The Greatest Mysteries of Jupiter’s Moons

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The Greatest Mysteries of Jupiter’s Moons

 The Greatest Mysteries of Jupiter's Moons

Each week this summer, Life’s Little Mysteries, a sister site to LiveScience, presents The Greatest Mysteries of the Cosmos, starting with the coolest stuff in our solar system.

The biggest planet in the solar system, Jupiter, also boasts the most moons, with 64 currently cataloged. Most of these moons are tiny, lumpy rocks — apparently asteroids captured by Jupiter’s gravity — and they swarm about the giant planet like so many bees around a hive.

Four of Jupiter’s moons, however, are quite substantial — so much so that they can be seen through a rudimentary telescope. The inventor of just that instrument, Italian astronomer Galileo Galilei, first saw the thusly named “Galilean moons” in 1610: Io, Europa, Ganymede and Callisto.

Together, these four moons comprise more than 99.9 percent of the mass of Jupiter’s satellites. Each of them has a distinctive character, and they all present vexing scientific puzzles. Here is a rundown of the top mysteries regarding Jupiter’s primary four moons.

Io, the hyperactive pizza moon

Io is the closest of the Galilean moons to Jupiter. This proximity is thought to help explain the moon’s uniquely hellish, sulfur-yellow, red-splotched and pockmarked appearance.

Those pocks, in fact, are volcanoes. Io sports 400 or so active volcanoes, as well as soaring mountains formed by tectonics. Overall, the moon is the most geologically active object in our solar system.

The energy powering this activity comes largely from a gravitational tug-of-war between Jupiter and the other three Galilean moons with Io caught in the middle. The constant stretching and compressing that this tug exerts on Io heats its interior, prompting the moon to often ooze out lava and spew sulfur and ash into space.

Such tidal forces, however, might not account for all this oomph. The history of variances in the gravitational flexing of Io also remains murky.

“I don’t think we know enough about the exact frequency of these things to adequately assess the whole mechanism,” said Scott Bolton, principal investigator for NASA’s Juno spacecraft mission, which launches this year to study Jupiter.

Given how interesting the moon is, “Io could be the focus of an entire mission,” added Bolton, who, in addition to his Juno post, is also director of the space science and engineering division at the Southwest Research Institute in San Antonio, Texas.

Europa, a smart bet for extraterrestrial life?

The moon of Jupiter that’s definitely highest on the list for someday getting its own dedicated mission is Europa. This icy-white object with brownish streaks on its surface stands as one of the best candidates for hosting extraterrestrial life in our solar system.

Under an icy crust anywhere from a couple to perhaps 20 miles (three to 32 kilometers) thick, Europa probably harbors a saltwater ocean. Depending on the assumptions and models used, this ocean could have twice the volume of all those on Earth. [Why Doesn’t Our Moon Have a Name?]

Understandably, astronomers are bubbling over with questions about this subterranean (sub-Europian?) sea. The chief query: “Might it allow for life development in any way?” asked Bolton.

The idea is not so far-fetched. Tidal flexing from Jupiter could keep the interior of Europa warm. This energy could, in turn, support microbial life analogous to that found around hydrothermal vents in Earth’s oceans. Cosmic rays from space striking the crustal ice could even free up oxygen to power bigger life forms, such as fish.

Ganymede, big and oddly magnetic

Jupiter’s largest moon, Ganymede, reigns as the biggest moon in the solar system. In face, it’s even larger than the planet Mercury.

Another distinction for Ganymede: it’s the only moon with its own magnetosphere, which is a region surrounding the world where charged particles from the sun are deflected by a magnetic field.

“How that [magnetosphere] gets created is very fascinating,” said Bolton. “We don’t know of another small body that has that.”

Ganymede’s magnetosphere is most likely made in a manner much like Earth’s, due to convection in the moon’s liquid iron core. Learning how it’s generated would help with better understanding our own planet’s magnetic field.

To boot, Ganymede might also a hidden ocean sloshing under its gray, rocky and icy crust. [Handy Chart: How Much Would You Weigh on Jupiter?]

Battered Callisto

The Galilean moon with the farthest orbit from Jupiter is Callisto. Unlike Io and Europa (and even Ganymede to an extent), where geologic activity has erased many craters, Callisto bears the scars of eons’ worth of meteorite impacts. The geologically dead moon is considered the most heavily cratered object in the solar system.

Callisto’s landscape is therefore among the oldest on record, aged some four billion years. Analyzing its surface materials would be like opening a time warp back to the early solar system.

Callisto might be full of surprises on the inside, too — an underground ocean could lurk here as well, yet another possible abode for alien life out in Jupiter’s neighborhood.

