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Juno Spacecraft Faced Challenges During Recent Jupiter Approach

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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Look Up! Residents of Maine and Michigan Might Catch a Glimpse of the Northern Lights Tonight
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The aurora borealis, a celestial show usually reserved for spectators near the arctic circle, could potentially appear over parts of the continental U.S. on the night of February 15. As Newsweek reports, a solar storm is on track to illuminate the skies above Maine and Michigan.

The Northern Lights (and the Southern Lights) are caused by electrons from the sun colliding with gases in the Earth’s atmosphere. The solar particles transfer some of their energy to oxygen and nitrogen molecules on contact, and as these excited molecules settle back to their normal states they release light particles. The results are glowing waves of blue, green, purple, and pink light creating a spectacle for viewers on Earth.

The more solar particles pelt the atmosphere, the more vivid these lights become. Following a moderate solar flare that burst from the sun on Monday, the NOAA Space Weather Prediction Center forecast a solar light show for tonight. While the Northern Lights are most visible from higher latitudes where the planet’s magnetic field is strongest, northern states are occasionally treated to a view. This is because the magnetic North Pole is closer to the U.S. than the geographic North Pole.

This Thursday night into Friday morning is expected to be one of those occasions. To catch a glimpse of the phenomena from your backyard, wait for the sun to go down and look toward the sky. People living in places with little cloud cover and light pollution will have the best chance of spotting it.

[h/t Newsweek]

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10 Facts About the Dwarf Planet Haumea
Kevin Gill, Flickr // CC BY-2.0
Kevin Gill, Flickr // CC BY-2.0

In terms of sheer weirdness, few objects in the solar system can compete with the dwarf planet Haumea. It has a strange shape, unusual brightness, two moons, and a wild rotation. Its unique features, however, can tell astronomers a lot about the formation of the solar system and the chaotic early years that characterized it. Here are a few things you need to know about Haumea, the tiny world beyond Neptune.

1. THREE HAUMEAS COULD FIT SIDE BY SIDE IN EARTH.

Haumea is a trans-Neptunian object; its orbit, in other words, is beyond that of the farthest ice giant in the solar system. Its discovery was reported to the International Astronomical Union in 2005, and its status as a dwarf planet—the fifth, after Ceres, Eris, Makemake, and Pluto—was made official three years later. Dwarf planets have the mass of a planet and have achieved hydrostatic equilibrium (i.e., they're round), but have not "cleared their neighborhoods" (meaning their gravity is not dominant in their orbit). Haumea is notable for the large amount of water ice on its surface, and for its size: Only Pluto and Eris are larger in the trans-Neptunian region, and Pluto only slightly, with a 1475-mile diameter versus Haumea's 1442-mile diameter. That means three Haumeas could fit sit by side in Earth—and yet it only has 1/1400th of the mass of our planet.

2. HAUMEA'S DISCOVERY WAS CONTROVERSIAL.

There is some disagreement over who discovered Haumea. A team of astronomers at the Sierra Nevada Observatory in Spain first reported its discovery to the Minor Planet Center of the International Astronomical Union on July 27, 2005. A team led by Mike Brown from the Palomar Observatory in California had discovered the object earlier, but had not reported their results, waiting to develop the science and present it at a conference. They later discovered that their files had been accessed by the Spanish team the night before the announcement was made. The Spanish team says that, yes, they did run across those files, having found them in a Google search before making their report to the Minor Planet Center, but that it was happenstance—the result of due diligence to make sure the object had never been reported. In the end, the IAU gave credit for the discovery to the Spanish team—but used the name proposed by the Caltech team.

3. IT'S NAMED FOR A HAWAIIAN GODDESS.

In Hawaiian mythology, Haumea is the goddess of fertility and childbirth. The name was proposed by the astronomers at Caltech to honor the place where Haumea's moon was discovered: the Keck Observatory on Mauna Kea, Hawaii. Its moons—Hi'iaka and Namaka—are named for two of Haumea's children.

4. HAUMEA HAS RINGS—AND THAT'S STRANGE.

Haumea is the farthest known object in the solar system to possess a ring system. This discovery was recently published in the journal Nature. But why does it have rings? And how? "It is not entirely clear to us yet," says lead author Jose-Luis Ortiz, a researcher at the Institute of Astrophysics of Andalusia and leader of the Spanish team of astronomers who discovered Haumea.

5. HAUMEA'S SURFACE IS EXTREMELY BRIGHT.

In addition to being extremely fast, oddly shaped, and ringed, Haumea is very bright. This brightness is a result of the dwarf planet's composition. On the inside, it's rocky. On the outside, it is covered by a thin film of crystalline water ice [PDF]—the same kind of ice that's in your freezer. That gives Haumea a high albedo, or reflectiveness. It's about as bright as a snow-covered frozen lake on a sunny day.

6. HAUMEA HAS ONE OF THE SHORTEST DAYS IN THE ENTIRE SOLAR SYSTEM.

If you lived to be a year old on Haumea, you would be 284 years old back on Earth. And if you think a Haumean year is unusual, that's nothing next to the length of a Haumean day. It takes 3.9 hours for Haumea to make a full rotation, which means it has by far the fastest spin, and thus shortest day, of any object in the solar system larger than 62 miles.

7. HAUMEA'S HIGH SPEED SQUISHES IT INTO A SHAPE LIKE A RUGBY BALL.

haumea rotation gif
Stephanie Hoover, Wikipedia // Public Domain

As a result of this tornadic rotation, Haumea has an odd shape; its speed compresses it so much that rather than taking a spherical, soccer ball shape, it is flattened and elongated into looking something like a rugby ball.

8. HIGH-SPEED COLLISIONS MAY EXPLAIN HAUMEA'S TWO MOONS.

Ortiz says there are several mechanisms that can have led to rings around the dwarf planet: "One of our favorite scenarios has to do with collisions on Haumea, which can release material from the surface and send it to orbit." Part of the material that remains closer to Haumea can form a ring, and material further away can help form moons. "Because Haumea spins so quickly," Ortiz adds, "it is also possible that material is shed from the surface due to the centrifugal force, or maybe small collisions can trigger ejections of mass. This can also give rise to a ring and moons."

9. ONE MOON HAS WATER ICE—JUST LIKE HAUMEA.

Ortiz says that while the rings haven't transformed scientists' understanding of Haumea, they have clarified the orbit of its largest moon, Hi'iaka—it is equatorial, meaning it circles around Haumea's equator. Hi'iaka is notable for the crystalline water ice on its surface, similar to that on its parent body.

10. TRYING TO SEE HAUMEA FROM EARTH IS LIKE TRYING TO LOOK AT A COIN MORE THAN 100 MILES AWAY.

It's not easy to study Haumea. The dwarf planet, and other objects at that distance from the Sun, are indiscernible to all but the largest telescopes. One technique used by astronomers to study such objects is called "stellar occultation," in which the object is observed as it crosses in front of a star, causing the star to temporarily dim. (This is how exoplanets—those planets orbiting other stars—are also often located and studied.) This technique doesn't always work for objects beyond the orbit of Neptune, however; astronomers must know the objects' orbits and the position of the would-be eclipsed stars to astounding levels of accuracy, which is not always the case. Moreover, Ortiz says, their sizes are oftentimes very small, "comparable to the size of a small coin viewed at a distance of a couple hundred kilometers."

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