NASA Jet Propulsion Laboratory via YouTube
NASA Jet Propulsion Laboratory via YouTube

The Juno Mission: NASA Celebrates Independence Day by Invading Jupiter

NASA Jet Propulsion Laboratory via YouTube
NASA Jet Propulsion Laboratory via YouTube

With planetary invasions being an Independence Day tradition, it's fitting that NASA's Juno spacecraft will enter Jupiter's orbit today, July 4, after a five-year journey to the outer solar system. Juno is the robot equivalent of Indiana Jones: a celestial archaeologist on an expedition to find Jupiter's core—and, hopefully, solve the mystery of the solar system's origin. 


Juno's insertion into Jupiter's orbit will begin at 8:18 p.m. PDT on July 4, 2016. This involves a 35-minute "burn," during which time the spacecraft reorients itself and the British-built Leros 1b engine fires up so as to slow Juno's speed. (Juno will be traveling 165,000 mph on arrival.) The burn is crucial, and a failure would mean that the spacecraft zips past Jupiter and into the void. Success, however, means Juno is sufficiently slowed to be captured by Jupiter's gravity and thus enters orbit.

Juno does all of this in autopilot, the final commands having been issued by humans on June 30 and blasted to the spacecraft using NASA's Deep Space Network. During orbital insertion, the spacecraft's science instruments and all unnecessary computer features are disabled. (More features increase the likelihood of computer crashes.) Jupiter's intense radiation environment is notoriously hard on spacecraft computers, and in the event that Juno's computer is zapped by a high-energy particle, it is designed to immediately reset and resume the burn. Scientists, meanwhile, will wait anxiously for Juno to send a message to the Deep Space Network that has been compared to the "emergency broadcast signal" on television and radio. A certain tone will mean the spacecraft has achieved a successful orbital insertion.

Juno's unique design—three colossal solar panels affixed to an 11.5-ft. spacecraft at the center—is dictated by the low levels of sunlight available in the outer solar system. The sun appears 1/25 as bright at Jupiter as at Earth. The spacecraft will remain oriented to collect as many photons as possible from the Sun, and will spin like a top, twice per minute in order to maintain stability and to allow each instrument on Juno's scientific payload to collect data from Jupiter.


Screengrab from NASA fact sheet. Image credit: NASA

Juno's science instruments—all but one built into the core part of the triple-bladed spacecraft—will each collect certain types of data for scientists to analyze back on Earth. The Gravity Science instrument will map the distribution of Jupiter's interior mass, and thus its gravity. The Magnetometer will meanwhile study Jupiter's magnetic field and its massive and mystifying polar magnetosphere. It will also examine Jupiter's interior dynamics. The Microwave Radiometer [PDF] will the study water content of Jupiter's deep atmosphere so as to reveal the oxygen content of Jupiter. An Ultraviolet Imaging Spectrograph and the Jovian Infrared Auroral Mapper will study Jupiter's atmosphere and auroras, while the JunoCam will take high-resolution photographs of Jupiter and its terrifying and beautiful atmosphere. (It has already returned images.)

But that's not all. The Radio and Plasma Wave Sensor and the Jovian Auroral Distribution Experiment will characterize the nature of the magnetic field and atmosphere, and auroras in particular. Lastly, the Jovian Energetic Particle Detector Instrument—JEDI—also concerns itself with Jupiter's magnetosphere, focusing on the "energy and distribution of ions, particularly hydrogen, helium, oxygen and sulphur, to see if there is any change over time." (What better than a Jedi to study energy that surrounds, penetrates, and binds?)


A lot. Thanks to the Galileo mission that ended in 2003, we do know much more about Jupiter and its system of moons than we did before. Among many other things, planetary scientists using Galileo data discovered giant thunderstorms along Jupiter's turbulent equator, complete with lightning strikes one thousand times more powerful than those found on Earth [PDF]. Cloudless "dry" spots of low humidity were discovered by a probe dropped into Jupiter, to its doom. The origin of the planet's rings were also worked out: They were formed from the debris left behind after meteoroid collisions with Jupiter's moons.

