The Alpha Capricornid Meteor Shower

July 24, 2021: Today, meteor storms are rare, but a few hundred years from now they could be commonplace. Consider this fireball, recorded by Thomas Ashcraft on July 21st, a preview of things to come:

“This is a probable alpha Capricornid,” says Ashcraft, who operates an automated meteor camera in rural New Mexico. “It was magnitude -11, about as bright as a waxing gibbous Moon.” Next: Turn up the volume. The soundtrack is a 54.309 MHz digital TV signal reflected from the fireball’s ionized trail.

Alpha Capricornid meteors are debris from Comet 169P/NEAT. They appear every year in late July, peaking around the July-August boundary with 5 to 9 meteors per hour. Many “alpha Caps” are slow, bright fireballs.

This is a minor shower today, but in the not-too-distant future, it could turn into a regular meteor storm. Researchers Peter Jenniskens (SETI Institute) and Jeremie Vaubaillon (Paris Observatory) have studied the alpha Capricornid debris stream. They believe it resulted from a major fragmentation event ~5000 years ago when as much as half of the original comet disintegrated. Since then, the debris has been drifting toward Earth.

“In the next 300 years, the alpha Capricornids are likely to grow into a major annual shower,” they write in an article in the Astronomical Journal. “Rates will increase dramatically in the 23rd and 24th centuries to a peak of ZHR = 2200/hr on an annual basis, half the visible shower peak rate during the 1999 Leonid storm.”

If they’re right, every alpha Capricornid we see today heralds a storm to come. Watch for them in the nights ahead slowly spilling out of the constellation Capricornus. The best time to look is during the hours around midnight when the shower’s radiant may be found in the southern sky beautifully bracketed by Jupiter and Saturn: sky map.

Bonus: Another meteor shower, the southern Delta Aquarids (SDAs), also peaks in late July, sending streaks of light from the same general part of the sky. SDAs zip along ~twice as fast as alpha Caps and tend to be fainter. Nevertheless, they will add to your midnight meteor count. Enjoy!

NLCs Setting Records

July 21, 2021: Noctilucent cloud (NLC) season is now 8 weeks old. This animation from NASA’s AIM spacecraft shows everything that has happened since the first clouds appeared in late May:

The last frame says it all: Noctilucent clouds are still bright and abundant. In fact, at the highest latitudes they are setting records.

“We’re seeing more clouds at 80°N than in any other year since AIM was launched,” says Cora Randall of the University of Colorado’s Laboratory for Atmospheric and Space Research. “Cloud frequencies at 80°N are around 85%, whereas it’s more typical to see frequencies of about 75%.” (‘Frequencies’ are a measure of patchiness. 100% is complete coverage; 0% is no clouds at all.)

“This morning, I watched a fantastic display, the best of the year so far ,” reports Marek Nikodem, who photographed the clouds from Szubin, Poland (53°N) on July 21st:

“It’s not the end of the season yet,” he says. Indeed, it’s not.

NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise up to the edge of space, about 83 km high, and crystalize around disintegrated meteoroids. When you see one, you’re literally seeing a cloud of frosted meteor smoke.

Earlier this summer, NLCs were seen in Europe as far south as the mediterranean coast of Spain (+37N). Given the current surge, another low-latitude excursion cannot be ruled out before the season ends in August. Watch for them!

Farside Explosion Touches Earth

July 15, 2021: Imagine an explosion on the farside of the sun so powerful, we could feel it here on Earth. It happened on July 13th. The debris emerged in a circular cloud known as a ‘halo CME‘:

Above: The July 13th CME imaged by SOHO coronagraphs

When space weather forecasters first saw this explosion, there was a moment of excitement. It appeared to be heading directly toward Earth. However, data from NASA’s STEREO-A spacecraft indicated otherwise. The CME was heading directly away from us–a farside event.

Now for the interesting part: Although the explosion occured on the farside, separated from Earth by the massive body of the sun, it still peppered our planet with high-energy particles. The Energetic and Relativistic Nuclei and Electron (ERNE) detector onboard SOHO recorded a surge in radiation not long after the CME appeared:

How did this radiation reach Earth? Rami Vainio, a professor of space physics at the University of Turku (Finland), who works with ERNE data says “it’s not possible to answer that question definitely without a detailed analysis involving multiple spacecraft.” However, he speculates that the lift-off of the CME may have created a global shock wave on the farside of the sun. Particles spilling over the edge might have spiraled toward our planet.