Bonus boggler: Ringed remnants of a destroyed moon

Since its discovery in 2000, a tiny moon just 2.5 miles (four kilometers) in diameter and given the designation S/2000 J 11 has gone missing. Astronomers think the moonlet has actually smashed into Himalia, Jupiter’s fifth most massive moon after the four Galileans.

That possible impact appears to have created a streak of material, observed in 2006, that might even be a whole new ring around Jupiter. The planet’s faint rings naturally do not get the fanfare of Saturn’s resplendent rings, but as with Saturn, moons play a key role in supplying the particles that make up the giant disks.

This story was provided by Life’s Little Mysteries, a sister site to LiveScience. Follow Life’s Little Mysteries on Twitter @llmysteries, then join us on Facebook.

How Much Would You Weigh on Other Planets?

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How Much Would You Weigh on Other Planets?

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 Whether you are a science fiction fan, a space enthusiast or one of the millions who have watched astronauts gamboling about the moon’s surface, you may have wondered how much you would weigh on other planets in the solar system.

To sort this out, it first helps to know a little Physics 101. [Would Humans Born On Mars Grow Taller than Earthlings? ]

Weight is the force gravity exerts on an object due to its mass. Mass, roughly, measures an object’s inertia, its resistance to being moved or stopped, once it’s in motion. Your mass remains constant across the universe (except in certain cases discussed in special relativity , but that is another story), while your weight changes depending on the gravitational forces acting on you, which vary from planet to planet.

Newton’s Law of Universal Gravitation says that everything that has mass attracts every other thing that has mass, pulling with a force (a) directly proportional to the product of the two objects’ masses and (b) inversely proportional to the square of the distance separating their centers.

In other words, although gravity increases linearly as objects grow more massive, it decreases exponentially as the distance between them increases (a phenomenon known as an inverse-square law). Whencalculating surface gravity, that distance refers to the space separating you (on the surface) from the planet’s center of mass. This means that a planet’s size actually has a greater relative impact on its gravity and on your weight on its surface than does its mass.

Written as a formula, Newton’s gravitation law looks something like this:

F = G((Mm)/r2)


  • F is the gravitational force between two objects,
  • G is the Gravitational Constant (6.674×10-11 Newtons x meters2 / kilograms2),
  • M is the planet’s mass (kg),
  • m is your mass (kg), and
  • r is the distance (m) between the centers of the two masses (the planet’s radius).

Without getting too bogged down in the math, we can see that this leads to a surprising result. Take the most massive planet in the solar system,Jupiter, which tips the scales at 316 times the mass of the Earth. You might imagine you would weigh 316 times as much there as here. However, because Jupiter’s radius balloons to roughly 11 times as large as Earth’s, its gravitational force drops off by a factor of 1/112 at its surface (assuming you could find a way to stand on gas clouds).

However, that does not mean that the proportion of Jupiter’s gravity to Earth’s is 316 / 112. To calculate the ratio between Earth’s surface gravity and that of any other celestial body, you must compute them separately using the formula above, and then divide the desired planet’s gravitational force by Earth’s. We will spare you the work:

  • Mercury: 0.38
  • Venus: 0.91
  • Earth: 1.00
  • Mars: 0.38
  • Jupiter: 2.34
  • Saturn: 1.06
  • Uranus: 0.92
  • Neptune: 1.19
  • Pluto: 0.06

Because weight = mass x surface gravity, multiplying your weight on Earth by the numbers above will give you your weight on the surface of each planet. If you weigh 150 pounds (68 kg.) on Earth, you would weigh 351 lbs. (159 kg.) on Jupiter, 57 lbs. (26 kg.) on Mars and a mere 9 lbs. (4 kg.) on the dwarf planet of Pluto.



Note that Mercury and Mars have the same proportional gravity, even though Mars is almost twice as massive as Mercury. Mars’ superior size, 1.4 times the diameter of Mercury, trumps the effect of its extra mass because of the inverse-square relationship between gravity and distance.

Uranus and Venus present an even more striking example of this phenomenon: Although Uranus lugs around 17.8 times the mass of Venus, its 4.2- times-larger diameter still negates the difference in proportional surface gravity.

Original story on Live Science.

Mysteries at Jupiter: NASA’s Juno Probe Reveals Cyclones, Auroras & Surprises

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Mysteries at Jupiter: NASA’s Juno Probe Reveals Cyclones, Auroras & Surprises

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Huge cyclones rage near Jupiter’s mysterious poles, and the giant planet’s powerful auroras are fundamentally different from Earth’s northern and southern lights.

Those are just two of the discoveries made by NASA’s Juno spacecraft during its first few close passes over Jupiter’s poles, mission scientists report in two studies published online today (May 25) in the journal Science.

