comet mcnaught [Archive] - Beastie Boys Message Board

drizl

01-20-2007, 03:50 PM

amazing.

how comets might bring life to planets:

Was Johnny Appleseed
a Comet?
A new experiment suggests that comet impacts could have sowed the seeds of life on Earth billions of years ago.

http://science.nasa.gov/headlines/y2001/ast05apr_1.htm

Listen to this story (requires RealPlayer)

April 5, 2001 -- Four billion years ago Earth was bombarded by a hail of comets and asteroids. The shattering collisions rendered our planet uninhabitable during a period scientists call the Late Heavy Bombardment (LHB).

It surely sounds like the LHB was an awful time for the beleaguered young planet -- but perhaps the pelting was a good thing after all, say researchers. Kamikaze comets could have delivered important organic molecules to Earth -- sowing the seeds for life.

Genesis by comets is a controversial idea, but it's just received an important boost. A NASA-supported experiment reveals that complex molecules hitchhiking aboard a comet could have survived an impact with Earth.

"Our results suggest that the notion of organic compounds coming from outer space can't be ruled out because of the severity of the impact event," says Jennifer Blank, a geochemist at the University of California, Berkeley. Blank and colleagues simulated a comet collision by shooting a soda-can sized bullet into a metal target containing a teardrop of water mixed with amino acids - the building blocks of proteins.

Not only did a good fraction of the amino acids survive, but many polymerized into chains of two, three and four amino acids, so-called peptides. Peptides with longer chains are called polypeptides, while even longer ones are called proteins.

Above: In this schematic diagram of Blank et al.'s apparatus the red arrow indicates the projectile, which is fired from the breach toward the stationary target (inset). The 3 smaller red triangles indicate transducer pins that measure the velocity of the projectile as it passes. "Upon impact, the sample container and a similarly-sized metal plug fly backwards into the recovery area, where they're trapped as gently as possible in layers of felt," adds Blank. Credit Jennifer Blank, UC Berkeley.

"The neat thing is that we got every possible combination of dipeptide, many tripeptides and some tetrapeptides," said Blank. "We saw variations in the ratios of peptides produced depending on the conditions of temperature, pressure and duration of the impact. This is the beginning of a new field of science."

Freezing the target to mimic an icy comet increased the survival rate of amino acids, she added.

Blank's ballistic test was designed to simulate the sort of impact that would have been frequent in Earth's earliest history when rocky, icy debris in our solar system combined to form the planets. Much of the debris would have resembled comets - dirty snowballs thought to be mostly slushy water surrounding a rocky core - slamming into Earth at velocities greater than 16 miles per second (25 km/sec).

The severity of the laboratory impact was akin to that of an oblique collision between the rocky surface of Earth and a comet coming in at an angle of less than 25 degrees from the horizon.

Right: In a related project conducted by members of NASA's Astrobiology Institute, scientists have created primitive organic cell-like structures. They did it in their laboratory by duplicating the harsh conditions of cold interstellar space! Did comets carry such protocells to Earth? [more information]

Benton Clark, chief scientist of Flight Systems at Lockheed Martin Astronautics, proposed in 1988 that if comets are slowed sufficiently -- by, e.g., drag from Earth's atmosphere, which would be greatest at low impact angles -- some water and organic compounds might survive the collision.

"At very low angles, we think that some water ice from the comet would remain intact as a liquid puddle concentrated with organic molecules," ideal for the development of life, Blank said. "This impact scenario provides the three ingredients believed necessary for life: liquid water, organic material and energy."

Though comet hunter Eugene Shoemaker estimated that in Earth's early history only a few percent of comets or asteroids arrived at low enough angles, the bombardment would have been heavy enough to deliver a significant amount of intact organic material and water, according to Blank's estimates.

One well-known model for the beginnings of life on Earth posits that terrestrial life sprang from complex molecules such as amino acids and sugars produced by electrical discharges in a primeval atmosphere replete with gases such as methane, hydrogen, ammonia and water. The famous Miller-Urey experiment in 1953, conducted by Stanley Miller and Harold Urey of the University of Chicago, demonstrated that a lightening-like discharge in a test tube filled with these molecules could produce amino acids.