Of particular interest are the green data points (51 to 100 MeV). These are the most energetic protons ERNE can detect. An uptick in green after the CME indicates unusually “hard” radiation—the kind accelerated in the leading edge of a fast-moving CME.

The source of the blast might have been the same sunspot (AR2838) that produced the first X-flare of Solar Cycle 25 on July 3rd. That sunspot is currently transiting the farside of the sun approximately where the CME came from. Within the next week AR2838 is expected to return–and then, maybe, the real fun begins. Stay tuned!

A Big Glowing Cloud of Marsdust

July 6, 2021: Dust storms on Mars are bigger than we thought; they even spill into space. According to a recent paper in JGR Planets, Mars appears to be leaking dust, filling a huge volume of the inner solar system with gritty debris. You can see it with your naked eye. The bright triangle in this image from the Haleakalā Observatory in Hawaii is marsdust:

“A friend described it as blazing,” says Rob Ratkowski, who took the picture on Feb. 10th. “It was bright and very obvious.”

It’s called Zodiacal Light, and astronomers have long wondered what causes it. The usually faint triangle is sunlight scattered by dust in the plane of our solar system. The dust, it turns out, comes from Mars.

NASA’s Juno spacecraft flew through the dust cloud en route to Jupiter between 2011 and 2016. Dust grains smashed into Juno at about 10,000 mph, chipping off submillimeter pieces of spacecraft. Juno’s oversized solar arrays turned out to be excellent dust detectors, registering as many as 200 hits per day.

Ironically, the sandblasting allowed researchers to map the cloud for the first time. One theory of Zodiacal Light held that asteroids were responsible. Yet, as Juno flew through the asteroid belt toward Jupiter, impact rates sharply dropped, sometimes to zero. Asteroids were not the answer. Instead, they realized, the dust must be coming from Mars. Orbital elements of the dust grains essentially match that of the Red Planet.

Mars is the dustiest place in the Solar System, with dust storms that envelop the entire planet for months. But how does this dust escape? During storms, dust is sometimes launched to very high altitudes in the Martian atmosphere; researchers call it ‘rocket dust‘. However, leaving Mars requires overcoming escape velocity (~5 km/s), and even rocket dust has trouble doing that. Dust grains would have an easier time launching from Phobos and Deimos; however, those small moons don’t produce enough dust to explain the Zodiacal Light.

So, there’s still a mystery here. Mars has the dust, but researchers haven’t yet figured out how Mars delivers it. Lead author John Leif Jørgensen (Technical University of Denmark) and colleagues hope other scientists will help them solve this final piece of the puzzle.

First X-flare of Solar Cycle 25

July 3, 2021: Now, Solar Cycle 25 has really begun. On July 3rd, new sunspot AR2838 produced the first X-class solar flare since Sept. 2017. NASA’s Solar Dynamics Observatory recorded the extreme ultraviolet flash:

The July 3rd explosion registered X1.5 on the Richter Scale of Solar Flares

A pulse of X-rays ionized the top of Earth’s atmosphere, causing a shortwave radio blackout over the Atlantic Ocean: blackout map. Mariners, aviators, and amateur radio operators may have noticed unusual propagation effects below 30 MHz just after 1429 UT.

X-flares are the strongest kind of solar flare. They are typically responsible for the deepest radio blackouts and the most intense geomagnetic storms. This is the first X-flare of young Solar Cycle 25. More are in the offing. During the previous solar cycle (Solar Cycle 24) the sun produced 49 of them. Forecasters believe that Solar Cycle 25 should be at least that active. We can therefore expect dozens more X-flares as the sun approaches Solar Maximum in the year ~2025. Solar flare alerts: SMS Text.

SOLAR FLARE CAUSES RARE ‘MAGNETIC CROCHET’: The X-flare of July 3rd did something rare. “It disturbed all of my instruments,” reports Rob Stammes, who operates a space weather observatory in Lofoten, Norway. The flare produced a radio burst, an ionospheric disturbance, a surge of electrical currents in the ground, and a deflection of the observatory’s local magnetic field. All of these are shown in the strip chart recording, below.

“This is a first in many years,” says Stammes. “The magnetic disturbance (circled in yellow) is especially rare.”

The phenomenon is called a ‘magnetic crochet.’ Radiation from the flare ionized the top of Earth’s atmosphere and caused currents to flow 60 km to 100 km above Earth’s surface. These currents, in turn, altered Earth’s polar magnetic field. Unlike geomagnetic disturbances that arrive with CMEs days after a flare, a magnetic crochet occurs while the flare is in progress. They tend to occur during fast impulsive flares like this one.

