China’s Doomed Space Station

March 26, 2018: China’s Tiangong-1 space station is about to return to Earth–as a massive fireball. According to the European Space Agency (ESA), the 8-ton spacecraft will re-enter the atmosphere sometime between March 30th and April 2nd. Tiangong-1 is about the size of a European cargo spacecraft, such as the ATV-1 which itself re-entered in 2008. This re-entry video of the ATV-1 shows what the Tiangong-1 fireball might look like:

Tiangong-1 was launched in Sept. 2011 to establish a foothold in Earth orbit for China’s fledgling space program. It served as a temporary home in space for two crews, including China’s first female astronauts, and provided a testbed for automated rendezvous and docking procedures. China lost control of Tiangong-1 in 2016 when a telemetry link failed. This made it impossible for mission controllers to guide the station to a re-entry over the South Pacific Ocean as originally planned. Instead, Tiangong-1 would re-enter on its own schedule as aerodynamic friction with Earth’s upper atmosphere slowly drained the station’s orbital energy.

Initially, Chinese officials speculated that re-entry would occur in late 2017. However, low solar activity delayed the splashdown. Sunspot numbers have plummeted recently as the solar cycle heads toward a deep solar minimum:

Without sunspots, the sun’s extreme ultraviolet radiation decreased. Earth’s upper atmosphere cooled and contracted, reducing aerodynamic friction that would otherwise bring Tiangong-1 down. “Late 2017” became the spring of 2018.

At the moment it is impossible to predict exactly where Tiangong-1 will re-enter. All we know is that it will disintegrate somewhere between +42.8 and -42.8 degrees latitude, the upper and lower limits of the station’s tilted orbit. This map from the ESA shows the re-entry zone:

Even with an uncontrolled re-entry, the odds strongly favor a descent over uninhabited land or ocean. According to the ESA, “[surviving fragments] will be scattered over a curved ellipsoid that is thousands of km in length and tens of km wide. The personal probability of being hit by a piece of debris from the Tiangong-1 is actually 10 million times smaller than the yearly chance of being hit by lightning.”

In other words, don’t worry. You’ll be lucky just to see the fireball. Approximately one day before the reentry, it will become possible to roughly predict re-entry ground tracks, and hence which regions on Earth might witness the disintegration. Stay tuned for updates.

Strange Aurora-like Arc Sighted over Alaska: It’s “Steve”!

March 25, 2018: Last night, something happened at the edge of space over Alaska. More than 200 km above Anchorage, a hot ribbon of ionized gas sliced through Earth’s magnetosphere, creating a luminous arc that rivaled the Moon in brightness. Sanjana Greenhill witnessed the apparition:

“We noticed this perfect arc developing across the sky,” says Greenhill. “It didn’t seem like the aurora since it wasn’t moving much. The arc got brighter and then faded and then got brighter again. And then it dawned on me, this is STEVE!”

STEVE is an aurora-like phenomenon that researchers are only beginning to understand. For many years, northern sky watchers reported the form occasionally dancing alongside auroras. It was widely called a “proton arc” until researchers pointed out that protons had nothing to do with it. So members of the Alberta Aurora Chasers group gave it a new name: “Steve” (since upgraded to STEVE, an acronym for ‘Strong Thermal Emission Velocity Enhancement’).

The first clues to the nature of STEVE came in 2016 when one of the European Space Agency’s Swarm satellites encountered the phenomenon. “As the satellite flew straight though ‘Steve,’ the temperature jumped by 3000°C and the data revealed a 25 km-wide ribbon of gas flowing westwards at about 6 km/s (13,000 mph),” reports Eric Donovan from the University of Calgary.

Donovan and a team of colleagues led by Elizabeth MacDonald of NASA’s Goddard Space Flight Center have just published a paper on STEVE. In it, they confirm that STEVE is distinct from ordinary auroras, usually forming to the south of active Northern Lights. The mauve and purple colored arcs, they say, are related to supersonic rivers of gas called “subauroral ion drifts” (SAIDs), which flow through Earth’s magnetic field. Earth-orbiting satelites have tracked thousands of SAIDs: they tend to appear near latitude +60 degrees, and occur more frequently during spring and fall than summer and winter.

This last point means that now is the season for STEVE. The onset of northern spring seems to lure the arc out of winter hiding.

“I saw STEVE for the first time on March 18th,” reports Giuseppe Petricca , who took this sequence of pictures from the Isle of Lewis in Scotland:

“It was an ever-changing tornado, with violet tones, always in movement, always with different shapes,” he says. “Another wonder of Nature!”

The mystery of STEVE is far from solved. Researchers still don’t understand why STEVE is purple–or for that matter why the underlying rivers of gas should glow at all. “Further spectral analysis and modeling are needed,” say MacDonald et al.

In other words, keep an eye out for STEVE.