Below: The Miller-Urey experiment generated electric sparks -- meant to model lightning -- in a mixture of gases thought to resemble Earth's early atmosphere. Click on the image for a short animation of the experiment. Credit: AccessExcellence.org

Other scientists believe that the building blocks of life on Earth arrived from space. Astronomers have detected many kinds of organic molecules in space, floating in clouds of gas or bound up in dust particles. They range from the simplest - water, ammonia, methane, hydrogen cyanide and alcohols, including ethyl alcohol - to more complex molecules.

Interestingly, of the more than 70 amino acids found in meteorites, only eight of them overlap with the group of 20 which occur commonly as structural components of proteins found in humans and all other life on Earth.

To test whether water and organic compounds could survive the high pressures and high temperatures of a collision, Blank and her colleagues worked for three years to design a steel capsule that would not rupture when hit with a mile-per-second (1.6 kilometer-per-second) bullet fired from an 80-mm bore cannon at the University of Chicago and later at Los Alamos National Laboratory. The target she and her team developed - a two-centimeter diameter stainless steel disk about a half-centimeter thick - was able to withstand about 200,000 times atmospheric pressure without bursting.

They filled the small cavity with water saturated with five amino acids: three from the list of 20 that comprise all proteins in humans (phenylalanine, proline and lysine) and two varieties detected in the Murchison meteorite (aminobutyric acid and nor-valine). That meteorite plummeted to the ground in 1969 in Australia and is thought to be from the core of a comet.

Sign up for EXPRESS SCIENCE NEWS delivery
The liquid contents were analyzed afterwards at Argonne using liquid chromatography and mass spectroscopy to determine the species and concentrations of molecules present.

The survival of a large fraction of the amino acids and their polymerization during the collision makes the idea of an extraterrestrial origin of organic compounds a strong contender against Miller-Urey style theories, Blank said.

"About one comet per year arriving in a low-angle impact would bring in the equivalent of all the organics produced in a year in an oxidizing atmosphere by the Miller-Urey electric discharge mechanism," Blank estimated. "An advantage is you get all of it together in a puddle of water rather than diluted in the oceans."

The next hitchhikers she plans to subject to a shock test are bacterial spores, which some have proposed arrived on Earth via comets to jump-start evolution.

http://www.sciencenews.org/articles/20020330/fob1.asp

Icy Birth? Amino acids form in simulations of space ice
Jessica Gorman

In another step toward understanding the origin of Earth's biological molecules, two independent laboratory experiments have produced amino acids—the building blocks of proteins—by simulating conditions in icy, interstellar space.

COMET DUST. Scaled-up plastic model, about 15 centimeters wide, represents interstellar dust particles in a piece of a comet.
Raymond and Beverly Sackler Laboratory for Astrophysics at Leiden Observatory, The Netherlands

The results, published in the March 28 Nature, suggest that some amino acids could have formed in giant clouds of icy particles and then hitched rides on comets and asteroids to planets throughout the universe, says Max Bernstein of NASA's Ames Research Center in Mountain View, Calif.

In the search for precursors to life on Earth, various researchers have created amino acids and other organic molecules in lab experiments that simulate specific environments, such as those on early Earth or asteroids. Researchers have also speculated that amino acids might form on interstellar ice particles that are exposed to ultraviolet light, yet until now, no one had shown that this could actually happen, says Bernstein.

"I think it's a really exciting justification of the notion that these building blocks can come from outer space," comments Jennifer Blank of the Lawrence Livermore National Laboratory in California (SN: 5/19/01, p. 317: http://www.sciencenews.org/20010519/bob13.asp).

In each of the new experiments, performed at very low temperatures and pressures, scientists chose small molecules found in space and deposited them on a surface while irradiating them with ultraviolet light. Bernstein and his colleagues made an icy layer of water, methanol, ammonia, and hydrogen cyanide. The other team, which includes scientists from four European institutions, used less water than the NASA team did. It also included carbon monoxide and carbon dioxide in its mix but no hydrogen cyanide.

After warming the samples to room temperature, the NASA group detected three amino acids: glycine, alanine, and serine. The European group identified 16 amino acids, including 6 that appear in life's proteins.

Uwe Meierhenrich of Bremen University in Germany says the creation of amino acids in the European group's experiment was a surprise. The team had been preparing interplanetary ice samples to test equipment for the upcoming Rosetta space probe, which will analyze a comet's chemistry.