Interplanetary Shock Wave Sparks Midsummer Auroras

June 30, 2021: This was not in the forecast. A low-amplitude interplanetary shock wave (data) hit Earth’s magnetic field during the early hours of June 30th, sparking mid-summer auroras over Canada:

Catalin Tapardel photographed the display from the Municipal District of Opportunity (#17) in Alberta. “I caught the auroras hovering just above an expanse of noctilucent clouds,” says Tapardel.

We don’t know where this shock wave came from. It might be the early arrival of the June 27th CME, originally expected July 1st, or perhaps a different stealthy CME that “flew under the radar” when it left the sun. If it’s the latter, another jolt could occur in the next 24 hours.

Update: Philip Granrud also saw the auroras from Kalispell, Montana. “…and a patch of noctilucent clouds, too!” he says. “It was a beautiful night in Montana.”

Huge Comet Discovery

June 23, 2021: Astronomers have just discovered a comet so big, it might actually be a minor planet. The object is named 2014 UN271. Astronomers Pedro Bernardinelli and Gary Bernstein found it in archival images from the Dark Energy Survey. It appears to be about 100 km wide, 2 or 3 times bigger than record-breaking Comet Hale-Bopp of the 1990s.

Above: A discovery image and orbit of huge Comet Bernardinelli-Bernstein

Now for the bad news. Although 2014 UN271 is falling toward the sun, we may never see it with our naked eyes. At closest approach in early 2031, the behemoth comet will be just outside the orbit of Saturn, too far for naked-eye viewing. Some astronomers are estimating a maximum brightness near magnitude +17, about the same as Pluto’s moon Charon.

It’s still an amazing discovery. 2014 UN271 has an extremely elongated orbit stretching from ~the neighborhood of Saturn out to a staggering distance of almost a light year. At the far reaches of its orbit, 2014 UN271 barely feels the sun’s gravity and could be snatched out of the Solar System altogether by the ephemeral pull of galactic tides. Discovering such a traveler during its brief time among the planets is very lucky indeed.

Above: Images of 2014 UN271 taken June 22, 2021. Credit: L. Demetz, L. Buzzi, A. Aletti

There is talk of a space mission to intercept 2014 UN271. The European Space Agency is building a probe called Comet Interceptor designed to investigate comets coming from deep space. It, or something like it, might be able to visit 2014 UN271 a decade from now.

With an object like this, we have to expect surprises. 2014 UN271 certainly poses no threat to Earth, but it could brighten more (or less) than expected. Multiple groups of astronomers have already detected signs of out-gassing even though 2014 UN271 is still beyond Uranus. Early signs of activity may bode well for future visibility through small telescopes if not the unaided eye.

Update: This object has been officially designated a comet and named Comet Bernardinelli-Bernstein (C/2014 UN271).

A Major Outbreak of Noctilucent Clouds

June 20, 2021: A week ago, noctilucent clouds (NLCs) were stuck inside the Arctic Circle. Suddenly, they have broken free. Over the weekend, people saw the clouds through the city lights of Paris, Madrid, Berlin and other European capitals. On June 20th, Francisco Gil photographed NLCs as far south as Valencia, Spain:

“It is pretty strange to observe noctilucent clouds from these latitudes,” says Gil.

Indeed it is. Valencia is at +39N, a latitude where NLCs are almost never seen. For most of their history (NLCs were discovered in the 19th century), the clouds have been found mainly near the Arctic Circle. Now they are spreading. The record low latitude, to date, was set in June 2019 when the clouds appeared near Los Angeles (+34 N). Gil’s sighting shows that they are in the 30s again.

This just in: Cameras at the Calar Alto Observatory in Spain recorded the clouds at an even lower altitude (+37.5N):

“I enjoyed installing the camera myself in 2007,” says Dr. Gerd Baumgarten of the Leibniz-Institute of Atmospheric Physics. “It took five years to capture the first NLC from that location, however since 2018 we’re getting about 2 events every year.”

NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise to the edge of space (~83 km high) and crystallize around disintegrated meteoroids. When you see one, you’re literally seeing a cloud of frosted meteor smoke.

Observing tips: Look west 30 to 60 minutes after sunset (or before sunrise) when the sun is just below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.

