Space Sugar a Clue to Life's Origins
By Guy Gugliotta
A cotton candy-like cloud of simple sugar drifts in the unspeakably
cold center of the Milky Way about 26,000 light years away, offering a
remote, yet tantalizing, hint of how the building blocks of life may have
reached Earth billions of years ago.
This frigid cloud is composed of molecular glycolaldehyde, a sugar that,
when it reacts with other sugars or carbon molecules, can form a more
complex sugar called ribose, the starting point for DNA and RNA, which
carry the genetic code for all living things.
Astronomers have known about sugar in space for some time, but new
research reported last week in the Astrophysical Journal Letters showed
that gaseous sugar could exist at extremely low temperatures, as are
found in regions on the fringes of the solar system where comets are
Thus, while many scientists agree that life probably derived from a rich
"primordial soup" concocted in the warm-water puddles of early Earth, the
new research offers fresh evidence for another popular view -- that life,
or at least some of its basic ingredients, may have flown in from
interstellar space aboard a comet or asteroid.
"These are long-standing questions," said astronomer Philip R. Jewell,
of the Robert C. Byrd Green Bank Telescope in West Virginia. "You want
to know what sort of molecules would form in the interstellar medium.
This is a clue."
A four-member team led by Jan M. Hollis, of NASA's Goddard Space Flight
Center, and Jewell, used Green Bank's 115-yard-diameter parabolic
reflector to examine Sagittarius B2, a cloud of dust and gas several
light-years wide at the heart of the Milky Way, in the direction of the
Green Bank is a radiotelescope that identifies specific molecules in the
cosmos by analyzing their radio emissions as they rotate end over end in
space. Each molecule has its own unique signature frequencies, derived
and catalogued through testing on Earth.
Jewell said the team had found glycolaldehyde in a warmer part of the
cloud in 2000, but this time detected it in an area where temperatures
were only 8 degrees above absolute zero, that is, minus 445 degrees
Fahrenheit. All molecular motion stops at absolute zero (minus 459
"Being that cold is interesting," said research astrophysicist Scott A.
Sandford, of NASA's Ames Research Center. "At 8 degrees kelvin, molecules
aren't going to be hopping off into the gas phase."
Finding complex molecules floating free in cold space so that their
radio signatures could be recognized was something of a surprise, Jewell
said, because at such low temperatures, they are much more likely to be
found frozen solid to dust particles in the cloud.
"You need something non-thermal to get the sugar molecules off the dust
grains," said Sandford, speaking from his Mountain View, Calif., office.
"A shock wave could go through the cloud, cause grain collisions and blow
the molecules into the gas phase." Heat will not work, he added, because
it would break down the sugar molecules into simpler compounds.
Jewell said shock waves are quite likely what happened: "This is a
star-forming region, and while star formation is a pretty hot process,
the shock waves would pass through the center of the region and out into
the colder outer areas," jarring the dust to release the sugar molecules.
It is unclear whether the glycolaldehyde, a simple "two-carbon" sugar
containing two carbon atoms, two oxygen atoms and four hydrogen atoms,
was frozen to the dust particles before the shock wave came by, or was
formed by interstellar chemistry after the shock wave liberated simpler
In either case, however, "the conclusions are pretty exciting," said
University of Arizona astrochemist Lucy M. Ziurys, director of the
Arizona Radio Observatory. Ziurys, an expert in developing radio
signatures for carbon molecules, has criticized the Green Bank team for
not being thorough enough, but said her own students had replicated the
Green Bank results.
"If sugar's in space, it's an important thing," Ziurys said in a
telephone interview. "You add a few more carbons, and you end up with a
sugar called ribose, and ribose is an essential component" of DNA and
What that means, however, is anybody's guess: "So suppose we have these
interstellar clouds that are producing sugar molecules, and they're found
throughout the galaxy," Ziurys said. "The big question is: Did the basic
ingredients of life begin out in these clouds or on a planet?"
"We don't have a clue," Sandford said. "This seems to raise the odds
that life could get started out there, but we don't know. That's why most
of these arguments tend to be of a general nature."
In our solar system, and presumably elsewhere, the colder reaches of
space are areas where particles of dust, ice and other debris bond in
ever-larger clumps that eventually become comets.
Most comets in the solar system were formed about 4.5 billion years ago
near the planets Uranus and Neptune and were subsequently cast into deep
space well beyond Pluto. They reenter the solar system when nearby stars
or large planets perturb their orbits.
Scientists long ago raised the possibility that early impacts from
comets -- or asteroids from the belt between Mars and Jupiter -- may have
brought Earth most of its water supply as well as the sugars and other
compounds that served as the building blocks of life. The Green Bank
research provides further evidence that this may have occurred.
Once liberated from their icy embrace and allowed to steep in warm water
on the Earth's surface, the sugars could have combined with other carbon
compounds to form ribose and, eventually, DNA and RNA.
But while this view appears to clash with more traditional thinking --
that the early Earth mixed its own soup without any help from space --
there is no reason why both phenomena could not have occurred.
"Current thinking is that sugars formed on the planet, but they could
have been deposited on the planet by a comet or by interstellar dust,"
Ziurys said. "The important thing is that one method does not exclude the
And "nothing says that the stuff that fell out of the sky was the key
thing, or the stuff that came from hydrothermal vents was the key thing,
or the stuff that was struck by lightning was the key thing," Sandford
said. "In the end, the chemical system that made life on Earth wasn't
worried about 'Made in' labels. It just grabbed what it needed."