: Stellarium

Every year in mid-August, Earth plows headlong into the debris left behind by Comet 109P/Swift-Tuttle.

Slamming into our atmosphere at 130,000 mph, the crumbles flash to light as the Perseid meteor shower. One

of the world’s most beloved cosmic spectacles, this year’s show promises to be a real crowd pleaser.

Not only will the Moon be absent, but the shower maximum happens around 3 a.m. CDT (8 UT) August 13 —

early morning hours across North America when the Perseid radiant is highest. How many meteors will you

see? Somewhere in the neighborhood of 50-100 meteors per hour. As always, the darker and less light

polluted your observing site, the more zips and zaps you’ll see.

Find a place where there’s as few stray lights as possible, the better to allow your eyes to dark-adapt. Comfort

is also key. Meteor showers are best enjoyed in a reclining position with as little neck craning as possible. Lie

back on a folding lawn chair with your favorite pillow and bring a blanket to stay warm. August nights can

bring chill and dew; a light coat and hat will make your that much more comfortable especially if you’re out for

an hour or more.

I’m always asked what’s the best direction to face. Shower meteors will show up in every corner of the sky,

but can all be traced backwards to a point in Perseus called the radiant. That’s the direction from which they

all appear to stream out of like bats flying out of a cave.

Another way to picture the radiant it is to imagine driving through a snowstorm at night. As you accelerate,

you’ll notice that the flakes appear to radiate from a point directly in front of you, while the snow off to the

sides streams away in long trails. If you’re driving at a moderate rate of speed, the snow flies past on nearly

parallel paths that appear to focus in the distance the same way parallel railroad tracks converge.

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Now replace your car with the moving Earth and comet debris for snow and you’ve got a radiant and a meteor

shower. With two caveats. We’re traveling at 18 1/2 miles per second and our “windshield”, the atmosphere, is

more porous. Snow bounces off a car windshield, but when a bit of cosmic debris strikes the atmosphere, it

vaporizes in a flash. We often think friction causes the glow of meteors, but they’re heated more by ram

pressure.

The incoming bit of ice or rock rapidly compresses and heats the air in front of it, which causes the particle to

vaporize around 3,000°F (1,650°C). The meteor or bright streak we see is really a hollow “tube” of glowing or

ionized air molecules created by the tiny rock as its energy of motion is transferred to the surrounding air

molecules. Just as quickly, the molecules return to their rest state and release that energy as a spear of light

we call a meteor.

Imagine. All it takes is something the size of a grain of sand to make us look up and yell “Wow!”

Speaking of size, most meteor shower particles range in size from a small pebble to beach sand and generally

weigh less than 1-2 grams or about what a paperclip weighs. Larger chunks light up as fireballs that shine as

bright as Venus or better. Because of their swiftness, Perseids are generally white and often leave chalk-like

trails called trains in their wakes.

This year’s shower is special in another way. According to Sky and Telescope magazine, meteor stream

modeler Jeremie Vaubaillon predicts a bump in the number of Perseids around 1:39 p.m. (18:39 UT) as Earth

encounters a debris trail shed by the Comet Swift-Tuttle back in 1862. The time favors observers in Asia where

the sky will be dark. It should be interesting to see if the prediction holds.

How To Watch

Already the shower’s active. Go out any night through about the 15th and you’ll see at least at least a handful

of Perseids an hour. At nightfall on the peak night of August 12-13, you may see only 20-30 meteors an hour

because the radiant is still low in the sky. But these early hours give us the opportunity to catch an earthgrazer

— a long, very slow-moving meteor that skims the atmosphere at a shallow angle, crossing half the sky or

more before finally fading out.

I’ve only seen one good earth-grazer in my earthly tenure, but I’ll never forget the sight. Ambling from low in

the northeastern sky all the way past the southern meridian, it remained visible long enough to catch it in my

telescope AND set up a camera and capture at least part of its trail!

The later you stay up, the higher the radiant rises and the more meteors you’ll see. Peak activity of 50-100

meteors per hour will occur between about 2-4 a.m. No need to stare at the radiant to see meteors. You can

look directly up at the darkest part of the sky or face east or southeast and look halfway up if you like. You’re

going to see meteors everywhere. Some will arrive as singles, others in short burst of 2, 3, 4 or more. I like to

face southeast with the radiant off to one side. That way I can see a mix of short-trailed meteors from near

the radiant and longer, graceful streaks further away just like the snow photo shows.

