Proof that Comets may have given Earth Life - KMSP-TV

Proof that Comets may have given Earth Life

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Many of the brightest minds have thought for years that some sort of mutation gave birth to the most primitive forms of life billions of years ago and eons of evolution got us to where we are today. But that "knowledge" might be falling victim to new discoveries. New research published in last week's Nature Geoscience magazine show that we may not only need to thank comets for the expansive amount of water on planet Earth, but they may be responsible for the very life that created humans. This could be a monumental step in understanding how the planet was formed and why it can sustain the life we know today. The jaw dropping details were summarized by Time magazine and are listed in full below:

"By rights, the earth should not be the cosmic garden it is. In a solar system of planets and moons that are solid rock or mostly gas, shrouded in clouds or atmosphere-free, scorchingly hot or bitterly cold, there's only one that's dripping wet. Earthlings like to refer to our home planet as the solar system's water world, and it's a jolly good thing it's as wet as it is, because without plenty of water, life (at least as we know it) would be impossible.

All the same, it's likely our planet was once a far drier, dustier place. You need only look at two of our nearby rocky neighbors — Mercury and Venus — for a reminder of what living so close to the blast furnace of the sun can do to you. Our atmosphere helps us retain the abundant water we do have, but how did it get to us in the first place?

One popular theory has long been comets. The solar system swarms with these little rogue bodies — perhaps a trillion of them, according to astronomers' back-of-the-envelope estimates — and shortly after the sun and planets formed, they were everywhere, flying randomly and free to collide with anything in their way. Since comets are essentially dirty snowballs made of rock, gas and water ice, a few crash landings on earth could have provided all the water we needed quite nicely.

But there was a problem with that theory. All of the comets astronomers observed were indeed packed with water ice, but a lot of it was what's known as heavy water, in which the hydrogen in the H2O mix is an isotope known as deuterium, with one proton and one neutron in its nucleus. The hydrogen found in ordinary water has no neutron. Since the overwhelming share of the water in earth's oceans is made with the light hydrogen atom, astronomers calculated that comets could have accounted for only about 10% of what's there. Now, according to a new paper published in the journal Nature, it appears that those scientists may have been wrong — and the reason for their error is that they were simply looking at the wrong comets.

The paper, co-authored by researchers at the California Institute of Technology, is based on observations conducted by the Herschel Space Observatory, a spacecraft launched by the European Space Agency in 2009. Herschel looked specifically at comet Hartley 2, a small comet discovered in 1986 with an estimated diameter of .75 to .99 mi. (1.2 to 1.6 km). Analyzing the chemical composition of Hartley 2's corona — or the gassy veil surrounding the main comet body — Herschel discovered that its concentration of heavy water was only about half that of any comets observed before. While that wouldn't entirely explain earth's particular heavy- and light-water mix, it does bring the chemistry a lot more into line — and gives the cometary explanation for earthly water a big boost.

"Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early earth," says physicist Dariusz Lis of Caltech, a co-author of the paper.

What distinguishes Hartley 2 from the other comets previously studied — apart from its chemistry — is the place it was born. The trajectory the comet follows in its vast looping swings toward and away from the sun suggests it originated in the Kuiper Belt, a ring of icy bodies circling the solar system some 50 times farther from the sun than the earth is. The trajectory of the other comets makes it likely they are natives of the Oort cloud, a vast swarm of comets completely surrounding the solar system up to 10,000 times more distant than the Kuiper Belt.

It's not clear why Oort comets and Kuiper comets would have different water chemistry, but the time each spent in close proximity to the sun before being gravitationally ejected into deep space may play a role. That, however, is as much of a guess as astronomers want to make. "Our study indicates that our understanding of the distribution of the lightest elements and their isotopes, as well as the dynamics of the early solar system, is incomplete," conceded Caltech planetary scientist Geoffrey Blake.

But if the science is incomplete, it's still more complete than it ever was before — making scientists more certain, too, about how our planet's water was delivered. Getting banged about by comets today could spell the end of all life on earth. But some 4 billion years ago, it may well have spelled the start.

(A look at where you could have expect to see comet Pan-Starrs early this year)

In those early days of the solar system, when Earth was a molten ball of flaming goo, it would have been hard for the proto-planet to stay hydrated. Once things had settled down some, incoming comets, which are little more than water ice and rock and were plentiful in what is known as the heavy bombardment phase of the solar system's past, could have imported all we needed (which you read about above). Under those wet conditions, the right elements could have started coming together to form precursors to amino acids, then the acids themselves and then, a few jillion steps later, butterflies and bunnies and all the rest. And that initial chemistry wouldn't even have had to have gotten started on Earth. Amino acids and amino acid precursors have been detected in both comets and meteorites, meaning they could have been imported to us ready-made.

All the same, there's one more thing that would help get the basic elements to join hands, and that would be energy—typically in the form of heat. That's something that ought to be hard to come by in a dirty snowball or a fragment of rock flying through space, but very easy to come by when an impact occurs or that comet impacting a very hot molten new planet. A watery object striking a dry body like Earth—or, in the alternative, a dry object striking an icy body like Jupiter's frozen moon Europa or Saturn's icy Enceladus—could shock-heat complex organic compounds into existence. Indeed, the Cassini spacecraft has detected those kinds of organics in water plumes that jet out from Enceladus.

Still, you can hardly test your theory by standing on a moon, waiting for a meteor to hit and then sampling the water. So a team of scientists from the U.K.'s Imperial College and the University of Kent came up with another way, one they described in a paper published in this week's Nature Geoscience.

The researchers first mixed up batches of water with raw chemical signatures matching the various types found in comets—though without any kinds of amino acid precursors. Then they sealed the water in containers and heated it to 932º F (600º C) to ensure that any traces of organic contaminants were destroyed. The water samples were then frozen, and steel projectiles—also heat-sterilized—were fired at them from a gas gun at high speed. Ice plus impact could, in theory, equal organics—and in one sample it did.

The winning solution was water with a mix of ammonia gas, carbon dioxide and methanol—all carbon, hydrogen, oxygen compounds. That formula produced not just precursors, but amino acids themselves. Give them 4.5 billion years—a longitudinal study if ever there was one—and who knows what they might turn into? The scientists don't have quite that much time, but lending support to their findings is the fact that computer simulations of the same impact events yield the same chemical results.

"The fact that impacts occur is without question," the authors wrote. "It is also known that comets contain significant quantities of the compounds used in this study, and that these compounds are found on the impacted surfaces of many of the icy bodies in the outer Solar System."

Visiting any of those bodies to study the chemistry and confirm the theories is not set to happen anytime soon, but it's at least on the agenda. NASA is looking at proposals for a robotic mission to Europa, and the European Space Agency has an even more ambitious one planned for launch in 2022. Called JUICE (a somewhat awkward acronym for JUpiter ICy moons Explorer) it will study Europa as well as its sister satellites Ganymede and Callisto. JUICE may not find life, but it will bring us closer to understanding how it got started—on Earth and perhaps on untold other worlds as well."

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