Why our sun can't have a superflare - a sudden brightening to many times its current brightness

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Wikipedia:Kepler-438 b - artist's impression of a superflare sterilizing the planet. It is an example of a planet orbiting in the habitable zone of a red dwarf star, that's thought to be uninhabitable because of superflares[1][2][3]. Sun-like stars can have them too - but it turns out that our sun can't do this

The idea that a superflare might be possible at all was a surprise from the Kepler data, the discovery that a tiny fraction of a percent of sun-like stars have “superflares” that are much more intense than any solar flares. The sun could suddenly brighten to as much as 100 times its current brightness. It would not sterilize Earth of all life, the ocean life would be largely unaffected, also life deep down underground. But surface life would be devastated. However, our Moon that it doesn't have layers of molten rock from prevous superflares, nor do our icy moons have signs of the ice melted in past superflares. Clearly our Earth has not encountered a superflare for billions of years.

Could our sun have such a flare in the future? The answer we now know is, that no, it can’t. Its magnetic field is not strong enough and the way its atmosphere spins sets a maximum to the amount of energy a flare can have, not much more than the level reached for the Carringon event in the nineteenth century.

Wuat is a flare[edit | edit source]

So first, what is a flare? Well they are often confused with Coronal Mass Eruptions. A flare is a momentary brightening of part of the sn, associated with x-rays. The light from it gets to Earth in eight minutes. A coronal mass eruption is an eruption of actual material from the sun, which is thrown out at huge speeds, and takes about three days to get here. This video explains the difference:

A superflare then would be a very bright spot appearing on the sun. The danger is from the light, which is so bright, and hot and also has X-rays.

Distinction from solar storms and coronal mass ejections[edit | edit source]

A coronal mass ejections sends particles in our direction, and they take three days to reach us instead of the eight minutes of the light from a superflare, and they can have effects on our magnetic field, and the main risk is of power cuts (they can also cause satellites to glitch).

A superflare would have no magnetic effects itself, though it would likely to be accompanied by a coronal mass ejection.

Instead, it would harm us through the light itself directly. If we got a genuine superflare, the largest such would be devastating, a short flash of energy up to a hundred times brighter than the sun.

So we expect heating effects and radiation damage, not magnetic effects.

==Are superflares possible in the future?

If we had anything like the Kepler superflares, it would melt thin layers of rocks on the Moon and melted ice on the moons of Jupiter. But there is no sign of anything like that happening in our solar system. Not now, and because some of the surfaces we can see are very old, not for billions of years in the past either. We can know that just from the Moon samples and our observations of icy moons from space.

This is something astronomers have known all along. However, back in 2013 then there were two ways to read the data. The problem in interpreting it is that we only observe any particular star over a very short period of time. There’s no immediately obvious way to find out what it does over timescales of millions, or billions of years by way of super flares. If we see a superflare is it just a short episode or has this star been doing it all its lifetime? Kepler can’t tell us the answer.

So the first possibility was that all sun like stars get occasional superflares, but they get them only a fraction of a percent of the time. If that was the case, then, our sun has not yet had a super flare phase, but some time in its billions of years lifetime it may happen to us.

Alternatively, the data may be telling us that only a tiny fraction of the stars are capable of them at all, and they get them all the time.

It could also be something between the two.

Latest data - can't happen at all[edit | edit source]

The latest research favours the second of those possibilities, at least for our sun. That it can’t get them at all.

This is based on energetic considerations and modeling. It seems that, at least for our sun, it doesn’t have the right dynamics for a superflare (See Can superflares occur on the Sun? A view from dynamo theory)

Superflare stars tend to:

  • Have shorter rotation periods than our sun (which rotates once every 24 days)
  • Are more active
  • Have stronger magnetic fields.
  • Have much larger sun spots 10% of the star covered or more
  • From modeling (not direct measurement) it seems that the more energetic superflares are from stars that have polar regions rotating faster than equatorial regions, the opposite of what we find with our sun.

The latest research suggests that stars with magnetic fields five times stronger than the sun and rotating much faster can get you as far as 100 times stronger than our sun’s flares, in the lower range of superflares. To get beyond that they probably need to have an anti-solar rotation curve, i.e. polar regions rotating faster than the equatorial regions (there are other ways of achieving it but this is the simplest).

Anyway all that rules out our sun as not able to have superflares, according to the latest research.

Large solar storms[edit | edit source]

This is a coronal mass ejection. It is very dramatic - but Earth is a long long way away from the sun and by the time it gets to us it’s main effects are tiny variations in the Earth’s magnetic field and some extra charged particles causing auroras.

The most dramatic of these coronal mass ejections, if they were to hit Earth directly, would give aurora almost to the equator, and the weak fluctuations in the magnetic field causes voltage instability in very long distance power-lines many kilometers long. That can lead to power cuts but the latest estimates are that they would be for hours to at most days, and only affect old transformers or ones that are at the end of their lives, because the latest equipment is hardened against this sort of thing. For details see my

Our sun produces many coronoal mass ejections - and as you can see from the video they shoot out in one particular direction. Normally not in the direction of our Earth. So we can look at what the strongest flares are that go out in any direction and then work out what it would be like if one of those were to hit the Earth.

From that we know that somewhat stronger solar storms are possible. There is also the record of a solar storm from 1859, called the Carrington event. This was a very bright flare, and then there was a solar storm, large enough to cause sparks fly from the terminals of telegraph lines, startling their operators and lead to auroras down nearly to the equator It seems to have been the largest event for 500 years.

There was another very large event in 775 AD which was detected by carbon 14 readings, which was probably comparable in energy to the Carrington event. The Carrington event didn’t have those C14 readings - probably because it wasn’t aimed directly at Earth. They are probably both the result of similar events, just the 775 one was more directly aimed at the Earth. The 775 AD signal is the strongest in the last 11,000 years. Paper here. That also suggests that these are about as strong as we can get.

Also we now have excellent data from the sun which makes it possible to calculate a maximum amount of energy that could be released as a solar flare. The result is that it is at most three times that estimated to be released during the Carrington event.

The calculation is in this paper: Can superflares occur on the Sun? A view from dynamo theory and the Wikipedia article Superflare. I added these latest results from 2018 to their last section Can superflares occur on the Sun? (Back before they indef blocked me from Wikipedia).

The only effects on Earth would be similar to a major solar magnetic storm - probably at most some power cuts for hours to days, and geostationary satellites glitching for minutes through to hours.

For more about the effects of solar storms, and why the latest studies say they would have only a few localized power cuts rather than shut down the power grid for the whole of the US for months, as they used to think was possible, see my Debunking: Solar Storms to end all life on Earth

This comes from my

References[edit | edit source]

  1. Perkins, Sid (2015). "Earth-like planet may be not so hospitable after all, thanks to blasts of radiation". Science. doi:10.1126/science.aad7455. ISSN 0036-8075. 
  2. 'Earth-like' Exoplanet Likely Not Habitable
  3. Sid Perkins, [https://www.sciencemag.org/news/2015/11/earth-planet-may-be-not-so-hospitable-after-all-thanks-blasts-radiation Earth-like planet may be not so hospitable after all, thanks to blasts of radiation} Science, Nov. 18, 2015