An experiment that fires powerful radio waves into the sky has created a patch of 'artificial ionosphere', mimicking the uppermost portion of Earth's atmosphere.
According to a report in Nature News, the experiment is called the 'High Frequency Active Auroral Research Program' (HAARP), near Gakona, Alaska.
It has spent nearly two decades using radio waves to probe Earth's magnetic field and ionosphere.
One of the most obvious results of the experiments is that they can create lights in the sky that are similar to auroras, the glowing curtains of light that naturally appear in the polar skies when electrons and other charged particles pour down from Earth's protective magnetosphere into the upper atmosphere.
There, at an altitude of about 250 kilometres, the charged particles collide with molecules of oxygen and nitrogen and make them emit light, similar to the process inside a fluorescent light bulb.
HAARP's high-frequency radio waves can accelerate electrons in the atmosphere, increasing the energy of their collisions and creating a glow.
The technique has previously triggered speckles of light while running at a power of almost 1 megawatt1.
But since the facility ramped up to 3.6 megawatts - roughly three times more than a typical broadcast radio transmitter - it has created full-scale artificial auroras that are visible to the naked eye.
But in February last year, HAARP managed to induce a strange bullseye pattern in the night sky.
Instead of the expected fuzzy, doughnut-shaped blob, surprising irregular luminescent bands radiated out from the centre of the bullseye, according to Todd Pedersen, a research physicist at the US Air Force Research Laboratory in Massachusetts, who leads the team that ran the experiment at HAARP.
The team modelled how the energy sent skywards from the HAARP antenna array would trigger these odd shapes.
They determined that the areas of the bullseye with strange light patterns were in regions of denser, partially ionized gas in the atmosphere, as measured by ground-based high-frequency radar used to track the ionosphere.
The scientists believe that these dense patches of plasma could be gas that was ionized by the HAARP emissions.
"This is the really exciting part - we've made a little artificial piece of ionosphere," Pedersen said.
"The novelty is not seeing the aurora - it's the fact that we can actually create enough high-energy electrons to form plasma," said Mike Kosch, chair of Experimental Space Science at Lancaster University, UK.
"It shows something completely different and new that we hadn't expected. We didn't know we could do that from a radio array on the ground," he added.