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Space News Update — September 20, 2019 —

Contents

In the News

Story 1: Comet's collapsing cliffs and bouncing boulders

Story 2:

A Distant Asteroid Collision Gave Earthly Biodiversity An Ancient Boost

Story 3: Hayabusa 2 completes practice run for deployment of last asteroid lander

Departments

The Night Sky

ISS Sighting Opportunities

Space Calendar

NASA-TV Highlights

Food for Thought

Space Image of the Week

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1. Comet's collapsing cliffs and bouncing boulders

Scientists analyzing the treasure trove of images taken by ESA's Rosetta mission have turned up more evidence for curious bouncing boulders and dramatic cliff collapses.

Rosetta operated at Comet 67P/Churyumov-Gerasimenko between August 2014 and September 2016, collecting data on the comet's dust, gas and plasma environment, its surface characteristics and its interior structure.

As part of the analysis of some 76 000 high-resolution imagescaptured with its OSIRIS camera, scientists have been looking for surface changes. In particular, they are interested in comparing the period of the comet's closest approach to the Sun—known as perihelion—with that after this most active phase, to better understand the processes that drive surface evolution.

Loose debris is seen all over the comet, but sometimes bouldershave been caught in the act of being ejected into space, or rolling across the surface. A new example of a bouncing boulder was recently identified in the smooth neck region that connects the comet's two lobes, an area that underwent a lot of noticeable large-scale surface changes over the course of the mission. There, a boulder about 10 m-wide has apparently fallen from the nearby cliff, and bounced several times across the surface without breaking, leaving "footprints" in the loosely consolidated surface material.

"We think it fell from the nearby 50 m-high cliff, and is the largest fragment in this landslide, with a mass of about 230 tonnes," said Jean-Baptiste Vincent of the DLR Institute for Planetary Research, who presented the results at the EPSC-DPS conference in Geneva today.

"So much happened on this comet between May and December 2015 when it was most active, but unfortunately because of this activity we had to keep Rosetta at a safe distance. As such we don't have a close

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enough view to see illuminated surfaces with enough resolution to exactly pinpoint the 'before' location of the boulder."

Studying boulder movements like these in different parts of the comet helps determine the mechanical properties of both the falling material, and the surface terrain on which it lands. The comet's material is in general very weak compared with the ice and rocks we are familiar with on Earth: boulders on Comet 67P/C-G are around one hundred times weaker than freshly packed snow.

Another type of change has also been witnessed in several locations around the comet: the collapse of cliff faces along lines of weakness, such as the dramatic capture of the fall of a 70 m-wide segment of the Aswan cliff observed in July 2015. But Ramy El-Maarry and Graham Driver of Birkbeck, University of London, may have found an even larger collapse event, linked to a bright outburst seen on 12 September 2015 along the northern-southern hemisphere divide.

"This seems to be one of the largest cliff collapses we've seen on the comet during Rosetta's lifetime, with an area of about 2000 square meters collapsing," said Ramy, also speaking at EPSC-DPS today.

During perihelion passage, the southern hemisphere of the comet was subjected to high solar input, resulting in increased levels of activity and more intensive erosion than elsewhere on the comet.

"Inspection of before and after images allow us to ascertain that the scarp was intact up until at least May 2015, for when we still have high enough resolution images in that region to see it," says Graham, an undergraduate student working with Ramy to investigate Rosetta's vast image archive.

"The location in this particularly active region increases the likelihood that the collapsing event is linked to the outburst that occurred in September 2015."

Looking in detail at the debris around the collapsed region suggests that other large erosion events have happened here in the past. Ramy and Graham found that the debris includes blocks of variable size ranging up to tens of meters, substantially larger than the boulder population following the Aswan cliff collapse, which is mainly comprised of boulders a few meters diameter.

"This variability in the size distribution of the fallen debris suggests either differences in the strength of the comet's layered materials, and/or varying mechanisms of cliff collapse," adds Ramy.

