June 25, 2019: On June 22nd at 21:25 UT, a small asteroid entered Earth’s atmosphere and exploded in broad daylight south of Puerto Rico. Airwaves recorded by the Comprehensive Nuclear Test Ban Treaty Organization’s infrasound station in Bermuda pegged the blast energy between 3 and 5 kilotons of TNT–a fraction of a WW II atomic bomb. The explosion was clearly visible in images from NOAA’s GOES-16 weather satellite:

Meteor expert Peter Brown of the University of Western Ontario says the infrasound signal is consistent with a “small multi-meter sized near-Earth asteroid.” According to data compiled by NASA’s Center for Near Earth Object Studies, asteroids of this size and energy hit Earth’s atmosphere about once a year. That means it’s rare–but not exceptionally so.

The asteroid fragmented as it ripped through the atmosphere. This infrared image from the GOES-16 satellite shows the space rock splitting into at least 3 pieces:

Many more fragments undoubtedly sprayed from the explosion, but the resulting meteorites are now at the bottom of the Caribbean or (in the case of dust-sized debris) floating on the sea surface. Samples would be very difficult to recover.

Earth is currently approaching the Taurid Swarm–a stream of rocky debris associated with the Tunguska Impact of 1908. Astronomers are eager for the close encounter, which begins in late June, so they can peer inside the swarm in search of dangerous asteroids. This fireball, however, is not a Taurid.

“Based on a preliminary orbit for the fireball, it does not appear to be part of the Taurid swarm,” says Paul Weigert of the University of Western Ontario. “Its orbit is typical of near-Earth asteroids which have escaped from the asteroid belt.”

UPDATE: This asteroid may have been discovered shortly before it struck by an Atlas Project Survey telescope: more.

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June 21, 2019: What do you get when you mix the summer solstice with one of the deepest Solar Minima in a century? Extreme noctilucent clouds.

“On June 21st, at least 80% to 90% of our sky was covered by bright electric-blue waves,” reports Jacob Kuiper of Steenwijk, The Netherlands. “It was unbelievable, so bright and vast. For sure, this was the most extreme display I have seen in 35 years of observing NLCs.”

During the outburst, Spaceweather.com received pictures from almost every country in Europe as far south as Italy. The clouds were even visible in downtown Paris:

“I’ve been waiting 10 years to see these clouds in Paris,” says photographer Sylvain Weiller. “Finally, the NLCs are back!”

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above the planet’s surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.

This close-up photo taken by Sebastian Voltmer of Spicheren, France, shows the clouds’ tell-tale wave structure:

This summer, extra moisture in the mesosphere has super-charged noctilucent clouds, allowing them to be sighted as far south as Rome, Italy; Los Angeles, California; and Paris, France. No one can predict exactly when they will appear. Tonight could be the night where you live.

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.

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June 21, 2019: The sun is blank–really blank. No sunspots have appeared for the past 34+ days, giving the sun the appearance of a giant orange billiard ball. This is a sign that Solar Minimum is underway. Earlier this year, a panel of experts from NOAA and NASA predicted that the solar cycle would reach its nadir sometime between July 2019 and Sept 2020. The current stretch of spotless suns is consistent with their forecast.

Above: The sun on June 21, 2019. Credit: NASA’s Solar Dynamics Observatory

What happens when sunspots vanish? For one thing, solar flares stop happening. No big explosions means no shortwave radio blackouts and fewer geomagnetic storms. Also, the sun dims. Sunspots are sources of extreme ultraviolet radiation (EUV). Without sunspots, EUV levels decrease, causing Earth’s upper atmosphere to cool and contract. Satellites and space junk stay in orbit longer as aerodynamic drag subsides.

During this phase of the solar cycle, the solar wind slows and the sun’s magnetic field weakens–shields down! This allows extra cosmic rays from deep space to penetrate the solar system. Indeed, recent high altitude balloon flights show increased radiation in Earth’s atmosphere. Extra cosmic rays can trigger lightning, alter the electro-chemistry of the upper atmosphere, and boost dose rates on commercial airplane flights.

