Rock Comet Approaches Earth

Dec. 11, 2017: You’ve heard of comets. But have you ever heard of a rock comet? They exist, and a big one is approaching Earth this week. 3200 Phaethon will fly past our planet on Dec. 16th only 10 million km away. Measuring 5 km in diameter, this strange object is large enough for amateur astronomers to photograph through backyard telescopes. A few nights ago, the Astronomy Club of the Sing Yin Secondary School in Hong Kong video-recorded 3200 Phaethon’s approach using a 4-inch refractor:

“We observed 3200 Phaethon from the basketball court of our school campus,” the club reports. “Our school is located close to the city center where the visual limiting magnitude is about 2 to 3. Despite the glare, we were able to record the motion of this object.” (For others who wish to do this, Bob King of Sky & Telescope has written an excellent set of observing tips.)

3200 Phaethon is the source of the annual Gemini meteor shower, which is also coming this week. Sky watchers can see dozens of Geminids per hour on Dec. 13th and 14th as gravelly bits of the rock comet disintegrate in Earth’s upper atmosphere. The best time to look is during the dark hours before sunrise when Gemini is high in the sky.

“This is 3200 Phaethon’s closest encounter with Earth until December of 2093, when it will come to within 1.8 million miles,” notes Bill Cooke of NASA’s Meteoroid Environment Office. Despite the proximity of the rock comet, he doesn’t expect to see any extra Geminids this year. “It would take at least another revolution around the sun before new material from this flyby could encounter Earth – probably longer.”

A “rock comet” is an asteroid that comes very close to the sun–so close that solar heating scorches plumes of dust right off its stony surface. 3200 Phaethon comes extremely close to the sun, only 0.14 AU away, less than half the distance of Mercury, making it so hot that lead could flow like water across its sun-blasted surface. Astronomers believe that 3200 Phaethon might occasionally grow a comet-like tail of gravelly debris–raw material for the Geminid meteor shower. Indeed, NASA STEREO-A spacecraft may have seen this happening in 2010. There is much to learn about 32900 Phaethon, which is why NASA radars will be pinging it as it passes by. Stay tuned for updates.

Atmospheric Radiation is Increasing

Dec. 9, 2017: Since the spring of 2015, Spaceweather.com and the students of Earth to Sky Calculus have been flying balloons to the stratosphere over California to measure cosmic rays. Soon after our monitoring program began, we quickly realized that radiation levels are increasing. Why? The main reason is the solar cycle. In recent years, sunspot counts have plummeted as the sun’s magnetic field weakens. This has allowed more cosmic rays from deep space to penetrate the solar system. As 2017 winds down, our latest measurements show the radiation increase continuing apace–with an interesting exception, circled in yellow:

In Sept. 2017, the quiet sun surprised space weather forecasters with a sudden outburst of explosive activity. On Sept. 3rd, a huge sunspot appeared. In the week that followed, it unleashed the strongest solar flare in more than a decade (X9-class), hurled a powerful CME toward Earth, and sparked a severe geomagnetic storm (G4-class) with Northern Lights appearing as far south as Arkansas. During the storm we quickened the pace of balloon launches and found radiation dropping to levels we hadn’t seen since 2015. The flurry of solar flares and CMEs actually pushed some cosmic rays away from Earth.

Interestingly, after the sun’s outburst, radiation levels in the stratosphere took more than 2 months to fully rebound. Now they are back on track, increasing steadily as the quiet sun resumes its progress toward Solar Minimum. The solar cycle is not expected to hit rock bottom until 2019 or 2020, so cosmic rays should continue to increase, significantly, in the months and years ahead. Stay tuned for updates as our balloons continue to fly.

Technical note: The radiation sensors onboard our helium balloons detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies, which span the range of medical X-ray machines and airport security scanners, trace secondary cosmic rays, the spray of debris created when primary cosmic rays from deep space hit the top of Earth’s atmosphere.

SPOTLESS SUN SPARKS PINK AURORAS

Nov. 23, 2017: On Nov. 22nd, the face of the sun was unblemished by sunspots, and NOAA classified solar activity as “very low.”  Nevertheless, the skies above Tromsø, Norway, exploded with a remarkable outburst of pink auroras. “Suddenly, the whole valley turned white (with a hint of pink),” says Frank Meissner, who witnessed and photographed the display. “It was over after about 20 seconds.”

How bright was it? “The brightness of the auroras may be compared to the car lights in the background of my photo,” points out Meissner.

In nearby Kvaløya, aurora tour guide Marianne Bergli witnessed a surge of pink that was, if anything, even more dramatic:

“Ironically, our guests stopped taking pictures,” says Bergli. “They were awestruck and frozen to the spot by the incredible pink and green lights overhead.”