Studying comet changes like these not only gives insight into the dynamic nature of these small bodies on short timescales, but the larger scale cliff collapses provide unique views into the internal structure of the comet, helping to piece together the comet's evolution over longer timescales.

"Rosetta's datasets continue to surprise us, and it's wonderful the next generation of students are already making exciting discoveries," adds Matt Taylor, ESA's Rosetta project scientist.

Source: Phys.org Return to Contents

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2. A Distant Asteroid Collision Gave Earthly Biodiversity An Ancient Boost

About 466 million years ago, there was an asteroid collision in the asteroid belt between Mars and Jupiter. The collision caused the breakup of a major asteroid, creating a shower of dust throughout the inner Solar System. That event is called the Ordovician Meteor Event, and its dust caused an ice age here on Earth.

That ice age contributed to an enormous boost in biodiversity on ancient Earth.

In recent decades, scientists have uncovered evidence showing how different events in space shaped life on Earth. The most well-known of these is the Chicxulub impact that brought the reign of the dinosaurs to an end some 66 million years ago. But there have been other events in space that

affected life on Earth, including a supernova that exploded about 2.6 million years ago that may have wiped out large ocean animals, and another supernova that exploded about 41,000 years ago and that may have helped wipe out the mammoths.

But in this case, the asteroid-dust ice age may have helped life on Earth rather than hindered it.

Scientists have known about the Ordovician Meteor Event (OME) for some time now. They know it was an L-chondrite asteroid because they can see its dusty residue in Earth’s stratified layers. In fact, the breakup of that 150 km. diameter ancient asteroid 467 million years ago still delivers almost a third of all the meteorites that strike Earth. That event was no trivial matter; it’s the largest asteroid breakup that we know of in the last 3 billion years.

Something else happened on Earth about 466 million years ago: the mid-Ordovician Ice Age. The climate was homogeneous before that, the same from pole to pole. But when the ice age came, the seas froze at the poles and the equatorial regions were much warmer than the polar regions. The different climatic regions spurred greater evolution of species, bringing about a boom in biodiversity.

But linking the Ordovician Meteor Event to the mid-Ordovician ice age has been controversial.

According to a new study titled “An extraterrestrial trigger for the mid-Ordovician ice age: Dust from the breakup of the L-chondrite parent body” the causal link between the OME and the ice age is now much stronger. The study was published in the journal Science Advances.

The authors of the study come from a variety of institutions around the world, including Lund University in Sweden. Their work focuses on sea-floor sediment data that came from the time of the Ordovician Meteor Event. The authors say that after the OME, there was an increase of three to four orders of magnitude in fine-grained material falling to Earth.

The amount of material falling to Earth had to have matched the amount blanketing the inner Solar System. “Extraordinary amounts of dust in the entire inner solar system during >2 Ma following the L-chondrite breakup cooled Earth and triggered Ordovician icehouse conditions, sea level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event,” the paper says.

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“Normally, Earth gains about 40,000 tons of extraterrestrial material every year,” says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and one of the paper’s authors. “Imagine multiplying that by a factor of a thousand or ten thousand.”

“Our hypothesis is that the large amounts of extraterrestrial dust over a time-frame of at least two million years played an important role in changing the climate on Earth, contributing to cooling,” says Heck.

“Our results show for the first time that such dust, at times, has cooled Earth dramatically,” says Birger Schmitz of Sweden’s Lund University, the study’s lead author and a research associate at the Field Museum. “Our studies can give a more detailed, empirical-based understanding of how this works, and this in turn can be used to evaluate if model simulations are realistic.”

The scientists focused on 466 million year old sedimentary sea rocks from the same time as the OME. They looked for traces of space dust, then compared it to tiny micrometeorites from Antarctica for comparison. “We studied extraterrestrial matter, meteorites and micrometeorites, in the sedimentary record of Earth, meaning rocks that were once sea floor,” says Heck. “And then we extracted the extraterrestrial matter to discover what it was and where it came from.”