To rule out contamination by natural amino acids, both research teams used a heavy isotope of carbon in their initial chemicals and found that same isotope in the final amino acids. Moreover, some amino acids have both a left- and a right-handed form, but living organisms contain almost exclusively the left-handed variety. So, most amino acids on Earth are in that form. The researchers produced a 50-50 mix of left-handed and right-handed forms in their samples, a confirmation that the amino acids derived from the experiment.

These studies may help explain how some amino acids formed initially, but they do not indicate why life incorporates only left-handed amino acids. One popular theory is that certain naturally occurring forms of UV radiation, called circularly polarized light, preferentially produce left-handed varieties in interstellar space. By running their experiments again with such UV light, the NASA group is now pursuing this possibility, says Bernstein.

Blank says that another question is, How long can such amino acids survive in their icy birthplaces?

"Really rich, robust chemistry taking place in the cosmos" contributes to making the molecules necessary for life, says Jeffrey Bada of the University of California at San Diego. He notes that interstellar ice chemistry is just one of many processes—including chemical reactions on asteroids or the early Earth—that could form amino acids

drizl

01-20-2007, 03:51 PM

http://www.timesonline.co.uk/article/0,,2087-2070393,00.html

Comet dust holds building blocks of life
Jonathan Leake, Science Editor

SCIENTISTS examining the first dust samples collected from a comet have found complex carbon molecules, supporting the theory that the ingredients for life on Earth originated in space.
The organic material was found in early studies of samples from the comet Wild 2 brought back to Earth by the Stardust space probe seven weeks ago.

Stardust collected hundreds of grains of dust as it flew through the tail of the comet two years earlier. Analysis suggests a high concentration of complex molecules of the kind thought necessary for the evolution of life.

“About 10% of this comet is made of organic materials. We don’t know exactly what they all are but it is very exciting,” said Don Brownlee, professor of astronomy at the University of Washington, who is Nasa’s principal investigator for the Stardust project.

Stardust was launched by Nasa in February 1999 and flew twice around the sun as it matched its speed to the comet’s. Then, in January 2004, somewhere between the orbits of Mars and Jupiter, it slipped into the comet’s tail of dust and exotic gases, passing within 147 miles of Wild 2’s nucleus.

Stardust swept up particles in a collector shaped like a tennis racket and packed with an absorbent material called aerogel, then spent two years lining itself up in an orbit that would return it to Earth. On January 15 it dropped a canister containing the precious comet dust, which landed by parachute.

Nasa’s Johnson space centre carved the aerogel into thin slices, each containing particles, and sent them out to researchers around the world. Next week they will share their findings at the Lunar and Planetary Science conference in Houston, Texas.

The samples will be a treasure trove of organic material, possibly including amino acids, the building blocks of proteins.

“What we want to know is how organic molecules actually form in comets and whether they helped deliver organic material to the Earth before life began,” said Brownlee.

The idea that comets delivered the basic components needed for life has growing support among astronomers. The theory is that the sun and planets began to form from a vast disc of interstellar dust, gases and debris about five billion years ago.

The sun would have formed first. Its radiation and gravity would then have had a powerful influence on the rest of the solar system, driving lighter molecules of compounds such as water, sulphur dioxide and carbon dioxide out from the inner solar system.

The process would also have produced billions of comets and meteorites. Earth was formed 4.6 billion years ago and, as it cooled, these bodies, some of them huge, bombarded it, bringing organic matter and water. The first stirrings of life appeared 3.5 billion years ago.

Earth’s atmosphere is still showered in dust, meteorites and other debris every day. This carries water and organic material including amino acids. But scientists are not sure whether this modern material has the same composition as the comets and meteorites that hit the young Earth.

Phil Bland, a Royal Society research fellow at Imperial College, London, who is working on the Stardust samples, said that comets — deep frozen for billions of years — were like time capsules. “We can compare what’s in them with what we see now, to work out the processes that have shaped our planet and all the others,” he said.

Monica Grady, professor of planetary and space science at the Open University, is a member of one of the teams examining the Stardust samples.

“Organic material delivered by comets and meteorites between those dates [4.6 billion to 3.5 billion years ago] is likely to have played a part in starting life on Earth,” she said.