This outburst was powered by a stream of solar wind flowing from a hole in the sun’s atmosphere. Such holes are common during Solar Minimum, and they require no sunspots to form. That’s why auroras continue throughout the 11-year solar cycle.

The pink color of the outburst tells us something interesting about the solar wind on Nov. 22nd: it seems to have been unusually penetrating. Most auroras are green–a verdant glow caused by energetic particles from space hitting oxygen atoms 100 km to 300 km above Earth’s surface. Pink appears when the energetic particles descend lower than usual, striking nitrogen molecules at the 100 km level and below.

In recent winters, big displays of pink and white auroras have coincided with spotless suns often enough to make observers wonder if there is a connection.  If so, more outbursts are in the offing as the sun continues its plunge toward a deep Solar Minimum. Stay tuned for pink!

Realtime Aurora Photo Gallery

Severe Space Weather on Mars

Oct. 4, 2017: More than 150 years after it happened, scientists are still taking about the Carrington Event—a solar storm in Sept. 1859 that sparked Northern Lights as far south as Cuba and sprayed the entire surface of Earth with high energy radiation.

On our planet, such global events are rare. On Mars, they happen surprisingly often—in fact, there was one just a few weeks ago.

The storm began on Sept. 10, 2017–a day the sun was supposed to be quiet: The solar cycle is currently at low ebb, near Solar Minimum, and strong flares are rare. Nevertheless, sunspot AR2673 erupted, producing a powerful X8-class solar flare that accelerated a potent spray of charged particles into space.

In a matter of hours, a “ground level event” (GLE) was underway on Mars. GLEs occur when energetic particles normally held at bay by a planet’s atmosphere or magnetic field penetrate all the way to the ground. Mars rover Curiosity detected the radiation spike as it crawled just south of the Martian equator.

“Radiation levels suddenly doubled and they remained high for nearly two days,” says Don Hassler of the Southwest Research Institute, principal investigator for Curiosity’s Radiation Assessment Detector (RAD). “This is the largest event we have seen since Curiosity landed in 2012.”

Earth was in the line of fire, too, but our planet’s magnetic field and thick atmosphere mitigated the effect of the storm. The terrestrial GLE on Sept. 10th was restricted to polar regions and amounted to a meager 6% increase–a tiny fraction of what happened on Mars.

Mars got walloped because, simply put, it is more vulnerable to space weather. The Red Planet has no global magnetic field to protect it, and an atmosphere only 1% as thick as Earth’s. Energetic particles from the Sept. 10th explosion peppered the entire dayside surface of Mars while auroras fringed the upper atmosphere all around the globe.

NASA’s MAVEN spacecraft saw the auroras using its ultraviolet imager. “If a human had been present, with eyes sensitive to visible light, they would have probably seen Mars lit up in green light (557.7nm) much like auroras on Earth,” says Sonal Jain of the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado.


Click to play a movie of the UV auroras on Mars

“Sonal had the excitement of being blown away when the raw data come in,” says his colleague Nick Schneider, also of LASP. “The auroras were 25 times brighter than the previous record.” Both scientists work with MAVEN data and specialize in Martian auroras.

“These global events are really interesting,” says Schneider. “On Earth It takes a truly extreme solar storm to cause global havoc thanks to the strength of our magnetic field. Mars’ lack of a global magnetic field means that planet-wide events are far more common. Indeed, since MAVEN went into Mars-orbit 3 years ago, we’ve seen a bunch of auroral displays that were probably global, even though this has been a really wimpy solar cycle.”

Hassler agrees. “Curiosity has seen 5 ground level events since 2012. They are not uncommon,” he says, “and they will probably grow stronger in the years ahead as we move through Solar Minimum and return to a more active phase of the solar cycle.”

Planners of future human missions to Mars will have to take into account the frequency of these “Martian Carrington Events,” increasingly revealed by rovers and orbiters of the Red Planet. Meanwhile, researchers are still poring over data from the latest, hoping to learn more. “Analysis of these observations, both at Mars and Earth, is just beginning,” says Hassler, “so stay tuned.”

CME Sweeps Aside Cosmic Rays

July 18,2017: On July 16th, a CME hit Earth’s magnetic field, sparking two days of geomagnetic storms and beautiful southern auroras. The solar storm cloud also swept aside some of the cosmic rays currently surrounding Earth. Spaceweather.com and the students of Earth to Sky Calculus launched a space weather balloon to the stratosphere hours after the CME arrived. We detected a 7% decrease in X-rays and gamma-rays (two tracers of secondary cosmic rays). Neutron monitors in the Arctic and Antarctic recorded similar decrements. For instance, these data from the Bartol Research Institute show a nearly 8% drop in cosmic ray neutrons reaching the South Pole:

This is called a “Forbush Decrease,” named after physicist Scott E. Forbush who first described it in the 20th century. Wherever CMEs go, cosmic rays are deflected by magnetic fields inside the solar storm clouds. As a result, when solar activity is high, cosmic radiation around Earth is relatively low–a yin-yang relationship that holds throughout all phases of the solar cycle.

