The Orionid Meteor Shower

Oct. 19, 2018: Right now, specks of dust from Halley’s Comet are disintegrating in Earth’s atmosphere, kicking off the annual Orionid meteor shower. NASA cameras caught more than a dozen Orionid fireballs streaking across the USA during the past 48 hours, and the show is expected to improve during the weekend as Earth moves deeper into Halley’s stream of debris:

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Above: This Orionid fireball, observed by Maciek Myszkiewicz in Oct. 2012, was as bright as a full Moon.

“The upcoming Orionids should provide a fairly good show for most visual observers,” says Peter Brown of the University of Western Ontario Meter Physics Group. “The shower’s radiant is already quite active and well defined in data from the Canadian Meteor Orbit Radar (CMOR).”

Orionids appear every year around this time when Earth crosses Halley’s debris stream, with the shower typically producing about 20 meteors per hour. Some of the brightest stars and constellations in the sky–e.g., Orion the Hunter, Sirius the Dog Star, and Taurus the Bull–form the shower’s backdrop. This makes the display extra-beautiful in disproportion to the raw number of meteors.

Some years, however, are even better than others. “Most notable was a short-lived outburst of relatively bright Orionids in 1993 observed several days before the predicted peak. This hints that there may be narrow filaments of larger meteoroids embedded in the overall debris stream,” says Brown. “We also observed enhanced Orionid activity in the years 2006 through 2009 with rates 2 to 3 times normal.”

This year’s shower has one thing going against it: The nearly full Moon. Lunar glare could reduce visible meteor rates 2- or 3-fold. The best time to look, therefore, is during the dark hours before sunrise when the Moon is sinking below the western horizon and the shower’s radiant in Orion is high in the southeast: sky map.

“Finding dark skies and clear weather in the early morning hours of Sunday, Oct 21st, just after the moon sets this year is the surest way to see these messengers from 1P/Halley,” says Brown. Enjoy the show!

Realtime Meteor Photo Gallery

 

Geomagnetic Thunder? Auroras Caught Making Noise

Oct. 10, 2018: On Oct. 7th, a solar wind stream hit Earth’s magnetic field, sparking a G1-class geomagnetic storm. In southern Finland, the night sky turned green as energetic particles rained down on the upper atmosphere. But there was more to the show than beautiful lights.

“The storm also produced a number of distinctive sounds including crackles and claps,” reports Prof. Emeritus Unto K. Laine of Finland’s Aalto University. “Here is a recording of one of the strongest sounds of the night–a sharp clap.” Click to listen:

“I recorded this in the vicinity of Fiskars village after midnight local time,” he says.

Auroral sounds are controversial. Over the centuries, there have been many reports of strange sounds under the Northern Lights. However, researchers have struggled to explain the phenomenon and sometimes suggested that they might be imaginary. Laine is a believer: “We have been recording sounds like these for almost 20 years as part of the Auroral Acoustics Project.” More samples may be found here.

Laine has developed arrays of microphones that can pinpoint the sounds through triangulation. He finds that they occur about 70 meters above the ground. Temperature inversion layers at that altitude can cause a separation of + and – charges in the air. During some geomagnetic storms, the charge separation breaks down, causing air to move and a faint “clap” to be heard.

Think of it as geomagnetic thunder.

A spectral analysis of the “thunderclap” (above) shows dominant frequencies between 1 kHz and 2 kHz, squarely in the range of human hearing. You have to be quiet to hear them, though.

“People who talk and walk around, concentrating on picture taking, might never hear a single sound related to aurora,” says Laine. “You have to stop all other activities and focus on listening. We Finns are probably good at this because we have received more than 300 reports of sound observations during the Auroral Acoustics Project.”

Over the years, Laine has learned that a geomagnetic storm, by itself, is not enough to produce these thunderclaps. “A strong inversion layer is also required,” he says. “The inversion layer acts like an electrostatic loudspeaker. Without it there are no sounds.” This explains why many geomagnetic storms are silent. The local weather has to be just right — as it was on Oct. 7th.

