Journal of Geophysical Research: Space Physics

Beginning roughly 60 kilometers above the surface of the Earth and extending hundreds of kilometers above that, the shell of plasma known as the ionosphere surrounds the planet. This ionized layer of Earth’s atmosphere is a complex structure that conducts electricity, interacts with radio waves, and continuously changes throughout the day. As the Sun shines on it, the onslaught of photons begins to strip away the electrons from molecules in the atmosphere, ionizing them and producing even more Continue reading >

Saturn’s magnetosphere exhibits phenomena with 10.7-hour periodicity that scientists do not fully understand. One proposed explanation is that twin vortices in the upper atmosphere at Saturn’s north and south poles generate currents that drive the magnetosphere periodicity. Smith analyzed the vortex model and the problems with it, considering the possible mechanisms by which atmospheric vortices could drive currents that generate the observed periodicity. He noted that the model has two problem Continue reading >

Since the 1970s, scientists have observed broadband electrostatic noise (BEN) coming from boundary layer regions in the Earth’s magnetosphere. Until recently, the cause of that noise was not well understood. Last year, scientist Ami DuBois was the first to experimentally show that by compressing a magnetized plasma, such as the plasma that makes up the magnetospheric boundary layer, she could create BEN. This year, DuBois et al. took the research one step further and examined more closely how c Continue reading >

The Earth’s magnetic field extends out into space, influencing charged particles in a region known as the magnetosphere. The magnetosphere is short and squat on the side of Earth that faces the Sun—the dayside—but it has a long tail extending away from the star on the nightside. This magnetotail is shaped by the powerful force of the solar wind, and huge amounts of plasma flow within it. On Earth, we see the effects of this flow in the dazzling lights of the auroras. Dramatic bursts of energy i Continue reading >

Unlike Earth, whose magnetic field deflects much of the incoming solar wind, the surface of the Moon absorbs most of the particles that the Sun sends its way. This creates a void behind the Moon that gradually refills with plasma, forming a cone-shaped “lunar wake.” However, the processes that govern refilling remain unclear, although models suggest they probably include a mixture of kinetic effects and effects particular to the dynamics of electrically conducting fluids. Zhang et al. now provi Continue reading >

There is no “edge of space,” no sharp demarcation where the Earth's atmosphere ends and outer space begins. Instead, there is the fuzzy, progressively thinning exosphere, a region filled mostly by neutral hydrogen atoms that stretches from 500 kilometers altitude to hundreds of thousands of kilometers above the Earth's surface. So far, the outer detectable limit of the exosphere is around 15.5 Earth radii—roughly half the distance between the Earth and the Moon. The diffuse aura that is the exo Continue reading >

Magnetic substorms, the disruptions in geomagnetic activity that cause brightening of aurora, may sometimes be driven by a different process than generally thought, a new study shows. Hwang et al. report observations using the Cluster spacecraft and ground-based magnetometers associated with the onset of a substorm. They saw two consecutive sudden jumps in the current sheet normal component of the magnetic field in the plasma sheet (the surface of dense plasma that lies approximately in Earth’s Continue reading >

A widely used model of Earth’s plasmasphere does not match observations, a new study indicates. Electron density in the plasmasphere—the region of cold, dense plasma that lies above about 1000 kilometers in altitude—plays a key role in space weather and affects how electromagnetic signals propagate. A theoretical model of the distribution of plasma developed in the early 1960s, known as the diffusive equilibrium model, is still widely in use. However, scientists have noted that the model is bas Continue reading >

In Saturn’s magnetosphere, neutral water released from the moon Enceladus becomes ionized. Where does this ionized gas go? Previous studies have indicated that some of this plasma must flow away from the planet through the magnetosphere and become lost to the solar wind. Using measurements from the ion mass spectrometer on the Cassini satellite, Thomsen et al. quantify how much plasma drifts radially outward through Saturn’s middle magnetosphere. They estimated the net mass loss between 1800 an Continue reading >

On 14 September 1997, NASA's Mars Global Surveyor spacecraft dipped into the red planet's thin atmosphere, the first of many passes meant to shorten the satellite's orbital path. For the next 5 months, the satellite periodically cruised through the thicker layers of the upper atmosphere and the wispy exosphere. The satellite's elongated orbit gave its sensors a good look at a broad swath of Mars's extended hydrogen exosphere. Using magnetic field observations, researchers measured the prevalenc Continue reading >

