Juno Is the First Solar-Powered Spacecraft in the Outer Solar System


Juno arrived at Jupiter last night, July 4, and safely entered into the gas giant's orbit. The successful maneuver had NASA scientists and engineers cheering; after traveling for nearly five years, the spacecraft was just one second off schedule, and when the 35-minute engine burn that slowed the craft enough to be snagged into orbit by Jupiter's gravity was complete, Juno successfully turned to face the Sun.

That was essential to the mission, because Juno is solar-powered—a feat once thought impossible for spacecraft operating far beyond the asteroid belt, where the Sun's rays are only scarcely felt. (Jupiter receives 1/25th the light of Earth.)

Juno will spend the next three months in a "capture orbit" phase, during which time its instruments will be calibrated and systems tested. Scientists will also use this time to get real-world (well, real-otherworld) practice with the science payload. Juno will then undergo a period reduction maneuver, in which its orbit is again changed in preparation for the science mission. Juno's job is to collect data on Jupiter's mysterious interior and study its gravity and magnetic fields. That begins on October 19.

From an engineering standpoint, Juno's July 4 arrival at Jupiter is fitting, as the endeavor is a sort of declaration of independence from the required use of nuclear power in missions to outer planets. Before Juno, such missions were previously required to pack under the hood what are called multi-mission radioisotope thermoelectric generators [PDF]—costly power sources fueled by NASA's diminishing supply of plutonium-238. Advances in solar panels, however, coupled with the clever designs by NASA's engineers and associates, have proven not only that solar power is possible for Juno, but also for NASA's coming flagship mission to the Jovian moon Europa.


Though they contain nuclear material, radioisotope thermoelectric generators (RTGs) are not nuclear reactors. The electricity generated by an RTG is derived from heat produced from its plutonium package. The heat is converted to electricity by way of thermocouples. (This isn't wild technology—your refrigerator uses thermocouples to turn its compressor on and off in order to regulate its temperature.) In short, the thermocouples of RTGs involve two dissimilar electricity-conducting metals, with each metal existing at a different temperature: one hot (heated by the naturally decaying plutonium) and one cold (chilled by the natural coldness of space). The temperature difference produces electricity in what is known as the Seebeck effect.

RTGs, while not particularly efficient power sources, are totally reliable, with a 0 percent failure rate of thermocouples in NASA spacecraft. They operate on the laws of physics; the decay rate of their radioactive packages is predictable for engineers, and because the generators have no moving parts, the uncertainty of wear-and-tear is removed from the equation.


RTGs are not without shortcomings. For one, NASA doesn't exactly have a warehouse filled with pellets of plutonium. In fact, the United States only has enough fuel for two more such generators beyond the Mars 2020 rover. Moreover, launching a plutonium-bearing power source into space requires enormous additional safety precautions on the part of NASA; extensive environmental impact planning involving the Environmental Protection Agency and the Department of Energy; and approval from the director of the Office of Science and Technology Policy. Local agencies are also brought to the table in the event of an accident or explosion. (It should be noted, however, that the risk is minimal. RTGs are designed to either burn up in the atmosphere in the event of a catastrophic launch or to survive a crash intact, the RTG keeping the plutonium secure. These situations actually happened in 1964, 1968, and 1970.)

Juno is fueled by sunlight that is collected by three 9-foot-by-29-foot solar panels. At Jupiter, these panels produce enough electricity to light five standard light bulbs. That doesn't sound like much, but it is ample for the spacecraft's science instrument payload. It took about one minute for the panels to expand after launch, and the full wingspan of Juno is about the size of the exterior set of the Millennium Falcon built for The Empire Strikes Back. (Mynocks would love chewing on Juno's solar-powered cables.) The spacecraft is oriented to keep the panels in continuous sunlight, and will continue to do so through completion of the mission. As noted by NASA, solar power in the outer planets has been made possible by a 50 percent increase in solar cell efficiency and radiation tolerance.