Realtime Aurora Photo Gallery

Earth Dodges a Meteor Storm

Oct. 13, 2018: On Oct. 8-9, Europeans outdoors around midnight were amazed when a flurry of faint meteors filled the sky. “It was a strong outburst of the annual Draconid meteor shower,” reports Jure Atanackov, a member of the International Meteor Organization who witnessed the display from Slovenia. Between 22:00 UT (Oct. 8) and 01:00 UT (Oct. 9), dark-sky meteor rates exceeded 100 per hour. In eastern France, Tioga Gulon saw “1 to 2 meteors per minute,” many of them shown here in an image stacked with frames from his video camera:

“It was a rare and impressive event,” says Atanackov.

It could easily have been 10 times more impressive. In fact, Earth narrowly dodged a meteor storm.

The European outburst occurred as Earth skirted a filament of debris from Comet 21P/Giacobini-Zinner. If that filament had shifted in our direction by a mere 0.005 AU (~500,000 miles), Earth would have experienced a worldwide storm of 1000+ meteors per hour. These conclusions are based on a computer model of the comet’s debris field from the University of Western Ontario’s Meteor Physics Group. Here it is, showing Earth shooting the gap between two filaments of comet dust:

Western Ontario postdoctoral researcher Auriane Egal created the model and predicted the outburst before it happened. Egal’s model was in good agreement with a rival model from NASA, so confidence was high. Meteors seen over Europe came from the larger filament on the right.

According to the models, Earth’s L1 and L2 Lagrange points were both forecast to have storm-level activity–especially L2 which would experience the Earth-equivalent of 4000+ meteors per hour. This prompted NASA to take a close look at the danger to spacecraft.

“The US has four space weather spacecraft at L1: ACE, SOHO, Wind, and DSCOVR,” says Bill Cooke of NASA’s Meteoroid Environment Office. “There is only one operational spacecraft at L2 – the European Space Agency’s GAIA – which was where most of the Draconid activity was expected to take place. GAIA shut down science operations for a few hours around the projected storm peak and re-oriented to turn the hard side of the vehicle towards the incoming debris. All of the spacecraft came through the Draconids without incident, and this shower provided a good test of our ability to forecast meteor activity outside of Earth orbit.”

Many readers have wondered if the outburst has anything to do with Comet 21P/Giacobini-Zinner’s close approach to Earth last month. “No,” says Cooke.  “The models show the outburst experienced at Earth was mainly caused by material ejected from the comet from 1945 to the mid 1960’s. The meteoroids were more than half a century old.”

Realtime Meteor Photo Gallery

Rads on a Plane: New Results

Oct. 3, 2018: Many people think that only astronauts need to worry about cosmic radiation. Not so. Ordinary air travelers are exposed to cosmic rays, too. A recent study from researchers at Harvard found that flight attendants have a higher risk of cancer than members of the general population, and the International Commission on Radiological Protection has classified pilots as occupational radiation workers.

How much radiation do you absorb? SSpaceweather.com and the students of Earth to Sky Calculus have been working to answer this question by taking cosmic ray detectors onboard commercial airplanes. Flying since 2015, we have collected more than 22,000 GPS-tagged radiation measurements over 27 countries, 5 continents, and 2 oceans.

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(A) A global overview of our flights. This map shows where we have been. (B) To show the density of our data, we zoom in to the Four Corners region of the USA. There are three major hubs in the map: Phoenix, Las Vegas, and Denver. You can’t see them, however, because they are overwritten by pushpins.

Here is what we have learned so far:

  1. Radiation always increases with altitude, with dose rates doubling every 5000 to 6000 feet. This make sense: The closer you get to space, the more cosmic rays you will absorb.
  2. At typical cruising altitudes, cosmic radiation is 40 to 60 times greater than natural sources at sea level.
  3. Passengers on cross-country flights across the USA typically absorb a whole body dose equal to 1 or 2 dental X-rays.
  4. On international flights, the total dose can increase ~five-fold with passengers racking up 5 to 6 dental X-rays.

