Month: November 2017

Magma Held In ‘Cold Storage’ Before Giant Volcano Eruption

Long Valley, California, has long defined the “super-eruption.” About 765,000 years ago, a pool of molten rock exploded into the sky. Within one nightmarish week, 760 cubic kilometers of lava and ash spewed out in the kind of volcanic cataclysm we hope never to witness.

The ash likely cooled the planet by shielding the sun, before settling across the western half of North America.

Here’s a rule of geoscience: The past heralds the future. So it’s not just morbid curiosity that attracts geoscientists to places like Long Valley. It’s an ardent desire to understand why super-eruptions happen, ultimately to understand where and when they are likely to occur again.

This week (Nov. 6, 2017), in the Proceedings of the National Academy of Sciences, a report shows that the giant body of magma — molten rock — at Long Valley was much cooler before the eruption than previously thought.

“The older view is that there’s a long period with a big tank of molten rock in the crust,” says first author Nathan Andersen, who recently graduated from the University of Wisconsin-Madison with a Ph.D. in geoscience. “But that idea is falling out of favor.

“A new view is that magma is stored for a long period in a state that is locked, cool, crystalline, and unable to produce an eruption. That dormant system would need a huge infusion of heat to erupt.”

It’s hard to understand how the rock could be heated from an estimated 400 degrees Celsius to the 700 to 850 degrees needed to erupt, but the main cause must be a quick rise of much hotter rock from deep below.

Instead of a long-lasting pool of molten rock, the crystals from solidified rock were incorporated shortly before the eruption, Andersen says. So the molten conditions likely lasted only a few decades, at most a few centuries. “Basically, the picture has evolved from the ‘big tank’ view to the ‘mush’ view, and now we propose that there is an underappreciation of the contribution of the truly cold, solidified rock.”

The new results are rooted in a detailed analysis of argon isotopes in crystals from the Bishop Tuff — the high-volume rock released when the Long Valley Caldera formed. Argon, produced by the radioactive decay of potassium, quickly escapes from hot crystals, so if the magma body that contained these crystals was uniformly hot before eruption, argon would not accumulate, and the dates for all 49 crystals should be the same.

And yet, using a new, high-precision mass spectrometer in the Geochronology Lab at UW-Madison, the research group’s dates spanned a 16,000 year range, indicating the presence of some argon that formed long before the eruption. That points to unexpectedly cool conditions before the giant eruption.

Better tools make better science, Andersen says. “The new instrument is more sensitive than its predecessors, so it can measure a smaller volume of gas with higher precision. When we looked in greater detail at single crystals, it became clear some must have been derived from magma that had completely solidified — transitioned from a mush to a rock.”

“Nathan found that about half of the crystals began to crystallize a few thousand years before the eruption, indicating cooler conditions,” says Brad Singer, a professor of geoscience at UW-Madison and director of the Geochronology Lab. “To get the true eruption age, you need to see the dispersion of dates. The youngest crystals show the date of eruption.”

The results have meaning beyond volcanology, however, as ash from Long Valley and other giant eruptions is commonly used for dating.

“These huge eruptions deposit ash all over the place, and that lets you make correlations in the rock record to aid geologic, biologic and climatic studies across the continent,” says Andersen. “This blanket of ash anchors you in time. The closer we can pin down the eruption age, the better we can study all facets of Earth’s history.”

“It’s controversial, but finding these older crystals means that part of this large magma body was very cool immediately prior to eruption,” says Singer, a volcanologist who was Andersen’s UW advisor. “This flies in the face of a lot of thermodynamics.”

A better understanding of the pre-eruption process could lead to better volcano forecasting — a highly useful but difficult proposition at present.

“This does not point to prediction in any concrete way,” says Singer, “but it does point to the fact that we don’t understand what is going on in these systems, in the period of 10 to 1,000 years that precedes a large eruption.”

CALET Makes First Direct Measurements Of High Energy Electrons In Space

The CALET Cosmic Ray experiment, led by Professor Shoji Torii from Waseda University in Japan, along with collaborators from LSU and other researchers in the U.S. and abroad, have successfully carried out the high-precision measurement of cosmic-ray electron spectrum up to 3 tera electron volts (TeV) by using the CALorimetric Electron Telescope (CALET) on the Japanese Experimental Module, the Exposed Facility on the International Space Station (ISS). This experiment is the first to make direct measurements of such high energy electrons in space.