“What we’ve learned so far is Earth-shattering. Or should I say, Jupiter-shattering,” Juno principal investigator Scott Bolton, of the Southwest Research Institute in San Antonio, said in a statement. [Photos: NASA’s Juno Mission to Jupiter]

“Discoveries about its core, composition, magnetosphere, and poles are as stunning as the photographs the mission is generating,” added Bolton, the lead author of one of the new Science studies and a co-author of the other.

The south pole of Jupiter is seen from an altitude of 32,000 miles (52,000 kilometers) in this enhanced color mosaic of images from NASA's JunoCam. Cyclones up to 600 miles wide (1,000 km) are visible.

The south pole of Jupiter is seen from an altitude of 32,000 miles (52,000 kilometers) in this enhanced color mosaic of images from NASA’s JunoCam. Cyclones up to 600 miles wide (1,000 km) are visible.

Credit: NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles SCOTT BOLTON – 3

The $1.1 billion Juno mission launched in August 2011 and arrived in orbit around Jupiter on July 4, 2016. Since then, the solar-powered spacecraft has been using eight instruments to study the gas giant’s composition, interior structure, and gravitational and magnetic fields. It will continue to do this work, barring some sort of malfunction, through at least February 2018, the end of Juno’s primary mission.

The mission’s name is a nod to the Roman goddess Juno, who was able to look through the clouds to see her frequently misbehaving husband Jupiter, the king of the gods, who was hiding within. Likewise, the Juno probe is peering beneath Jupiter’s thick clouds to learn about the planet’s formation and evolution — information that could shed light on the history of our solar system as a whole, NASA officials have said.

Juno makes most of the measurements relevant to this goal during its close flybys, which occur once every 53.5 days and bring the probe within about 3,100 miles (5,000 kilometers) of Jupiter’s poles. (The original mission blueprint called for Juno to maneuver to a less elliptical orbit and make these flybys every 14 days, but an issue with two helium valves in the spacecraft’s propulsion system nixed that plan.)

GIF showing infrared emission from Jupiter, as observed by NASA's Juno spacecraft.

GIF showing infrared emission from Jupiter, as observed by NASA’s Juno spacecraft.

Credit: S.J. Bolton et al., Science (2017)

Juno has now made five of these data-collecting “perijove passes.” The first came on Aug. 27, 2016, and the most recent occurred just last week, on May 19. The two new Science papers report results just from the first few flybys, as well as some measurements Juno made as it neared Jupiter in June 2016.

Before Juno, no spacecraft had ever gotten close-up looks at Jupiter’s poles. These mysterious regions are beautiful and bizarre, the Bolton-led study reports.

“When you look over the poles, all of those zones and belts are gone,” Bolton said in a Science podcast that was also released today, referring to the striped cloud patterns prevalent at Jupiter’s lower latitudes. “You see this bluish hue to it, and there’s tons of these cyclone and anticyclonic storms spinning around the poles. It almost looks like meteor craters, but, of course, it’s all atmosphere. It’s all gas.” [Photos: Jupiter, the Solar System’s Largest Planet]

It’s unclear what, exactly, drives these polar cyclones, some of which are up to 870 miles (1,400 km) wide, or if they’re stable over long periods, Bolton said.

“Over the course of the mission, we’ll be able to watch the poles and see how they evolve,” he said in the podcast. “Maybe these cyclones are always there, but maybe they just come and go.”

Juno also has been mapping out the concentration of water and ammonia deep within Jupiter’s atmosphere. Data gathered during the first few passes has revealed that ammonia abundances vary quite a bit from place to place — a discovery that surprised the mission team.

“Most scientists have felt that, as soon as you go down a little bit into Jupiter, everything would be well-mixed, and we’re finding that that’s just not true at all,” Bolton said. “There’s structure down deep, but it doesn’t seem to match the zones and belts. And so we’re still trying to figure it out.”

Juno’s measurements during the first few close passes also show that Jupiter’s magnetic field is nearly two times stronger than scientists had predicted. And the probe’s gravity data suggest that “there’s a lot of strange, deep motions that possibly are going on inside of Jupiter,” Bolton said.

“What Juno’s results are showing us is that our ideas of giant planets maybe are a little bit oversimplified,” he added. “They’re more complex than we thought; the motions that are going on inside are more complicated. It’s possible that they formed differently than [suggested by] our simple ideas.”

The southern lights of Jupiter, auroras at the planet's south pole, glow in this animation of false-color images from NASA's Juno spacecraft. The red hues suggest emissions from deeper in Jupiter's atmosphere, while green and white indicate higher regions.

The southern lights of Jupiter, auroras at the planet’s south pole, glow in this animation of false-color images from NASA’s Juno spacecraft. The red hues suggest emissions from deeper in Jupiter’s atmosphere, while green and white indicate higher regions.