Using our database, we can investigate patterns of radiation around the world. For instance, this plot compares aviation radiation over the tropics vs. the Arctic:

arctic_tropics

We see that the Arctic is a high radiation zone. This comes as no surprise. Researchers have long known that particles from space easily penetrate Earth’s magnetic field near the poles, while the equator offers greater resistance. That’s why auroras are in Sweden instead of Mexico. Generally speaking, passengers flying international routes over the poles absorb 2 to 3 times more radiation than passengers at lower latitudes.

We can also look at individual countries–e.g., Sweden vs. the USA vs. Chile:

countries

As an Arctic country, Sweden has the most radiation–no surprise. The continental USA straddles the middle–again, no surprise. A mid-latitude country can be expected to have middling radiation. Chile, however, is more of a puzzle.

Although Chile does not cross the equator, it has some of the lowest readings in our database. This phenomenon is almost certainly linked to Chile’s location on the verge of the South Atlantic Anomaly–a distortion in Earth’s magnetic field that affects radiation levels. We are actively investigating the situation in Chile with additional flights, and will report results in a future blog.

Because our home base is in the USA, we spend a lot of time flying there. The US dataset is so dense, we can investigate regional differences across the country–for example, New England vs. the Southwest:

newengland_southwest

The two curves are indistinguishable below ~30,000 feet, but at higher altitudes they diverge. By the time a plane reaches 40,000 feet, it would experience 30% more radiation over New England than the same plane flying above the desert Southwest. According to our measurements so far, New England is the “hottest” region of the continental USA, radiation-wise, with the Pacific Northwest a close second.

Perhaps the most important outcome of our work so far is E-RAD–a new predictive model of aviation radiation. We can now predict dose rates on flights in areas where we have flown before. Because it is constantly updated with new data, E-RAD naturally keeps up with variables that affect cosmic rays such as the solar cycle and changes in Earth’s magnetic field.

Here is an example of a recent flight we took from Baltimore to Las Vegas, comparing E-RAD’s predictions with actual measurements:

eradvreality

The two agree within 10% for most of the flight. These errors are constantly shrinking as we add new readings to our database.

The results in this report are offered as a preview of what we are learning. Our database is growing almost-daily with new flights to new places, and we will have more results to share in the weeks ahead. We’ve created a website to showcase what we are learning and ultimately to let you, the reader, interact with our databases as well: RadsonaPlane.com.

Visit RadsonaPlane.com

 

The Chill of Solar Minimum

Sept. 27, 2018: The sun is entering one of the deepest Solar Minima of the Space Age. Sunspots have been absent for most of 2018, and the sun’s ultraviolet output has sharply dropped. New research shows that Earth’s upper atmosphere is responding.

“We see a cooling trend,” says Martin Mlynczak of NASA’s Langley Research Center. “High above Earth’s surface, near the edge of space, our atmosphere is losing heat energy. If current trends continue, it could soon set a Space Age record for cold.”

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Above: The TIMED satellite monitoring the temperature of the upper atmosphere

These results come from the SABER instrument onboard NASA’s TIMED satellite. SABER monitors infrared emissions from carbon dioxide (CO2) and nitric oxide (NO), two substances that play a key role in the energy balance of air 100 to 300 kilometers above our planet’s surface. By measuring the infrared glow of these molecules, SABER can assess the thermal state of gas at the very top of the atmosphere–a layer researchers call “the thermosphere.”

“The thermosphere always cools off during Solar Minimum. It’s one of the most important ways the solar cycle affects our planet,” explains Mlynczak, who is the associate principal investigator for SABER.

When the thermosphere cools, it shrinks, literally decreasing the radius of Earth’s atmosphere. This shrinkage decreases aerodynamic drag on satellites in low-Earth orbit, extending their lifetimes. That’s the good news. The bad news is, it also delays the natural decay of space junk, resulting in a more cluttered environment around Earth.

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Above: Layers of the atmosphere. Credit: NASA

To help keep track of what’s happening in the thermosphere, Mlynczak and colleagues recently introduced the “Thermosphere Climate Index” (TCI)–a number expressed in Watts that tells how much heat NO molecules are dumping into space. During Solar Maximum, TCI is high (“Hot”); during Solar Minimum, it is low (“Cold”).