They used acid to eat away the rock, leaving only the space dust behind. Then they analyzed the chemical makeup of the dust. They looked for evidence of extraterrestrial origin in the form of He3, an isotope of helium that comes from the Sun but is absent on Earth. Finding these isotopes and other rare minerals that come from space, like chromites, prove the dust is extraterrestrial in origin.

The authors of this study are the first to show that the mid-Ordovician ice age is linked to the Ordovician Meteor Event. “The timing appears to be perfect,” he says. The dust from the OME would have blocked out sunlight, triggering global cooling and the ice age.

But this ice age wasn’t catastrophic for life on Earth. Quite the opposite. All this dust settle to Earth over a two million year period, meaning the cooling was gradual, not catastrophic. As a result, life had a chance to adapt. That adaptation led to a boom in new life forms, as species adapted to new climate conditions. That boom is called the Great Ordovician Biodiversification Event (GOBE.)

Heck is quick to caution people against drawing false conclusions. Just because this type of climate change led to greater biodiversity, it doesn’t mean we can take climate change lightly.

“In the global cooling we studied, we’re talking about timescales of millions of years,” said Heck. “It’s very different from the climate change caused by the meteorite 65 million years ago that killed the dinosaurs, and it’s different from the global warming today–this global cooling was a gentle nudge. There was less stress.”

If this gradual cooling sounds like a solution we could implement to limit global climate change, Heck throws cold water on that idea, too. “Geoengineering proposals should be evaluated very critically and very carefully, because if something goes wrong, things could become worse than before.”

Source: Universe Today Return to Contents

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3. Hayabusa 2 completes practice run for deployment of last asteroid lander

Japan’s Hayabusa 2 spacecraft deployed two target markers Monday above asteroid Ryugu in a rehearsal for the release of the mission’s final landing robot next month.

The robotic asteroid explorer released the two 4-inch (10-centimeter) ball-shaped markers seven minutes apart Monday, after the Hayabusa 2 spacecraft descended to a distance of about 3,300 feet (1 kilometer) from Ryugu.

The Japan Aerospace Exploration Agency, or JAXA, released a pair of images showing the target markers, each covered in a reflective film, after their release from Hayabusa 2. The target markers are unpowered and entirely passive objects designed as navigation aids for Hayabusa 2 around the asteroid.

With both target markers away, Hayabusa 2 fired its thrusters to begin an ascent back to a home position farther from the asteroid. Ground teams are in the final stages of planning another descent toward Ryugu in October, during which Hayabusa 2 will deploy the last of four landing robots to the asteroid’s surface.

“We released two target markers from an altitude of about 1 kilometer, and these images were just released,” said Makoto Yoshikawa, Hayabusa 2’s mission manager at JAXA. “The purpose of this release is a rehearsal of the release of the MINERVA-II-2 small rover next month.”

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Hayabusa 2’s cameras will track the movement of the two navigation aids as they fly in space around Ryugu over the next several days. Scientists expect Ryugu’s tenuous gravity will pull the target markers to the asteroid’s surface within a week.

“We can observe the target marker’s orbit around Ryugu and we can then determine the gravity field of Ryugu in detail, so this is a new operation,” Yoshikawa said Tuesday in a press briefing at the European Planetary Science Congress.

Hayabusa 2 is in the final phase of its science campaign at asteroid Ryugu, where it arrived in June 2018 after a three-and-a-half year journey from Earth. The spacecraft has conducted two touch-and-go landings on Ryugu — one in February and another in July — to gather pristine asteroid samples for return to Earth.

Last year, Hayabusa 2 deployed three mobile landers to hop around Ryugu. Two MINERVA-II landers, developed in Japan, and a larger robot named MASCOT managed by the German and French space agencies beamed back images and scientific data from Ryugu’s surface.

One more lander remains in Hayabusa 2’s toolkit.

