Waving solar seaweed

Spicules shooting up from the Sun as seen by the Solar Dynamics Observatory in April. The full disk image is also worth a look. Image credit: NASA/SDO/AIA

One of the many mysteries about our Sun is how its outer atmosphere (corona) gets heated to more than 20 times its surface temperature. Well, it looks like new observations of waving solar seaweed by the sensitive Solar Dynamics Observatory (SDO) might hold the answer.

Of course by ‘seaweed’ I don’t mean the stuff you get here on Earth. No, I’m talking about spicules – giant fountains of plasma which can reach 32,000 miles high (they also look lovely when imaged by the SDO as you can see above). They sway back and forth in the solar atmosphere thanks to ripples in the Sun’s magnetic field called Alfven waves. NASA’s released a neat movie showing them in action.

These waves were thought to be responsible for carrying energy up into the corona, and thus providing the heat needed to get it to the extreme temperatures seen. However, when they were directly observed for the first time in 2007 they looked to be too weak to accomplish this adequately. Luckily for theorists, more recent observations by the SDO have found much more powerful waves, meaning that they can transport enough energy after all.

This is just a quick overview of the story. If you want more information check out the NASA press release or the longer version I wrote for Astronomy Now Online. I wanted to write something about it here too to give me an excuse to post the beautiful SDO image at the top!

ResearchBlogging.orgMcIntosh SW, De Pontieu B, Carlsson M, Hansteen V, Boerner P, & Goossens M (2011). Alfvénic waves with sufficient energy to power the quiet solar corona and fast solar wind. Nature, 475 (7357), 477-80 PMID: 21796206

ResearchBlogging.orgDe Pontieu B, McIntosh SW, Carlsson M, Hansteen VH, Tarbell TD, Schrijver CJ, Title AM, Shine RA, Tsuneta S, Katsukawa Y, Ichimoto K, Suematsu Y, Shimizu T, & Nagata S (2007). Chromospheric alfvenic waves strong enough to power the solar wind. Science (New York, N.Y.), 318 (5856), 1574-7 PMID: 18063784


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Wow, just wow. This is the Sun as seen by the recently launched Solar Dynamics Observatory (SDO). It’s actually a combined image, showing several different wavelengths at once (blues and greens represent hotter regions than reds). The SDO is the most advanced solar spacecraft ever launched, and it shows in the level of detail visible in this picture. Just look at all that material streaming out into space; ‘space weather’ like that can seriously disrupt satellites. Understanding what’s going on inside the Sun, and therefore predicting the most violent solar events, is one of the main aims of the SDO mission.

Luckily, on 30th March, not long after the SDO instruments were switched on, the Sun obliged those of us who like spectacular first light images (and I think that probably includes everyone) by throwing off a giant solar eruption. And here it is:

(if you can’t see anything there click here…)

I love the sense of scale you get when the movie zooms out to show the whole disc.

Oh, one final thing, even the SDO’s launch produced great pictures when it destroyed a sundog. It was clearly a good omen for the mission!