The scientists and engineers behind NASA's next flagship endeavor—the ambitious multiple-flyby mission to Europa, which doesn't have a launch date yet—tested Juno's solar panels and found that the technology would work for their mission as well. Accordingly, the Europa team abandoned RTGs and embraced the much less-expensive solar panels. (Less expensive both in terms of hardware and in the requisite environmental impact planning for nuclear power sources.) To that end, Juno began paying science dividends before it was even finished being built. The discoveries it makes in October will be a delightful bonus.

15 Podcasts That Will Make You Feel Smarter

It's easy to feel overwhelmed by all the podcast options out there, but narrowing down your choices to the titles that will teach you something while you listen is a good place to start. If you're interested in learning more about philosophy, science, linguistics, or history, here are podcasts to add to your queue.


The Habitat is the closest you can get to listening to a podcast recorded on Mars. At the start of the series, five strangers enter a dome in a remote part of Hawaii meant to simulate a future Mars habitat. Every part of their lives over the next year, from the food they eat to the spacesuits they wear when they step outside, is designed to mimic the conditions astronauts will face if they ever reach the red planet. The experiment was a way for NASA to test plans for a manned mission to Mars without leaving Earth. The podcast, which is produced by Gimlet media and hosted by science writer Lynn Levy, ends up unfolding like a season of the Real World with a science fiction twist.


Can’t pick a topic to educate yourself on? Stuff You Should Know from How Stuff Works is the podcast for you. In past episodes, hosts Chuck Bryant and Josh Clark (both writers at How Stuff Works) have discussed narwhals, Frida Kahlo, LSD, Pompeii, hoarding, and Ponzi schemes. And with three episodes released a week, you won’t go long without learning about a new subject.


Language nerds will find a kindred spirit in Helen Zaltzman. In each episode of her Radiotopia podcast The Allusionist, the former student of Latin, French, and Old English guides listeners through the exciting world of linguistics. Past topics include swearing, small talk, and the differences between British and American English.


Listening to all of Philosophize This! is cheaper than taking a philosophy class—and likely more entertaining. In each episode, host Stephen West covers different thinkers and ideas from philosophy history in an approachable and informative way. The show proceeds in chronological order, starting with the pre-Socratic era and leading up most recently to Jacques Derrida.


In 2016, Radiolab, one of the most popular and well-established educational podcasts out there, launched a show called More Perfect. Led by Radiolab host Jad Abumrad, each episode visits a different Supreme Court case or event that helped shape the highest court in the land. Because of that, the podcast ends up being about a lot more than just the Supreme Court, exploring topics like police brutality, gender equality, and free speech online.


The Watergate scandal was such a important chapter in American history that it has its own suffix—but when asked to summarize the events, many people may draw a blank. Slow Burn, a podcast from Slate, gives listeners a refresher. In eight episodes, host Leon Neyfakh tells the story of the Nixon’s demise as it unfolded, all while asking whether or not citizens would be able to recognize a Watergate-sized scandal if it happened today.


Instead of using a broad scope to examine World War II, the Washington Post podcast Letters From War focuses on hundreds of letters exchanged by four brothers fighting in the Pacific during the period. Living U.S. military veterans tell the sibling's story while reflecting on their own experiences with war.


Just because you’re a grown-up doesn’t mean you have to miss out on the soothing sound of LeVar Burton’s voice reading to you. The former host of Reading Rainbow now hosts LeVar Burton Reads, a podcast from Stitcher aimed at adults. In each episode, he picks a different piece of short fiction to narrate: Just settle into a comfortable spot and listen to him tell stories by authors like Haruki Murakami, Octavia Butler, and Ursula K. Le Guin.


Brains On! is an educational podcast for young audiences, but adults have something to gain from listening as well. Every week, host Molly Bloom is joined by a new kid co-host who helps her explore a different topic. Tune in for answers to questions like "What makes paint stick?" and "How do animals breathe underwater?"