The CALET team published its first results in Physical Review Letters November 1.

The CALET experiment is funded by the Japanese Space Agency (JAXA), the Italian Space Agency (ASI), and NASA. John Wefel, professor emeritus in LSU’s Department of Physics & Astronomy, serves as the spokesperson for the U.S. CALET team, which includes LSU (lead U.S. institution), NASA Goddard Space Flight Center, Washington University, and the University of Denver. Other LSU researchers working with the project are PhD student Nick Cannady, research associates Doug Granger and Amir Javaid, former LSU undergraduate Anthony Ficklin, and professors of physics and astronomy Greg Guzik and Mike Cherry.

“High energy electrons are difficult to measure, but important because they potentially provide information about nearby astrophysical sources of high energy radiation and/or dark matter,” said Cherry. “The initial results provide a hint of anticipated structure in the high energy spectrum, which may indicate the presence of a nearby source of high energy particles like a pulsar or the annihilation of dark matter.”

CALET was installed on the ISS in August 2015 and has been accumulating scientific data since October 2015 with a goal of five years of operation. CALET is the first Japanese-led space-based mission dedicated to cosmic ray observations.

The origin and acceleration of cosmic rays are still one of the cosmic mysteries, and cosmic-ray electrons are one of the most important targets of high-energy cosmic ray research. However, in order to observe high-energy electrons, it is required to have (1) high-precision energy measurement of each cosmic ray particle, (2) sensitivity to detect the very rare electron flux, and (3) the capability to identify electrons buried under the over 1,000 times higher flux of cosmic ray protons. Thus the measurement of electrons above 1 TeV has been a difficult goal to achieve.

The calorimeter of CALET, with its unique and crucial capabilities, enables scientists to perform accurate measurement of cosmic-ray electrons into the TeV region thanks to the long-term exposure available on the ISS.
This measurement demonstrates the ability of CALET to do a precise direct measurement of electrons above 1 TeV that was difficult for past experiments. With five years of observations, CALET will achieve nearly six times higher statistics compared to this first result, and will allow for reduction of the systematic uncertainties, including that from the detector response. The goal of the project is to push the energy limit to 20 TeV and to obtain the precise energy spectrum, hopefully making it possible to demonstrate definitively the presence of nearby astrophysical cosmic ray sources and/or to reveal the nature of dark matter.

Hubble Sees Nearby Asteroids Photobombing Distant Galaxies

Like rude relatives who jump in front your vacation snapshots of landscapes, some of our solar system’s asteroids have photobombed deep images of the universe taken by NASA’s Hubble Space Telescope. These asteroids reside, on average, only about 160 million miles from Earth-right around the corner in astronomical terms. Yet they’ve horned their way into this picture of thousands of galaxies scattered across space and time at inconceivably farther distances.

This Hubble photo of a random patch of sky is part of a survey called Frontier Fields. The colorful image contains thousands of galaxies, including massive yellowish ellipticals and majestic blue spirals. Much smaller, fragmentary blue galaxies are sprinkled throughout the field. The reddest objects are most likely the farthest galaxies, whose light has been stretched into the red part of the spectrum by the expansion of space.

Intruding across the picture are asteroid trails that appear as curved or S-shaped streaks. Rather than leaving one long trail, the asteroids appear in multiple Hubble exposures that have been combined into one image. Of the 20 total asteroid sightings for this field, seven are unique objects. Of these seven asteroids, only two were earlier identified. The others were too faint to be seen previously.

The trails look curved due to an observational effect called parallax. As Hubble orbits around Earth, an asteroid will appear to move along an arc with respect to the vastly more distant background stars and galaxies.

This parallax effect is somewhat similar to the effect you see from a moving car, in which trees by the side of the road appear to be passing by much more rapidly than background objects at much larger distances. The motion of Earth around the Sun, and the motion of the asteroids along their orbits, are other contributing factors to the apparent skewing of asteroid paths.

All the asteroids were found manually, the majority by “blinking” consecutive exposures to capture apparent asteroid motion. Astronomers found a unique asteroid for every 10 to 20 hours of exposure time.

The Frontier Fields program is a collaboration among NASA’s Great Observatories and other telescopes to study six massive galaxy clusters and their effects. Using a different camera, pointing in a slightly different direction, Hubble photographed six so-called “parallel fields” at the same time it photographed the massive galaxy clusters. This maximized Hubble’s observational efficiency in doing deep space exposures. These parallel fields are similar in depth to the famous Hubble Deep Field, and include galaxies about four-billion times fainter than can be seen by the human eye.

