Mid-afternoon. Carol has been doing laundry
on and off since before dawn. You both had pick-what-you-want from the fridge
and cupboards for lunch. You’ve been thinking about ‘Prince’ and his death. You
and Carol both enjoyed some of his songs. – Amorella
1509
hours. He will be missed but we have his compositions and music to listen to at
our own pleasure and to remember him by.
You and
Carol had Papa John’s pizza for supper – excellent as always. Then, for you,
off to the story for a few groceries. Tomorrow you are off to Kim and Paul’s
for the day and night, returning Wednesday after seeing Aunt Patsy and Uncle
John. Aunt Patsy is ninety-five years old today. You found an interesting
article to ponder on. Here it is. Post. - Amorella
** **
BBC Earth:
Where to
find life in the blackest vacuum of outer space
On the face of
it space is dark, cold and full of lethal radiation – but maybe life has found
a way to cling on in the blackness
By Philip Ball
25
April 2016
When
we think about whether or not aliens exist, we generally imagine them on a
vaguely Earth-like planet circling a distant star. We do not normally think of
them living out in space itself.
But
maybe that is not such a ridiculous idea. In April 2016, researchers reported
that some of the key building blocks of life can be produced from simple
substances under harsh conditions mimicking those of interstellar space.
Cornelia Meinert
at the University of Nice, France and colleagues showed that a mixture of
frozen water, methanol and ammonia – all compounds known to exist in the vast
"molecular clouds" from which stars form – can be transformed into a wide range of
sugar molecules when exposed to ultraviolet rays, which pervade
space. The sugars included ribose, which is a part of the DNA-like molecule
RNA.
This
suggests that the fundamental molecules of life might be formed in outer space,
and then delivered to planets like Earth by icy comets and meteorites.
The
finding is actually not surprising. We have known for decades that other
building blocks of life can be formed from chemical reactions like this, before
being incorporated into comets, asteroids and planets.
However, there is a more
intriguing possibility. Life itself might not have needed a warm and
comfortable planet bathed in sunlight to get going. If the raw ingredients were
already out there in interplanetary limbo, might life have started there too?
Ideas
about the origins of life do not often consider this scenario. It is hard
enough to figure out how life could have begun on the early Earth, let alone at
temperatures close to absolute zero and the near vacuum of interstellar space.
Making
the basic building blocks of life, like sugars and amino acids, is the easy
part. There are lots of chemically-plausible ways to do that, starting with the
simple molecules found in young solar systems.
The
hard bit is persuading these complicated molecules to assemble into something
capable of life-sustaining processes like replication and metabolism. Nobody
has ever done this, or come up with a completely plausible way it might happen,
in the nurturing environment of a warm, rocky planet – let alone in space.
Still, there is no fundamental
reason why life might not arise far from any star, in what is often regarded as
the barren desert of interstellar space. Here is how it might happen.
First,
we had better agree on what counts as "life". It does not necessarily
have to look like anything familiar.
As
an extreme case, we can imagine something like the Black Cloud in astronomer
Fred Hoyle's classic 1959
science-fiction novel of that name: a kind of sentient gas that
floats around in interstellar space, and is surprised to discover life on a
planet.
But
Hoyle could not offer a plausible explanation for how a gas, with an
unspecified chemical make-up, could become intelligent. We probably need to
imagine something literally a bit more solid.
While
we cannot be sure that all life is carbon-based, as it is on Earth, there are
good reasons to think that it is likely. Carbon is much more versatile as a
building block for complex molecules than, say, silicon, the favourite element
for speculations about alternative alien biochemistries.
Astrobiologist Charles Cockell
at the University of Edinburgh in the UK thinks that the broad basis of life on
Earth – that it is carbon-based and requires water – "reflects a universal
norm". He concedes that "I have a quite conservative view, which
science generally proves is misguided." But still, for now let's stick
with carbon-based life. How could it be generated in outer space?
The
basic chemistry is not a problem. As well as sugars, life on Earth needed amino
acids, the building blocks of proteins. But we know that these can be formed in
outer space too, because they have been found in "primitive"
meteorites that have never seen a planetary surface.
They
might be made on icy grains from some variation of a chemical reaction called
the Strecker
synthesis, after the 19th-Century German chemist who discovered
it. The reaction involves simple organic molecules called ketones or aldehydes,
which combine with hydrogen cyanide and ammonia. Alternatively, light-driven
chemistry triggered by ultraviolet light will do the job.
It
looks at first as though these reactions should not take place in deepest
space, without a source of heat or light to drive them. Molecules encountering
one another in frigid, dark conditions do not have enough energy to get a
chemical reaction started. It is as if they run into a barrier that is too high
for them to jump over.
However, in the 1970s the Soviet
chemist Vitali Goldanski showed otherwise. Some chemicals
could react even when chilled to just four degrees above
absolute zero, which is about as cold as space gets. They just needed a bit of
help from high-energy radiation such as gamma-rays or electron beams – like the
cosmic rays that whizz through all of space,
Under
these conditions, Goldanski found that the carbon-based molecule formaldehyde,
which is common in molecular clouds, could link up into polymer chains several
hundred molecules long.
Goldanski
believed that such space-based reactions might have helped the molecular
building blocks of life assemble from simple ingredients like hydrogen cyanide,
ammonia and water.
But
it is far more difficult to coax such molecules to combine into more complex
forms. The high-energy radiation that might help get the first reactions
started then becomes a problem.