Solar Minimum won’t last forever. Forecasters expect sunspot numbers to increase after 2019-2020, climaxing in a new Solar Maximum around 2023-2026.  Meanwhile, stay tuned for more blank suns.

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June 21, 2019: Last night in Texas, a flurry of red sprites exploded from the top of a powerful thunderstorm. One of the the red forms was so tall and bright, people saw it 200 miles away in Oklahoma. “My boys and I saw it with our unaided eyes,” reports Paul Smith, who photographed the event from the shores of Lake Thunderbird, OK. This may be the first time that a sprite’s reflection has been captured in water:

Naked-eye sightings of sprites are rare, mainly because they are so fleeting. But this one left an impression. “My eleven-year-old son Thomas described it as a ‘huge orange-y-brown flash of lines high in the sky,'” says Smith. “My seven-year-old James just exclaimed ‘what the heck was that?'”

At first glance, Smith’s capture resembles a Gigantic Jet–that is, a type of “sprite on steroids.” But lightning expert Oscar van der Velde of the Universitat Politècnica de Catalunya thinks it may be something else:

“In early days of sprite research, they were called ‘palm trees’ by researchers from the University of Alaska,” van der Velde explains. “It is, basically, a bushy group of red sprites on top, with a secondary purple discharge hanging below. These types of events are quite rare. You need a big, active mesoscale convective system to produce them.”

Palm tree sprites are a topic of cutting edge research. “We haven’t even been able to confirm that they indeed originate from the thundercloud,” says van der Velde.

“Last night was so much fun,” adds Smith. “In addition to the sprites, my son Thomas photographed Jupiter and our Moon with the Nikon coolpix 80x zoom camera. We also saw a nice bolide exploding over the storms. The kid’s reactions were priceless.”

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June 19, 2019: The 2019 season for noctilucent clouds (NLCs) has been remarkable, maybe the best ever, with NLCs appearing as far south as Los Angeles CA and Albuquerque NM. What’s going on? Researchers aren’t sure, but Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics has just found an important clue.

“The mesosphere is quite wet,” she says. “Water vapor concentrations are at their highest levels for the past 12 years.”

Noctilucent clouds form when summertime wisps of water vapor rise to the top of the atmosphere. Water molecules stick to specks of meteor smoke, gathering into icy clouds that glow electric blue when they are hit by high altitude sunlight.

When noctilucent clouds began appearing at unusually low latitudes in early June, Harvey took a look at data from NASA’s Microwave Limb Sounder–a satellite-based sensor that can measure water in the upper atmosphere. Her results are shown in the animated plot below.

“The red line is 2019, while other colors trace previous years,” explains Harvey. “The plot cycles from low to high latitudes,” showing a wave of moisture in the mesosphere.

It’s a veritable tidal wave. Water vapor concentrations at lower latitudes (35 to 45 N) have nearly doubled their normal values, providing a surplus of H₂O molecules for noctilucent clouds. Researchers aren’t sure where the water is coming from, though.

“Planetary wave activity could be transporting cold air and high water vapor to the ‘noctilucent zone,'” speculates James Russell of Hampton University’s Center for Atmospheric Sciences. “We’ve seen this happen before during mid-latitude outbreaks of noctilucent clouds.”

The solar cycle may be helping, too. Right now a deep Solar Minimum is underway. Ultraviolet radiation that would normally destroy water in the mesosphere is at low ebb.

The wave appears to be breaking. “As we enter the 3rd week of June, the water has stopped increasing,” notes Harvey. “Poleward of 70N the water content has been dropping for a few weeks, and right around the north pole it’s getting quite dry. At mid-latitudes (35-65N), water content is still high, but it’s leveling off.”

No one knows what will happen next. Another wave could bring renewed sightings of NLCs at low latitudes. Or conditions could return to normal, restoring the clouds to their usual habitat near the Arctic Circle.  Says Russell, “this all points to mysteries of the atmosphere that have not been solved.” Stay tuned!