And yet for all we've learned, Jupiter remains a giant, terrifying mystery. Enter Juno, named after the wife of Jupiter in Roman mythology. Among the goddess's powers: the ability to see through clouds. And that power is in great demand at Jupiter, the largest known planet in the solar system. No one is completely certain what comprises Jupiter, and its oxygen content remains a mystery. Oxygen percentages might seem like snooze-level science geekery, but the answer to that question, according to NASA, is "the most important missing piece in our understanding of how our solar system formed." Moreover, it remains a mystery whether Jupiter is gas all the way down, or whether there a giant metal Earth-sized planet at its center. (Cybertron?) Just how far down do Jupiter's famous brown and tan cloud bands of clouds go? What's causing Jupiter's spectacular auroras? Juno will help us to answer these questions.

Hubble captures vivid auroras in Jupiter's atmosphere in June 2016. Image credit:


Juno will orbit a path along Jupiter's poles [PDF], which NASA describes as "best for mapping and monitoring a planet" and the same type of orbit used by many of Earth's satellites. This means that Juno will be the first spacecraft to get a good look at Jupiter's poles. Each orbit around Jupiter will take 11 days. Because a Jupiter day is only 10 hours long, this means that Juno will have mapped and studied the entire planet in 33 orbits. These orbits will get perilously close to the tops of Jupiter's clouds—a distance of 3100 miles. NASA notes that if Jupiter were a basketball, Juno would be flying one-third of an inch from the ball's surface. 

In October 2017, the spacecraft's mission will end and it will be "deorbited," plunging beneath Jupiter's clouds, where it will ultimately disintegrate. While this might seem like an ignominious end, it is, in fact, a heroic one. By sacrificing itself in the unforgiving hell that is the interior of Jupiter, Juno spares the surrounding moons of the Jovian system the risk of Earthly contamination. Europa, to name one such moon, is thought to harbor life. When the Europa missions get underway, we will know for sure that the life discovered is not of terrestrial origin. 

You can follow the Juno mission on NASA TV or on NASA's Eyes on the Solar System application. 

More Details Emerge About 'Oumuamua, Earth's First-Recorded Interstellar Visitor

In October, scientists using the University of Hawaii's Pan-STARRS 1 telescope sighted something extraordinary: Earth's first confirmed interstellar visitor. Originally called A/2017 U1, the once-mysterious object has a new name—'Oumuamua, according to Scientific American—and researchers continue to learn more about its physical properties. Now, a team from the University of Hawaii's Institute of Astronomy has published a detailed report of what they know so far in Nature.

Fittingly, "'Oumuamua" is Hawaiian for "a messenger from afar arriving first." 'Oumuamua's astronomical designation is 1I/2017 U1. The "I" in 1I/2017 stands for "interstellar." Until now, objects similar to 'Oumuamua were always given "C" and "A" names, which stand for either comet or asteroid. New observations have researchers concluding that 'Oumuamua is unusual for more than its far-flung origins.

It's a cigar-shaped object 10 times longer than it is wide, stretching to a half-mile long. It's also reddish in color, and is similar in some ways to some asteroids in our solar system, the BBC reports. But it's much faster, zipping through our system, and has a totally different orbit from any of those objects.

After initial indecision about whether the object was a comet or an asteroid, the researchers now believe it's an asteroid. Long ago, it might have hurtled from an unknown star system into our own.

'Oumuamua may provide astronomers with new insights into how stars and planets form. The 750,000 asteroids we know of are leftovers from the formation of our solar system, trapped by the Sun's gravity. But what if, billions of years ago, other objects escaped? 'Oumuamua shows us that it's possible; perhaps there are bits and pieces from the early years of our solar system currently visiting other stars.

The researchers say it's surprising that 'Oumuamua is an asteroid instead of a comet, given that in the Oort Cloud—an icy bubble of debris thought to surround our solar system—comets are predicted to outnumber asteroids 200 to 1 and perhaps even as high as 10,000 to 1. If our own solar system is any indication, it's more likely that a comet would take off before an asteroid would.