“Right now, it is very low indeed,” says Mlynczak. “SABER is currently measuring 33 billion Watts of infrared power from NO. That’s 10 times smaller than we see during more active phases of the solar cycle.”

Although SABER has been in orbit for only 17 years, Mlynczak and colleagues recently calculated TCI going all the way back to the 1940s. “SABER taught us to do this by revealing how TCI depends on other variables such as geomagnetic activity and the sun’s UV output–things that have been measured for decades,” he explains.

tci

Above: An historical record of the Thermosphere Climate Index. Mlynczak and colleagues recently published a paper on the TCI showing that the state of the thermosphere can be discussed using a set of five plain language terms: Cold, Cool, Neutral, Warm, and Hot.

As 2018 comes to an end, the Thermosphere Climate Index is on the verge of setting a Space Age record for Cold. “We’re not there quite yet,” says Mlynczak, “but it could happen in a matter of months.”

“We are especially pleased that SABER is gathering information so important for tracking the effect of the Sun on our atmosphere,” says James Russell, SABER’s Principal Investigator at Hampton University. “A more than 16-year record of long-term changes in the thermal condition of the atmosphere more than 70 miles above the surface is something we did not expect for an instrument designed to last only 3-years in-orbit.”

Soon, the Thermosphere Climate Index will be added to Spaceweather.com as a regular data feed, so our readers can monitor the state of the upper atmosphere just as researchers do. Stay tuned for updates.

References:

Martin G. Mlynczak, Linda A. Hunt, James M. Russell, B. Thomas Marshall, Thermosphere climate indexes: Percentile ranges and adjectival descriptors, Journal of Atmospheric and Solar-Terrestrial Physics, https://doi.org/10.1016/j.jastp.2018.04.004

Mlynczak, M. G., L. A. Hunt, B. T. Marshall, J. M. RussellIII, C. J. Mertens, R. E. Thompson, and L. L. Gordley (2015), A combined solar and geomagnetic index for thermospheric climate. Geophys. Res. Lett., 42, 3677–3682. doi: 10.1002/2015GL064038.

Mlynczak, M. G., L. A. Hunt, J. M. Russell III, B. T. Marshall, C. J. Mertens, and R. E. Thompson (2016), The global infrared energy budget of the thermosphere from 1947 to 2016 and implications for solar variability, Geophys. Res. Lett., 43, 11,934–11,940, doi: 10.1002/2016GL070965

 

Japanese Robots Land on Asteroid Ryugu

 Sept. 22,, 2018: This weekend, Japan made history by deploying two rovers on the surface of a near-Earth asteroid. The mechanical explorers dropped from their mothership, Hayabusa2, less than 100 meters above Ryugu, and now they are hopping across the space rock’s cratered landscape. This picture was taken by Rover-1A in mid-hop:

Hopping is necessary because the asteroid’s gravity is too weak for simple rolling.  Instead of wheels, the rovers have rotating motors inside that allow them to shift their momentum and, thus, make little jumps across the asteroid’s rugged surface. Mission controllers are taking great care that the rovers, which measure 18 cm by 7 cm and weigh only 1 kg, do not fly into space.

As historic as this achievement is, it is only the beginning: Rover-1A and 1B are on a reconnaissance mission for two more robots slated to land later this year.  In October, Hayabusa2 will release MASCOT (Mobile Asteroid Surface Scout), a larger lander made by the German Aerospace Center. MASCOT will be followed, in turn, by another Japanese robot.


Above: Hayabasa2 photographs its own shadow on the asteroid. Credit: JAXA

Exploring Ryugu is important. Classified as a potentially hazardous asteroid, this 900-meter wide space rock can theoretically come closer to our planet than the Moon. This makes it a potential target for asteroid mining. Hayabasa2 will discover what valuable metals may be waiting there. Ryugu is also a very primitive body, possibly containing a chemical history of the formation of our solar system billions of years ago.

