What you might have missed: an aurora that isn’t an aurora; tiny droplets; habitable icy exoplanets; and megafauna decline

When is an aurora not an aurora?

The northern and southern lights might be the best-known phenomena that light up the night sky.

But the most mysterious ones are those you’ve probably never heard of: the mauve and white streaks called STEVE – Strong Thermal Emission Velocity Enhancement – and glowing green streaks called “picket fence” that form as their frequent companion.

They were first recognised as different from the common auroras in 2018. Now, Claire Gasque – a PhD candidate in physics at the University of California Berkeley – has proposed a physical explanation for the picket fence. Her paper is published the journal Geophysical Research Letters.

Gasque calculated that electric fields parallel to Earth’s magnetic field, in a region of the upper atmosphere farther south from where the auroras form, could produce the colour spectrum.

The next step is to launch a rocket from Alaska through these phenomena and measure the strength and direction of the electric and magnetic fields.

A photograph of a purple light in the night sky, accompanied by bars of green light
Steve (mauve and white streaks) and picket fence (green). Credit: The European Space Agency

A new way to make tiny droplets for science

Droplets are important in a variety of scientific fields.

In microreactors, droplets can be used to create different reaction environments or mix different chemicals. In drug delivery systems, droplets can be used to deliver drugs or other agents to specific tissues or organs. In crystallisation studies, droplets can be used to control the growth of crystals. And in cell culture platforms, droplets can be used to grow cells in a controlled environment, which can help to improve cell viability and proliferation.

Rutvik Lathia, a PhD student at the Indian Institute of Science is lead researcher on a new study detailing a technique to encapsulate liquid droplets. The report is published in Nature Communications.

Researchers carefully coated droplets with small hydrophobic (oil-loving) beads, turning them into so-called Liquid Marbles (LM). They were also able to use wax to create a solid shell instead.

This method reduced the evaporation rate of droplets by up to 200 times, increasing their lifetime.

Three close up photographs of tiny droplets covered in a layer of material
Liquid and solid shell droplet encapsulation prepared by capillary assisted cloaking. Credit: Rutvik Lathia and Chandan Modak

People, not the climate, caused the decline of the giant mammals

New research suggests that the success of our human ancestors came at the expense of other large mammals, or megafauna, that they hunted.

“We’ve studied the evolution of large mammalian populations over the past 750,000 years,” says Jens-Christian Svenning, a professor at Aarhus University, Denmark, and co-author of the study in Nature Communications. “For the first 700,000 years, the populations were fairly stable, but 50,000 years ago the curve broke and populations fell dramatically and never recovered.”

They looked at the DNA of 139 large living mammals – species that have survived for the past 50,000 years without becoming extinct – finding that the populations have also declined over the period.

“For the past 800,000 years, the globe has fluctuated between ice ages and interglacial periods about every 100,000 years. If climate was the cause [of megafauna decline], we should see greater fluctuations when the climate changed prior to 50,000 years ago. But we don’t. Humans are therefore the most likely explanation,” he adds.

Black and white illustration of prehistoric people hunting a mammoth
First printed in Bryant & Gay, 1883. Wood carving by E. Bayard.

The search for habitable icy exoplanets expands

A NASA study has found 17 exoplanets outside of our solar system that could have oceans of liquid water beneath their icy shells.

The search for life in the Universe typically focuses on exoplanets that are in a star’s “habitable zone” – at a distance where temperatures allow liquid water to exist on their surfaces.

“Our analyses predict that these 17 worlds may have ice-covered surfaces but receive enough internal heating from the decay of radioactive elements and tidal forces from their host stars to maintain internal oceans,” says Dr Lynnae Quick of NASA’s Goddard Space Flight Center in the US, lead author of the paper in The Astrophysical Journal.

“Thanks to the amount of internal heating, all planets in our study could also exhibit cryovolcanic eruptions in the form of geyser-like plumes.” 

They identified that 2 of the exoplanets are close enough that signs of these eruptions could be observed with telescopes.

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