Extraterrestrial metals called 'ghosts' create stunning visions in the sky

In June 2019, scientists in Spain went out in search of ghosts. Are Wisps of green hues, dancing on pink lightning at high altitudes during storms, were only discovered in May of that year. What were they? The only way to know was to capture one.

But these ghosts are difficult to see with the naked eye and appear only for an instant.

“Seeing a ghost is really difficult,” says María Passas-Varo, a researcher at the Institute of Astrophysics of Andalusia.

But on September 21, 2019, they finally captured one with a specialized camera: a green spectrum flickering in the crown of a maelstrom of fuchsia jellyfish-shaped lightning 80 kilometers above the Mediterranean Sea. And after painstakingly unraveling the various wavelengths of light emitted by the ghost, scientists discovered its elemental composition.

In a recent study in the journal Nature Communications, Passas-Varo and his colleagues revealed that the ghost's pale emerald green complexion came, in part, from excited oxygen atoms, similar to the glow of auroras; Nitrogen also plays a role. But the main contributor was iron. It was a surprise because after all they came from space.

Better understanding ghosts and other ephemeral lightning-like entities can help scientists interpret the chemistry and physics of Earth's upper atmosphere.

Ghosts are a type of transient light event (TLE) first described by scientists in 1989. TLEs include blue jets, shooting upward from storm clouds, as well as upper atmospheric lightning with crimson hues that can take shapes like carrots and jellyfish, and known as sprites.

To capture their own ghost, Passas-Varo's team pointed a spectrographic camera—which can use light to determine chemistry—into the upper atmosphere from an observation post in Castellgalí, Spain. All the researchers could do was wait for goblin storms to appear and hope that at least one had a ghost.

“It was a matter of luck,” Passas-Varo said.

The ghost they photographed was largely composed of extraterrestrial iron. The camera also revealed the presence of nickel, sodium and silicon. The complex chemical soup added a yellow-orange tint to the ghost's green glow.

All of those elements often come from micrometeoroids and deep space dust particles that fall into the upper atmosphere. That means the ghosts could indeed be seen as interplanetary visitors.

ROBIN GEORGE ANDREWS. THE NEW YORK TIMES