Launched in December 2014, Hayabusa2 reached asteroid Ryuga in June of this year. It is scheduled to orbit the asteroid for about a year and a half before returning to Earth in late 2020, carrying samples of Ryugu for analysis by researchers. Stay tuned for updates!

Student-Built Space Weather Satellite Targets Killer Electrons

Sept. 20, 2018: Last Saturday, a Delta II rocket blasted off at dawn from the Vandenberg AFB in California. Soon thereafter NASA reported the successful deployment of the ICESat-2 satellite, designed to make 3D laser images of Earth’s surface.

Here’s what most news stations did not report: A pair of tiny satellites were tucked inside the rocket, and they were successfully deployed as well. Built by students at UCLA, ELFIN-A and ELFIN-B are now orbiting Earth, monitoring the ebb and flow of “killer electrons” around our planet.

“We’ve just received our first downlink of data from ELFIN-A,” reports Ryan Caron, Development Engineer at UCLA’s Department of Earth, Planetary, and Space Sciences. Click to listen:

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That may sound like ordinary static, but the signal is full of meaning. As mission controllers turn on ELFIN’s science instruments, the static-y waveforms will carry unique information about particles raining down on Earth from the inner Van Allen Radiation Belt.

“Sensors onboard our two cubesats detect electrons in the energy range 50 keV to 4.5 MeV,” says Caron. “These are the so-called ‘killer electrons,’ which can damage spacecraft and cause electrical disruptions on the ground. They also give rise to the majestic aurora borealis.”

“ELFIN is doing something new,” says Vassilis Angelopoulos, a UCLA space physicist who got his doctorate at UCLA and serves as ELFIN’s principal investigator. “No previous mission was able to measure the angle and energy of killer electrons as they rain down on Earth’s atmosphere. ELFIN will help us investigate how disturbances called ‘Electromagnetic Ion Cyclotron waves’ knock these electrons out of the Van Allen Belts and scatter them down toward Earth.”

ELFIN-A and ELFIN-B are cubesats, each weighing about eight pounds and roughly the size of a loaf of bread. They are remarkable not only for their cutting edge sensors, but also for their origin. The two satellites were almost completely designed and built by undergraduate students at UCLA. Working for more than 5 years, a succession of 250 students created the two Electron Losses and Fields Investigation CubeSats –“ELFIN” for short.

“Just seeing all the hundreds of hours of work, the many sleepless nights, the stressing out that you’re not going to make a deadline — just seeing it go up there … I’m probably going to cry,” says Jessica Artinger, an astrophysics major and geophysics and planetary science minor who helped build the satellites and witnessed their launch.

The ELFIN website has interactive tools so the public can track and listen to the spacecraft as it passes overhead twice a day. The CubeSats are expected to remain in space for two years, after which they will gradually fall out of orbit and burn up in the atmosphere like shooting stars.

ELFIN has been supported with funding from the National Science Foundation and NASA, with technical assistance from the Aerospace Corporation among other industry partners and universities.

 

Equinox Cracks in Earth’s Magnetic Field

Sept. 14, 2018: The northern autumnal equinox is only a week away. That means one thing: Cracks are opening in Earth’s magnetic field. Researchers have long known that during weeks around equinoxes fissures form in Earth’s magnetosphere. Solar wind can pour through the gaps to fuel bright displays of Northern Lights. Here’s an example from Yellowknife, Canada:

“On Sept. 5-6, we could see auroras in the sky all night long, with a bright outburst of pink shortly after midnight,” says photographer Yuichi Takasaka.

During the display, a weak stream of solar wind was blowing around Earth. At this time of year, that’s all it takes. Even a gentle gust can breach our planet’s magnetic defenses.

This is called the the “Russell-McPherron effect,” named after the researchers who first explained it. The cracks are opened by the solar wind itself. South-pointing magnetic fields inside the solar wind oppose Earth’s north-pointing magnetic field. North and South partially cancel one another, opening a crack. This cancellation can happen at any time of year, but it happens with greatest effect around the equinoxes. Indeed, a 75-year study shows that September is one of the most geomagnetically active months of the year–a direct result of “equinox cracks.”