This picture is of the parallel field for the galaxy cluster Abell 370. It was assembled from images taken in visible and infrared light. The field’s position on the sky is near the ecliptic, the plane of our solar system. This is the zone in which most asteroids reside, which is why Hubble astronomers saw so many crossings. Hubble deep-sky observations taken along a line-of-sight near the plane of our solar system commonly record asteroid trails.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

Another Close-By Planetary System?

The ALMA Observatory in Chile has detected dust around the closest star to the Solar System, Proxima Centauri. These new observations reveal the glow coming from cold dust in a region between one to four times as far from Proxima Centauri as the Earth is from the Sun. The data also hint at the presence of an even cooler outer dust belt and may indicate the presence of an elaborate planetary system. These structures are similar to the much larger belts in the Solar System and are also expected to be made from particles of rock and ice that failed to form planets.

Proxima Centauri is the closest star to the Sun. It is a faint red dwarf lying just four light-years away in the southern constellation of Centaurus (The Centaur). It is orbited by the Earth-sized temperate world Proxima b, discovered in 2016 and the closest planet to the Solar System. But there is more to this system than just a single planet. The new ALMA observations reveal emission from clouds of cold cosmic dust surrounding the star.

The lead author of the new study, Guillem Anglada [1], from the Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain, explains the significance of this find: “The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”

Dust belts are the remains of material that did not form into larger bodies such as planets. The particles of rock and ice in these belts vary in size from the tiniest dust grain, smaller than a millimetre across, up to asteroid-like bodies many kilometres in diameter [2].

Dust appears to lie in a belt that extends a few hundred million kilometres from Proxima Centauri and has a total mass of about one hundredth of the Earth’s mass. This belt is estimated to have a temperature of about -230 degrees Celsius, as cold as that of the Kuiper Belt in the outer Solar System.

There are also hints in the ALMA data of another belt of even colder dust about ten times further out. If confirmed, the nature of an outer belt is intriguing, given its very cold environment far from a star that is cooler and fainter than the Sun. Both belts are much further from Proxima Centauri than the planet Proxima b, which orbits at just four million kilometres from its parent star [3].

Guillem Anglada explains the implications of the discovery: “This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”

Proxima Centauri’s planetary system is also particularly interesting because there are plans — the Starshot project — for future direct exploration of the system with microprobes attached to laser-driven sails. A knowledge of the dust environment around the star is essential for planning such a mission.

Co-author Pedro Amado, also from the Instituto de Astrofísica de Andalucía, explains that this observation is just the start: “These first results show that ALMA can detect dust structures orbiting around Proxima. Further observations will give us a more detailed picture of Proxima’s planetary system. In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”

Minerals In Volcanic Rock Offer New Insights Into The First 1.5 Billion Years Of Earth’s Evolution

The first 1.5 billion years of Earth’s evolution is subject to considerable uncertainty due to the lack of any significant rock record prior to four billion years ago and a very limited record until about three billion years ago. Rocks of this age are usually extensively altered making comparisons to modern rock quite difficult. In new research conducted at LSU, scientists have found evidence showing that komatiites, three-billion-year old volcanic rock found within the Earth’s mantle, had a different composition than modern ones. Their discovery may offer new information about the first one billion years of Earth’s development and early origins of life.

Results of the team’s work has been published in the October 2017 edition of Nature Geoscience.

The basic research came from more than three decades of LSU scientists studying and mapping the Barberton Mountains of South Africa. The research team, including LSU geology professors Gary Byerly and Huiming Bao, geology PhD graduate Keena Kareem, and LSU researcher Benjamin Byerly, conducted chemical analyses of hundreds of komatiite rocks sampled from about 10 lava flows.

“Early workers had mapped large areas incorrectly by assuming they were correlatives to the much more famous Komati Formation in the southern part of the mountains. We recognized this error and began a detailed study of the rocks to prove our mapping-based interpretations,” said Gary Byerly.