If there’s a lull in activity, don’t think it’s over. Meteor showers have strange rhythms of their own. Five

minutes of nothing can be followed by multiple hits or even a fireball. Get into the feel of the shower as you

sense spaceship Earth speeding through the comet’s dusty orbit. Embrace the chill of the August night under

the starry vacuum.

(NASA TV will broadcast a live program about this year’s Perseid meteor shower from 10 p.m. EDT

Wednesday, Aug. 12 to 2 a.m. Thursday, Aug. 13. Anyone can join in the conversation by tweeting questions

to @NASA_Marshall with the hashtag #askNASA.)

Source: UniverseToday Return to Contents

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The Night Sky

Source: Sky and Telescope Return to Contents

Tuesday, August 11

The red long-period variable star Chi Cygni is

near maximum! As of August 7th it was

reported at magnitude 4.5. See the article

and comparison-star chart in the August Sky

& Telescope, page 51.

Wednesday, August 12

The Perseid meteor shower should be at its

peak late tonight, ideally so for North

America. And there's no moonlight. Bundle up

warmly (it gets cold under a clear, open

August sky late at night), and lie back in a

reclining lawn chair. You may see about a

meteor a minute on average. The later you

watch the better. See Plan for the Perseids!

More is in the August Sky & Telescope, page

48.

Thursday, August 13

These moonless August nights are prime

Milky Way time. After dark, the Milky Way is a

great, mottled glowing band running from

Sagittarius in the south up and left across

Aquila and through the big Summer Triangle

very high in the east, then on down through

Cassiopeia to Perseus low in the north-

northeast.

Friday, August 14

• This is the time of year when the Teapot asterism of Sagittarius stands highest in the south soon

after dark. The Teapot is about the size of your fist at arm's length. It's tipping and pouring to the

right, from its triangular spout.

Saturday, August 15

• Spot Saturn in the southwest after dark. The brightest star left or lower left of it is orange Antares.

Draw a line from Antares through Saturn, extend the line almost as much farther on, and you hit

fainter Beta Librae (Zubeneschamali). Much farther on, you come to Arcturus.

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ISS Sighting Opportunities (from Denver)

Date Visible Max Height Appears Disappears

Tue Aug 11, 8:56 PM 1 min 10° 10 above N 10 above NNE

Tue Aug 11, 10:32 PM 1 min 20° 14 above NNW 20 above N

Wed Aug 12, 9:39 PM 3 min 15° 11 above NNW 13 above NE

Wed Aug 12, 11:15 PM < 1 min 13° 13 above NW 13 above NW

Thu Aug 13, 8:46 PM 2 min 12° 10 above N 10 above NNE

Thu Aug 13, 10:23 PM < 1 min 29° 21 above NNW 29 above N

Fri Aug 14, 9:29 PM 3 min 23° 15 above NNW 20 above NE

Fri Aug 14, 11:04 PM < 1 min 10° 10 above WNW 10 above WNW

Sighting information for other cities can be found at NASA’s Satellite Sighting Information

NASA-TV Highlights (all times Eastern Time Zone)

Tuesday, August 11

2 p.m. - Replay of the ISS Expedition 45/Visiting Crew News Conference at Star City, Russia (recorded

August 10) (all channels)

2:30 p.m. - Video File of the Expedition 45/Visiting Crew’s Ceremonial Visit to the Gagarin Museum in

Star City, Russia and their Visit to Red Square and the Kremlin in Moscow (starts at 2:45 p.m.) (all

channels)

Wednesday, August 12

10 p.m. - Live Coverage of 2015 Perseid Meteor Shower (all channels)

Thursday, August 13

9 a.m., - Educational Event with Scott Kelly and Kjell Lindgren (all channels)

11 a.m. - NASA RS-25 Test Social (NTV-1 (Public), NTV-2 (Education))

4:30 p.m. - Live Coverage of NASA’s RS-25 Engine Test (all channels)

