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Juno Spacecraft Faced Challenges During Recent Jupiter Approach

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A composite image of Jupiter’s cloud formations as seen through the eyes of Juno’s Microwave Radiometer, which can see up to 250 miles into the planet's atmosphere with its largest antenna. The belts and bands visible on the surface are also visible in modified form in each layer below. Image credit: NASA/JPL-Caltech/SwRI/GSFC

 
Last week, NASA's Juno spacecraft reached perijove, the closest point of its 53.5-day orbit around Jupiter, when it passed less than 3000 miles from the gas giant's clouds. But during its approach, the onboard computer suddenly detected an unexpected condition and turned off unnecessary subsystems, entering “safe mode.” The solar-powered spacecraft then went "power positive," shutting down the cameras and reorienting itself toward the Sun, where it linked up with the Deep Space Network back on Earth. Then it waited for humans to evaluate the situation and provide guidance.

It was a disappointing outcome for the Southwest Research Institute scientists leading the mission, including principal investigator Scott Bolton. Because the science instruments were shut down during the flyby, no data were collected. But this outcome was also a necessary one. In space, power is king. Engineers can often fix—or find inventive workarounds to—problems of enormous complexity, even from hundreds of millions of miles away. The one thing that is non-negotiable, however, is power. The spacecraft must be alive to receive commands. So in this case, "safe mode" is a good thing—the robot did exactly what it was supposed to do in this situation.

According to the original plan, the October 19 maneuver was not meant to be a science orbit, but rather, a "period reduction maneuver." The Juno team initially intended to fire the same rocket motor that performed the daring insertion maneuver on July 4, when it purposefully slowed its engines enough to be caught by Juno’s gravity and orbit the poles. If successful, last week's rocket firing would have slowed the spacecraft and changed its orbit from 53.5 days to two weeks.

While preparing for the maneuver, however, the team noticed that the valves in the spacecraft's propulsion system were behaving sluggishly, as though the valves were "sticky." Rather than take any chances with the spacecraft's delicate orbit, they decided to postpone the maneuver and switch on the science instruments instead, making this a science pass.

The scientific investigation of Jupiter is tied to a two-hour window every orbit when the spacecraft reaches perijove. During that time, the spacecraft travels from Jupiter's north pole to its south. Whether it makes this traversal following a 14-day orbit or roughly 7.5-week orbit makes no difference at all; the current longer orbit simply means it will take longer to reach the completion of the mission.

Then the plan for a science pass fell through too when the spacecraft switched into safe mode.

Although these are two disappointing events in a row, everything will be okay, Bolton said at a press event during the 2016 meeting of the American Astronomical Society's Division for Planetary Sciences. The team can still fire the rocket in the future. Until then, they will work to determine what caused the safe mode and why the valves were behaving oddly. Bolton explained that the team is in no rush. "Fortunately, the way we designed Juno, and the orbit we went into, is very flexible," he said. "It allows very flexible science."

Though this flyby was a wash, a previous, successful flyby on August 27 has yielded extraordinary science. Then, an instrument called a microwave radiometer peered into Jupiter's atmosphere, giving scientists the first-ever look beneath the planet's clouds. Peeling away layers of the atmosphere as though it were an onion and looking as deeply within as 250 miles, scientists discovered that the atmosphere retains the famous structure of the zones and belts of clouds visible from telescopes.

"Whatever is making those colors—whatever is making those stripes—is still existing pretty far down into Jupiter," Bolton said. "That came as a surprise to many of the scientists. We didn't know if [Jupiter's appearance] was skin deep—just a very thin layer—or whether it goes down." Another surprise was that the colorful zones and belts also appear to evolve and change at various depths. This hints at the deep dynamics and chemistry of Jupiter's atmosphere, though the details still require much analysis.

NASA/JPL-Caltech/SwRI/MSSS/Alex Mai

 
During that same pass, Juno's camera captured images as the spacecraft crossed the "terminator" of Jupiter—that is, the line between the sunlit side of the planet and the side in darkness. Think of a half-moon: The terminator is the line where the bright half meets the dark half.

The above image of the sunlit half was created by citizen scientist Alex Mai using data from the spacecraft's JunoCam instrument. (Raw images from the mission are available at JunoCam for both public and professional use.) Meanwhile, the shadows revealed the topology of Jupiter's atmosphere—another first. A particularly pronounced feature was a cyclone raging even above Jupiter's base atmosphere. It's 53 miles tall and 4350 miles wide—half the size of the Earth.

"Imagine the kind of atmosphere you're dealing with," marveled Bolton.

For now, scientists will need to imagine a little longer. Juno's next flyby of Jupiter will be on December 11.

