At the end of 1981, Editorial Mezquita (a subsidiary of Editorial Alhambra) published my book entitled La Vida en Otros Mundos (Life in Other Worlds), one of whose chapters addressed the question in the title of this post. When the book was discontinued, it was again published in 1992 by MacGraw Hill of Spain, in an updated version, in a collection dedicated to science popularization, which kept my book in its catalog for around a decade. It is currently out of print.
Since then, things haven't changed much. Subsequent research has added a couple of satellites that weren’t considered in the 80s and the 90s to the list of bodies where it might be possible to find microscopic life. Of course, nobody expects to find intelligent life, or multicellular animals and plants, in any body in the solar system outside the Earth, although in science-fiction literature those things happen.
The bodies suspected of harboring life in
the solar system outside the Earth are the following:
- Planet Mars. The results of analyses
carried out in 1976 by the Viking 1 and 2 capsules at two widely separated
points on Mars were negative. Of course, that does not prove that there is
no life on Mars. Perhaps there isn’t at those two points, but there could
be somewhere else; or the experiments carried out were not well chosen. Even
if they were, they could have failed to detect life. Since then, there has
often been talk of the possibility of life on Mars, either because of the presence
of water, which could have been abundant in the past, or for other reasons,
as happened in 1996, when NASA announced the discovery of fossils of
microscopic living beings in a meteorite of Martian origin found in
Antarctica. However, this announcement had later to be retracted, when the
origin of those microfossils was attributed to causes unrelated to life.
- Europa, satellite of Jupiter. Its surface
is covered with ice, and it is thought that under this ice there could be
an ocean of liquid water. Since liquid water is an essential component of
life, its presence was immediately linked to the possibility of the existence
of life in that satellite. Just now we have no data, it is only
speculation.
- Titan, satellite of Saturn. For some
time, it was the greatest hope of the search for extraterrestrial life in
the solar system. Titan has large oceans or lakes, although not of water,
but of hydrocarbons, as well as an atmosphere of hydrogen and methane. The
temperature on its surface is about 180ºC below zero. If there were life
on Titan, it would be very different from life on Earth.
- Enceladus, satellite of Saturn. It is much
smaller than the previous ones; its diameter is just about 500 km. Its
case is similar to Europa, for its surface is covered with ice, under
which there could be a global ocean of liquid water. Recently this
satellite made headlines: in September 2022, the existence of
phosphorus in Enceladus was confirmed. Thus, the satellite contains the
six most important ingredient elements for life: carbon, hydrogen, oxygen,
nitrogen, sulfur and phosphorus. There are also other elements very
important for life on Earth, such as sodium, potassium, calcium, chlorine
and magnesium, but they are not usually considered as essential as the
previous six.
While
speaking about this, people tend to forget, and sometimes fall into, what I
called in a post in this blog the
fallacy of life on Mars: the fact that the presence of water and certain chemical
elements may be a necessary condition for the existence of life,
but that is not enough to ensure that there is life: to conclude that, a sufficient condition would have to be
fulfilled.
It
would be very interesting to find life (albeit microscopic) in the solar system
outside Earth. Then we could compare it with life on Earth, and draw consequences
about the possible existence
of life in planetary systems other than ours. For the time being, with just
one known case (ours), we almost have no evidence.
Thematic thread on Life in other Worlds: Preceding Next
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