So where did 'Oumuamua come from? That's still unknown. It's possible it could've been bumped into our realm by a close encounter with a planet—either a smaller, nearby one, or a larger, farther one. If that's the case, the planet remains to be discovered. They believe it's more likely that 'Oumuamua was ejected from a young stellar system, location unknown. And yet, they write, "the possibility that 'Oumuamua has been orbiting the galaxy for billions of years cannot be ruled out."

As for where it's headed, The Atlantic's Marina Koren notes, "It will pass the orbit of Jupiter next May, then Neptune in 2022, and Pluto in 2024. By 2025, it will coast beyond the outer edge of the Kuiper Belt, a field of icy and rocky objects."

Last month, University of Wisconsin–Madison astronomer Ralf Kotulla and scientists from UCLA and the National Optical Astronomy Observatory (NOAO) used the WIYN Telescope on Kitt Peak, Arizona, to take some of the first pictures of 'Oumuamua. You can check them out below.

Images of an interloper from beyond the solar system — an asteroid or a comet — were captured on Oct. 27 by the 3.5-meter WIYN Telescope on Kitt Peak, Ariz.
Images of 'Oumuamua—an asteroid or a comet—were captured on October 27.

U1 spotted whizzing through the Solar System in images taken with the WIYN telescope. The faint streaks are background stars. The green circles highlight the position of U1 in each image. In these images U1 is about 10 million times fainter than the faint
The green circles highlight the position of U1 in each image against faint streaks of background stars. In these images, U1 is about 10 million times fainter than the faintest visible stars.
R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Color image of U1, compiled from observations taken through filters centered at 4750A, 6250A, and 7500A.
Color image of U1.
R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Editor's note: This story has been updated.

8 Useful Facts About Uranus
Uranus as seen by the human eye (left) and with colored filters (right).
Uranus as seen by the human eye (left) and with colored filters (right).

The first planet to be discovered by telescope, Uranus is the nearest of the two "ice giants" in the solar system. Because we've not visited in over 30 years, much of the planet and its inner workings remain unknown. What scientists do know, however, suggests a mind-blowing world of diamond rain and mysterious moons. Here is what you need to know about Uranus.


Uranus is the seventh planet from the Sun, the fourth largest by size, and ranks seventh by density. (Saturn wins as least-dense.) It has 27 known moons, each named for characters from the works of William Shakespeare and Alexander Pope. It is about 1784 million miles from the Sun (we're 93 million miles away from the Sun, or 1 astronomical unit), and is four times wider than Earth. Planning a trip? Bring a jacket, as the effective temperature of its upper atmosphere is -357°F. One Uranian year last 84 Earth years, which seems pretty long, until you consider one Uranian day, which lasts 42 Earth years. Why?


Most planets, as they orbit the Sun, rotate upright, spinning like tops—some faster, some slower, but top-spinning all the same. Not Uranus! As it circles the Sun, its motion is more like a ball rolling along its orbit. This means that for each hemisphere of the planet to go from day to night, you need to complete half an orbit: 42 Earth years. (Note that this is not the length of a complete rotation, which takes about 17.25 hours.) While nobody knows for sure what caused this 98-degree tilt, the prevailing hypothesis involves a major planetary collision early in its history. And unlike Earth (but like Venus!), it rotates east to west.


You might have noticed that every non-Earth planet in the solar system is named for a Roman deity. (Earth didn't make the cut because when it was named, nobody knew it was a planet. It was just … everything.) There is an exception to the Roman-god rule: Uranus. Moving outward from Earth, Mars is (sometimes) the son of Jupiter, and Jupiter is the son of Saturn. So who is Saturn's father? Good question! In Greek mythology, it is Ouranos, who has no precise equivalent in Roman mythology (Caelus is close), though his name was on occasion Latinized by poets as—you guessed it!—Uranus. So to keep things nice and tidy, Uranus it was when finally naming this newly discovered world. Little did astronomers realize how greatly they would disrupt science classrooms evermore.