Within the rocks, they discovered original minerals called fresh olivine, which had been preserved in remarkable detail. Though the mineral is rarely found in rocks subjected to metamorphism and surface weathering, olivine is the major constituent of Earth’s upper mantle and controls the nature of volcanism and tectonism of the planet. Using compositions of these fresh minerals, the researchers had previously concluded that these were the hottest lavas to ever erupt on Earth’s surface with temperatures near 1600 degrees centigrade, which is roughly 400 degrees hotter than modern eruptions in Hawaii.

“Discovering fresh unaltered olivine in these ancient lavas was a remarkable find. The field work was wonderfully productive and we were eager to return to the lab to use the chemistry of these preserved olivine crystals to reveal clues of the Archean Mantle,” said Kareem.

The researchers suggest that maybe a chunk of early-Earth magma ocean is preserved in the approximately 3.2 billion year-old minerals.

“The modern Earth shows little or no evidence of this early magma ocean because convection of the mantle has largely homogenized the layering produced in the magma ocean. Oxygen isotopes in these fresh olivines support the existence of ancient chunks of the frozen magma ocean. Rocks like this are very rare and scientifically valuable. An obvious next step was to do oxygen isotopes,” said Byerly.

This study grew out of work taking place in LSU’s laboratory for the study of oxygen isotopes, a world-class facility that attracts scientists from the U.S. and international institutions for collaborative work. The results of the study were so unusual that it required extra care to be certain of the results. Huiming Bao, who is also the head of LSU’s oxygen isotopes lab, said that the team triple and quadruple checked the data by running with different reference minerals and by calibrating with other independent labs.

“We attempted to reconcile the findings with some of the conventional explanations for lavas with oxygen isotope compositions like these, but nothing could fully explain all of the observations. It became apparent that these rocks preserve signatures of processes that occurred over four billion years ago and that are still not completely understood,” said Benjamin Byerly.

Oxygen isotopes are measured by the conversion of rock or minerals into a gas and measuring the ratios of oxygen with the different masses of 16, 17, and 18. A variety of processes fractionate oxygen on Earth and in the Solar System, including atmospheric, hydrospheric, biological, and high temperature and pressure.

“Different planets in our solar system have different oxygen isotope ratios. On Earth this is modified by surface atmosphere and hydrosphere, so variations could be due either to heterogeneous mantle (original accumulation of planetary debris or remnants of magma ocean) or surface processes,” said Byerly. “Either might be interesting to study. The latter because it would also provide information about the early surface temperature of Earth and early origins of life.”

Atmospheric Beacons Guide NASA Scientists In Search For Life

Some exoplanets shine brighter than others in the search for life beyond the solar system. New NASA research proposes a novel approach to sniffing out exoplanet atmospheres. It takes advantage of frequent stellar storms — which hurl huge clouds of stellar material and radiation into space — from cool, young dwarf stars to highlight signs of habitable exoplanets.

Traditionally, researchers have sought potential biosignatures as ways of identifying inhabited worlds: byproducts from life as we know it such as oxygen or methane that over time accumulate in the atmosphere to detectable amounts. But with current technology, according to Vladimir Airapetian, lead author of a Scientific Reports study published on Nov. 2, 2017, identifying these gases on distant terrestrial exoplanets is time-consuming, requiring days of observation time. The new study suggests hunting for cruder signatures of potentially habitable worlds instead, which would be easier to detect with current resources in less time.

“We’re in search of molecules formed from fundamental prerequisites to life — specifically molecular nitrogen, which is 78 percent of our atmosphere,” said Airapetian, who is a solar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and at American University in Washington, D.C. “These are basic molecules that are biologically friendly and have strong infrared emitting power, increasing our chance of detecting them.”

Present life on Earth tells Airapetian and his team of researchers they should look for atmospheres rich with water vapor and nitrogen, and oxygen, the product of life. Oxygen and nitrogen free-float stably in their molecular form — that is, two atoms of either oxygen or nitrogen bound together in one molecule. But in the vicinity of an active dwarf star, extreme space weather sparks distinct chemical reactions, which researchers can use as indicators of atmospheric composition.

Stars like our Sun are turbulent in their adolescence and frequently produce powerful eruptions that fling stellar particles ahead of them to near-light speeds. Unlike our Sun, some yellow and most orange stars — which are a bit cooler than the Sun — may continue to produce these strong stellar storms for billions of years, generating frequent swarms of high-energy particles.