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Land Cover CCI, ESA
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Afternoon Map
European Space Agency Releases First High-Res Land Cover Map of Africa
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Land Cover CCI, ESA

This isn’t just any image of Africa. It represents the first of its kind: a high-resolution map of the different types of land cover that are found on the continent, released by The European Space Agency, as Travel + Leisure reports.

Land cover maps depict the different physical materials that cover the Earth, whether that material is vegetation, wetlands, concrete, or sand. They can be used to track the growth of cities, assess flooding, keep tabs on environmental issues like deforestation or desertification, and more.

The newly released land cover map of Africa shows the continent at an extremely detailed resolution. Each pixel represents just 65.6 feet (20 meters) on the ground. It’s designed to help researchers model the extent of climate change across Africa, study biodiversity and natural resources, and see how land use is changing, among other applications.

Developed as part of the Climate Change Initiative (CCI) Land Cover project, the space agency gathered a full year’s worth of data from its Sentinel-2A satellite to create the map. In total, the image is made from 90 terabytes of data—180,000 images—taken between December 2015 and December 2016.

The map is so large and detailed that the space agency created its own online viewer for it. You can dive further into the image here.

And keep watch: A better map might be close at hand. In March, the ESA launched the Sentinal-2B satellite, which it says will make a global map at a 32.8 feet-per-pixel (10 meters) resolution possible.

[h/t Travel + Leisure]

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NSF/LIGO/Sonoma State University/A. Simonnet
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Space
Astronomers Observe a New Kind of Massive Cosmic Collision for the First Time
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NSF/LIGO/Sonoma State University/A. Simonnet

For the first time, astronomers have detected the colossal blast produced by the merger of two neutron stars—and they've recorded it both via the gravitational waves the event produced, as well as the flash of light it emitted.

Physicists believe that the pair of neutron stars—ultra-dense stars formed when a massive star collapses, following a supernova explosion—had been locked in a death spiral just before their final collision and merger. As they spiraled inward, a burst of gravitational waves was released; when they finally smashed together, high-energy electromagnetic radiation known as gamma rays were emitted. In the days that followed, electromagnetic radiation at many other wavelengths—X-rays, ultraviolet, optical, infrared, and radio waves—were released. (Imagine all the instruments in an orchestra, from the lowest bassoons to the highest piccolos, playing a short, loud note all at once.)

This is the first time such a collision has been observed, as well as the first time that both kinds of observations—gravitational waves and electromagnetic radiation—have been recorded from the same event, a feat that required co-operation among some 70 different observatories around the world, including ground-based observatories, orbiting telescopes, the U.S. LIGO (Laser Interferometer Gravitational-Wave Observatory), and European Virgo gravitational wave detectors.

"For me, it feels like the dawning of a next era in astrophysics," Julie McEnery, project scientist for NASA's Fermi Gamma-ray Space Telescope, one of the first instruments to record the burst of energy from the cosmic collision, tells Mental Floss. "With this observation, we've connected these new gravitational wave observations to the rest of the observations that we've been doing in astrophysics for a very long time."

A BREAKTHROUGH ON SEVERAL FRONTS

The observations represent a breakthrough on several fronts. Until now, the only events detected via gravitational waves have been mergers of black holes; with these new results, it seems likely that gravitational wave technology—which is still in its infancy—will open many new phenomena to scientific scrutiny. At the same time, very little was known about the physics of neutron stars—especially their violent, final moments—until now. The observations are also shedding new light on the origin of gamma-ray bursts (GRBs)—extremely energetic explosions seen in distant galaxies. As well, the research may offer clues as to how the heavier elements, such as gold, platinum, and uranium, formed.

Astronomers around the world are thrilled by the latest findings, as today's flurry of excitement attests. The LIGO-Virgo results are being published today in the journal Physical Review Letters; further articles are due to be published in other journals, including Nature and Science, in the weeks ahead. Scientists also described the findings today at press briefings hosted by the National Science Foundation (the agency that funds LIGO) in Washington, and at the headquarters of the European Southern Observatory in Garching, Germany.

(Rumors of the breakthrough had been swirling for weeks; in August, astronomer J. Craig Wheeler of the University of Texas at Austin tweeted, "New LIGO. Source with optical counterpart. Blow your sox off!" He and another scientist who tweeted have since apologized for doing so prematurely, but this morning, minutes after the news officially broke, Wheeler tweeted, "Socks off!") 

The neutron star merger happened in a galaxy known as NGC 4993, located some 130 million light years from our own Milky Way, in the direction of the southern constellation Hydra.

