You’ve heard of sunspots, but how about Sun dots? A recent solar mission has snapped photos of tiny, bright dots on the Sun, and astronomers are contemplating their cause.

Solar Orbiter images of Sun
These images from Solar Orbiter, taken on 30 May 2020, show a variety of small-scale structures.
Adapted from Solar Orbiter / EUI Team / ESA & NASA; CSL, IAS, MPS, PMOD / WRC, ROB, UCL / MSSL

Something New on the Sun

In the short time since its launch in February 2020, Solar Orbiter has already returned some incredible photos and data of the Sun. The joint European Space Agency–NASA mission is expected to have its biggest scientific breakthroughs when it tilts its orbit to be able to see the Sun’s poles — a region that we’ve never photographed — but it has already revealed never-before-seen phenomena like the miniature explosions on the Sun’s surface called solar campfires.

Solar Orbiter trajectory
An illustration of the dates of major orbital milestones in the Solar Orbiter mission. Click to enlarge.
ESA / S.Poletti

Today’s article dives into some of the exquisite data from Solar Orbiter to investigate an even smaller-scale phenomenon: the fleeting appearance of dozens of tiny, bright dots.

Seeing Spots

Dots on the Sun
Solar Orbiter Extreme Ultraviolet Imager (left) and post-processing image (right) of the dots, which are indicated by the yellow boxes.
Adapted from Tiwari et al. / Astrophysical Journal 2022

A team led by Sanjiv Tiwari (Lockheed Martin Solar and Astrophysics Laboratory and Bay Area Environmental Research Institute) began their investigation of these dots with Solar Orbiter observations from 20 May 2020, when the Sun’s dynamic activity cycle was at a simmer. Using images from the Extreme Ultraviolet Imager, Tiwari and collaborators analyzed a region where loops and strands of magnetic flux were poking through the Sun’s surface. The images revealed tiny spots faintly visible against the bright background of hot plasma.

Solar Orbiter Extreme Ultraviolet Imager (left) and post-processing image (right) of the dots, which are indicated by the yellow boxes. [Adapted from Tiwari et al. 2022]After applying image processing techniques to enhance the appearance of the dots, the authors were able to characterize 170 of them as they emerged and faded over the course of an hour. On average, the dots are round, 30% brighter than their surroundings, about the size of Germany, and last just 50 seconds before fading. About half of them retained their roundness throughout their short lives, while others split into two, merged with other dots, or elongated and gave rise to small explosive events.

Making a Magnetic Connection

Extreme ultraviolet vs. magnetic field
A Solar Dynamics Observatory extreme-ultraviolet image with an unsharp mask applied (left) and the line-of-sight magnetic field strength for the same region (right). The dot being studied is indicated by the yellow square.
Adapted from Tiwari et al. / Astrophysical Journal 2022

The team also analyzed images and magnetic field measurements from the Solar Dynamics Observatory, a spacecraft that surveys the Sun from Earth orbit. (The team noted that any features that pop up in the Solar Orbiter images do so 3.22 minutes before they appear in the Solar Dynamics Observatory images due to the time it takes light to travel between the two spacecraft.) The magnetic field measurements revealed that the dots tended to be concentrated in areas with strong magnetic fields or regions where inward- and outward-pointing magnetic field lines are found close together.

So, what causes these dots? Using magnetohydrodynamic simulations, the team confirmed that most dots are associated with interacting magnetic field lines and potentially occur when field lines snaking out from beneath the solar surface connect with those already above the surface. However, a smaller number of dots were free of tangled magnetic field lines, and they may have instead been formed by shock waves moving through the region.

With Solar Orbiter making its way closer to the Sun over the next few years, we should be able to get a better view of these dots and better understand their origins. Who knows what kind of dots we’ll be able to spot then!


“SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation,” Sanjiv K. Tiwari et al 2022 ApJ 929 103. doi:10.3847/1538-4357/ac5d46

This post originally appeared on AAS Nova, which features research highlights from the journals of the American Astronomical Society.


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