NLCs, Stuck Inside the Arctic Circle

June 14, 2021: The season for noctilucent clouds (NLCs) is now 3 weeks old. This animation from NASA’s AIM spacecraft shows a thickening spiral of frosted meteor smoke around the North Pole:

Above: Noctilucent clouds from May 21st through June 11th. Credit: NASA/AIM

Noctilucent clouds form every year, approximately now, when summertime wisps of water vapor rise to the edge of space and crystallize around disintegrated meteoroids. The icy clouds float 83 km above Earth’s surface, making them (by far) our planet’s highest clouds.

Mid-June to July is typically when NLCs are most widespread. At the moment, though, they’re mostly confined inside the Arctic Circle. Some spillage into mid-latitudes has been reported from Canada, Scotland, Poland, the Netherlands, and England. This is a far cry from the low latitude excursions of recent years. In June 2019, for instance, NLCs were seen as far south as Los Angeles and Las Vegas.

What’s holding the clouds back? To answer this question, Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP) took a look at current conditions in the mesosphere where NLCs form. “The time series below shows that water vapor in the mesosphere is relatively high,” she notes.

This is actually good news for noctilucent clouds, which form only when the mesosphere is both cold and wet. In the plot, red traces 2021. This year has been among the wettest since AIM was launched in 2007.

Now for the not-so-good news: Harvey has also looked at temperature in the mesosphere and “it is just ‘middle of the road,'” she says. Unremarkable cold above the North Pole appears to be slowing the clouds’ growth.

There is plenty of water in the mesosphere. The temperature just needs to drop so more H2O molecules can latch on to specks of meteor smoke. If that happens, 2021 could still shape up to be a good year for noctilucent clouds.

Stay tuned.

The Termination Event

June 10, 2021: Something big may be about to happen on the sun. “We call it the Termination Event,” says Scott McIntosh, a solar physicist at the National Center for Atmospheric Research (NCAR), “and it’s very, very close to happening.”

If you’ve never heard of the Termination Event, you’re not alone.  Many researchers have never heard of it either. It’s a relatively new idea in solar physics championed by McIntosh and colleague Bob Leamon of the University of Maryland – Baltimore County. According to the two scientists, vast bands of magnetism are drifting across the surface of the sun. When oppositely-charged bands collide at the equator, they annihilate (or “terminate”). There’s no explosion; this is magnetism, not anti-matter. Nevertheless, the Termination Event is a big deal. It can kickstart the next solar cycle into a higher gear.

Above: Oppositely charged magnetic bands (red and blue) march toward the sun’s equator where they annihilate one another, kickstarting the next solar cycle. [full caption]

“If the Terminator Event happens soon, as we expect, new Solar Cycle 25 could have a magnitude that rivals the top few since record-keeping began,” says McIntosh.

This is, to say the least, controversial. Most solar physicists believe that Solar Cycle 25 will be weak, akin to the anemic Solar Cycle 24 which barely peaked back in 2012-2013. Orthodox models of the sun’s inner magnetic dynamo favor a weak cycle and do not even include the concept of “terminators.”

“What can I say?” laughs McIntosh. “We’re heretics!”

The researchers outlined their reasoning in a December 2020 paper in the research journal Solar Physics. Looking back over 270 years of sunspot data, they found that Terminator Events divide one solar cycle from the next, happening approximately every 11 years. Emphasis on approximately. The interval between terminators ranges from 10 to 15 years, and this is key to predicting the solar cycle.

Above: The official forecast for Solar Cycle 25 (red) is weak; McIntosh and Leamon believe it will be more like the strongest solar cycles of the past.

“We found that the longer the time between terminators, the weaker the next cycle would be,” explains Leamon. “Conversely, the shorter the time between terminators, the stronger the next solar cycle would be.”

Example: Sunspot Cycle 4 began with a terminator in 1786 and ended with a terminator in 1801, an unprecedented 15 years later. The following cycle, 5, was incredibly weak with a peak amplitude of just 82 sunspots. That cycle would become known as the beginning of the “Dalton” Grand Minimum.

Solar Cycle 25 is shaping up to be the opposite. Instead of a long interval, it appears to be coming on the heels of a very short one, only 10 years since the Terminator Event that began Solar Cycle 24. Previous solar cycles with such short intervals have been among the strongest in recorded history.

These ideas may be controversial, but they have a virtue that all scientists can appreciate: They’re testable. If the Termination Event happens soon and Solar Cycle 25 skyrockets, the “heretics” may be on to something. Stay tuned for updates.