Lately, cosmic rays around Earth have been intensifying as the solar cycle plunges toward minimum. The CME of July 16th reversed that trend–but only for a few days. Solar activity has returned to low levels and cosmic rays are on the rise again.

Why do we care about cosmic rays? For one thing, they penetrate commercial airlines, dosing passengers and flight crews so much that pilots are classified as occupational radiation workers. Some research shows that cosmic rays can seed clouds and trigger lightning, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

Giant ‘ELVE’ Appears over Europe

On April 2nd, high above a thunderstorm in the Czech republic, an enormous ring of light appeared in the night sky. Using a low-light video camera, amateur astronomer Martin Popek of Nýdek photographed the 300 km-wide donut hovering near the edge of space:

“It appeared for just a split second alongside the constellation Orion” says Popek.

This is an example of an ELVE (Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Sources). First seen by cameras on the space shuttle in 1990, ELVEs appear when a pulse of electromagnetic radiation from cloud-to-ground lightning propagates up toward space and hits the base of Earth’s ionosphere. A faint ring of deep-red light marks the broad ‘spot’ where the EMP hits.

“For this to happen, the lightning needs to be very strong–typically 150-350 kilo-Ampères,” says Oscar van der Velde, a member of the Lightning Research Group at the Universitat Politècnica de Catalunya. “For comparison, normal cloud-to-ground flashes only reach 10-30 kA.”

ELVEs often appear alongside red sprites, which are also sparked by strong lightning. Indeed, Popek’s camera caught a cluster of sprites dancing nearby.

ELVEs are elusive–and that’s an understatement. Blinking in and out of existence in only 1/1000th of a second, they are completely invisible to the human eye. For comparison, red sprites tend to last for hundredths of a second and regular lightning can scintillate for a second or more. Their brevity explains why ELVEs are a more recent discovery than other lightning-related phenomenon. Learn more about the history and physics of ELVEs here and here.

Realtime Sprite Photo Gallery

Mystery of the Missing Noctilucent Clouds

June 15, 2017: In late May 2017, observers in Europe began seeing electric-blue tendrils snaking over the western horizon at sunset. The summer season for noctilucent clouds (NLCs) was apparently beginning. Normally, the strange-looking clouds surge in visibility in the weeks immediately after their first sighting. This year, however, something mysterious happened. Instead of surging, the clouds vanished. During the first two weeks of June 2017, Spaceweather.com received ZERO images of NLCs — something that hasn’t happened in nearly 20 years.

Where did they go? Researchers have just figured it out: There’s been a “heat wave” in the polar mesosphere, a region in Earth’s upper atmosphere where NLCs form. Relatively warm temperatures have wiped out the clouds.

Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics made the discovery using temperature data from the Microwave Limb Sounder onboard NASA’s Aura satellite. “In early May, the summer mesosphere was cooling down as usual, approaching the low temperatures required for NLCs,” she says. “But wouldn’t you know it? Right after May 21st the temperature stopped cooling over the pole! In fact, it warmed a degree or two over the next week. The warming resulted in 2017 being the WARMEST summer mesopause in the last decade.”

She is describing the red curve in this 10-year plot of polar mesospheric temperature trends:

Warm temperatures are an anathema to NLCs. The icy clouds form 83 km above Earth when the air temperature drops below 145 K (-128 C), allowing scarce water molecules to get together and crystallize on specks of meteor smoke. Even a couple of degrees of warming is enough to obliterate the fragile clouds.

“We don’t know why the mesosphere warmed up,” says Cora Randall, Professor and Chair of the University of Colorado Department of Atmospheric and Oceanic Sciences.  “It’s probably a complex process involving the propagation of atmospheric gravity waves, which affect the flow of air in the upper atmosphere. We’re looking into it.”

Meanwhile, the heat wave may be coming to an end. “In the last week, the north polar mesopause has started cooling again,” says Harvey. This means NLCs should soon return, bouncing back to normal as temperatures drop. High latitude sky watchers should be alert for electric-tendrils creeping out of the sunset in the nights ahead–and if you see anything, submit your pictures here!

Realtime Noctilucent Cloud Photo Gallery

Solar Wind Summons “Steve”

May 21, 2017: During Saturday morning’s solar wind storm, photographer Harlan Thomas stationed himself among the Hoodoos in the badlands of Alberta, Canada. He hoped to catch a display of auroras. This is what he saw:

“Steve appeared!” says Thomas. “I photographed him behind the silhouettes of the Hoodoos alongside Jupiter and a green picket fence aurora.”

