Artist's concept of aurorae on Ganymede - auroral belt shifting may indicate a subsurface saline ocean. Credit: NASA/ESA
Jupiter is well known for its spectacular aurorae, thanks in no small part to the Juno orbiter and recent images taken by the James Webb Space Telescope (JWST). Like Earth, these dazzling displays result from charged solar particles interacting with Jupiter’s magnetic field and atmosphere. Over the years, astronomers have also detected faint aurorae in the atmospheres of Jupiter’s largest moons (aka. the “Galilean Moons“). These are also the result of interaction, in this case, between Jupiter’s magnetic field and particles emanating from the moons’ atmospheres.
Detecting these faint aurorae has always been a challenge because of sunlight reflected from the moons’ surfaces completely washes out their light signatures. In a series of recent papers, a team led by the University of Boston and Caltech (with support from NASA) observed the Galilean Moons as they passed into Jupiter’s shadow. These observations revealed that Io, Europa, Ganymede, and Callisto all experience oxygen-aurorae in their atmospheres. Moreover, these aurorae are deep red and almost 15 times brighter than the familiar green patterns we see on Earth.
EIELSON AIR FORCE BASE, Alaska -- The Aurora Borealis, or Northern Lights, shines above Bear Lake here Jan. 18. The lights are the result of solar particles colliding with gases in Earth's atmosphere. Early Eskimos and Indians believed different legends about the Northern Lights, such as they were the souls of animals dancing in the sky or the souls of fallen enemies trying to rise again. (U.S. Air Force photo by Senior Airman Joshua Strang)
Auroral activity on Earth varies over time. As the magnetic poles drift, auroras can appear at different latitudes around the globe. Solar activity also affects them, with powerful solar storms pushing the auroras further into mid-latitudes.
In an effort to better understand how auroras move around, how they’ll move in the future, and when powerful solar storms might pose a threat, a team of researchers have tracked auroral activity for the last 3,000 years.
In the course of studying Mars, scientists have come to identify some key similarities to Earth’s own. One notable example is the way our atmospheres interact with sunlight to produce dazzling displays of energy. On Earth, these include not just the aurorae near the polar regions (Aurora Borealis and Australis), but the constant green glow that is the result of oxygen molecules interacting with sunlight (aka. “airglow”).
On Earth, airglow can be seen “edge-on” from space, as exemplified by the many spectacular images that are taken by astronauts aboard the International Space Station (ISS). This phenomenon was recently observed around Mars for the first time by the ESA’s Trace Gas Orbiter (TGO), which arrived at Mars in 2016 a part of the ExoMars program. Like aurorae, this observation is yet another example of how Mars is “Earth’s Twin.”
Alberta Aurora Chasers capture STEVE, the new-to-science upper atmospheric phenomenon, on the evening of April 10th, 2018 in Prince George, British Columbia, Canada. Credit: Ryan Sault
Since time immemorial, people living in the Arctic Circle or the southern tip of Chile have looked up at the night sky and been dazzled by the sight of the auroras. Known as the Aurora Borealis in the north and Aurora Australis in the south (the “Northern Lights” and “Southern Lights”, respectively) these dazzling displays are the result of interactions in the ionosphere between charged solar particles and the Earth’s magnetic field.
However, in recent decades, amateur photographers began capturing photos of what appeared to be a new type of aurora – known as STEVE. In 2016, it was brought to the attention of scientists, who began trying to explain what accounted for the strange ribbons of purple and white light in the night sky. According to a new study, STEVE is not an aurora at all, but an entirely new celestial phenomenon.
The study recently appeared in the Geophysical Research Letters under the title “On the Origin of STEVE: Particle Precipitation or Ionospheric Skyglow?“. The study was conducted by a team of researchers from the Department of Physics and Astronomy from the University of Calgary, which was led by Beatriz Gallardo-Lacourt (a postdoctoral associate), and included Yukitoshi Nishimura – an assistant researcher of the Department of Atmospheric and Oceanic Sciences at the University of California.
STEVE, as imaged by Dave Markel in the skies above northern Canada. Copyright: davemarkelphoto
STEVE first became known to scientists thanks to the efforts of the Alberta Aurora Chasers (AAC), who occasionally noticed these bright, thin streams of white and purple light running from east to west in the night sky when photographing the aurora. Unlike auroras, which are visible whenever viewing conditions are right, STEVE was only visible a few times a year and could only be seen at high latitudes.
Initially, the photographers thought the light ribbons were the result of excited protons, but these fall outside the range of wavelengths that normal cameras can see and require special equipment to image. The AAC eventually named the light ribbons “Steve” – a reference to the 2006 film Over the Hedge. By 2016, Steve was brought to the attention of scientists, who turned the name into a backronym for Strong Thermal Emission Velocity Enhancement.
For their study, the research team analyzed a STEVE event that took place on March 28th, 2008, to see if it was produced in a similar fashion to an aurora. To this end, they considered previous research that was conducted using satellites and ground-based observatories, which included the first study on STEVE (published in March of 2018) conducted by a team of NASA-led scientists (of which Gallardo-Lacourt was a co-author).
This study indicated the presence of a stream of fast-moving ions and super-hot electrons passing through the ionosphere where STEVE was observed. While the research team suspected the two were connected, they could not conclusively state that the ions and electrons were responsible for producing it. Building on this, Gallardo-Lacourt and her colleagues analyzed the STEVE event that took place in March of 2008.