The MINERVA-II-2 mobile lander was developed by a consortium of Japanese universities as a piggyback payload for Hayabusa 2. The robot is smaller than a soccer ball, but carries mechanisms to allow it to move around the asteroid, along with a camera, a thermometer, photodiode, and an accelerometer.

Hayabusa 2 is scheduled to depart Ryugu by the end of this year using plasma engines, aiming for a return to Earth in December 2020, when the craft will release a parachute-equipped re-entry capsule to land in Australia.

Scientists will retrieve the asteroid specimens for detailed analysis.

“If we have 0.1 grams (of material), we can do all the sample analysis, but we hope we will have much more,” Yoshikawa said.

“We want to study the organic matter on Ryugu because we want to know the origin of life on the Earth, and we think Ryugu has original matter that became life,” he said. “So our main purpose is analysis of the organic matter on the surface of Ryugu.”

Source: Spaceflight Now Return to Contents

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The Night Sky Friday, Sept. 20 • Cassiopeia displays its flattened-W shape high in the northeast these evenings. The W is tilted left. To the ancient Greeks Cassiopeia was a mythical African queen. Her husband Cepheus, dimmer and more sprawled out, is currently the next constellation to her upper right. Both lie along the winter Milky Way.

• In the center of Cepheus, these moonless evenings are a good time to bring out your binoculars or scope and try for the unusually small, compact open cluster NGC 7160 — as Matt Wedel tells in the September Sky & Telescope, page 43.

Saturday, Sept. 21 • Last-quarter Moon (exact at 10:41 p.m. Eastern Daylight Time). Tonight the Moon rises around midnight daylight-saving time, depending on your location. Watch for it to peek above the east-northeast horizon lower right of Capella and lower left of the Pleiades.

By the first sign of Sunday's dawn the Moon is shining high in the southeast, now with Orion to its lower right and Gemini to its lower left. How often do you examine the Moon with your telescope when the Moon is its late-night waning phases? To most of us, the waxing Moon of evening is much more familiar — when lunar mountains and crater walls cast their shadows in the opposite direction.

Sunday, Sept. 22 • Fall begins late tonight; the September equinox occurs at 3:50 a.m. September 23rd EDT. This is when the Sun crosses the equator (Earth's equator and therefore the celestial equator too), heading south for the season. Sunrise and sunset are very nearly 12 hours apart, and the Sun rises and sets practically at the east and west points on your horizon.

• Every year around when summer turns to autumn, Deneb takes over from brighter Vega as the zenith star after nightfall (for skywatchers at mid-northern latitudes).

Monday, Sept. 23 • "My favorite observations allow me to make comparisons," writes Matt Wedel in the October Sky & Telescope: "similar objects at different distances, or objects of different sizes at the same distance." For binocular observers he offers some examples at the bowl of the Sagittarius Teaspoon, which is currently just above the bright landmark Saturn. See his Binocular Highlight column on page 43 of the October issue.

Tuesday, Sept. 24 • In the west, off to left of the Big Dipper, bright Arcturus, the "Spring Star," shines a little lower at nightfall each week. From Arcturus, the narrow kite-shaped pattern of Bootes extends 24° to the upper right.

Source: Sky & Telescope Return to Contents

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ISS Sighting Opportunities For Denver: Date Visible Max Height Appears Disappears Fri Sep 20, 7:31 PM 6 min 39° 11° above SSW 10° above ENE Fri Sep 20, 9:09 PM 1 min 25° 20° above WNW 25° above NW Sat Sep 21, 8:21 PM 3 min 39° 28° above WNW 16° above NNE Sun Sep 22, 7:32 PM 4 min 66° 34° above WSW 11° above NE Sun Sep 22, 9:10 PM 1 min 15° 13° above NW 15° above NNW Mon Sep 23, 8:21 PM 3 min 19° 18° above NW 11° above NNE Tue Sep 24, 7:33 PM 3 min 27° 25° above NW 11° above NNE Tue Sep 24, 9:10 PM 1 min 11° 10° above NNW 11° above N Sighting information for other cities can be found at NASA’s Satellite Sighting Information NASA-TV Highlights (all times Eastern Daylight Time) September 20, Friday 11 a.m. - SpaceCast Weekly (All Channels)

