Several years ago, amateur astronomers first spotted a rare type of aurora nicknamed " the dunes " because of its luminous, rolling wave patterns. Last year, astronomers proposed a possible underlying mechanism—an increase in the density of oxygen atoms—although the theory was admittedly speculative. Now, a new analysis by researchers at the University of Helsinki provides evidence to confirm that explanation, according to a recent paper published in the journal AGU Advances.

Most people have a passing familiarity with the atmospheric phenomenon known as aurora borealis , aka the northern lights (or the southern lights if they appear in the southern hemisphere). The spectacular kaleidoscopic effects are the result of charged particles from the Sun being dumped into the Earth's magnetosphere , where they collide with oxygen and nitrogen molecules—an interaction that excites those molecules and makes them glow. Auroras typically present as shimmering ribbons in the sky, with green, purple, blue, and yellow hues. The lights tend to only be visible in polar regions because the particles follow the Earth's magnetic field lines, which fan out from the vicinity of the poles.

Discoveries of possible new types of auroras are rare. Back in 2016, enthusiasts observed a different kind of aurora that was visible at more southern latitudes. The aurora looked like a ribbon of pink or mauve light, sometimes with "picket fence" columns of green light passing through the ribbon.

Enlarge / The Cassiopeia A supernova which left this remnant behind occurred about 11,000 light years away—much too far to pose a significant threat—and its wavefront likely reached Earth about 300 years ago. (credit: NASA/JPL-Caltech )

A paper released this week by University of Illinois Urbana-Champaign astronomy and physics professor Brian Fields makes a case for distant supernovae as a cause of a past mass extinction event—specifically, the Hangenberg event, which marks the boundary between the Devonian and Carboniferous periods. Fields has proposed this sort of thing before , and both this and his earlier piece are fascinating exercises of "what-if." Each models the effects a supernova could have on Earth's biosphere, and how we might go looking for evidence that it happened.

It's important to understand, however, that neither of these papers should be taken as indications that there is evidence that the events referenced were caused by a supernova, or as representative of any general scientific consensus to that effect. They're simply intriguing proposals, and they indicate what sort of evidence we should look for.

Existential threats

If you say "mass extinction" and "space" in the same sentence, the first thing on most peoples' minds is an asteroid impact with the Earth—even if dinosaur fans think of the Chicxulub crater , and pop culture fans think instead of movies such as Deep Impact or Armageddon .

Enlarge / This image is a colour composite made from exposures from the Digitized Sky Survey 2 (DSS2). It shows the area around the red supergiant star Betelgeuse. (credit: ESO/Digitized Sky Survey 2/Davide De Martin. )

Betelgeuse is one of the closest massive stars to Earth. It's also an old star, and it has reached the stage when it glows a dull red and expands, with the hot core only having a tenuous gravitational grip on its outer layers. This combination means that we're actually able to resolve different areas on the star's surface, despite the fact that it resides over 700 light years away.

That ability came in handy late last year when Betelgeuse did something unusual: it dimmed so much that the difference was visible to the naked eye. Telescopes pointed at the giant were able to determine that—rather than a tidy, uniform drop in luminance—Betelgeuse's dimming was unevenly distributed , giving the star an odd, squished shape when viewed from Earth. That raised lots of questions about what was going on with the giant, with some experts speculating that, because of Betelgeuse's size and advanced age, the strange behavior was a sign of a supernova in the making.

Now, an international team of international observers is here to throw cold water on the possible explosion. Said researchers were lucky to have the Hubble pointed at Betelgeuse before, during, and after the dimming event. Combined with some timely ground observations, this data indicates a rather mundane reason for the star getting darker: a big burp that formed a cloud of dust near the star.

Despite its distance from the Sun, the asteroid belt will disintegrate as it expands. (credit: NASA/ESA/STScI )

We tend to view the bodies of the Solar System as creations of gravity, which pulled their parts together and hold them in place as they orbit. But as we saw with ideas about the formation of Arrokoth , there are lots of situations where gravity is essentially a constant for long periods of time. And given enough of that time, relatively small forces like friction from sparse gas clouds or pressure from the light of the Sun can add up and create dramatic changes. In fact, a remarkable number of these potential influences have been identified and simulated.

One of these has been named the YORP effect, for its developers, Yarkovsky, O'Keefe, Radzievskii, and Paddack. It describes how light can alter the rotational properties of orbiting bodies. In a recent edition of the Monthly Notices of the Royal Astronomical Society, Dimitri Veras and Daniel Scheeres decided to calculate what happens as the Sun ages, the intensity of its light increases dramatically, and the entire asteroid belt gets YORPed.

A (perhaps too) bright future

It's pretty widely understood that, as the Sun ages, it will expand until its outer edges come close to the Earth's orbit. What's less widely recognized is that it will get quite a lot brighter than it is at present. Other stars with masses similar to the Sun can get thousands of times brighter than the Sun in the last stages of their fusion-driven lives, allowing effects that might otherwise be a bit weak to become dominant.