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June 15, 2019: If you’ve never seen a cloud of frosted meteor smoke, now is the time to look. 2019 is shaping up to be the best year for noctilucent clouds (NLCs) … maybe ever. Normally confined to near-Arctic latitudes, NLCs have been seen this month in most US states. On Friday morning, June 14th, Don Davis saw them, astonishingly, from the city of Joshua Tree not far from Los Angeles CA:

“They were dim but distinct,” says Davis. “I photographed them easily using a 4 second exposure at ISO 400.”

Davis’s sighting at +34.1 degrees sets the record for low-latitude observations of NLCs, breaking the previous record set only five days earlier by Brian Guyer at the National Weather Service in Albuquerque, New Mexico (+35.1 degrees).

“I’m shocked to report that I saw the noctilucent clouds while venturing outdoors for a weather observation shortly after sunset,” says Guyer, who is a senior meteorologist. “When I noticed the faint blue wavy tendrils far off to the north, I asked myself, ‘am I really seeing noctilucent clouds from here?’ I’m happy to see that other folks are also seeing these beautiful spectacles of nature at lower latitudes.”

Noctilucent clouds form every year when wisps of summertime water vapor rise to the top of Earth’s atmosphere and crystallize around specks of meteor smoke. The season typically starts in late May, peaks in July, and peters out in August. If NLCs are being seen in California and New Mexico in June, the season’s peak in early July could be very special indeed.

Noctilucent clouds have been creeping south for years–a possible result of climate change and/or the solar cycle. 2019 has broken all the old records for southern sightings, bringing the clouds into the mainstream of mid- to low-latitude sky watching. Now everyone should be alert for NLCs.

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.

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June 13, 2019: Picture this: An astronaut climbs aboard his spacecraft and blasts off from Earth. At the apex of the flight, he experiences something strange. Weightlessness? Space sickness? No. He changes color! This doesn’t happen to human astronauts, but it does happen to halobacteria, an extreme-loving microbe from Earth that might be able to live on Mars.

In recent weeks, Spaceweather.com and the students of Earth to Sky Calculus have been flying halobacteria to the stratosphere. Why? To see if the salt-loving microbes might be able to survive on the Red Planet. The stratosphere is a good place to find out because conditions in Earth’s stratosphere are remarkably similar to conditions on the surface of Mars.

The quick answer is YES. Halobacteria do survive–for brief trips, at least. Halobacteria that we launch into the stratosphere come back alive a few hours later, and we can easily culture them in an incubator.

But they don’t come back unchanged. We find that halobacteria color-shift during their trip to the edge of space. On Earth, they’re pink. When they reach the stratosphere, they turn yellow–and they remain yellow even after they return to the ground. Just by looking at the color of a sample, we can tell if it has been to the stratosphere.

Back in the lab, something even more interesting happens. When we culture the “space-traveling” yellow halobacteria, allowing them to feed and multiply, their descendants turn pink again! The descendants undo the effects of the balloon flight, resetting themselves for another trip.

What’s happening? The answer involves bacteriorhodopsin.

Bacteriorhodopsin is a protein used by halobacteria to help feed themselves When food sources become scarce, halobacteria photosynthesize sunlight for energy. Unlike plants, however, they don’t use green chlorophyll. Halobacteria use purple bacteriorhodopsin.

Bacteriorhodopsin has two stable forms–a purple form and a yellow form, each with a different shape. During photosynthesis, bacteriorhodopsin toggles back and forth between these forms, blinking yellow and purple. Because of this color-shifting ability, technologists have long been interested in using bacteriorhodopsin as a kind of “electronic ink” in tablets and smart phones.

When we launch halobacteria to the stratosphere, the microbes turn yellow–and stay yellow. They stop cycling back to their purple state as they would normally do during photosynthesis. Perhaps UV rays in the stratosphere denature the bacteriorhodopsin proteins. Denaturing means they lose their shape, permanently changing their color.

