Telescope images captured of the sun on March 11, 2012 show what appears to be a planet-size shadowy object tethered to the sun by a dark filament. In the image sequence, a burst of brightly lit material can be seen erupting from the sun’s surface surrounding the dark object, after which the orb detaches from the sun and shoots out into space.
The footage, a composite of images captured by the Solar Dynamics Observatory and processed by scientists at NASA’s Goddard Space Flight Center, has quickly garnered attention on YouTube, where viewers are suggesting it shows a UFO spacecraft refueling by sucking up solar plasma, or at the very least, the birth of a new planet.
However, according to NASA scientists, the feature is actually a little-understood, but frequently observed, type of solar activity called a “prominence,” and the way it is situated beneath another solar feature gives it its otherworldly appearance.
The thread extending from the lower left edge of the sun in the video is known as a “prominence,” a feature containing cooler, denser plasma than the surrounding 3.5 million-degree Fahrenheit corona, said Joseph Gurman, project scientist in the Solar Physics Laboratory at NASA Goddard. It isn’t yet known exactly how prominences develop, but these dense plasma loops can extend from the sun’s surface thousands of miles into space.
“When prominences are that extended in height above the limb (edge of the sun), it’s usually a sign that they’re about to erupt, as this one did,” Gurman told Life’s Little Mysteries.
C. Alex Young, a solar astrophysicist at NASA’s Goddard Space Flight Center who runs a website called The Sun Today, explained that the prominence is situated below a tunnel-shape feature called a filament channel, (coronal prominence cavity, or polar crown cavity). “When you look at it from the edge of the sun, what you actually see is a spherical object. You’re actually looking down the tunnel. And this tunnel sits up top of the filament,” Young explained at The Sun Today. He added that the development of these structures is quite common. Alex Young’s video can be seen below.
But why is the prominence dark? Gurman explained that all the light in the SDO images is the same color — a specific wavelength that is emitted by iron atoms that have been ionized 13 times, known as Fe XIV. The dark filament seen in the images (the refueling UFO’s “tether,” according to YouTube users) is a part of the prominence that happens to absorb light of this color, making it appear dark. “The absorption is typically seen in lines such as Fe XIV only in the thinnest, densest parts of the prominence, which is here seen edge-on as it rotates over the solar limb,” he said.
In the image sequence, there is a burst of activity around the prominence, and then it and the filament channel shoot out into space immediately afterward. According to Gurman, the first event was probably an outburst of the sun’s magnetic field called a coronal mass ejection. “It’s generally accepted, though still not conclusively proven, that prominence eruptions occur when the overlying magnetic field that contains the prominence material is disrupted,” he said.
Another image showing the same coronal mass ejection and prominence eruption was captured by the Solar and Heliospheric Observatory on Monday. In this image, which captured light in the visible wavelength range, a bright swirl of material from the prominence trails the fainter edge of the coronal mass ejection as the two plunge into space.
Less exciting than a refueling UFO or a brand new planet, maybe — but there’s nothing quite like the truth.
You see a lot of these types of “odd-thing-near-sun” things on YouTube, based off video feed from the Solar Dynamics Observatory. That’s basically because the SDO is new (just two years old), and people are not used to the amazing displays the sun puts on. Some of which will be new to science as this the the best view we’ve ever had of the sun.
There are numerous papers describing these cavities, so I’ll just give some links, extracts and images:
We propose to define a polar crown cavity as a density depletion sitting above denser polar crown filament plasma drained down the cavity by gravity. As part of the polar crown filament, plasma at different temperatures (ranging from 50 000 K to 0.6 MK) is observed at the same location on the cavity dips and sustained by a competition between the gravity and the curvature of magnetic field lines.
Cavities are commonly observed as part of a CME, but may also exist before eruption (Sterling and Moore 2004; Gibson et al. 2006). Such quiescent cavities appear as dark, semi-circular or circular regions, often surrounding a central prominence (relatively cool and dense plasma suspended in the solar corona), and embedded in a helmet-shaped white-light streamer (Figure 1, left). They are ubiquitous: several may be visible on a given day; and can be long-lived (on the order of months): either reforming or only partly erupting in CMEs.
At the limb, the geometry of the cavity enclosure becomes
more visible because of projection against the background sky.
One typically then sees a white-light coronal streamer, often
with a hollow cavity underneath. Such cavities sometimes form
long-duration X-ray arcade events and launch coronal mass
ejections (CMEs) of the “streamer blowout” type.
Seen in the accompanying movie, forward modeling was used to predict morphology of a coronal prominence cavity. The animation shows EUV observations of a cavity from NASA’s STEREO spacecraft on the top/left, as well as the forward-modeled predicted EUV for the coronal cavity on the bottom/right. As time goes by in the movie, it’s possible to see the 3-dimensional, tunnel-like cavity rotate past.