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Comet's water 'like that of
Earth's oceans'
Comet Hartley 2 was also the subject of the Deep Impact probe study
Comet Hartley 2 contains water more like that found on Earth than all the
comets we know about, researchers say.
A study using the Herschel space telescope aimed to measure the fraction
of deuterium, a rare type of hydrogen, present in the comet's water.
Like our oceans, it had half the amount of deuterium seen from other
comets.
The result, published in Nature, hints at the idea that much of the Earth's
water could have initially come from cometary impacts.
Just a few million years after its formation, the early Earth was rocky and
dry; most likely, something brought the water that covers most of the
planet today.
Water has something of a molecular fingerprint in the amount of deuterium
it contains, and only about half a dozen comets have been measured in
this way - and all of them have exhibited a deuterium fraction twice as
high as the oceans.
Asteroids, by contrast, give rise to the meteors and meteorites that arrive
on Earth, making their deuterium fraction more well-established.
Meteoritic material has roughly the same proportion of deuterium that the
Earth's oceans contain, and so the assumption has been that if water
arrived from elsewhere, it came from asteroids.
Clouded measure
Comets carry much more water than asteroids, but it
may or may not be like the water found on Earth
Until now, all of the comets that have been measured have been so-called
Oort Cloud objects, believed to have been formed early in the Solar
System's history in the region of the giant planets Neptune and Uranus and
kicked out to a great distance as they bumped into the planets and each
other.
Comet Hartley 2 is the first "Kuiper Belt" object to undergo the deuterium
analysis. Kuiper belt objects formed not far outside our Solar System, and
comets that originate there have much shorter orbits than those from the
Oort Cloud.
An international team using the Herschel telescope to peer at the comet,
they found it had a deuterium fraction much closer to that of our oceans.
Report co-author Ted Bergin of the University of Michigan said that opened
up the possibility that comets at least contributed to our water supply.
"The reservoir of Earth ocean-like material is much larger than we thought,
and it encompasses cometary material, which we hadn't recognised," he
told BBC News.
"We have to think really hard and try to get a better understanding of
what is going in our Solar System, and whether you can really rule out
comets as the source of Earth's water."
They might not be ruled out, but they are not the definitive answer either;
much of what we believe happened in the early Solar System is based on
computer models.
James Greenwood of Wesleyan University in the US said such models may
need adjusting in light of the new evidence - and that more such studies
are needed to assess whether many Kuiper Belt objects are like Hartley 2.
"If the short-period comets are all like this one comet, then this could be a
significant source of our early water," he told BBC News.
"It opens up a new can of worms for us."
Alessandro Morbidelli of the Observatory of Cote d'Azur argues that the
result shows that the distinction between the potential water sources may
need to be called into question.
"In the past, scientists thought that these asteroids and comets were
completely different classes of bodies. Now, several new results show that
primitive asteroids and comets are brothers and sisters," he told BBC News.
"This new view changes at least the semantics of the question on the
orgin of the Earth's water. The question becomes more technical: 'from
which region of the disc and by which dynamical mechanism came the
(objects) that delivered the water to the Earth?'"
Herschel has some time left to address the question, but what all the
researchers agree is that the Atacama Large Millimeter Array of telescopes
in Chile - which has just shown off its first results - will soon be able to
resolve these questions with never-before-seen sensitivity.
BBC News - Comet's water 'like that of Earth's oceans'
Earth's oceans'
Comet Hartley 2 was also the subject of the Deep Impact probe study
Comet Hartley 2 contains water more like that found on Earth than all the
comets we know about, researchers say.
A study using the Herschel space telescope aimed to measure the fraction
of deuterium, a rare type of hydrogen, present in the comet's water.
Like our oceans, it had half the amount of deuterium seen from other
comets.
The result, published in Nature, hints at the idea that much of the Earth's
water could have initially come from cometary impacts.
Just a few million years after its formation, the early Earth was rocky and
dry; most likely, something brought the water that covers most of the
planet today.
Water has something of a molecular fingerprint in the amount of deuterium
it contains, and only about half a dozen comets have been measured in
this way - and all of them have exhibited a deuterium fraction twice as
high as the oceans.
Asteroids, by contrast, give rise to the meteors and meteorites that arrive
on Earth, making their deuterium fraction more well-established.
Meteoritic material has roughly the same proportion of deuterium that the
Earth's oceans contain, and so the assumption has been that if water
arrived from elsewhere, it came from asteroids.
Clouded measure
Comets carry much more water than asteroids, but it
may or may not be like the water found on Earth
Until now, all of the comets that have been measured have been so-called
Oort Cloud objects, believed to have been formed early in the Solar
System's history in the region of the giant planets Neptune and Uranus and
kicked out to a great distance as they bumped into the planets and each
other.
Comet Hartley 2 is the first "Kuiper Belt" object to undergo the deuterium
analysis. Kuiper belt objects formed not far outside our Solar System, and
comets that originate there have much shorter orbits than those from the
Oort Cloud.
An international team using the Herschel telescope to peer at the comet,
they found it had a deuterium fraction much closer to that of our oceans.
Report co-author Ted Bergin of the University of Michigan said that opened
up the possibility that comets at least contributed to our water supply.
"The reservoir of Earth ocean-like material is much larger than we thought,
and it encompasses cometary material, which we hadn't recognised," he
told BBC News.
"We have to think really hard and try to get a better understanding of
what is going in our Solar System, and whether you can really rule out
comets as the source of Earth's water."
They might not be ruled out, but they are not the definitive answer either;
much of what we believe happened in the early Solar System is based on
computer models.
James Greenwood of Wesleyan University in the US said such models may
need adjusting in light of the new evidence - and that more such studies
are needed to assess whether many Kuiper Belt objects are like Hartley 2.
"If the short-period comets are all like this one comet, then this could be a
significant source of our early water," he told BBC News.
"It opens up a new can of worms for us."
Alessandro Morbidelli of the Observatory of Cote d'Azur argues that the
result shows that the distinction between the potential water sources may
need to be called into question.
"In the past, scientists thought that these asteroids and comets were
completely different classes of bodies. Now, several new results show that
primitive asteroids and comets are brothers and sisters," he told BBC News.
"This new view changes at least the semantics of the question on the
orgin of the Earth's water. The question becomes more technical: 'from
which region of the disc and by which dynamical mechanism came the
(objects) that delivered the water to the Earth?'"
Herschel has some time left to address the question, but what all the
researchers agree is that the Atacama Large Millimeter Array of telescopes
in Chile - which has just shown off its first results - will soon be able to
resolve these questions with never-before-seen sensitivity.
BBC News - Comet's water 'like that of Earth's oceans'