The worldwide press coverage of the Upper Atmosphere Research Satellite (UARS) break-up last week certainly brings into sharp focus the number of satellites in orbit around the Earth, and the subsequent risk to the inhabitants of our planet if these objects return to Earth via the pull of gravity.
Since the beginning of the Space Age back in 1957, there have only been a small handful of man-made objects that have been considered a risk, albeit small, to life forms on Earth.
The biggest risk has been considered to be by large, heavy objects falling to Earth. For example, in 1971 the US space station Skylab (75 tons) fell to Earth, and in 2001 so did the Russian Space station MIR (135 tons).
The decay of MIR was interesting – a controlled descent was undertaken, intended to make the whole process safer.
For smaller objects, such as UARS – only a mere bus-sized six-and-a-half tons, to accurately predict the exact impact site is virtually impossible. In this case, the object broke up on its descent into a number of unknown parts, but, more importantly, the air drag over the final orbits could not be predicted precisely.
Many of the parts would have burned up in the atmosphere, but a few of those parts – NASA estimated 26 – made it down, and as far as we know, no one was injured.
Long, long odds
There is another way to look at this, however. On the plus side, as far as human life is concerned, the odds of being hit by a satellite have been quoted as risky as 1 in 22 trillion. Today, even with a human population of approximately 7 billion people, much of the Earth is very sparsely populated, and most people now live in cities. You will have to take up counter-arguments with NASA – for example, “what about the fish?” (I believe the estimate of risk extends to all life forms on Earth.) To date, there are NO recorded cases of any physical damage to life, cars, buildings, etc, by satellite or space station debris returning to Earth.
However, having said that, there is one notable exception: In 1978 a Russian spy satellite, Cosmos 954, containing a small nuclear reactor (used as a power source), crashed into Canada. The debris came down over portions of the Northwest Territories, Alberta and Saskatchewan.
Some of the satellite debris was recovered and found to be slightly radioactive. The Canadian Government eventually received three million Canadian dollars from the USSR in compensation. Since the end of the Cold War, these types of satellites are no longer in use
Satellite views common
Many man-made satellites can be seen every night, either with the naked eye or with a pair of binoculars. Typically, a satellite will look like a moving star and will take a few minutes to cross the sky. With this in mind, it can be easy to be confused with high flying aircraft.
One of the brightest man-made objects is, of course, the International Space Station (ISS), which can make some spectacular passes over the Cayman Islands. So check the Heavens Above website out – don’t forget to register (it’s free) and add in your own latitude and longitude. A list of the brightest satellites crossing in the next few days can be then seen along with other astronomical information.
Don’t worry too much about the eventual decay of the ISS just yet, it will come down one day – hopefully by a “controlled descent”, possibly as early as 2016 due to lack of international funding. The ISS is a staggering 450 tons; some modules will be reused on the next generation of space stations.
The night sky
Now, while we are still in one piece, let’s turn to the night sky. High in the sky almost overhead is the easily seen bright planet Jupiter. Small telescopes will reveal up to four moons, as well as the banding on atmosphere of the planet itself. It is particularly bright at the moment because it is close to “opposition” (29 October). This is an astronomical term meaning, in this case, that the planet is at its closest to the Earth. It is still quite a distance from us though, at 400 million miles.
Now we can go on a cosmic journey to far greater distances. Move your eyes not far from Jupiter, to the West, to see the Great Square of Pegasus, which is particularly interesting for two reasons. First, it is easily identifiable in that it is a region almost devoid of stars, and second, it can be used as a signpost to the famous Andromeda Galaxy, (also called M31) which can be seen with the naked eye, although it is much more impressive using binoculars. We view this object as a faint blob of light – indeed as a “fuzzy object”. It starts to become impressive when you realise that you are looking at one of the most distant objects that can be seen with the naked eye. In fact, light from M31 takes two-and-a-half million years to reach us!
M31 and our own galaxy are similar; great islands of stars travelling across the Universe.
Each galaxy comprises of hundreds of billions of stars; our galaxy, which contains our own star (the Sun), can be seen easily, known to us all as the Milky Way. As one of the nearest galaxies to our own, M31 is a popular choice amongt amateur astrophotographers.
One final twist; M31 and our Milky Way galaxy are on a collision course – but don’t worry, the crash is not due for another five billion years!
On Friday, 30 September, the Cayman Islands Astronomy Society meets at Pedro’s Castle at 7.30pm. If there is more than 50 per cent cloud cover, the event will be called off.