When these particles reach an exoplanet, they flood its atmosphere with enough energy to break molecular nitrogen and oxygen into individual atoms, and water molecules into hydroxyl — one atom each of oxygen and hydrogen, bound together. From there, the reactive nitrogen and oxygen atoms spark a cascade of chemical reactions that ultimately produce what the scientists call atmospheric beacons: hydroxyl, more molecular oxygen, and nitric oxide — a molecule made of one nitrogen and one oxygen atom.

Airapetian and his colleagues used a model to calculate just how much nitric oxide and hydroxyl would form and how much ozone would be destroyed in an Earth-like atmosphere around an active star. Earth scientists have used this model for decades to study how ozone — which forms naturally when sunlight strikes oxygen — in the upper atmosphere responds to solar storms, but it found a new application in this study; Earth is, after all, the best case study available in the search for life.

Using a computer simulation, the researchers exposed the model atmosphere to the space weather they’d expect from a cool, active star. They found that ozone drops to a minimum and fuels the production of atmospheric beacons.

For researchers, these chemical reactions are very useful. When starlight strikes the atmosphere, spring-like bonds within the beacon molecules absorb the energy and vibrate, sending that energy back into space as heat, or infrared radiation. Scientists know which gases emit radiation at particular wavelengths of light, so by looking at all the radiation coming from the atmosphere, it’s possible to get a sense of what’s in the atmosphere itself.

Forming a detectable amount of these beacons requires a large quantity of molecular oxygen and nitrogen. So, if they are detected, these compounds could indicate an atmosphere filled with biologically friendly chemistry, as well as Earth-like atmospheric pressure — and thus the possibility of a habitable world, one needle in a vast haystack of exoplanets.

This approach is also meant to weed out exoplanets without an Earth-like magnetic field. “A planet needs a magnetic field, which shields the atmosphere and protects the planet from stellar storms and radiation,” Airapetian said. “If stellar winds aren’t so extreme as to compress an exoplanet’s magnetic field close to its surface, the magnetic field prevents atmospheric escape, so there are more particles in the atmosphere and a stronger resulting infrared signal.”

Airapetian and his colleagues used data from NASA’s Earth-studying TIMED mission — short for Thermosphere Ionosphere Mesophere Energetics Dynamics — to simulate how infrared observations of these beacons might appear. The data came from TIMED’s spectroscopy instrument called SABER — short for Sounding of the Atmosphere using Broadband Emission Radiometry — which studies the very same chemistry that generates the atmospheric beacons, as it occurs in Earth’s upper atmosphere in response to solar activity.

“Taking what we know about infrared radiation emitted by Earth’s atmosphere, the idea is to look at exoplanets and see what sort of signals we can detect,” said Martin Mlynczak, a co-author of the paper and the SABER associate principal investigator at NASA’s Langley Research Center in Hampton, Virginia. “If we find exoplanet signals in nearly the same proportion as Earth’s, we could say that planet is a good candidate for hosting life.”

The SABER data showed the frequency of intense stellar storms is directly related to the strength of the heat signals from the atmospheric beacons. With more storms, more beacon molecules are generated and the infrared signal would be strong enough, the scientists estimate, to be observed from nearby exoplanets with a six to 10-meter space-based telescope in just two hours of observation time.

“This is an exciting new proposed way to look for life,” said Shawn Domagal-Goldman, a Goddard astrobiologist not connected with the study. “But as with all signs of life, the exoplanet community needs to think hard about context. What are the ways non-biological processes could mimic this signature?”

With the right kind of star, this work could lead to new strategies in the search for life that identify not just potentially habitable planets, but planetary systems, as the way a planet’s atmosphere interacts with its parent star also has a key effect on its habitability. If promising signals are detected, researchers can coordinate observations with a future space-based observatory such as NASA’s James Webb Space Telescope, increasing the likelihood of discovering such a potential system.

“New insights on the potential for life on exoplanets depend critically on interdisciplinary research in which data, models and techniques are utilized from NASA Goddard’s four science divisions: heliophysics, astrophysics, planetary and Earth sciences,” Goddard senior astrophysicist and co-author William Danchi said. “This mixture produces unique and powerful new pathways for exoplanet research.”

NASA Investigates Invisible Magnetic Bubbles In Outer Solar System

Space may seem empty, but it’s actually a dynamic place populated with near-invisible matter, and dominated by forces, in particular those created by magnetic fields. Magnetospheres — the magnetic fields around most planets — exist throughout our solar system. They deflect high-energy, charged particles called cosmic rays that are spewed out by the Sun or come from interstellar space. Along with atmospheres, they happen to protect the planets’ surfaces from this harmful radiation.