There’s a lot of misinformation out there—if you’re determined to sort out fact from fiction, it can be hard to know where to start. The team of “friendly fact checkers” at the Science Vs podcast from Gimlet is here to help. GMOs, meditation, birth control, Bigfoot—these are just a few of the topics that are touched upon in the weekly show. The goal of each episode is to replace any preconceived notions you have with hard science.


No one knows for sure what the future holds, but Flash Forward lays out the more interesting possibilities. Some of the potential futures that host and producer Rose Eveleth explores are more probable than others (a future where no one knows which news sources to trust isn’t hard to imagine; one where space pirates drag a second moon into orbit perhaps is), but each one is built on real science.


What motivates the everyday choices we make? That’s the question Shankar Vedantam tries to answer on the NPR podcast Hidden Brain. The show looks at how various unconscious patterns shape our lives, like what we wear and who we choose to spend time with.


The fact that it’s hosted by Mental Floss founders Will Pearson and Mangesh Hattikudur isn’t the only reason we love Part-Time Genius. The podcast from How Stuff Works wades into topics you didn’t know you were curious about, like the origins of Nickelodeon and the hidden secrets at the Vatican. Each episode will leave you feeling educated and entertained at the same time.


It’s a big universe out there—if you want to learn as much about it as possible, start with Astronomy Cast. Fraser Cain, publisher of the popular site Universe Today, and Dr. Pamela L. Gay, director of the virtual research facility CosmoQuest, host the podcast. They cover a wide range of topics, from the animals we’ve sent to orbit to the color of the universe.


The Science of Happiness podcast from PRI is here to improve your life, one 20-minute episode at a time. Science has proven that adopting certain practices, like mindfulness and gratitude, can make us happier—as does letting go of less unhealthy patterns like grudges and stressful thinking. With award-winning professor Dacher Keltner as your host, you can learn how to incorporate these science-backed strategies for happiness into your own life.

ESO, A. Müller et al.
Here's the First Confirmed Image of a Planet Being Born
ESO, A. Müller et al.
ESO, A. Müller et al.

One of the newest landmarks in the observable universe has finally been captured, according to the European Southern Observatory. The image, snapped at its Very Large Telescope (VLT) in Chile, marks the first time a newborn planet has been seen as it forms. 

The image was documented by SPHERE, an instrument at the VLT that's built to identify exoplanets. It shows a planet, dubbed PDS 70b, taking shape in the disc of gas and star dust surrounding the young dwarf star PDS 70. In the past, astronomers have caught glimpses of what may have been new planets forming, but until now it had been impossible to tell whether such images just showed shapes in the dust or the beginnings of true planet formation. The results of the research will be shared in the journal Astronomy & Astrophysics [PDF].

This latest cornograph (an image that blocks the light of a star to make its surroundings visible) depicts the new planet clearly as a bright blob beside the black star. The two bodies may look close in the photo, but PDS 70b is roughly 1.8 billion miles from PDS 70, or the distance of Uranus to the Sun. SPHERE also recorded the planet's brightness at different wavelengths. Based on information gathered from the instrument, a team of scientists led by Miriam Keppler of the Max Planck Institute for Astronomy says that PDS 70b is a gas giant a few times the mass of Jupiter with a surface temperature around 1830°F and a cloudy atmosphere.

Astronomers known that planets form from solar clouds which stars leave behind when they come into a being, but until now, the details surrounding the phenomena have been mysterious. “Keppler’s results give us a new window onto the complex and poorly understood early stages of planetary evolution,” astronomer André Müller said in a press release. “We needed to observe a planet in a young star’s disc to really understand the processes behind planet formation.”

This is just the latest history-making image captured by the ESO's Very Large Telescope. In the last 20 years, it has documented nebulae, light from gravitational waves, and interacting galaxies.


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