Ultraviolet
and other forms of radiation can induce reactions like those Meinert
demonstrated. But Cockell says they are just as likely to smash molecules as
they are to form them. Potential biomolecules – progenitors of proteins and
RNA, say – would be broken apart faster than they were being produced.
"Ultimately the question is
whether other completely alien environments would give rise to self-replicating
chemical systems that can evolve," says Cockell. "I don't see why
that wouldn't happen in very cold environments or on the surfaces of ice
grains, but generally I think these environments aren't very conducive to very
complex molecules."
Planets
offer two much gentler energy sources: heat and light. Life on Earth is largely
powered by sunlight, and it is a fair bet that life on "exoplanets"
around other stars would draw on the energy reserves of their own suns.
Vital
heat can also come from elsewhere. Some scientists believe that the first life
on Earth was not powered by sunlight, but by volcanic energy released from the
planet's interior at hot vents in the deep sea. Even today, these vents still
spew out a warm, mineral-rich brew.
There
is also heat in Jupiter's major moons. This comes from the huge tidal forces
exerted by the giant planet, which squeeze the interiors of the moons and heat
them up through friction. This tidal energy keeps the sub-surfaces of the icy
moons Europa
and Ganymede
melted into oceans, and makes Io's
surface fiery and volcanic.
It is hard to see how molecules
clinging to icy grains in interstellar space could find any such nurturing
energy. But that might not be the only option out there.
In
1999, planetary scientist David Stevenson
of the California Institute of Technology proposed that galaxies
might be full of "rogue planets" floating beyond the outermost
reaches of a stellar neighbourhood, too far from their "parent" star
to feel its gravity, heat or light.
These
worlds, Stevenson said, could have formed like any other regular planet, close
to a nascent star and within its surrounding nebula of gas and dust.
But
then the gravitational tug of large planets, like our own Jupiter and Saturn,
could sling some planets on "escape trajectories", propelling them off
beyond their solar system into the empty space between stars.
That might seem to consign them
to a cold and barren future. Yet Stevenson argued that, on the contrary, these
rogue planets might be "the most common sites of life in the
Universe" – because they might stay warm enough to support liquid water
under, as it were, their own steam.
All
of the rocky planets in the inner solar system come with two internal heat
sources.
First,
each planet has a fiery core still hot from the primordial fury of its
formation. On top of that, they contain radioactive elements. These warm up the
interior of the planet with their decay, just as a lump of uranium is warm to
the touch. On Earth, radioactive decay inside the mantle contributes about half
of the total heating.
Primordial
heat and radioactive decay inside rocky rogue planets could warm them for
billions of years – perhaps enough to keep the planets volcanically active and
provide the energy for life to start.
Rogue
planets could also have dense, heat-retaining atmospheres. Compared with gas
giants like Jupiter and Saturn, Earth's atmosphere is thin and tenuous, because
the Sun's heat and light have stripped away lighter gases like hydrogen.
Mercury is so close to the Sun that it barely has any atmosphere at all.
Yet
on an Earth-sized rogue planet, far beyond its parent star's influence, much of
the original atmosphere might remain in place. Stevenson estimated that the
resulting temperature and pressure could be enough to sustain liquid water at
the surface, even without any sunlight.
What's more, rogue planets would
not be plagued by giant meteorite impacts, as Earth has
been. They might even be ejected from their native solar system
with moons in tow, giving them the benefit of some heating by tidal forces.
Even
if a rogue planet did not have a thick atmosphere, it could still be habitable.
In
2011, planetary scientist Dorian Abbot
and astrophysicist Eric Switzer
at the University of Chicago calculated
that planets about three and a half times the size of the Earth could become
covered over with a thick layer of ice. This would insulate an ocean of liquid
water many kilometres below the surface, heated by its interior.
"The
total biological activity would be lower than on a planet like Earth, but you
should still be able to have something," says Abbot.
He
hopes that when space
probes investigate the subsurface oceans of Jupiter's icy moons
in the coming decades, we will learn more about the possibilities of life on
iced-over rogue planets.
Abbot and Switzer called these
orphaned worlds "Steppenwolf planets", because, they say, "any
life in this strange habitat would exist like a lone wolf wandering the
galactic steppe". The habitable lifetime of such a planet could be up to
ten billion years or so, similar to that
of Earth, says Abbot.
If
these ideas are right, then outside our solar system rogue planets in
interstellar space could be the closest places where extraterrestrial life
exists.
They
would be very hard to spot at such a distance, being dark and relatively tiny.
But
with luck, say Abbot and Switzer, such a planet passing within about a thousand
times the Earth-Sun distance could just about be discerned from the small
amount of sunlight it would reflect and the infrared radiation of its own
warmth. We might hope to see it with the telescopes currently used to look for
exoplanets around other stars.
If
life can originate and survive on an interstellar Steppenwolf planet, say Abbot
and Switzer, there is a profound implication: life "must be truly
ubiquitous in the Universe".
It would be a strange kind of
life on these interstellar worlds. Imagine bathing in warm volcanic springs
under perpetual night, like a winter vacation in Iceland. But if that is all
you had ever known, it would seem like home.
Selected and edited from -- http://www.bbcDOTcom/earth/story/20160422-where-to-find-life-in-the-blackest-vacuum-of-outer-space
No comments:
Post a Comment