Realtime “Steve” Photo Gallery


“Equinox Cracks” Forming in Earth’s Magnetic Field

March 11. 2018: The vernal equinox is less than 10 days 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 Arctic lights. One such episode occurred on March 9th. “The sky exploded with auroras,” reports Kristin Berg, who sends this picture from Tromsø, Norway:

During the display, a stream of solar wind was barely grazing Earth’s magnetic field. At this time of year, that’s all it takes. Even a gentle gust of solar wind 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. The two, N vs. S, partially cancel one another, weakening our planet’s magnetic defenses. 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 March is the most geomagnetically active month of the year, followed closely by September-October–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. While the cracks are open, magnetic fields on Earth are connected to those on the sun. Theoretically, it would be possible to pick a magnetic field line on terra firma and follow it all the way back to the solar surface. There’s no danger to people on Earth, however, because our atmosphere protects us, intercepting the rain of particles. The afterglow of this shielding action is called the “aurora borealis.”

Stay tuned for more Arctic lights as spring approaches.

Realtime Aurora Photo Gallery

The Worsening Cosmic Ray Situation

March 5, 2018: Cosmic rays are bad–and they’re getting worse.

That’s the conclusion of a new paper just published in the research journal Space Weather. The authors, led by Prof. Nathan Schwadron of the University of New Hampshire, show that radiation from deep space is dangerous and intensifying faster than previously expected.


The story begins four years ago when Schwadron and colleagues first sounded the alarm about cosmic rays. Analyzing data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard NASA’s Lunar Reconnaissance Orbiter (LRO), they found that cosmic rays in the Earth-Moon system were peaking at levels never before seen in the Space Age. The worsening radiation environment, they pointed out, was a potential peril to astronauts, curtailing how long they could safely travel through space.

This figure from their original 2014 paper shows the number of days a 30-year old male astronaut flying in a spaceship with 10 g/cm2 of aluminum shielding could go before hitting NASA-mandated radiation limits:


In the 1990s, the astronaut could spend 1000 days in interplanetary space. In 2014 … only 700 days. “That’s a huge change,” says Schwadron.

Galactic cosmic rays come from outside the solar system. They are a mixture of high-energy photons and sub-atomic particles accelerated toward Earth by supernova explosions and other violent events in the cosmos. Our first line of defense is the sun:  The sun’s magnetic field and solar wind combine to create a porous ‘shield’ that fends off cosmic rays attempting to enter the solar system. The shielding action of the sun is strongest during Solar Maximum and weakest during Solar Minimum–hence the 11-year rhythm of the mission duration plot above.

The problem is, as the authors note in their new paper, the shield is weakening: “Over the last decade, the solar wind has exhibited low densities and magnetic field strengths, representing anomalous states that have never been observed during the Space Age. As a result of this remarkably weak solar activity, we have also observed the highest fluxes of cosmic rays.”

Back in 2014, Schwadron et al used a leading model of solar activity to predict how bad cosmic rays would become during the next Solar Minimum, now expected in 2019-2020.  “Our previous work suggested a ∼ 20% increase of dose rates from one solar minimum to the next,” says Schwadron. “In fact, we now see that actual dose rates observed by CRaTER in the last 4 years exceed the predictions by ∼ 10%, showing that the radiation environment is worsening even more rapidly than we expected.” In this plot bright green data points show the recent excess:


The data Schwadron et al have been analyzing come from CRaTER on the LRO spacecraft in orbit around the Moon, which is point-blank exposed to any cosmic radiation the sun allows to pass. Here on Earth, we have two additional lines of defense: the magnetic field and atmosphere of our planet. Both mitigate cosmic rays.

But even on Earth the increase is being felt. The students of Earth to Sky Calculus have been launching space weather balloons to the stratosphere almost weekly since 2015. Sensors onboard those balloons show a 13% increase in radiation (X-rays and gamma-rays) penetrating Earth’s atmosphere:


X-rays and gamma-rays detected by these balloons are “secondary cosmic rays,” produced by the crash of primary cosmic rays into Earth’s upper atmosphere. They trace radiation percolating down toward our planet’s surface. The energy range of the sensors, 10 keV to 20 MeV, is similar to that of medical X-ray machines and airport security scanners.

How does this affect us? Cosmic rays penetrate commercial airlines, dosing passengers and flight crews so much that pilots are classified by the International Commission on Radiological Protection as occupational radiation workers. Some research shows that cosmic rays can seed clouds and trigger, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

Cosmic rays will intensify even more in the years ahead as the sun plunges toward what may be the deepest Solar Minimum in more than a century. Stay tuned for updates.


Schwadron, N. A., et al (2014), Does the worsening galactic cosmic radiation environment observed by CRaTER preclude future manned deep space exploration?, Space Weather, 12, 622–632, doi:10.1002/2014SW001084.

Schwadron, N. A., et al (2018), Update on the worsening particle radiation environment observed by CRaTER and implications for future human deep-space exploration, Space Weather, doi: 10.1002/2017SW001803.