“Steve” is the purple arc bisecting the sky. For many years, northern sky watchers have reported this luminous form occasionally dancing among regular auroras. It was widely called a “proton arc” until researchers pointed out that protons probably had nothing to do with it. So members of the Alberta Aurora Chasers group gave it a new name: “Steve.”

No one fully understands the underlying physics of the purple ribbon. However, one of the European Space Agency’s Swarm satellites recently flew overhead while Steve was active, providing some clues.

http://www.esa.int/spaceinvideos/content/view/embedjw/485279
This ESA video shows Swarm satellites orbiting above ground-based aurora imagers: more

“As the satellite flew straight though ‘Steve,’ data from the electric field instrument showed very clear changes,” reports Eric Donovan from the University of Calgary. “The temperature 300 km above Earth’s surface jumped by 3000°C and the data revealed a 25 km-wide ribbon of gas flowing westwards at about 6 km/s compared to a speed of about 10 m/s either side of the ribbon.”

Steve’s visit to Alberta on May 20, 2017, coincided with another exotic auroral form: the green “picket fence.” These vertical rays are thought to trace lines of magnetic force connecting Earth to space. Luminous green columns show where beams of energetic particles are being guided toward Earth’s upper atmosphere by magnetic fields.

Both Steve and the picket fence are filamentary structures associated with beams or ribbons of gas. Coincidence? Hardly. Pictures of the two phenomena show that they often appear together. Consider it another clue.

Realtime “Steve” Photo Gallery

“Steve” Sighted over Calgary

May 18, 2017: For years, northern sky watchers have occasionally spotted a mysterious ribbon of purple light dancing among the aurora borealis. It was widely called a “proton arc” until researchers pointed out that protons probably had nothing to do with it. So members of the Alberta Aurora Chasers group gave it a new name: “Steve.” Recent widespread reporting about Steve has led to even more sightings–and indeed he appeared just this week over Calgary:

“Steve hung out with me for about 15 minutes on May 17th,” reports photographer Harlan Thomas, who witnessed a spectacular display of auroras over Twisted Ponds. The lights appeared as Earth moved through a stream of fast-moving solar wind that briefly interacted with our planet two days ago.

Steve is still a mystery. No one fully understands the underlying physics of the ribbon.  However, one of the European Space Agency’s SWARM satellites recently flew overhead while Steve was active, providing some clues.

“As the satellite flew straight though Steve, data from the electric field instrument showed very clear changes” reports Eric Donovan from the University of Calgary. “The temperature 300 km above Earth’s surface jumped by 3000°C and the data revealed a 25 km-wide ribbon of gas flowing westwards at about 6 km/s compared to a speed of about 10 m/s either side of the ribbon.”

These clues, confirmed and supplemented by similar flybys in the future, may yet crack the mystery of this phenomenon. For now, Steve is unpredictable and may appear in the aurora gallery at any time. Stay tuned!

Realtime Aurora Photo Gallery

Anthropogenic Space Weather

May 18, 2017: Space weather can have a big effect on human society. Sometimes human society returns the favor. A new study entitled “Anthropogenic Space Weather” just published in Space Science Reviews outlines how human activity shapes the space around our planet. A prime example: Human radio transmissions form a bubble in space protecting us from “killer electrons.”

Co-author Phil Erickson of MIT’s Haystack Observatory explains: “As Van Allen discovered in the 1950s and 1960s, there are two radiation belts surrounding Earth with a ‘slot’ between them. Our research is focused on the the outer radiation belt, which contains electrons with energies of a million or more electron-volts. These ‘killer electrons’ have the potential to damage spacecraft, even causing permanent failures.”

During strong geomagnetic storms, the outer radiation belt expands, causing the killer electrons to approach Earth. But NASA’s Van Allen Probes, a pair of spacecraft sent to explore the radiation belts, found that something was stopping the particles from getting too close.

“The penetration of the outer belt stopped right at the same place as the edge of VLF strong transmissions from humans on the ground,” says Erickson. “These VLF transmissions penetrate seawater, so we use them to communicate with submarines. They also propagate upward along Earth’s magnetic field lines, forming a ‘bubble’ of VLF waves that reaches out to about 2.8 Earth-radii–the same spot where the ultra-relativistic electrons seem to stop.”

VLF radio waves clear the area of killer electrons “via a wave-particle gyro-resonance,” says Erickson. “Essentially, they are just the right frequency to scatter the particles into our atmosphere where their energy is safely absorbed.”

“Because powerful VLF transmitters have been operating since before the dawn of the Space Age, it is possible that we have never observed the radiation belts in their pristine, unperturbed state,” notes the team, which includes John Foster, a colleague of Erickson at MIT and a key leader of this research, along with Dan Baker at the University of Colorado Boulder.

Other anthropogenic effects on space weather include artificial radiation belts created by nuclear tests, high-frequency wave heating of the ionosphere, and cavities in Earth’s magnetotail formed by chemical release experiments. Download the complete paper here.