There is current talk of sending men & women to Mars. Mars is not exactly the most hospitable place in this solar system for human life, but that is not the only problem:- a new problem is being able to NOT be fried alive whilst getting there. And, whilst the photo of sunspots above may cause you to think that the danger comes from the Sun, it is actually the reverse. Local radiation from our Sun keeps Cosmic Ray radiation from the Galaxy at bay, and it looks like the Sun may be due to enter into a historic sunspot minimum.
It has long been known that the Sun sometimes has dark(er) spots on it’s surface (they are not easy to see, since looking directly at the sun is so dangerous - you can quickly permanently damage your eyesight, so do not do it). The best--and least dangerous--way to see those spots is to project the sun’s image on to a piece of white card. It has also been known since at least 1843 (through the work of Samuel Heinrich Schwabe (1789–1875), a German astronomer) that the number of sunspots increases & decreases on a regular pattern of 11 years from minimum-to-minimum, and this is known as the Solar Cycle.
That cycle is far more complicated than what has been said so far:-
The cycle was discovered by George Ellery Hale in 1908 to actually be 22 years. The sunspots are magnetised, and the polarity of that magnetism is reversed between hemispheres (eg if northern hemisphere sunspots are magnetised North-South, those in the southern hemisphere are magnetised S-N). Further, that magnetism reverses itself in both hemispheres from one 11-year sunspot cycle to the next. In fact, the whole of the surface of the Sun is magnetised, and it suffers the same magnetic reversals across the same period as do the sunspots.
The maximum number of sunspots varies from one maximum to the next. Recently we seem to have had large numbers of sunspots at the max, but 300 years ago (between 1645 and 1715) there were virtually none - the idea of sunspot maxima and/or minima did not make any sense. That period has been called the “Maunder Minimum” (named after Edward and Annie Maunder, a husband & wife team). It also cannot be a coincidence that the very same period saw the Little Ice Age, a time when major rivers like the Thames & the Trent froze over during the Winter, houses began to be built with chimneys for the first time, and with walls 10 foot (3 metres) thick to try to keep out the cold.
There have been continuous measurements of the numbers of sunspots since about 1749. A chap called Rudolf Wolf (1816–1893), a Swiss astronomer was the first person to discover & document all solar observations back to the 17th Century. He began a numbering system for current Solar Cycles which gave the March 1755 - June 1766 cycle an index of ‘1’. The current cycle is number ‘24’:-
Cycle 24 is reckoned to have begun December 2008. We are likely to be at sunspot maximum at this moment, and the numbers are half those at the last cycle, which itself was much lower than earlier cycles in recent times. It is exceptionally difficult to predict whilst in the middle of measurements, and especially as the cycle is exceptionally variable, but it does look like we may be due another minima, perhaps like the Dalton Minimum or (god forbid) another Maunder Minimum.
Now, since last Saturday’s Doctor Who featured a solar Coronal Mass Ejection threatening all life on Earth, and as those are more frequent during the top of the Sunspot Cycle (like, now!) and have in the past been responsible for shutting down Canada’s Power Lines & thus their power supply, you would think it reasonable that a reduction in sunspots means a reduction in danger in space. Well, I did, anyway. How foolish.
NASA currently has a “Lunar Reconnaissance Orbiter” (LRO) circling the moon. One of the instruments on board is called the Cosmic Ray Telescope for the Effects of Radiation (CRaTER). Originally, the LRO was intended to gather intelligence ahead of a new US manned moon programme. The latter has now been cancelled. According to the CRaTER data that cancellation was a Good Idea. Professor Nathan Schwadron & his colleagues write:-
Galactic cosmic radiation presents a more significant challenge: the time to 3 per cent Risk of Exposure Induced Death REID) in interplanetary space was less than 400 days for a 30 year old male and less than 300 days for a 30 year old female in the last cycle 23–24 minimum. The time to 3 per cent REID is estimated to be ~20 per cent lower in the coming cycle 24–25 minimum. If the heliospheric magnetic field continues to weaken over time, as is likely, then allowable mission durations will decrease correspondingly.
The Space Station is OK, as that is still offered protection by the Earth’s atmosphere (both physical & magnetic), as it is in Low Earth Orbit. But travelling to Mars? Perhaps not for a few decades.
--------- Alex Kemp