Perhaps you have heard that tens of thousands of objects orbit Earth. That includes all the many satellites that monitor our weather, help us study Earth’s resources, make communication possible, and allow countries to spy on each other. Much of what’s up there is space junk: spent upper rocket stages, dead satellites, and debris from collisions. NASA tracks more than 45,000 objects larger than four inches. More satellites and collision debris are added to that total every year.
Every
object in Earth orbit will eventually fall back down. On average, a satellite
or a piece of one falls out of orbit once a week. Most of the stuff will simply
disintegrate due to friction with our atmosphere. But some will survive to
reach the lower levels of our atmosphere or even to strike the ground. Larger and
denser objects often survive atmospheric passage. And these pose the greatest
danger. Not only are people on the ground at potential risk, so are airplanes.
One
research paper estimated that by 2030, any given commercial airline flight will have a
1 in 1000 chance of being hit by a returning piece of space debris. At any
given time, there are 12,000 to 14,000 commercial planes in the air. Collisions
between airplanes and space junk seem almost inevitable.
The
odds are even worse in areas of high airplane traffic. Ewan Wright and a group
of researchers at the University of British Columbia in Vancouver, Canada,
studied the possibility of such collision events. He stated, “There is a 26 percent
chance of an uncontrolled space debris reentry in busy airspaces such as the
Northeastern United States or Northern Europe each year.” The chances that the
bit of space debris falling in high air traffic areas will actually hit a plane
are quite small. But, as we launch more and more satellites each year, that risk
will increase.
No
one is suggesting that we should halt all satellite launches, but many researchers
are urging that we start evaluating ways to mitigate the risks. "Aircraft
can be affected by smaller pieces of debris. For example, airplanes flying
through the ash of a volcano are risky because of the small particles,"
European Space Agency space debris system engineer Benjamin Virgili Bastida
said. "Kind of a similar thing could happen with re-entering debris."
Bastida and several colleagues published a paper in the Journal of Space Safety
Engineering. The paper outlines the possible need to close airspace if there is
a high potential of falling space debris.
None
of the experts is suggesting that you stop taking airline flights. But they strongly
express the need to study the problem and determine the best strategies for
mitigating the dangers of returning space debris.
Each month, I write an astronomy-related column piece
for the Oklahoman newspaper. After
it is published there, I post that same column to my blog page.
This is reprinted with
permission from the Oklahoman and www.Oklahoman.com.
