12186Saturn's Titan --A Unique Window on the Origins of Life on Earth
- Sep 17 7:37 PMInteresting post from the Daily Galaxy.What are some SF stories that have been set on Titan?Chris
Sent: 9/17/2013 6:31:19 P.M. Eastern Daylight Time
Subj: The Daily Galaxy: News from Planet Earth & Beyond
Posted: 17 Sep 2013 08:52 AM PDT
Glimpses of the events that nurtured life on Earth more than 3.5billion years ago are coming from an unlikely venue almost 1 billion miles away, according to the leader of an effort to understand Saturn's Titan, one of the most unusual moons in the solar system.Titan, the largest of Saturn's several dozen moons, is providing insights into the evolution of life unavailable elsewhere, said Jonathan Lunine, the David C. Duncan Director of the Center for Radiophysics and Space Research at Cornell University. "Data sent back to Earth from space missions allow us to test an idea that underpins modern science's portrait of the origin of life on Earth," Lunine said.
"We think that simple organic chemicals present on the primordial Earth, influenced by sunlight and other sources of energy, underwent reactions that produced more and more complex chemicals. At some point, they crossed a threshold -- developing the ability to reproduce themselves. Could we test this theory in the lab? These processes have been underway on Titan for billions of years. We don't have a billion years in the lab. We don't even have a thousand years."
Lunine is one of about 260 scientists involved with the Cassini-Huygens mission, explained that only two celestial objects in the solar system have the large amounts of organic substances on their surfaces to provide such information. They are Titan and Earth.
Organic substances on Earth, however, have been cycled through living things countless times. Titan's organic materials, which include deposits of methane and other hydrocarbons as large as some of the Great Lakes, are in pristine condition -- never, so far as anyone knows, in contact with life.
Titan is the only moon in the solar system known to have an atmosphere. Like Earth, most of it consists of nitrogen, with methane the second-most abundant. Sunlight strikes Titan's upper atmosphere, breaking that compound into pieces that react with each other and nitrogen to form organic compounds. Those include ethane, acetylene, hydrogen cyanide, cyanoacetylene and others -- all familiar terrestrial chemicals.
"We've got a very good inventory of what's there in the atmosphere," Lunine said. "What we've only recently begun to understand is the fate of these organics at the surface of Titan."
Lunine explained that for a long time, Mars had captured the public's and scientists' imagination as a possible location to find interesting organic chemistry and hints at life outside the Earth -- and for good reason: It is an Earth-like planet relatively close to the Sun. But scientists have only found simple organic materials on the red planet.
Recent research has provided fascinating hints that liquid water may exist deep under Titan's surface. Other data suggest that areas of Titan's seafloor may be similar to areas of Earth's seafloors where hydrothermal vents exist. These passways into Earth's interior spout hot, mineral-rich water that fosters an array of once-unknown forms of life. Lunine also cited research that has identified prime potential landing spots on Titan should the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) or other space agencies decide on another mission to Titan.
Scientists now know, thanks to the joint NASA-ESA spacecraft that arrived at Saturn in 2004 after a seven-year journey through the solar system, that Titan shares a surprising number of features with Earth. The enormous volumes of data that Cassini's 12 scientific instruments and the Huygens surface probe streamed back to Earth paint a complex picture of Titan's surface and the dense atmosphere that enshrouds it. Rivers flow into lakes. Wind sweeps across dunes. Giant storms brew, and clouds float across the hazy sky.
The catch is that Titan, nearly a billion miles from the Sun and a little larger than the Earth's own moon, is mostly frozen. It only receives about 1 percent of the sunlight that Earth gets. As a result, it is unimaginably frigid. At minus 290 degrees Fahrenheit -- that's 160 degrees colder than the coldest recorded temperature in Antarctica -- its water ice is rock solid, at least on the surface. And the rivers and lakes? They are made of liquid hydrocarbons, ethane and methane, which on balmy Earth are the main components of natural gas. Titan's deposits may be 10-100 times greater than all of Earth's oil and gas reserves, estimates suggest.
The research was part of a symposium on "Chemical Frontiers in Solar System Exploration," which covers the gamut of the latest discoveries in space science, and experimental design and devices that are pushing the field to new levels. The following topics were among more than 30 presentations in the symposium.
The Daily Galaxy via the American Chemical Society
Posted: 17 Sep 2013 09:50 AM PDT
Building a terrestrial planet requires raw materials that weren't available in the early history of the universe. The Big Bang filled space with hydrogen and helium. Chemical elements like silicon and oxygen - key components of rocks - had to be cooked up over time by stars. But how long did that take? How many of such heavy elements do you need to form planets, especially rocky, Earthlike planets?Studies have shown that Jupiter-sized gas giants tend to form around stars containing more heavy elements than the Sun. However, research by a team of astronomers found that planets smaller than Neptune are located around a wide variety of stars, including those with fewer heavy elements than the Sun. Astronomers call chemical elements heavier than hydrogen and helium "metals." As a result, rocky worlds like Earth could have formed earlier than expected in the universe's history.
"Terrestrial worlds could form at almost any time in our galaxy's history," said Smithsonian astronomer David Latham (Harvard-Smithsonian Center for Astrophysics). "You don't need many earlier generations of stars."Latham played a lead role in a study released this past April, which was led by Lars A. Buchhave from the University of Copenhagen.
They measure the metal content, or metallicities, of other stars using the Sun as a benchmark. Stars with more heavy elements are considered metal-rich while stars with fewer heavy elements are considered metal-poor.
In 2012, Latham and his colleagues examined more than 150 stars known to have planets, based on data from NASA's Kepler spacecraft. They measured the stars' metallicities and correlated that with the sizes of the associated planets. Large planets tended to orbit stars with solar metallicities or higher. Smaller worlds, though, were found around metal-rich and metal-poor stars alike. "Giant planets prefer metal-rich stars. Little ones don't," explained Latham.
They found that terrestrial planets form at a wide range of metallicities, including systems with only one-quarter of the Sun's metal content. Their discovery supports the "core accretion" model of planet formation. In this model, primordial dust accumulates into mile-sized planetesimals that then coalesce into full-fledged planets. The largest, weighing 10 times Earth, can then gather surrounding hydrogen and become a gas giant.
A gas giant's core must form quickly since hydrogen in the protoplanetary disk dissipates rapidly, swept away by stellar winds in just a few million years. Higher metallicities might support the formation of large cores, explaining why we're more likely to find a gas giant orbiting a metal-rich star."This result fits with the core accretion model of planet formation in a natural way," said Latham.
The image at the top of the page is by data visualization artist Jer Thorp, who teamed up with Oblong Industries to create an interactive, gestural visualization of the data sent back by NASA's Kepler spacecraft. Kepler has returned quite a bit of data on its mission to find earth-like exoplanets in other parts of the Milky Way galaxy.
The Daily Galaxy via Harvard-Smithsonian Center for Astrophysics
You are subscribed to email updates from The Daily Galaxy --Great Discoveries Channel: Sci, Space, Tech
To stop receiving these emails, you may unsubscribe now.
Email delivery powered by Google Google Inc., 20 West Kinzie, Chicago IL USA 60610