Friday, August 14

6 a.m. - ISS Progress 58 Undocking Coverage (Undocking scheduled at 6:19 a.m. ET) (all channels)

Watch NASA TV online by going to the NASA website. Return to Contents

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Space Calendar

Aug 11 - Apollo Asteroid 2011 QG21 Near-Earth Flyby (0.052 AU)

Aug 11 - Asteroid 4999 MPC Closest Approach To Earth (2.127 AU)

Aug 11 - Asteroid 1940 Whipple Closest Approach To Earth (2.163 AU)

Aug 11 - 40th Anniversary (1975), Acapulco Meteorite Fall in Mexico

Aug 12 - Perseids Meteor Shower Peak

Aug 12 - Comet 51P-A/Harrington Perihelion (1.699 AU)

Aug 12 - Comet 51P/Harrington Perihelion (1.700 AU)

Aug 12 - Comet 297P/Beshore At Opposition (2.080 AU)

Aug 12 - Comet P/2007 T6 (Catalina) At Opposition (3.360 AU)

Aug 12 - Apollo Asteroid 2004 AS1 Near-Earth Flyby (0.078 AU)

Aug 12 - Asteroid 6600 Qwerty Closest Approach To Earth (1.076 AU)

Aug 12 - Asteroid 11365 NASA Closest Approach To Earth (1.156 AU)

Aug 12 - 55th Anniversary (1960), Echo 1 Launch

Aug 13 - Comet 67P/Churyumov-Gerasimenko Perihelion (1.243 AU)

Aug 13 - Asteroid 701 Oriola Occults HIP 105412 (6.0 Magnitude Star)

Aug 13 - Apollo Asteroid 2011 AK5 Near-Earth Flyby (0.071 AU)

Aug 13 - Apollo Asteroid 232691 (2004 AR1) Near-Earth Flyby (0.075 AU)

Aug 13 - Apollo Asteroid 3752 Camillo Closest Approach To Earth (1.089 AU)

Aug 13 - Asteroid 9133 d'Arrest Closest Approach To Earth (1.297 AU)

Aug 13 - Rasmus Bartholin's 390th Birthday (1625)

Aug 14 - Cassini, Orbital Trim Maneuver #418 (OTM-418)

Aug 14 - Comet C/2013 US10 (Catalina) Closest Approach To Earth (1.089 AU)

Aug 14 - Comet 104P/Kowal At Opposition (1.648 AU)

Aug 14 - Comet 190P/Mueller Closest Approach To Earth (1.839 AU)

Aug 14 - Asteroid 21 Lutetia At Opposition (9.0 Magnitude)

Aug 14 - Atira Asteroid 2010 XB11 Closest Approach To Earth (0.744 AU)

Aug 14 - Asteroid 2848 ASP Closest Approach To Earth (1.918 AU)

Aug 14 - Asteroid 41488 Sinbad Closest Approach To Earth (3.387 AU)

Aug 15 - Comet 325P/Yang-Gao Perihelion (1.431 AU)

Aug 15 - Comet 162P/Siding Spring Closest Approach To Earth (1.690 AU)

Aug 15 - Comet C/2011 KP36 (Spacewatch) At Opposition (4.308 AU)

Aug 15 - Asteroid 5870 Baltimore Closest Approach To Earth (1.967 AU)

Aug 15 - Asteroid 2483 Guinevere Closest Approach To Earth (3.240 AU)

Aug 15 - 45th Anniversary (1970), Comet 82P/Gehrels Near-Jupiter Flyby (0.00143 AU)

Source: JPL Space Calendar Return to Contents

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Food for Thought

Atmospheric Escape and Flowing N2 Ice Glaciers – What Resupplies Pluto’s Nitrogen? – by SwRI Researcher Kelsi Singer

Backlit by the sun, Pluto’s atmosphere rings its silhouette like a luminous halo in this image taken by NASA’s New

Horizons spacecraft. Image Credit: NASA/JHUAPL/SwRI

Hi, I’m Kelsi Singer, a postdoctoral researcher at the Southwest Research Institute, working on NASA’s New

Horizons mission and specializing in geology and geophysics. One of my areas of expertise is impact cratering. That

subject may not seem related to Pluto’s atmosphere or nitrogen at first, but let me tell you about research that New

Horizons principal investigator Alan Stern and I conducted and published as a prediction paper before the flyby of

Pluto.

