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Asteroids, Not Comets, Birthed Earth's Oceans?

 
 
Reply Thu 11 Dec, 2014 02:13 pm
I can understand water being delivered to Earth by asteroids and don't dispute it. But, it seems to me that if water can be on an asteroid without all boiling away, why couldn't some have remained on Earth also? I am not a scientist, but it seems odd to me. - eb
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Asteroids, not comets, likely delivered Earth's ancient oceans from space, concludes a Wednesday study from the Rosetta spacecraft, now in orbit around a comet that is a frozen relic from the dawn of the planets.

Where did the Earth's oceans come from? the new study asks, investigating a long-debated question of whether the water on our planet's surface was delivered during a bombardment of comets some 3.8 billion years ago. Not likely, mission scientists conclude, pointing instead to ancient asteroids, which were covered with frost in the early solar system.

"Terrestrial water was probably brought by asteroids," says Rosetta study leader Kathrin Altwegg of the University of Bern in Switzerland. She finds that source "more likely than comets."

These are the first scientific results from the European Space Agency craft, which is orbiting the lumpy 2.5-mile-wide (4.1 kilometers) comet 67P/Churyumov-Gerasimenko, the mission team reports in the journal Science. (See: "Touchdown! Comet Landing to Offer Clues to Solar System's Birth.")

Rosetta arrived at the lumpy ice ball last month, delivering a probe that lost power and went into hibernation during its first days on the comet. Comet 67P is now more than 260 million miles (418 million kilometers) from the sun, awaiting a solar warm-up that will spark its cometary tail.

Planetary Pinball

Comets are chunks of ice and dust zipping through the far reaches of space and occasionally zooming past the sun. A shooting gallery of them accompanied the birth of the solar system some 4.6 billion years ago, with comets and asteroids slamming into each other for another 800 million years. The epoch was capped by a pummeling of the Earth, the moon, and other planets known as the Late Heavy Bombardment.

Some of the bullets stopped by the early Earth were undoubtedly comet impacts, and planetary scientists have long suggested that these icebergs in space may have provided the waters of the early oceans.

When Earth first formed into a sphere, it was likely a ball of magma that would have boiled off any surface water, Altwegg notes, which is why scientists are looking to the skies to explain the origins of oceans in the first place.

Scientific suspicions that comets brought Earth's water were reinforced three years ago, when Europe's Herschel space telescope spotted ice with a chemistry signal similar to Earth's in the comet Hartley 2. That comet, like comet 67P, is thought to have originated in the Kuiper belt, just outside the orbit of Neptune.

It looks like those suspicions have been doused. "We found something different," says Altwegg, and "more exciting." She heads the team operating a spectrometer aboard Rosetta, which is circling in orbit some 14 miles (23 kilometers) above comet 67P.

With the spectrometer, the researchers measured the amount of deuterium, a heavier isotope of hydrogen, found in the ice on the surface of the comet. Normal water is built with hydrogen atoms, but "heavy" water contains deuterium instead.

On comet 67P's icy surface, the study concludes, the ratio of heavy water to normal water is roughly three times more than the ratio in Earth's oceans.

That rules out comets from the Kuiper belt delivering water to the early Earth, Altwegg says, because even a few deuterium-loaded comets like comet 67P would have spiked the punch bowl of the early Earth with heavy water.

"It is a very exciting study that raises more questions than it answers," says geophysicist Nicolas Dauphas of the University of Chicago, who was not part of the discovery team. "The mission is a tremendous success for space exploration and for science in Europe."

Asteroid Answers

Since Kuiper belt comets apparently don't share Earth's heavy water ratio, Altwegg argues that impacts with asteroids, small rocky bodies largely found between Mars and Jupiter, must have delivered the water in our oceans. (See: "Asteroids and Comets.")

In its earliest era, the sun wasn't as warm as it is today, she says, which would have allowed frozen water to remain on asteroids instead of boiling off. Deuterium is thought to have more often agglomerated in the coldest and most distant reaches of the early solar system, where comets dwell, so asteroids' ice likely packed much less of the heavy stuff.

But some outside experts are less convinced, citing the low numbers of comets so far investigated. Altwegg also speculated that some water baked out of the Earth's crust during the Late Heavy Bombardment era, adding to extraterrestrial contributions. (See: "Mystery of Earth's Water Origin Solved.")

"Each comet is different, and the question of their contribution to Earth's atmosphere and oceans is still open," Dauphas says.

The questions remain as to what sort of water emerges from comet 67P once it starts melting in the sun's glare next year, producing a cometary tail. Perhaps the surface ice of the comet is enriched with heavy water, while the interior isn't. (Related: "Comet Catcher: The Rosetta Landing.")

Once the comet reaches a distance of about 250 million miles (400 million kilometers) from the sun this spring, that activity should pick up, Altwegg says, and a tail should sprout from comet 67P. Until then, the spectrometer aboard the spacecraft will continue to refine its measurements.