Gravitational wave astronomy is barely a year and a half old. The first detection of gravitational waves—physicists describe them as ripples in space-time—came in fall 2015, when the signal from a pair of merging black holes was recorded by the LIGO detectors. The discovery was announced in February 2016 to great fanfare, and was honored with this year's Nobel Prize in Physics. Virgo, a European gravitational wave detector, went online in 2007 and was upgraded last year; together, they allow astronomers to accurately pin down the location of gravitational wave sources for the first time. The addition of Virgo also allows for a greater sensitivity than LIGO could achieve on its own.

LIGO previously recorded four different instances of colliding black holes—objects with masses between seven times the mass of the Sun and a bit less than 40 times the mass of the Sun. This new signal was weaker than that produced by the black holes, but also lasted longer, persisting for about 100 seconds; the data suggested the objects were too small to be black holes, but instead were neutron stars, with masses of about 1.1 and 1.6 times the Sun's mass. (In spite of their heft, neutron stars are tiny, with diameters of only a dozen or so miles.) Another key difference is that while black hole collisions can be detected only via gravitational waves—black holes are black, after all—neutron star collisions can actually be seen.

"EXACTLY WHAT WE'D HOPE TO SEE"

When the gravitational wave signal was recorded, on the morning of August 17, observatories around the world were notified and began scanning the sky in search of an optical counterpart. Even before the LIGO bulletin went out, however, the orbiting Fermi telescope, which can receive high-energy gamma rays from all directions in the sky at once, had caught something, receiving a signal less than two seconds after the gravitational wave signal tripped the LIGO detectors. This was presumed to be a gamma-ray burst, an explosion of gamma rays seen in deep space. Astronomers had recorded such bursts sporadically since the 1960s; however, their physical cause was never certain. Merging neutron stars had been a suggested culprit for at least some of these explosions.

"This is exactly what we'd hoped to see," says McEnery. "A gamma ray burst requires a colossal release of energy, and one of the hypotheses for what powers at least some of them—the ones that have durations of less than two seconds—was the merger of two neutron stars … We had hoped that we would see a gamma ray burst and a gravitational wave signal together, so it's fantastic to finally actually do this."

With preliminary data from LIGO and Virgo, combined with the Fermi data, scientists could tell with reasonable precision what direction in the sky the signal had come from—and dozens of telescopes at observatories around the world, including the U.S. Gemini telescopes, the European Very Large Telescope, and the Hubble Space Telescope, were quickly re-aimed toward Hydra, in the direction of reported signal.

The telescopes at the Las Campanas Observatory in Chile were well-placed for getting a first look—because the bulletin arrived in the morning, however, they had to wait until the sun dropped below the horizon.

"We had about eight to 10 hours, until sunset in Chile, to prepare for this," Maria Drout, an astronomer at the Carnegie Observatories in in Pasadena, California, which runs the Las Campanas telescopes, tells Mental Floss. She was connected by Skype to the astronomers in the control rooms of three different telescopes at Las Campanas, as they prepared to train their telescopes at the target region. "Usually you prepare a month in advance for an observing run on these telescopes, but this was all happening in a few hours," Drout says. She and her colleagues prepared a target list of about 100 galaxies, but less than one-tenth of the way through the list, by luck, they found it: a tiny blip of light in NGC 4993 that wasn't visible on archival images of the same galaxy. (It was the 1-meter Swope telescope that snagged the first images.)

A NEW ERA OF ASTROPHYSICS

When a new star-like object in a distant galaxy is spotted, a typical first guess is that it's a supernova (an exploding star). But this new object was changing very rapidly, growing 100 times dimmer over just a few days while also quickly becoming redder—which supernovae don't do, explains Drout, who is cross-appointed at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto. "We ended up following it for three weeks or so, and by the end, it was very clear that this [neutron star merger] was what we were looking at," she says.

The researchers say they can't be sure if the resulting object was another, larger neutron star, or whether it would have been so massive that it would have collapsed into a black hole.

As exciting as the original detection of gravitational waves last year was, Drout is looking forward to a new era in which both gravitational waves and traditional telescopes can be used to study the same objects. "We can learn a lot more about these types of extreme systems that exist in the universe, by coupling the two together," she says.

The detection shows that "gravitational wave science is moving from being a physics experiment to being a tool for astronomers," Marcia Rieke, an astronomer at the University of Arizona who is not involved in the current research, tells Mental Floss. "So I think it's a pretty big deal."

Physicists are also learning something new about the origin of the heaviest elements in the periodic table. For many years, these were thought to arise from supernova explosions, but spectroscopic data from the newly observed neutron star merger (in which light is broken up into its component colors) suggests that such explosion produce enormous quantities of heavy elements—including enough gold to put Fort Knox to shame. (The blast is believed to have created some 200 Earth-masses of gold, the scientists say.) "It's telling us that most of the gold that we know about is produced in these mergers, and not in supernovae," McEnery says.

Editor's note: This post has been updated.

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