Solar System’s Protective Shield is Weakening; Solar Wind Velocity at Record Low

Article written: 25 Sep , 2008
Updated: 24 Dec , 2015

Solar wind output is at its lowest since accurate records began 50 years ago. This finding comes from the seasoned ESA/NASA solar probe Ulysses, which completed nearly three polar orbits of the Sun from 1993 to 2008 (it is still functioning today, but at a reduced capacity). Although a weakening of the solar wind may not sound very important, the effects of this reduction will have serious implications, diminishing the natural defences of the heliopause (our Solar System’s invisible barrier) which protects us from high energy cosmic rays blasting through intergalactic space…

The heliosphere (NASA/Feimer)

The heliosphere (NASA/Feimer)

Ulysses has orbited the Sun four times longer than was originally planned. This tough solar satellite was launched in 1990 on board Space Shuttle Discovery, and in 1992, the probe used Jupiter to slingshot it out of the Solar System’s ecliptic to begin taking in situ measurements of solar wind speed and density at all latitudes from pole-to-pole. This is an unprecedented mission that continues to function today. However, Ulysses’ plutonium fuel in its radioisotope thermoelectric generator (RTG) is dwindling to the point where this landmark mission will die from old age over the coming months.

And yet, the geriatric spaceship still reveals characteristics about our Sun that we could never hope to observe confined to the ecliptic plane. So, in (possibly) one of Ulysses’ biggest discoveries to date, scientists have uncovered the strange phenomenon that the solar wind output has decreased to an all-time low (since accurate records began half a century ago), as the Ulysses Principal Investigator explains:

The Sun’s 1.5 million km-per-hour solar wind inflates a protective bubble around the Solar System and can influence how things work here on Earth and even out at the boundary of our Solar System, where it meets the galaxy. Ulysses data indicate the solar wind’s global pressure is the lowest we have seen since the beginning of the space age.” – Dave McComas, Principal Investigator for the Ulysses solar wind instrument and senior Executive Director at the Southwest Research Institute in San Antonio, Texas.

This “protective bubble” is also known as the heliosphere, a huge volume of space in which all the planets, asteroids and comets are deep inside. It is the total extent of the Sun’s influence, pushing out into interstellar space, the limit of which is known as the heliopause. The heliopause is formed through a balance between the outward pressure of the solar wind and the inward pressure of the interstellar medium, should one of these pressures fluctuate, the heliopause will expand or contract. Should the solar wind pressure decrease, the heliopause will shrink under the greater interstellar medium pressures. This is exactly what Ulysses has detected: a reduction in solar wind pressure.

So what does this mean to us? The heliopause blocks and deflects the majority of damaging high energy interstellar particles (a.k.a. cosmic rays). Should the solar wind weaken, the heliopause will become a less-effective shield, letting more cosmic rays into the Solar System.

Galactic cosmic rays carry with them radiation from other parts of our galaxy. With the solar wind at an all-time low, there is an excellent chance that the heliosphere will diminish in size and strength. If that occurs, more galactic cosmic rays will make it into the inner part of our Solar System.” – Ed Smith, NASA’s Ulysses Project Scientist from the Jet Propulsion Laboratory, California.

Artist impression of Ulysses (ESA)

Artist impression of Ulysses (ESA)

The effects of this happening will be far-reaching and could severely impact the future of manned exploration of the Solar System.

Solar physicists made this discovery when analysing Ulysses data from the probe’s third scan of the solar wind and interplanetary magnetic field (IMF) from the Sun’s north to south poles. On comparison with previous scans, it was found that the solar wind pressure and the radial component of the magnetic field embedded in the solar wind had decreased by 20%. The magnetic field strength surrounding Ulysses had dropped by a huge 36%.

So what could this be attributed to? Physicists simply do not know. Perhaps it might be related to the extended solar minimum in recent months, as Smith appears to suggest. “The sun cycles between periods of great activity and lesser activity,” Smith said. “Right now, we are in a period of minimal activity that has stretched on longer than anyone anticipated.”

Compelling results from a compelling solar mission

Source: ESA

23 Responses

  1. Eric Near Buffalo says

    I’m not going to worry about this, as the article mentions at the end that we’re in an extended minimum period. If the Sun itself has cycles, why wouldn’t the heliosphere and Solar Wind?

    The problem is, we won’t find out for sure because the satellite is going to die in the coming months.

  2. dave s says

    Some scientists have reported that an increase in cosmic rays will increase cloud cover on Earth causing a cooling effect. Is this line of thinking still considered correct?

  3. Jon Hanford says

    With the diminished size and strength of the heliosphere, I would think ground-based UHECR observatories like H.E.S.S., VERITAS, MAGIC, etc. may be able to see an increase in these cosmic ray fluxes during this time. Sounds like good news for them.