Despite a decade of observations from NASA's Cassini spacecraft, Saturn's most enticing moon, Titan, still holds many mysteries in its thick atmosphere. What spurs the growth of large chemical compounds high in the moon's ionosphere? Why is the chemistry so efficient at creating unsaturated and aromatic hydrocarbons? To better explain Titan's variable upper atmosphere, Westlake et al. enlisted Cassini's Plasma Spectrometer (CAPS) Ion Beam Spectrometer (IBS) to measure large hydrocarbon ions. Th Continue reading >

In Earth’s magnetotail, sharp increases in the magnetic field known as dipolarization fronts are associated with high-speed plasma flows that connect Earth’s ionosphere via electric currents. Some aspects of these dipolarization fronts have puzzled scientists; in particular, the dip in magnetic field that occurs just ahead of the dipolarization front layer is not well understood. Sun et al. analyze observations made using the Cluster satellites to elucidate the details of electric fields associ Continue reading >

Saturn’s moon Titan is the only moon in the solar system that has an atmosphere as thick as Earth’s, consisting of more than 98% nitrogen, roughly 1.4% of methane, and smaller amounts of other gases. NASA’s Cassini satellite has been circling Saturn since 2004, witnessing more than one-third of its 29-year orbit around the Sun, allowing it to observe the changing of the seasons. However, a new study finds that the seasons are not the only thing changing Titan’s atmosphere: its chemical makeup f Continue reading >

Every day, thousands of pounds of meteor debris enter Earth's atmosphere and eventually settle on the surface. Only a small fraction of these particles is large enough to be seen as shooting stars; most burn up high in the atmosphere, leaving behind a haze of tiny particles—meteoric smoke—suspended about 70–100 kilometers above Earth’s surface. The dust is mostly 4.6-billion-year-old leftovers from the messy accretion process of solar system formation, which the planet picks up as it passes thr Continue reading >

Scientists watched Earth’s upper atmosphere intently as the Sun went quiet during the recent solar minimum, which lasted from 2007 to 2010. At that time, spacecraft saw temperatures and densities decline in our planet’s thermosphere as a result of the shift in the Sun's activity. Simultaneously, however, deep convection—caused by solar heating near Earth’s surface—remained similar to levels seen during the prior solar maximum.Vadas et al. looked at the influence of gravity waves—created by dist Continue reading >

Scientists on NASA's Mercury orbiter, the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft, have watched in recent years as coronal mass ejections from the Sun sent solar winds sailing toward the solar system's innermost planet during the recent peaks of the solar cycle. The team studied what the most extreme of these events do to the planet's magnetosphere—the region controlled by Mercury's weak magnetic field.Since the spacecraft arrived in 2011, its observ Continue reading >

A new modeling study sheds light on how the magnetosphere of Uranus compares to those of other planets. Magnetospheres around the inner planets Mercury and Earth are primarily driven by the solar wind—the charged particles spewed out from the Sun—through magnetic reconnection, in which the planet’s magnetic field lines break and reconnect, releasing energy in the process. It has not been clear how this fundamental and important process works where the solar wind encounters Uranus’s magnetosphe Continue reading >

Magnetic substorms, disruptions in the coupled magnetosphere-ionosphere system that cause brightening of the aurora, are driven by magnetic activity that starts in the Earth’s magnetotail—the stretched-out region of Earth’s magnetic field on the far side from the Sun—and is transmitted to the ionosphere through a phenomenon called a substorm current wedge. New findings from simulations provide insight into the nature of these current wedges. In a substorm current wedge, a portion of the electr Continue reading >

The Earth’s magnetosphere has profound influences on space weather—geomagnetic storms born in the magnetosphere have the potential to disrupt satellite and terrestrial communications. The most dynamic part of the magnetosphere is the magnetotail, which appears on the nightside of the Earth and is composed of many different complex structures. The magnetotail is inundated with smaller magnetic disturbances called substorms, sometimes multiple times a day. Substorms are characterized by explosiv Continue reading >

The connection between sudden warming events in the stratosphere and changes in the density of electrons in the ionosphere has been established observationally for decades, but the physical mechanisms linking the stratosphere and the ionosphere are less well studied. Using the extreme 2009 sudden stratospheric warming as a case study, Pedatella et al. conducted simulations that combined the Whole Atmosphere Community Climate Model eXtended version (WACCM-X) and the Thermosphere-Ionosphere-Meso Continue reading >