September 23, Monday 12 p.m. – Coverage of the launch of the JAXA HTV-8 cargo craft mission to the International Space Station; launch scheduled at 12:30 p.m. EDT (All Channels) 4 p.m. - Video file of the International Space Station Expedition 61-62/Soyuz MS-15 rollout to the launch pad and launch pad Interviews at the Baikonur Cosmodrome in Kazakhstan – Johnson Space Center via Baikonur, Kazakhstan (Media Channel)

September 24, Tuesday 11 a.m.–12:30 p.m. – Replay of the Russian State Commission Meeting and final International Space Station Expedition 61-62 pre-launch crew news conference in Baikonur, Kazakhstan (Skripochka, Meir, Almansoori) (All Channels)

Watch NASA TV on the Net by going to the NASA website. Return to Contents

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Space Calendar • Sep 20 - Comet 101P/Chernykh At Opposition (1.542 AU) • Sep 20 - Amor Asteroid 2019 RP2 Near-Earth Flyby (0.022 AU) • Sep 20 - Aten Asteroid 297418 (2000 SP43) Near-Earth Flyby (0.068 AU) • Sep 20 - Aten Asteroid 2015 SD Near-Earth Flyby (0.081 AU) • Sep 20 - Eustachio Manfredi's 345th Birthday (1674) • Sep 21 - Comet P/2009 WX51 (Catalina) At Opposition (3.058 AU) • Sep 21 - Comet 81P/Wild At Opposition (3.832 AU) • Sep 21 - Apollo Asteroid 2017 SL16 Near-Earth Flyby (0.020 AU) • Sep 21 - Apollo Asteroid 2019 RB3 Near-Earth Flyby (0.049 AU) • Sep 21 - Apollo Asteroid 2019 RE2 Near-Earth Flyby (0.050 AU) • Sep 21 - Asteroid 5441 Andymurray Closest Approach To Earth (2.055 AU) • Sep 21 - 5th Anniversary (2014), MAVEN, Mars Orbit Insertion • Sep 21 - 45th Anniversary (1974), Mariner 10, 2nd Mercury Flyby • Sep 21 - 70th Anniversary (1949), Beddgelert Meteorite Fall (Hit Hotel in Wales) • Sep 21 - Gustav Holst's 145th Birthday (1874) • Sep 22 - Comet 2P/Encke At Opposition (2.255 AU) • Sep 22 - Comet 332P/Ikeya-Murakami At Opposition (3.279 AU) • Sep 22 - Comet 332P-B/Ikeya-Murakami At Opposition (3.284 AU) • Sep 22 - Comet 332P-I/Ikeya-Murakami At Opposition (3.287 AU) • Sep 22 - Comet 332P-D/Ikeya-Murakami At Opposition (3.288 AU) • Sep 22 - Comet 332P-C/Ikeya-Murakami At Opposition (3.294 AU) • Sep 22 - Comet 332P-H/Ikeya-Murakami At Opposition (3.295 AU) • Sep 22 - Comet 332P-A/Ikeya-Murakami At Opposition (3.296 AU) • Sep 22 - Comet 332P-C/Ikeya-Murakami At Opposition (3.299 AU) • Sep 22 - Apollo Asteroid 2019 QZ1 Near-Earth Flyby (0.032 AU) • Sep 22 - Aten Asteroid 2100 Ra-Shalom Closest Approach To Earth (0.180 AU) • Sep 22 - Apollo Asteroid 6063 Jason Closest Approach To Earth (2.266 AU) • Sep 22 - Apollo Asteroid 306367 Nut Closest Approach To Earth (2.439 AU) • Sep 22 - Saul Perlmutter's 60th Birthday (1959) • Sep 23 - Autumnal Equinox, 07:50 UT • Sep 23 - Aten Asteroid 2007 TQ24 Near-Earth Flyby (0.062 AU) • Sep 23 - Asteroid 21 Lutetia Closest Approach To Earth (1.083 AU) • Sep 23 - Asteroid 4047 Chang'E Closest Approach To Earth (1.103 AU) • Sep 23 - Asteroid 3018 Godiva Closest Approach To Earth (1.120 AU) • Sep 23 - Apollo Asteroid 5731 Zeus Closest Approach To Earth (1.410 AU) • Sep 23 - Asteroid 6336 Dodo Closest Approach To Earth (1.253 AU) • Sep 23 - Asteroid 4221 Picasso Closest Approach To Earth (1.834 AU) • Sep 23 - Jupiter Trojan 1437 Diomedes At Opposition (4.205 AU) • Sep 23 - Hugo von Seeliger's 170th Birthday (1849) • Sep 23 - Hippolyte Fizeau's 200th Birthday (1819) • Sep 24 - [Sep 13] Beidou 3 M19 & M20 CZ-3B/YZ-1 Launch • Sep 24 - Comet C/2019 B1 (Africano) Closest Approach To Earth (2.580 AU) • Sep 24 - Apollo Asteroid 523934 (1998 FF14) Near-Earth Flyby (0.028 AU) • Sep 24 - Asteroid 6123 Aristoteles Closest Approach To Earth (1.182 AU) • Sep 24 - Asteroid 4017 Disneya Closest Approach To Earth (1.338 AU) • Sep 24 - Asteroid 4372 Quincy Closest Approach To Earth (1.609 AU) • Sep 24 - Asteroid 274860 Emilylakdawalla Closest Approach To Earth (2.096 AU)

