28
C. Cecchi-Pestellini
have constructed. Dyson went further and proposed to search for evidences of such
structures, as a proof of the existence of such civilizations elsewhere in the Galaxy.
The presence of a Dyson sphere is an extremely fascinating idea, but Tabby’s star
is not the place where we should look for. A huge number of follow-up observations
performed in an extended spectral range, from blue light all the way to infrared light,
show that radiation of shorter wavelength is preferentially blocked in all the observed
obscuration events. The natural conclusion is that this wavelength-dependent extinction is quite the same as in the general interstellar medium, and it is caused by
simple, familiar dust, drifting between us and the star in tendrils of varying thickness. Although the source of the dust remains a mystery (see e.g., [3]), the evidence
for aliens around one of the weirdest stars in our galaxy is not looking promising.
Should we be disappointed?
Perhaps not. Dust is a crucial ingredient in a remarkable story that links interstellar
chemistry with star and planet formation to suggest that the origins of life on Earth—
and perhaps elsewhere—may lie in space. Dust grains have a number of absolutely
fundamental roles to play in the Universe as we know it today. We may emphasize
different parts of the story (for example, the roles of dust in chemistry or in star
formation) but it is the comprehensive picture of dust throughout the whole saga
that makes it compelling. This complete story makes clear that for a Universe like
ours, dust is required to make molecular hydrogen and initiate chemistry, including
complex chemistry, and to permit the formation of stars. Dust also provides the raw
material for planets, and may even seed them with the molecular building blocks of
life.
The interstellar medium is rich in molecules, and especially in organic molecules.
It’s only in the last half-century that we’ve begun to realize that the interstellar
medium can be not only molecular, but that interstellar chemistry is remarkably
complex for what seems a quite hostile environment. Of course, the chemistry of
life is much more complex than interstellar chemistry. But wherever life begins, it
must start from the kinds of molecules that are readily available in interstellar space.
Because the formation of stars and planets is a violent event, the intricate chemical
history of the gas from which a planet forms may be obliterated, requiring chemical
evolution to be continuously restarted. Nevertheless, the chemical mechanisms that
generate biomolecules in space are replicated in protoplanetary systems, so that there
is a potential connection between prebiotic organic chemistry and the chemistry we
observe on going in the interstellar medium. Nature has had a four-billion-year head
start in implementing controlled chemical evolution, and in doing that a central role
has been played by dust.
5.2 Making Complex Molecules from Simple
Interstellar Ices
The inventory of the molecular Universe is continually progressing [4]. The nature
of the selection of molecular species is not transparent. Hydrogen and helium atoms
C. Cecchi-Pestellini
have constructed. Dyson went further and proposed to search for evidences of such
structures, as a proof of the existence of such civilizations elsewhere in the Galaxy.
The presence of a Dyson sphere is an extremely fascinating idea, but Tabby’s star
is not the place where we should look for. A huge number of follow-up observations
performed in an extended spectral range, from blue light all the way to infrared light,
show that radiation of shorter wavelength is preferentially blocked in all the observed
obscuration events. The natural conclusion is that this wavelength-dependent extinction is quite the same as in the general interstellar medium, and it is caused by
simple, familiar dust, drifting between us and the star in tendrils of varying thickness. Although the source of the dust remains a mystery (see e.g., [3]), the evidence
for aliens around one of the weirdest stars in our galaxy is not looking promising.
Should we be disappointed?
Perhaps not. Dust is a crucial ingredient in a remarkable story that links interstellar
chemistry with star and planet formation to suggest that the origins of life on Earth—
and perhaps elsewhere—may lie in space. Dust grains have a number of absolutely
fundamental roles to play in the Universe as we know it today. We may emphasize
different parts of the story (for example, the roles of dust in chemistry or in star
formation) but it is the comprehensive picture of dust throughout the whole saga
that makes it compelling. This complete story makes clear that for a Universe like
ours, dust is required to make molecular hydrogen and initiate chemistry, including
complex chemistry, and to permit the formation of stars. Dust also provides the raw
material for planets, and may even seed them with the molecular building blocks of
life.
The interstellar medium is rich in molecules, and especially in organic molecules.
It’s only in the last half-century that we’ve begun to realize that the interstellar
medium can be not only molecular, but that interstellar chemistry is remarkably
complex for what seems a quite hostile environment. Of course, the chemistry of
life is much more complex than interstellar chemistry. But wherever life begins, it
must start from the kinds of molecules that are readily available in interstellar space.
Because the formation of stars and planets is a violent event, the intricate chemical
history of the gas from which a planet forms may be obliterated, requiring chemical
evolution to be continuously restarted. Nevertheless, the chemical mechanisms that
generate biomolecules in space are replicated in protoplanetary systems, so that there
is a potential connection between prebiotic organic chemistry and the chemistry we
observe on going in the interstellar medium. Nature has had a four-billion-year head
start in implementing controlled chemical evolution, and in doing that a central role
has been played by dust.
5.2 Making Complex Molecules from Simple
Interstellar Ices
The inventory of the molecular Universe is continually progressing [4]. The nature
of the selection of molecular species is not transparent. Hydrogen and helium atoms