But not all magnetospheres are created equal: Venus and Mars do not have magnetospheres at all, while the other planets — and one moon — have ones that are surprisingly different.

NASA has launched a fleet of missions to study the planets in our solar system — many of which have sent back crucial information about magnetospheres. The twin Voyagers measured magnetic fields as they traveled out to the far reaches of the solar system, and discovered Uranus and Neptune’s magnetospheres. Other planetary missions including Galileo, Cassini and Juno, and a number of spacecraft that orbit Earth, provide observations to create a comprehensive understanding of how planets form magnetospheres, as well as how they continue to interact with the dynamic space environment around them.

Earth

Earth’s magnetosphere is created by the constantly moving molten metal inside Earth. This invisible “force field” around our planet has a general shape resembling an ice cream cone, with a rounded front and a long, trailing tail that faces away from the sun. The magnetosphere is shaped that way because of the near-constant flow of solar wind and magnetic field from the Sun-facing side.

Earth’s and other magnetospheres deflect charged particles away from the planet — but also trap energetic particles in radiation belts. Auroras are caused by particles that rain down into the atmosphere, usually not far from the magnetic poles.

It’s possible that Earth’s magnetosphere was essential for the development of conditions friendly to life, so learning about magnetospheres around other planets and moons is a big step toward determining if life could have evolved there.

Mercury

Mercury, with a substantial iron-rich core, has a magnetic field that is only about 1 percent as strong as Earth’s. It is thought that the planet’s magnetosphere is compressed by the intense solar wind, limiting its extent. The MESSENGER satellite orbited Mercury from 2011 to 2015, helping us understand our tiny terrestrial neighbor.

Jupiter

After the Sun, Jupiter has by far the strongest and biggest magnetic field in our solar system — it stretches about 12 million miles from east to west, almost 15 times the width of the Sun. (Earth’s, on the other hand, could easily fit inside the Sun — except for its outstretched tail.) Jupiter does not have a molten metal core; instead, its magnetic field is created by a core of compressed liquid metallic hydrogen.

One of Jupiter’s moons, Io, has powerful volcanic activity that spews particles into Jupiter’s magnetosphere. These particles create intense radiation belts and auroras around Jupiter.

Ganymede, Jupiter’s largest moon, also has its own magnetic field and magnetosphere — making it the only moon with one. Its weak field, nestled in Jupiter’s enormous shell, scarcely ruffles the planet’s magnetic field.

Saturn

Saturn’s huge ring system transforms the shape of its magnetosphere. That’s because oxygen and water molecules evaporating from the rings funnel particles into the space around the planet. Some of Saturn’s moons help trap these particles, pulling them out of Saturn’s magnetosphere, though those with active volcanic geysers — like Enceladus — spit out more material than they take in. NASA’s Cassini mission followed in the Voyagers’ wake, and studied Saturn’s magnetic field from orbit around the ringed planet between 2004 and 2017.

Uranus

Uranus’ magnetosphere wasn’t discovered until 1986, when data from Voyager 2’s flyby revealed weak, variable radio emissions and confirmed when Voyager 2 measured the magnetic field directly. Uranus’ magnetic field and rotation axis are out of alignment by 59 degrees, unlike Earth’s, whose magnetic field and rotation axis are nearly aligned. On top of that, the magnetic field does not go directly through the center of the planet, so the strength of the magnetic field varies dramatically across the surface. This misalignment also means that Uranus’ magnetotail — the part of the magnetosphere that trails behind the planet, away from the Sun — is twisted into a long corkscrew.

Neptune

Neptune was also visited by Voyager 2, in 1989. Its magnetosphere is offset from its rotation axis, but only by 47 degrees. Similar to Uranus, Neptune’s magnetic field strength varies across the planet. This means that auroras can appear across the planet — not just close to the poles, like on Earth, Jupiter and Saturn.

And beyond

Outside of our solar system, auroras, which indicate the presence of a magnetosphere, have been spotted on brown dwarfs — objects that are bigger than planets but smaller than stars. There’s also evidence to suggest that some giant exoplanets have magnetospheres, but we have yet to see conclusive proof. As scientists learn more about the magnetospheres of planets in our solar system, it can help us one day identify magnetospheres around more distant planets as well.