Source: JPL Space Calendar Return to Contents

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Food for Thought

Study captures six galaxies undergoing sudden, dramatic transitions

Galaxies come in a wide variety of shapes, sizes and brightnesses, ranging from humdrum ordinary galaxies to luminous active galaxies. While an ordinary galaxy is visible mainly because of the light from its stars, an active galaxy shines brightest at its center, or nucleus, where a supermassive black hole emits a steady blast of bright light as it voraciously consumes nearby gas and dust.

Sitting somewhere on the spectrum between ordinary and active galaxies is another class, known as low-ionization nuclear emission-line region (LINER) galaxies. While LINERs are relatively common, accounting for roughly one-third of all nearby galaxies, astronomers have fiercely debated the main source of light emission from LINERs. Some argue that weakly active galactic nuclei are responsible, while others maintain that star-forming regions outside the galactic nucleus produce the most light.

A team of astronomers observed six mild-mannered LINER galaxies suddenly and surprisingly transforming into ravenous quasars—home to the brightest of all active galactic nuclei. The team reported their observations, which could help demystify the nature of both LINERs and quasars while answering some burning questions about galactic evolution, in the Astrophysical Journal on September 18, 2019. Based on their analysis, the researchers suggest they have discovered an entirely new type of black hole activity at the centers of these six LINER galaxies.

"For one of the six objects, we first thought we had observed a tidal disruption event, which happens when a star passes too close to a supermassive black hole and gets shredded," said Sara Frederick, a graduate student in the University of Maryland Department of Astronomy and the lead author of the research paper. "But we later found it was a previously dormant black hole undergoing a transition that astronomers call a 'changing look,' resulting in a bright quasar. Observing six of these transitions, all in relatively quiet LINER galaxies, suggests that we've identified a totally new class of active galactic nucleus."

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All six of the surprising transitions were observed during the first nine months of the Zwicky Transient Facility (ZTF), an automated sky survey project based at Caltech's Palomar Observatory near San Diego, California, which began observations in March 2018. UMD is a partner in the ZTF effort, facilitated by the Joint Space-Science Institute (JSI), a partnership between UMD and NASA's Goddard Space Flight Center.