Whatever causes the color change, the descendants of flown halobacteria put their proteins back together again–ready for more trips to space.

We’re preparing to fly a batch of the descendants to see if they are even tougher than their predecessors. Stay tuned

 

June 11, 2019: On June 8th and 9th, many people who have never previously heard of “noctilucent clouds” (NLCs) found themselves eagerly taking pictures of them–from moving cars, through city lights, using cell phones and iPads. “I have never seen clouds like this before!” says Tucker Shannon, who took this picture from Corvallis, Oregon:

“I heard that they may have been seeded by meteoroids,” says Shannon.

That’s correct. NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above the planet’s surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.

Noctilucent clouds used to be a polar phenomenon. In recent years, however, researchers have noticed their electric-blue forms creeping south. Is it climate change? Or the solar cycle? No one knows for sure.

This past weekend, even veteran observers were stunned by the clouds’ intensity and southern reach. At one point, they were visible in Freedom, Oklahoma (latitude +36.7 N). As far as we know, that is the lowest latitude sighting ever. Other notable low-latitude sightings include San Francisco, California, and the Cedar Breaks National Monument in Utah.

Still images of NLCs capture only a fraction of their magic. These small videos recorded by Keven Lapp outside Edmonton, Alberta, show their hypnotic fine-structured rippling motions:

“This was one of the largest NLCs that I’ve ever seen,” says Lapp. “The time lapse was taken between 2:40 AM and 3:24 AM local time.”

At present, no one can predict exactly when these noctilucent clouds will re-appear. Recent events suggest that even mid-latitude observers should be alert. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.

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June 5, 2019: On June 30, 1908, in broad daylight, a meteoroid hurtled out of the blue sky over Russia’s Tunguska river and exploded, leveling a forest. The event, which researchers are still studying today, kickstarting a new field of astronomy: Daytime meteor showers¹.

Most people don’t know it, but some of the strongest meteor showers of the year happen when the sun is up. In fact, one of them is underway now. Today’s sky map from Canada’s Meteor Orbit Radar (CMOR) in western Ontario shows a hot spot in the constellation Aries only 20 degrees from the sun.

“These are Arietid meteors, and they peak every year in early June as Earth passes through a debris stream linked to the unusual comet 96P/Machholz,” says professor Peter Brown of the University of Western Ontario. “At their peak on June 7th, we expect our radar to detect one Arietid every 20 seconds. This makes them the 5th strongest radar shower of the year.”

In fact, people can see daylight meteors–a few at least. The trick is to look just before dawn when the shower’s radiant is barely above the horizon and the sun is barely below.

“The Arietids an observer would see before dawn are quite impressive as they are all Earthgrazers, skimming the atmosphere almost horizontally overhead,” notes Brown. “Earthgrazers tend to be slow and very bright.”

It turns out that June is the best month of the year for daytime meteor showers. When the Arietids subside, another daytime shower will take over: The zeta Perseids peak on June 13th. And then another: The beta Taurids on June 29th.

The beta Taurids are particularly interesting because researchers suspect it may be responsible for the Tunguska explosion of 1908. This June the Taurid debris swarm will make its closest approach to Earth since 1975. Many astronomers, including Brown, will use large telescopes to search for signs of hazardous objects as the swarm passes by.

Stay tuned for updates.

End note: (1) Tunguska was a dramatic example of a daytime meteor. It took 30+ years after the explosion, however, for the field of daytime meteor studies to gain its footing. Brown explains: “The first daytime showers were observed and recognized by  astronomers at Jodrell Bank shortly after World War II, really kickstarting the field. As early as 1940, studies of the orbit of the nighttime Taurids suggested the stream should intersect the Earth during the day in June. At that time, predictions were made by Fred Whipple of a daytime component to the Taurid stream in June (the Beta Taurids/Zeta Perseids). In the 1970s, the peak date for the Beta Taurids (about June 30) and the radiant location were matched by Lubor Kresak to the Tunguska fireball–at which time he posited a link between the Beta Taurids and Tunguska.”