NASA and European spacecraft have been detecting these cracks for years. Small ones are about the size of California, and many are wider than the entire planet. There’s no danger to people on Earth. Our planet’s atmosphere intercepts the rush of incoming particles with no harm done and a beautiful afterglow.

Stay tuned for more Arctic lights as autumn approaches.

Realtime Aurora Photo Gallery

Green Comet Makes Closest Approach to Earth

Sept. 9, 2018: On Sept. 10th, Comet 21P/Giacobini-Zinner (“21P” for short) makes its closest approach to Earth in 72 years–only 58 million km from our planet. The small but active comet is easy to see in small telescopes and binoculars shining like a 7th magnitude star. Michael Jäger of Weißenkirchen, Austria, photographed 21P approaching our planet on Sept. 9th:

“Comet 21P is currently in the constellation Auriga,” says Jäger. “I caught it just as it was passing by star clusters M36 and M38.”

The comet’s close approach to Earth coincides with a New Moon, providing a velvety-dark backdrop for astrophotography. The best time to look is during the dark hours before sunrise when the constellation Auriga is high in the eastern sky. If you have a GOTO telescope, use these orbital elements to point your optics. Detailed sky maps can help, too.

Shining just below the limit of naked-eye visibility, the comet will remain easy to photograph for the rest of September. If you can only mark one date on your calendar, however, make it Sept. 15th. On that night, 21P will cross directly through the middle of the star cluster M35 in the constellation Gemini. Astronomer Bob King writing for Sky and Telescope notes that “the binocular view should be unique with the rich cluster appearing to sprout a tail!”


Click to view an interactive 3D orbit of 21P/Giacobini-Zinner. Credit: NASA/JPL

21P/Giacobini-Zinner is the parent of the annual Draconid meteor shower, a bursty display that typically peaks on Oct. 8th. Will the shower will be extra-good this year? Draconid outbursts do tend to occur in years near the comet’s close approach to the sun. However, leading forecasters do not expect an outburst this year despite the comet’s flyby. In case they are mistaken, many eyes next month will be on the shower’s radiant in the constellation Draco.

Got a picture of Comet 21P/Giacobini-Zinner? Submit it here.

159 Years Ago, A Geomagnetic Megastorm

Sept. 2, 2018: Picture this: A billion-ton coronal mass ejection (CME) slams into Earth’s magnetic field. Campers in the Rocky Mountains wake up in the middle of the night, thinking that the glow they see is sunrise. No, it’s the Northern Lights. People in Cuba read their morning paper by the red illumination of aurora borealis. Earth is peppered by particles so energetic, they alter the chemistry of polar ice.

Hard to believe? It really happened 159 years ago. This map shows where auroras were sighted in the early hours of Sept. 2, 1859:

As the day unfolded, the gathering storm electrified telegraph lines, shocking technicians and setting their telegraph papers on fire. The “Victorian Internet” was knocked offline. Magnetometers around the world recorded strong disturbances in the planetary magnetic field for more than a week.

The cause of all this was an extraordinary solar flare witnessed the day before by British astronomer Richard Carrington. His sighting on Sept. 1, 1859, marked the discovery of solar flares and foreshadowed a new field of study: space weather. According to a NASA-funded study by the National Academy of Sciences, if a similar “Carrington Event” occurred today, it could cause substantial damage to society’s high-tech infrastructure and require years for complete recovery.

carrsket

In Sept. 1859, this large sunspot unleashed a record-setting solar flare. Sketch by R. C. Carrington.

Could it happen again? In fact, a similar event did happen only 6 years ago. On July 23, 2012, a powerful explosion on the sun hurled a Carrington-class CME away from the sun. Fortunately, it missed. “If it had hit, we would still be picking up the pieces,” says Prof. Daniel Baker of the University of Colorado, who summarized the event at NOAA’s Space Weather Workshop in 2014.

In a paper published just a few months ago, researchers from the University of Birmingham used Extreme Value Theory to estimate the average time between “Carrington-like flares.” Their best answer: ~100 years, a value which suggests we may be overdue for a really big storm.