Incidentally, it is not pronounced "your anus," but rather, "urine us" … which is hardly an improvement.


Uranus and Neptune comprise the solar system's ice giants. (Other classes of planets include the terrestrial planets, the gas giants, and the dwarf planets.) Ice giants are not giant chunks of ice in space. Rather, the name refers to their formation in the interstellar medium. Hydrogen and helium, which only exist as gases in interstellar space, formed planets like Jupiter and Saturn. Silicates and irons, meanwhile, formed places like Earth. In the interstellar medium, molecules like water, methane, and ammonia comprise an in-between state, able to exist as gases or ices depending on the local conditions. When those molecules were found by Voyager to have an extensive presence in Uranus and Neptune, scientists called them "ice giants."


Planets form hot. A small planet can cool off and radiate away heat over the age of the solar system. A large planet cannot. It hasn't cooled enough entirely on the inside after formation, and thus radiates heat. Jupiter, Saturn, and Neptune all give off significantly more heat than they receive from the Sun. Puzzlingly, Uranus is different.

"Uranus is the only giant planet that is not giving off significantly more heat than it is receiving from the Sun, and we don't know why that is," says Mark Hofstadter, a planetary scientist at NASA's Jet Propulsion Laboratory. He tells Mental Floss that Uranus and Neptune are thought to be similar in terms of where and how they formed.

So why is Uranus the only planet not giving off heat? "The big question is whether that heat is trapped on the inside, and so the interior is much hotter than we expect, right now," Hofstadter says. "Or did something happen in its history that let all the internal heat get released much more quickly than expected?"

The planet's extreme tilt might be related. If it were caused by an impact event, it is possible that the collision overturned the innards of the planet and helped it cool more rapidly. "The bottom line," says Hofstadter, "is that we don't know."


Although it's really cold in the Uranian upper atmosphere, it gets really hot, really fast as you reach deeper. Couple that with the tremendous pressure in the Uranian interior, and you get the conditions for literal diamond rain. And not just little rain diamondlets, either, but diamonds that are millions of carats each—bigger than your average grizzly bear. Note also that this heat means the ice giants contain relatively little ice. Surrounding a rocky core is what is thought to be a massive ocean—though one unlike you might find on Earth. Down there, the heat and pressure keep the ocean in an "in between" state that is highly reactive and ionic.


Unlike Saturn's preening hoops, the 13 rings of Uranus are dark and foreboding, likely comprised of ice and radiation-processed organic material. The rings are made more of chunks than of dust, and are probably very young indeed: something on the order of 600 million years old. (For comparison, the oldest known dinosaurs roamed the Earth 240 million years ago.)


The only spacecraft to ever visit Uranus was NASA's Voyager 2 in 1986, which discovered 10 new moons and two new rings during its single pass from 50,000 miles up. Because of the sheer weirdness and wonder of the planet, scientists have been itching to return ever since. Some questions can only be answered with a new spacecraft mission. Key among them: What is the composition of the planet? What are the interactions of the solar wind with the magnetic field? (That's important for understanding various processes such as the heating of the upper atmosphere and the planet's energy deposition.) What are the geological details of its satellites, and the structure of the rings?

The Voyager spacecraft gave scientists a peek at the two ice giants, and now it's time to study them up close and in depth. Hofstadter compares the need for an ice-giants mission to what happened after the Voyagers visited Jupiter and Saturn. NASA launched Galileo to Jupiter in 1989 and Cassini to Saturn in 1997. (Cassini was recently sent on a suicide mission into Saturn.) Those missions arrived at their respective systems and proved transformative to the field of planetary science.

"Just as we had to get a closer look at Europa and Enceladus to realize that there are potentially habitable oceans there, the Uranus and Neptune systems can have similar things," says Hofstadter. "We'd like to go there and see them up close. We need to go into the system." 


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