Rays of aurora borealis reach 60 miles and higher over the Pacific Northwest on Jan. 20, 2016 in this photo taken by astronauts Scott Kelly and Tim Peake from the International Space Station. Credit: NASA
They began by using images from ground-based cameras that record auroras over North America, which they then combined with data from the National Oceanic and Atmospheric Administration‘s (NOAA) Polar Orbiting Environmental Satellite 17 (POES-17). This satellite, which can measure the precipitation of charged particles into the ionosphere, was passing directly over the ground-based cameras during the STEVE event.
What they found was that the POES-17 satellite detected no charged particles raining down on the ionosphere during the event. This means that STEVE is not likely to be caused by the same mechanism as an aurora, and is therefore an entirely new type of optical phenomenon – which the team refer to as “skyglow”. As Gallardo-Lacourt explained in an AGU press release:
“Our main conclusion is that STEVE is not an aurora. So right now, we know very little about it. And that’s the cool thing, because this has been known by photographers for decades. But for the scientists, it’s completely unknown.”
Looking ahead, Galladro-Lacourt and her colleagues seek to test the conclusions of the NASA-led study. In short, they want to find out whether the streams of fast ions and hot electrons that were detected in the ionosphere are responsible for STEVE, or if the light is being produced higher up in the atmosphere. One thing is for certain though; for aurora chasers, evening sky-watching has become more interesting!
Seeing the Northern or Southern Lights is an awe-inspiring experience, but do you know the science behind their beauty? This video from Per Byhring and the physics department at the University of Oslo explains how particles originating from deep inside the core of the Sun creates aurorae in the atmosphere of Earth.
The video takes a look at how cloud of electrically charged particles emanate from the Sun, and what happens when this plasma reaches the Earth and interacts with the planet’s magnetic field, which creates fantastic light shows in the extreme northern and southern latitudes.
Photographer Terje Sorgjerd spent a week capturing what he called “one of the biggest aurora borealis shows in recent years,” and the results are simply stunning. The footage was shot in and around Kirkenes and Pas National Park in the very north part of Norway, which borders Russia, at 70 degree north and 30 degrees east. Temperatures were around -25 Celsius, Sorgjerd said.
If you weren’t lucky enough to be in the right place or the right time to see any of the aurora produced by the Sun’s recent spate of activity, skywatchers around the world have started posting videos online of some really spectacular Northern Lights. Above, is the view on August 4, 2010 from Telemark, Norway. Below are more sights, also from August 4, from Latvia and Risør, Norway. These videos were posted on CitizenTube, a newsy version of YouTube. Continue reading “Stunning Aurora Videos”
Hubble's view of Saturn with a double view of its fluttering aurorae. Credit: NASA, ESA and Jonathan Nichols (University of Leicester)
In January and March 2009, researchers using Hubble took advantage of a rare opportunity to record Saturn when its rings are edge-on, resulting in a unique look featuring both of the giant planet’s poles. And Saturn cooperated by providing an incredible double light show with Saturn’s own northern and southern lights. Since Saturn is only in this position every 15 years or so, this favorable orientation has allowed a sustained study of the two beautiful and dynamic aurorae.
Since it takes Saturn almost thirty years to orbit the Sun, the opportunity to image both of its poles occurs only twice in that period. Hubble has been snapping pictures of the planet at different angles since the beginning of the mission in 1990, but 2009 brought a unique chance for Hubble to image Saturn with the rings edge-on and both poles in view. At the same time Saturn was approaching its equinox so both poles were equally illuminated by the Sun’s rays.
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These recent observations go well beyond just a still image and have allowed researchers to monitor the behavior of both Saturn’s poles in the same shot over a sustained period of time. The movie they created from the data, collected over several days during January and March 2009, has aided astronomers studying both Saturn’s northern and southern aurorae. Given the rarity of such an event, this new footage will likely be the last and best equinox movie that Hubble captures of our planetary neighbor.
Despite its remoteness, the Sun’s influence is still felt by Saturn. The Sun constantly emits particles that reach all the planets of the Solar System as the solar wind. When this electrically charged stream gets close to a planet with a magnetic field, like Saturn or the Earth, the field traps the particles, bouncing them back and forth between its two poles. A natural consequence of the shape of the planet’s magnetic field, a series of invisible “traffic lanes” exist between the two poles along which the electrically charged particles are confined as they oscillate between the poles. The magnetic field is stronger at the poles and the particles tend to concentrate there, where they interact with atoms in the upper layers of the atmosphere, creating aurorae, the familiar glow that the inhabitants of the Earth’s polar regions know as the northern and southern lights.
At first glance the light show of Saturn’s aurorae appears symmetric at the two poles. However, analysing the new data in greater detail, astronomers have discovered some subtle differences between the northern and southern aurorae, which reveal important information about Saturn’s magnetic field. The northern auroral oval is slightly smaller and more intense than the southern one, implying that Saturn’s magnetic field is not equally distributed across the planet; it is slightly uneven and stronger in the north than the south. As a result, the electrically charged particles in the north are accelerated to higher energies as they are fired toward the atmosphere than those in the south. This confirms a previous result obtained by the space probe Cassini, in orbit around the ringed planet since 2004.
Source: ESA