"The Herschel observation cannot prove that comets delivered water to Earth," says planetary scientist Paul Hartogh, of the Max Planck Institute for Solar System Research in Göttingen, Germany, "while the Rosetta observation cannot prove that Earth water stems from [asteroids]."

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Type: Discussion • Score: 9 • Views: 3,018 • Replies: 8
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rosborne979
 
  1  
Reply Thu 11 Dec, 2014 07:54 pm
@edgarblythe,
I'm a little surprised that the original theory about comets being the source was intended to be so specific. Whenever I heard that theory I always thought the media was just using the word "comet" as a general reference to all the space debris which occupied the solar disk at the time of the earth's formation. So I always assumed that the bulk of the earth's mass and ratio's of composition came from the asteroids in this orbital distance from the sun.

I guess the scientists never thought enough water could exist on the asteroids and therefor just assumed that water-laden comets must have been the only other source. The simpler solution of course it that the water exists on the same objects (asteroids) which formed the bulk of the planet. And I guess that's what is being confirmed finally with these compositional analyses of asteroids.

If I had to make a prediction based on a simple understanding of how the planets formed, I would expect that the general composition of the asteroids in each of the orbital positions for each planet, matches the planets that formed there (precisely because the planets are conglomerations of the asteroids which were there), and therefor the general composition of the asteroids between Earth and Mars (to this day) will eventually be found to be in between the composition of Mars and Earth.

We already know that the solar disk from which all the planets formed was stratified in such a way that the rocky planets formed nearer the sun and the gas giants formed farther away. I suspect that the solar disk was probably stratified in an even more granular fashion and that the planetary compositions match that granularity.
0 Replies
 
PUNKEY
 
  1  
Reply Sat 13 Dec, 2014 10:20 am
To me "comet" is an excuse/explanation for the Big Bang theory.

Asteroid implies a moving source of energy. You mean there has just been ONE of these incidences?
rosborne979
 
  2  
Reply Sat 13 Dec, 2014 07:59 pm
@PUNKEY,
PUNKEY wrote:
To me "comet" is an excuse/explanation for the Big Bang theory.

Asteroid implies a moving source of energy. You mean there has just been ONE of these incidences?
What?
0 Replies
 
knaivete
 
  1  
Reply Sat 13 Dec, 2014 10:45 pm
@edgarblythe,
I'm with you Edgar, and it's a great topic - probably more controversial than some I can think of. And not only but also.


http://upload.wikimedia.org/math/2/0/a/20a739e1642dde225c73e2bc2b083768.png

http://en.wikipedia.org/wiki/Origin_of_water_on_Earth
0 Replies
 
FBM
 
  1  
Reply Sat 13 Dec, 2014 11:01 pm
@PUNKEY,
We just landed on a comet, Japan has just launced a mission to bring back samples from an asteroid, and water vapor has been detected on an asteroid, Ceres.
0 Replies
 
InfraBlue
 
  1  
Reply Sun 14 Dec, 2014 08:11 am
@PUNKEY,
PUNKEY wrote:

To me "comet" is an excuse/explanation for the Big Bang theory.

Asteroid implies a moving source of energy. You mean there has just been ONE of these incidences?



The issue about the source of earth's water coming from either comets or asteroids isn't about the Big Bang. The Big Bang had occurred billions of years earlier.
0 Replies
 
Setanta
 
  1  
Reply Sun 14 Dec, 2014 12:54 pm
I never trusted them damned asteroids . . . i knew they was up to no good.
0 Replies
 
FBM
 
  1  
Reply Thu 5 Feb, 2015 12:05 am
http://www.space.com/28352-huge-asteroid-vesta-water-flows.html?cmpid=514630_20150205_39950637&adbid=10152621842851466&adbpl=fb&adbpr=17610706465

Quote:
Surprise! Water Once Flowed on Huge Asteroid Vesta
by Mike Wall, Space.com Senior Writer | January 27, 2015 11:00am ET


Liquid water apparently flowed on the surface of the huge asteroid Vesta briefly in the relatively recent past, a surprising new study suggests.

"Nobody expected to find evidence of water on Vesta. The surface is very cold and there is no atmosphere, so any water on the surface evaporates," study lead author Jennifer Scully, a postgraduate researcher at UCLA, said in a NASA statement. "However, Vesta is proving to be a very interesting and complex planetary body."

Scully and her colleagues analyzed images of Vesta — the second-largest object in the main asteroid belt between Mars and Jupiter — captured by NASA's Dawn spacecraft, which orbited the 318-mile-wide (512 kilometers) protoplanet from July 2011 through September 2012. [Photos: Asteroid Vesta and NASA's Dawn Spacecraft]

The researchers noticed curved gullies and fan-shaped deposits within eight different Vesta impact craters. These craters are young compared to the 4.56-billion-year-old Vesta; all of them are thought to have formed within the last few hundred million years.

On average, the gullies are about 3,000 feet (900 meters) long and 100 feet (30 m) wide, researchers said. They bear a striking resemblance to channels carved by "debris flows" here on Earth, which occur when a small amount of water gets dirt and small rocks moving.
...


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