Credit: NASA/JPL-Caltech/SWRI

Earth’s auroras result when the solar wind — charged particles streaming from the sun — slam into the planet’s atmosphere, generating a glow. (Earth’s magnetic field funnels these particles toward the poles, which explains the phenomenon’s other name: the northern and southern lights.)

Scientists already knew that the solar wind is a major driver of Jovian auroras, and that the planet’s rotation is involved as well. But Juno has given researchers a chance to study the phenomenon in unprecedented detail; no other spacecraft had ever flown close to the planet’s auroral regions before, Bolton said.

The second newly published Science study, which was led by John Connerney of the Space Research Corporation and NASA’s Goddard Space Flight Center in Maryland, details what the Juno team learned about the auroras and Jupiter’s magnetosphere from the initial perijove passes. Once again, there were some surprises.

For example, the particles associated with Jupiter’s auroras seem to be different than the ones responsible for Earth’s most stunning light shows, study team members said.

“We can see that it doesn’t work exactly like we expected, or as the Earth does,” Bolton said. “We haven’t been able to see particles necessarily going up and down in both directions like we would’ve expected to cause the aurora. So there’s definitely some strange phenomena that we still need to comb through and understand better.”

Further close flybys should allow the Juno team to investigate such questions, he added.

“We’re at the beginning of the mission, so these first results are sort of telling us some of our models and ideas are wrong and need to be corrected,” Bolton said. “And we have some ideas of which way to go, but it really takes some more data to really test whatever theories we put together and see if we’re right.”

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These Hellish Storms on Jupiter Are Mesmerizing to Watch

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These Hellish Storms on Jupiter Are Mesmerizing to Watch

 Jupiter’s north pole is a mesmerizing stew of glowing storms in a new video released by NASA.

Using data from NASA’s Juno mission, researchers created a 3D flyover of the gas giant’s north pole in infrared. It shows the turbulent dynamics of the pole, which is topped by a huge cyclone about 2,500 miles (4,000 kilometers) across. Ringing this monster atmospheric storm are eight other cyclones with diameters ranging from 2,500 to 2,900 miles (4,000 to 4,700 km).

The Juno spacecraft launched on Aug. 5, 2011, and entered Jupiter’s orbit on July 4, 2016, flying as low as 2,200 miles (3,500 km) over the highest cloud tops of the planet, according to NASA. The goal of the mission is to understand the atmosphere, magnetosphere and gravity fields of the fifth planet from the sun, which, in turn, will help planetary scientists grasp howJupiter formed and how it has changed over the lifetime of the solar system, according to the space agency. [In Photos: The Most Powerful Storms in the Solar System]

Juno mission scientists unveiled the new animation Wednesday (April 11) at the European Geosciences Union General Assembly in Vienna. The video uses data collected by the Jovian Infrared Auroral Mapper (JIRAM) aboard Juno. This instrument images the infrared portion of the spectrum, which is invisible to the human eye. By monitoring infrared wavelengths, JIRAM can “see” up to 45 miles (70 km) below the clouds that swirl around Jupiter, according to a statement from NASA’s Jet Propulsion Laboratory.

Jupiter's north pole is swirling with cyclones.
Jupiter’s north pole is swirling with cyclones.

Credit: NASA

This multilayer view helps scientists understand how Jupiter’s interior rotates, study investigator Tristan Guillot, of the University of Côte d’Azur in France, said in that statement.

“Thanks to the amazing increase in accuracy brought by Juno’s gravity data, we have essentially solved the issue of how Jupiter rotates: The zones and belts that we see in the atmosphere rotating at different speeds extend to about 1,900 miles (3,000 km),” Guillot said.

Deeper than that, he said, and the powerful magnetic field of Jupiter keeps the largely hydrogen-and-helium atmosphere swirling at a uniform speed.

In other work presented at the Vienna meeting, Juno researchers mapped Jupiter’s magnetic field, modeling the deep-interior “dynamo” where the rotation of the planet creates the magnetic field. They discovered surprising complexities and irregularities in the magnetic field, including more complexity in the northern hemisphere than in the southern hemisphere.

Juno will make its 12th data-collecting pass around the planet on May 24, according to NASA.

The animation data used to create the lava-like video of Jupiter’s pole came from Juno’s fourth pass over the gas giant. Yellow areas are warmer, and thus deeper in the planet’s atmosphere; dark areas are colder and higher. According to NASA, the temperature of Jupiter’s cloud tops is about minus 234 degrees Fahrenheit (minus 148 degrees Celsius).

“Now our work can really begin in earnest — determining the interior composition of the solar system’s largest planet,” Guillot said.

Original article on Live Science.