New Horizons has returned striking images of both Pluto’s surface and its atmosphere. Pluto’s atmosphere is similar

to Earth’s in that it is predominantly composed of nitrogen (N). But Pluto’s atmosphere is ~98% N, while Earth’s is

only ~78% N. Pluto’s atmosphere is also considerably thinner than Earth’s with ~10,000 times lower pressure at

the surface.

The nitrogen in Pluto’s atmosphere (in the form of N2 gas) is actually flowing away and escaping the planet at an

estimated rate of hundreds of tons per hour. We also see what looks like flowing ice on Pluto’s surface in high

resolution images made by New Horizons. The water ice (H2O) that we are familiar with on Earth would be

completely rigid and stiff at Pluto’s surface temperatures, but ice made out of N2 would be able to flow like a

glacier.

So where does all of this nitrogen come from?

One possibility we tested was that cometary impactors could be delivering the necessary material. We explored

several different ways that impacts from comets could bring nitrogen to the surface and atmosphere of Pluto and

resupply the escaping nitrogen:

1) Could comets hitting Pluto directly deliver enough N to Pluto’s surface and atmosphere?

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2) Could these comets excavate or expose enough N2 ice from the near-surface layers on Pluto by forming impact

craters?

—> The short answer is that none of these cratering effects seem like they could supply enough nitrogen.

In our prediction paper, we suggested the next most likely suspect for supplying this N is heat and geologic activity

inside Pluto itself. This activity could process nitrogen out of Pluto’s rocky interior and get it to the surface. We

currently have only a tiny fraction of the data back from the New Horizons flyby, but the fact that there are young-

looking areas on Pluto hints at relatively recent geologic activity.

Stay tuned as we get more data back from the New Horizons spacecraft over the coming months, which will refine

our estimates of Pluto’s atmospheric escape and provide more images of Pluto’s surface to assess the types and

timing of geologic activity.

Source: NASA New Horizons Blog Return to Contents

There has been quite a bit of buzz about dwarf planets lately. Ever since the discovery of Eris in 2005, and the

debate that followed over the proper definition of the word “planet”, this term has been adopted to refer to planets

beyond Neptune that rival Pluto in size. Needless to say, it has been a controversial subject, and one which is not

likely to be resolved anytime soon.

In the meantime, the category has been used tentatively to describe many Trans-Neptunian objects that were

discovered before or since the discovery of Eris. Sedna, which was discovered in the outer reaches of the Solar

System in 2003, is most likely a dwarf planet. And as the furthest known object from the Sun, and located within

the hypothetical Oort Cloud, it is quite the fascinating find.

To be a dwarf planet, a celestial body must be in hydrostatic equilibrium – meaning that it is symmetrically rounded

into a spheroid or ellipsoid shape. With a surface albedo of 0.32 ± 0.06 – and an estimated diameter of between

915 and 1800 km (compared to Pluto’s 1186 km) – Sedna is bright enough, and also large enough, to be spheroid

in shape.

Source: UniverseToday Return to Contents

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Space Image of the Week

Hubble Finds a Little Gem

Image credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt

Text credit: European Space Agency

Explanation: This colorful bubble is a planetary nebula called NGC 6818, also known as the Little Gem Nebula. It is located in the constellation of Sagittarius (The Archer), roughly 6,000 light-years away from us. The rich glow of the cloud is just over half a light-year across — humongous compared to its tiny central star — but still a little gem on a cosmic scale.

When stars like the sun enter "retirement," they shed their outer layers into space to create glowing clouds of gas called planetary nebulae. This ejection of mass is uneven, and planetary nebulae can have very complex shapes. NGC 6818 shows knotty filament-like structures and distinct layers of material, with a bright and enclosed central bubble surrounded by a larger, more diffuse cloud.

Scientists believe that the stellar wind from the central star propels the outflowing material, sculpting the elongated shape of NGC 6818. As this fast wind smashes through the slower-moving cloud it creates particularly bright blowouts at the bubble’s outer layers.

Source: NASA Return to Contents