Thursday, May 23, 2019

Comet Provides New Clues to Origins of Earth"s Oceans - Jet Propulsion Laboratory


The mystery of why Earth has so much water, allowing our “blue

marble” to support an astounding array of life, is clearer with new

research into comets. Comets are like snowballs of rock, dust, ice, and other

frozen chemicals that vaporize as they get closer to the Sun, producing the

tails seen in images. A new study reveals that the

water in many comets may share a common origin with Earth’s oceans, reinforcing

the idea that comets played a key role in bringing water to our planet billions

of years ago.


The Stratospheric Observatory for Infrared Astronomy, SOFIA, the world’s largest airborne observatory, observed

Comet Wirtanen as it made its closest approach to Earth inDecember

2018
. Data collected from the high-flying observatory

found that this comet contains “ocean-like” water. Comparing

this with information about other comets, scientists suggest in a new study

that many more comets than previously thought could have delivered water to

Earth. The findings were published in Astronomy and

Astrophysics Letters.


“We have identified a vast

reservoir of Earth-like water in the outer reaches of the solar system,”

said Darek Lis, a scientist at NASA’s Jet Propulsion Laboratory, in Pasadena,

California, and lead author of the study. “Water was crucial for the

development of life as we know it. We not only want to understand how Earth’s

water was delivered, but also if this process could work in other planetary

systems.”


Dirty Snowballs


Planets

form
from debris orbiting in a disk shape around a

star; small pieces of debris can stick together and grow larger over time.

Leftover debris remains in regions of our own solar system like the Kuiper Belt,

beyond Neptune, or theOort Cloud,

far past Pluto. Comets come from these areas, but we can only see them when

their orbits bring them closer to the Sun. The heat from the Sun causes some of

the dirty snow to vaporize, creating the fuzzy halo or “coma” of

water vapor, dust and ice grains seen in comet images.


Scientists predict that the water in Earth’s

oceans came from water-carrying bodies in the early solar system that collided

with our planet, similar to today’s ice-rich asteroids or comets. But

scientists do not know where in the formative disk these objects originated.


Water

Types


Water is also known by its chemical name H2O

because it’s made of two hydrogen atoms and one oxygen atom. But using special

instruments, scientists can detect two types: regular water, H2O,

and heavy water, HDO, which has an extra neutrally-charged particle called a

neutron inside one of the hydrogen atoms. Scientists compare the amount of

heavy to regular water in comets. If comets have the same ratio of these water

types as Earth’s oceans, it indicates that the water in both may share a common

origin.


But measuring this ratio is difficult. Ground

and space telescopes can study this level of detail in comets only when they

pass near Earth, and missions to visit comets, like Rosetta, are rare. Scientists have only been able to study this ratio in about

a dozen comets since the 1980s. Additionally, it is difficult

to study a comet’s water from the ground because water in Earth’s atmosphere blocks

its signatures.


New Observations


Observing at high altitudes above much of the

Earth’s atmospheric water allowed SOFIA to accurately measure the ratio of

regular to heavy water in Comet Wirtanen. The data showed that Comet Wirtanen’s

water ratio is the same as the Earth’s oceans.


When the team compared the new SOFIA data with previous

studies of comets, they found a surprising commonality. The ratio of regular to

heavy water was not linked to the origin of the comets – whether they were from

the Oort Cloud or the Kuiper Belt. Instead, it was related to how much water

was released from ice grains in the comet’s coma compared to directly from the

snowy surface. This could imply that all comets could have a heavy-to-regular

water ratio similar to Earth’s oceans, and that they could have delivered a

large fraction of water to Earth.


“This is the first

time we could relate the heavy-to-regular water ratio of all comets to a single

factor,” noted Dominique Bockelée-Morvan, scientist at the Paris

Observatory and the French National Center for Scientific Research and second

author of the paper. “We may need to rethink how we study comets because

water released from the ice grains appears to be a better indicator of the

overall water ratio than the water released from surface ice.”


More studies are needed to see if these findings

hold true for other comets. The next time a comet is forecast to fly close

enough for this type of study will be in November 2021.


SOFIA, the Stratospheric Observatory

for Infrared Astronomy, is a Boeing 747SP jetliner modified to carry a 106-inch

diameter telescope. It is a joint project of NASA and the German Aerospace

Center, DLR. NASA’s Ames Research Center in California’s Silicon Valley manages

the SOFIA program, science and mission operations in cooperation with the

Universities Space Research Association headquartered in Columbia, Maryland,

and the German SOFIA Institute (DSI) at the University of Stuttgart. The

aircraft is maintained and operated from NASA’s Armstrong Flight Research

Center Building 703, in Palmdale, California.


News Media Contact


Nicholas Veronico


SOFIA Science Center


Ames Research Center, Silicon Valley, California


650-604-4589 / 650-224-8726


nicholas.a.veronico@nasa.gov



Elizabeth Landau


NASA Headquarters, Washington


818-359-3241


elandau@jpl.nasa.gov



Calla Cofield


Jet Propulsion Laboratory, Pasadena, Calif.


626-808-2469


calla.e.cofield@jpl.nasa.gov



2019-097



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