  4. Member
    Jon says

    Could a deeper solar minimum indicate a just as unexpectedly large maximum?

    I’m curious about other measurements of the sun. Could this lack of activity allow it to contract and really get restarted with a bang?

  5. Tyler Durden says

    OMG Gamma Ray Burst coming unimpeded into the solar system and baking the planet killing all life including bacteria!


  6. Simon says

    Isn’t the density of the interstellar medium the solar system is travelling through a factor here

  7. Todd Coolen says

    This could be a result of the solar system ‘bobbing’ above and below the galactic plane and now we are in the calm of the transition between magnetic polar shifts as we go through this plane. Just a thought…

  8. Rey says

    IMO, Nature has realized that we humans have reached a level of technological and mental advancement that would lead us to discover the truth about our existence somewhere in the future.

    Since Nature doesn’t want us discovering the truth (for reasons we will never understand), I think nature is making its initial moves to eradicate us, just like Chess i.e. weakening the Heliopause/sphere so that we are more vulnerable to the external radiation (GRB), either from the stars nearby (why do you think there are stars 😀 or meteorites, they were there to destroy things, they are part of the design) or maybe the weakening is a phase where our own Sun will produce damaging radiation, who knows.

    After all life forms are eradicated on Earth, the meteorite/planetary bombardment is next but of course, it could be much more complex than this. Like I said, it’s just like Chess and nature is very good at it that we humans can’t win.

    Live your lives well.

  9. HotHead says

    maybe tin-foil hats are not so crazy after all 🙂
    p.s. that’s aluminum foil to you guys in bankrupt-land

  10. Astrofiend says

    My god Rey – where do you come up with this fluff?

    Anyway – I say awesome – it’ll bring the heliopause in closer, and we can get our Voyagers and Pioneers through it to check it out. Hopefully.

  11. Rey says

    I said “IMO” 😀 Geez, at least Hollywood would be making a movie basing from what I’ve written 😀

  12. UncleDougie says

    Ian is getting himself prepared for the inevitable breakthrough of global cooling. “I saw it coming”.

    All you need to know about “Global Warming”–two words:

    Khabibullo Abdusamatov.

  13. Feenixx says

    “This could be a result of the solar system ‘bobbing’ above and below the galactic plane and now we are in the calm of the transition between magnetic polar shifts as we go through this plane. Just a thought…”

    The solar system does not actually bob above and below the galactic plane – it’s an illusion of perspective, due to the “precession” of the tilt of the Earth relative to the galactic plane…. sort of like a 2D projection…

  14. Dominion says

    If there is a significant enough reduction in the heliosphere, could it effect the objects in the Kuiper belt?

  15. NoAstronomer says

    I would be interested to know more about the justification for this statement:-

    “The heliopause blocks and deflects the majority of damaging high energy interstellar particles (a.k.a. cosmic rays)”

    Since we have minimal knowledge about cosmic ray flux outside the solar system.

    As Jon points out an increase in cosmic rays should already be observable from our current observatories.

  16. Tyler Durden says


    Why would you tell people to look up the name of a person who directly says the globe is warming thanks to solar activity, and then put global warming in quotes as though you’re saying it doesn’t exist?

    Pick a position here.

    Global warming does exist. The cause may be up for debate – whether it is happening, however, is not.

    Also not currently up for debate is whether it will be a problem for us – it will.

    Regardless of whether we’re causing it or not, it will have devastating effects on the human race and we must do everything in our power to reverse it.

  17. EdF says

    Finally, something we can’t blame human activity with.

  18. jerry says

    A fifty year minimum is not earth shattering. Since the flux is this low now, it probably has been many times in the past.

  19. Norman Fields says

    Ohh, NO!!!!! The SUN !!!! Not the SUN! You mean the solar wind is weakening??

    It must be Bush’s fault. After all, he’s the Prezzy Dent, so it must be his fault.

    Hey, I know!! Let’s ask Al Gore how to fix it. All we need is higher taxes, and the Democrats to teach us what to do to cure the Solar System!!!

    Teach us, Al!! SAVE us, Democratic Party!!!!!

    Ow. My jaw hurts, I’m laughing so hard. Thirty four or thirty five years ago, the climate scare was global cooling, and the imminent ice age. Lately, it’s been global warming, which can (shall) lead to a new ice age, because warming water shall evaporate, rise, and form clouds, which shall reflect sunlight from the Earth, lowering global temperatures, causing a new ice age. What’s the next tragedy going to be? “This just in, scientists have determined that all the tragedies of the past 100 years would have happened anyway! There was no way to prevent them! Pictures at eleven!”

  20. Tyler Durden says

    “Thirty four or thirty five years ago, the climate scare was global cooling, and the imminent ice age.”

    Why do globla warming deniers (I call them this because they’re about as credible as Holocaust deniers) always try to reference “global cooling” as a reason that global warming is invalid?

