How cold is Space?
2025-03-28 15:00:04
Do
you think space, or rather the vacuum, is cold? During my survey on the
web during the past few months, it clearly showed that most people
would answer yes to that question.
Fact
is that only matter can have a temperature, which is the speed of its
molecules. The faster the molecules in a material move, the warmer that
material is. Per definition, an absolute vacuum is a void, nothingness
and therefore it cannot have any temperature. In as far as the space of
the Universe is an absolute vacuum, that space cannot have any
temperature and it is thus not cold.
However,
an absolute vacuum does not really exist; there are molecules whirling
around everywhere in space. Actually, some recent theories say that all
these molecules whirling around, constitute more mass than all the
visible galaxies contain together - its called dark matter. Even so, the
density of these molecules is so incredibly low, that in practical
terms, as far as space technology is concerned, interplanetary space
behaves as an absolute vacuum. Even the Moon, that actually does have an
atmosphere in the sense that the density of its gas molecules is
considerably higher than in free space, can yet be seen as an absolute
vacuum environment in practical terms for human activity there.
This
means that the molecules that are there, do not have a measurable
contact (convection) heat exchange effect with other materials around
and thus a Moon vehicle or base on the Moon can neither be cooled, nor
heated by these molecules. The same is valid for space vehicles
traveling around in the Solar System; they also have no measurable heat
exchange with the molecules moving in the vacuum around.
Even
on Mars, that has a well defined atmosphere, such heat exchange effects
would not have much significance for human activity there, though it
would be noticeable nonetheless. Surely, the air temperature on Mars can
locally come up to plus 30 degr. C, but that doesnt mean you would feel
it, the same as on Earth, because the Mars air is so much thinner.
The
atmospheric pressure on Mars is just 6 mbar, compared to Earts
atmospheric pressure of 1000 mbar. No industrial vacuum pump on Earth
could reach such a low pressure and it is yet called a vacuum pump.
Hence, in technical terms, also Mars could be seen as a vacuum
environment for astronauts, just not an absolute one, as it is on the
Moon.
This
all means that space, the vacuum, is a perfect temperature insulator
for convection heat. The only heat exchange that can be done between
bodies in the vacuum is through radiation, because the vacuum lets
electromagnetic energy pass through. Very fortunate, so we can get light
and warmth from the Sun, all being electromagnetic radiation. The
frequency of this radiation is a measure for how much energy it
transmits.
The higher the frequency, the more powerful the radiation is
and usually penetrates deeper into materials. X-rays have a very high
frequency and are therefore powerful enough to penetrate our bodies,
which for example is used in medical applications. Gamma rays are even
more powerful and are generated by decaying atoms - nuclear radiation.Heat
radiation is called infra-red, because the color red is the lower
frequency limit of what our eyes can see (violet the upper).
Infra-red
has a too low frequency for our eyes to see and we feel it as heat
instead. Its frequency relates to the temperature of the emitting body,
the higher the frequency, the warmer that body is. This causes the so
called green-house effect, because certain materials are more
transparent for higher than for lower frequencies.
The surface
temperature of the Sun is 6000 Kelvin and the according frequency can
penetrate the Earths atmosphere. As it hits the ground, most of it gets
absorbed and warms up the ground material - ever noticed how hot beach
sand can be?
However,
the thus generated temperatures are much lower (fortunately) than that
of the Sun and the Earths atmosphere is not transparent for the
according lower frequencies and so it warms up, partially by absorbing
the energy that the warm ground radiates off and partially through
convection heat exchange between air and ground material molecules and
part by what it absorbs itself directly. The same principle is valid
for glass and that is why your car gets so hot inside, when it is parked
in the sun. Likewise the temperature in green houses rise above
surrounding air temperatures, as is the purpose of those.
Latest News
