[meteorite-list] Space Observatory Provides Clues To Creation Of Earth's Oceans (Herschel/Comet Hartley 2)

[Ron Baalke]

Oct. 5, 2011

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Whitney Clavin 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-4673 
whitney.clavin at jpl.nasa.gov 
RELEASE: 11-338

SPACE OBSERVATORY PROVIDES CLUES TO CREATION OF EARTH'S OCEANS

WASHINGTON -- Astronomers have found a new cosmic source for the same 
kind of water that appeared on Earth billions of years ago and 
created the oceans. The findings may help explain how Earth's surface 
ended up covered in water. 

New measurements from the Herschel Space Observatory show that comet 
Hartley 2, which comes from the distant Kuiper Belt, contains water 
with the same chemical signature as Earth's oceans. This remote 
region of the solar system, some 30 to 50 times as far away as the 
distance between Earth and the sun, is home to icy, rocky bodies 
including Pluto, other dwarf planets and innumerable comets. 

"Our results with Herschel suggest that comets could have played a 
major role in bringing vast amounts of water to an early Earth," said 
Dariusz Lis, senior research associate in physics at the California 
Institute of Technology in Pasadena and co-author of a new paper in 
the journal Nature, published online Oct. 5. "This finding 
substantially expands the reservoir of Earth ocean-like water in the 
solar system to now include icy bodies originating in the Kuiper 
Belt." 

Scientists theorize Earth started out hot and dry, so that water 
critical for life must have been delivered millions of years later by 
asteroid and comet impacts. Until now, none of the comets previously 
studied contained water like Earth's. However, Herschel's 
observations of Hartley 2, the first in-depth look at water in a 
comet from the Kuiper Belt, paint a different picture. 

Herschel peered into the comet's coma, or thin, gaseous atmosphere. 
The coma develops as frozen materials inside a comet vaporize while 
on approach to the sun. This glowing envelope surrounds the comet's 
"icy dirtball"-like core and streams behind the object in a 
characteristic tail. 

Herschel detected the signature of vaporized water in this coma and, 
to the surprise of the scientists, Hartley 2 possessed half as much 
"heavy water" as other comets analyzed to date. In heavy water, one 
of the two normal hydrogen atoms has been replaced by the heavy 
hydrogen isotope known as deuterium. The ratio between heavy water 
and light, or regular, water in Hartley 2 is the same as the water on 
Earth's surface. The amount of heavy water in a comet is related to 
the environment where the comet formed. 

By tracking the path of Hartley 2 as it swoops into Earth's 
neighborhood in the inner solar system every six and a half years, 
astronomers know that it comes from the Kuiper Belt. The five comets 
besides Hartley 2 whose heavy-water-to-regular-water ratios have been 
obtained all come from an even more distant region in the solar 
system called the Oort Cloud. This swarm of bodies, 10,000 times 
farther afield than the Kuiper Belt, is the wellspring for most 
documented comets. 

Given the higher ratios of heavy water seen in Oort Cloud comets 
compared to Earth's oceans, astronomers had concluded that the 
contribution by comets to Earth's total water volume stood at 
approximately 10 percent. Asteroids, which are found mostly in a band 
between Mars and Jupiter but occasionally stray into Earth's 
vicinity, looked like the major depositors. The new results, however, 
point to Kuiper Belt comets having performed a previously 
underappreciated service in bearing water to Earth. 

How these objects ever came to possess the tell-tale oceanic water is 
puzzling. Astronomers had expected Kuiper Belt comets to have even 
more heavy water than Oort Cloud comets because the latter are 
thought to have formed closer to the sun than those in the Kuiper 
Belt. Therefore, Oort Cloud bodies should have had less frozen heavy 
water locked in them prior to their ejection to the fringes as the 
solar system evolved. 

"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," said co-author Geoffrey Blake, 
professor of planetary science and chemistry at Caltech. "In the 
early solar system, comets and asteroids must have been moving all 
over the place, and it appears that some of them crash-landed on our 
planet and made our oceans." 

Herschel is a European Space Agency cornerstone mission, with science 
instruments provided by consortia of European institutes. NASA's 
Herschel Project Office is based at the agency's Jet Propulsion 
Laboratory in Pasadena, Calif., which contributed mission-enabling 
technology for two of Herschel's three science instruments. The NASA 
Herschel Science Center, part of the Infrared Processing and Analysis 
Center at Caltech in Pasadena, supports the U.S. astronomical 
community. 

For NASA's Herschel website, visit: 

http://www.nasa.gov/herschel 

For ESA's Herschel website, visit: 

http://www.esa.int/SPECIALS/Herschel/index.html 
	
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