“Intriguing Hints” –Our 30-Light-Year Voyage Through the Local Interstellar Cloud






Our solar system has been voyaging through the very low density Local Interstellar Cloud, a region about 30 light-years across that's as sparse as a handful of air stretched over a column that is hundreds of light years long, or about one atom per three cubic centimeters of space. Earth and our Sun has been traveling through the Cloud for somewhere between 40,000 and 150,000 years and will probably not emerge for another 20,000 years. A mere blip in our 250 million-year orbit through the Milky Way.

Previous measurements of interstellar helium atoms by the Ulysses spacecraft indicated the solar system may be emerging from the local cloud. But the latest IBEX data, which detected incoming atoms moving at a slower speed, show the heliosphere is still embedded within the local cloud.

In February 2012, NASA's Interstellar Boundary Explorer (IBEX), the centerpiece of a $169 million mission mapping the frontier of the sun's influence, detected atoms from interstellar space streaming by Earth, that are different from the chemical make-up of the solar system.

"Our solar system is different than the space right outside it, suggesting two possibilities," said David McComas, IBEX principal investigator, at the Southwest Research Institute in San Antonio. "Either the solar system evolved in a separate, more oxygen-rich part of the galaxy than where we currently reside, or a great deal of critical, life-giving oxygen lies trapped in interstellar dust grains or ices, unable to move freely throughout space."

"We've directly measured four separate types of atoms from interstellar space and the composition just doesn't match up with what we see in the solar system," said Eric Christian, IBEX mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "IBEX's observations shed a whole new light on the mysterious zone where the solar system ends and interstellar space begins."

The data hints that the region of interstellar space just outside the solar system may be deficient in oxygen compared to its abundance inside the heliosphere –a teardrop-shaped bubble blown out by the force from the solar winds that blocks most dangerous cosmic radiation from reaching Earth.

The IBEX satellite observed hydrogen, oxygen, neon and helium atoms that originated in interstellar space, the vacuous medium between stars in the Milky Way galaxy and found 74 oxygen atoms for every 20 neon atoms in the interstellar material, compared with 111 oxygen atoms for every 20 neon atoms inside the solar system. Most of the interstellar medium is made up of hydrogen and helium. Heavier elements, such as oxygen and neon, are spread by exploding supernovae at the end of a star's life cycle, according to NASA.

The "local bubble" exists in a network of cavities in the interstellar medium, probably carved by massive star explosions millions of years ago. The interstellar medium (or ISM) is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space.

The ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales, with stars forming within the densest regions of the ISM and molecular clouds, and replenishes the ISM with matter and energy through planetary nebulae, stellar winds, and supernovae.

This interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, and therefore its lifespan of active star formation.

NASA astronomer's best guess is depicted in the map (below) of the surrounding 1500 light years constructed from multiple observations and deductions. The Local Interstellar Cloud (LIC), shown in violet, which is flowing away from the Scorpius-Centaurus Association of young stars).


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The LIC resides in a low-density hole in the interstellar medium (ISM) called the Local Bubble, shown in black. Nearby, high-density molecular clouds including the Aquila Rift surround star forming regions, each shown in orange.

The Gum Nebula, shown above and below in green, is a region of hot ionized hydrogen gas. This complex nebula is thought to be a supernova remnant over a million years old, sprawling across the southern constellations Vela and Puppis. Inside the Gum Nebula is the Vela Supernova Remnant, shown in pink, which is expanding to create fragmented shells of material like the LIC. Future observations will aid astronomers to learn more about the local Galactic Neighborhood and how it might have affected Earth's past climate.

Over 13 billion years ago at least one of the domains of life may have begun in nebular clouds. If restricted to the Milky Way, which is 13.6 billion years old, the first chemical combinations would have had billions of years to become a self-replicating organism with a DNA genome long before the existence of Earth.

Nebular clouds are thought to be most likely environment for synthesizing and promoting the evolution of molecules needed for the origin of life. The building blocks for DNA could have been generated or combined within interstellar clouds and DNA would become part of the molecular-protein-amino acid complex. Hydrogen, oxygen, carbon, calcium, sulfur, nitrogen and phosphorus for example are continually irradiated by ions, which can generate small organic molecules which evolve into larger complex organic molecules that result in the formation of amino acids and other compounds.

Phosphorus, for example, is rare in our solar system and may have been non-existent on the early Earth; phosphorus is essential for the manufacture of DNA.

Polarized radiation in the nebula cloud leads to the formation of proteins, nucleobases and then DNA. The combination of hydrogen, carbon, oxygen, nitrogen, cyanide and several other elements, could create adenine, which is a DNA base, whereas oxygen and phosphorus could ladder DNA base pairs. Glycine has also been identified in the interstellar clouds.

Fast forward 4.6 billion years, on Earth the steps leading from the random mixing of chemicals to the first nano-particle would likely require hundreds of millions and even billions of years before the first self-replicating molecular compound was fashioned. Even after billions of years, the first replicon may not have possessed DNA.

Koninga, N., et al., (2008). Organic molecules in the spectral line survey of Orion KL with the Odin Satellite from 486–492 GHz and 541–577 GHz. Proceedings of the International Astronomical Union, 4, 29-30.

Kensei K., et al., (2008). Formation of amino acid precursors with large molecular weight in dense clouds and their relevance to origins of bio-homochirality. Proceedings of the International Astronomical Union, 4:465-472.

The Daily Galaxy via NASA/IBEX

Image credits: NASA



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