    Newsflash: your argument is a complete fallacy.

    It’s like arguing that Einstein’s theory of relativity is wrong because “not long before that, people were saying that there were only 3 laws and thought they had gravity figured out then!”

    Science is not static. If it were, we’d all still be thinking that the Earth is the center of the universe and everything revolves around us.

    And besides, global cooling was a MINORITY VIEWPOINT.

    “In the 1970s, there was increasing awareness that estimates of global temperatures showed cooling since 1945. Of those scientific papers considering climate trends over the next century, only 10% inclined towards future cooling, while most papers predicted future warming.”

    So 1 in 10 people were just as WRONG as you are WRONG now to be mocking the idea of global warming.

    I’m sorry that the Earth changing is against your political ideology. I’d suggest you adopt a new ideology which doesn’t require you to reject reality to try to make the facts fit your worldview rather than the other way around.

    The failure here is in your view, not in the hard data collected over decades. Deal with it.

  21. geokstr says

    Tyler says:

    “Also not currently up for debate is whether it will be a problem for us – it will. Regardless of whether we’re causing it or not, it will have devastating effects on the human race and we must do everything in our power to reverse it….I’m sorry that the Earth changing is against your political ideology. I’d suggest you adopt a new ideology which doesn’t require you to reject reality to try to make the facts fit your worldview rather than the other way around.”

    That is in fact very debatable.

    First of all, ice cores and other geological
    evidence (note: not a computer model) show that for much of the earth’s past, it was a darn site warmer than even the computer models predict it will get now. And in every one of those periods, the earth was lush with life, with rainforests pretty much everywhere.

    How exactly will it be bad for the human race when the vast tundra of Siberia, the Yukon and Alaska become breadbaskets? All the resources now under hundreds of feet of ice will be readily accessible. It is likely that the amounts of fossil fuels, natural gas and metal ores to be found there dwarfs the known reserves by orders of magnitude (but since you are an AGW proponent, I’m willing to bet the farm you’re against fossil fuels anyway – it sort of goes with the closed mindset, doesn’t it?)

    And even the IPCC claims that at the current pace of sea level change, it will only go up less than a foot in the next century. And it will happen so slowly that even the affected coastal populations will just gradually relocate to those now temperate tundras. There will be no 60-ft walls of water crashing down over the levees of New Orleans or floating the windmills of the Netherlands.

    What you are demanding we do is spend trillions of dollars on the chance that we are actually experiencing global warming that we can do something about. If we are not the cause, then it is highly likely it is far beyond our means to do anything about anyway. And despite the proclamation of the demi-god algore, it is by no means certain that it is even occurring, much less that we are the proximate cause.’

    You say the earth is definitely warming, but in actuality the observations show that we have been cooling since 2000. It’s gotten so bad for your side’s credibility that your latest infallible computer models are now saying that this cooling will continue for at least 10-15 more years, but hey, trust us, warming will come roaring back afterwards. In the meantime, just in case we’re right, let’s bankrupt our society, and put an end to civilization itself.

    Maybe we could just have a world-wide lottery. Every one in a thousand people would be allowed to live, riding only bicycles of course, and the rest would have to commit hari-kari, in an environmentally safe manner.

    A guy in Europe has now developed the most promising new technology to combat global warming. It’s a device you clamp on both the back and front end of cows, to trap the copious methane emissions.

    So, to sum up, I’m sorry that your political ideology is driving your scientific positions. There is another group who invented that strategy; they are called “creationists”. Perhaps you should get an open mind.

    Lastly, calling those of us who won’t drink your Kool-Aid “deniers” to equate us to Nazi sympathizers is typical left wing smear tactics. Bite me. I’ve had it up to here with fanatics of all stripes that seem to be infecting our society. Global warming, real or not, is a naked power grab by the intellectual class, nothing less.

  22. Eric Near Buffalo says

    I look at it this way. Climate is something that will change forever until the Sun bakes this planet dry. The “Little Ice Age” occured from the Middle Ages up to about 200 years ago. Did we cause that? Highly doubtful. Why can’t people get their heads around the idea that maybe, just maybe, Global Warming or even climate change (as I like to refer to it) isn’t even about warming. It’s about climate indifference. Hot and dry one year, temperate and wet the next. That’s how it was here in Buffalo last summer and this summer, respectively.

    Why does our ego feel the need to blame it’s existence on what happens to our surroundings? I understand that we just might be to blame. To what degree, I can’t predict or even proclaim.

    As Geokstr said, sea levels are not going to rise over night. We’ll be able to move people and businesses with plenty of time to spare should the levels rise more than 1 foot this century.

    We cannot let our government and governmentally funded scientists throw us into a panic. We should however learn to live within our means and do it in a cleaner and much more effective way.

  23. Aqualung says

    This is the NATURAL cause of Global Warming

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