Changing look transitions have been documented in other galaxies—most commonly in a class of active galaxies known as Seyfert galaxies. By definition, Seyfert galaxies all have a bright, active galactic nucleus, but Type 1 and Type 2 Seyfert galaxies differ in the amount of light they emit at specific wavelengths. According to Frederick, many astronomers suspect that the difference results from the angle at which astronomers view the galaxies.

Type 1 Seyfert galaxies are thought to face Earth head-on, giving an unobstructed view of their nuclei, while Type 2 Seyfert galaxies are tilted at an oblique angle, such that their nuclei are partially obscured by a donut-shaped ring of dense, dusty gas clouds. Thus, changing look transitions between these two classes present a puzzle for astronomers, since a galaxy's orientation towards Earth is not expected to change.

Frederick and her colleagues' new observations may call these assumptions into question.

"We started out trying to understand changing look transformations in Seyfert galaxies. But instead, we found a whole new class of active galactic nucleus capable of transforming a wimpy galaxy to a luminous quasar," said Suvi Gezari, an associate professor of astronomy at UMD, a co-director of JSI and a co-author of the research paper. "Theory suggests that a quasar should take thousands of years to turn on, but these observations suggest that it can happen very quickly. It tells us that the theory is all wrong. We thought that Seyfert transformation was the major puzzle. But now we have a bigger issue to solve."

Frederick and her colleagues want to understand how a previously quiet galaxy with a calm nucleus can suddenly transition to a bright beacon of galactic radiation. To learn more, they performed follow-up observations on the objects with the Discovery Channel Telescope, which is operated by the Lowell Observatory in partnership with UMD, Boston University, the University of Toledo and Northern Arizona University. These observations helped to clarify aspects of the transitions, including how the rapidly transforming galactic nuclei interacted with their host galaxies.

"Our findings confirm that LINERs can, in fact, host active supermassive black holes at their centers," Frederick said. "But these six transitions were so sudden and dramatic, it tells us that there is something altogether different going on in these galaxies. We want to know how such massive amounts of gas and dust can suddenly start falling into a black hole. Because we caught these transitions in the act, it opens up a lot of opportunities to compare what the nuclei looked like before and after the transformation."

Unlike most quasars, which light up the surrounding clouds of gas and dust far beyond the galactic nucleus, the researchers found that only the gas and dust closest to the nucleus had been turned on. Frederick, Gezari and their collaborators suspect that this activity gradually spreads from the galactic nucleus—and may provide the opportunity to map the development of a newborn quasar.

"It's surprising that any galaxy can change its look on human time scales. These changes are taking place much more quickly than we can explain with current quasar theory," Frederick said. "It will take some work to understand what can disrupt a galaxy's accretion structure and cause these changes on such short order. The forces at play must be very extreme and very dramatic."

Source: Phys.org Return to Contents

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Space Image of the Week

Juno spacecraft sees moon’s otherworldly shadow on Jupiter Fresh images from NASA’s Juno spacecraft show an ethereal shadow cast by Jupiter’s volcanic moon Io on the planet’s swirling cloud tops. The JunoCam imager captured views of Io’s distinct shadow on Jupiter during its most recent passage near the giant planet, and skilled image analysts immediately set to work processing the data into dazzling renderings showing a black circle amid Jupiter’s churning clouds. Kevin Gill, a software engineer at NASA’s Jet Propulsion Laboratory, created this mosaic from imagery taken by the JunoCam instrument. Juno spotted the eclipse during a Sept. 12 encounter near Jupiter, the 22nd such flyby since arriving in orbit around the solar system’s largest planet on July 4, 2016. The spacecraft carries instruments to study Jupiter’s internal structure and weather, along with sensors to measure and map the planet’s strong magnetic field and gravity. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill Source: Spaceflight Now Return to Contents