[meteorite-list] NEOWISE Identifies Greenhouse Gases in Comets

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4776

NEOWISE Identifies Greenhouse Gases in Comets
Jet Propulsion Laboratory
November 23, 2015

After its launch in 2009, NASA's NEOWISE spacecraft observed 163 comets 
during the WISE/NEOWISE prime mission. This sample from the space telescope 
represents the largest infrared survey of comets to date. Data from the 
survey are giving new insights into the dust, comet nucleus sizes, and 
production rates for difficult-to-observe gases like carbon dioxide and 
carbon monoxide. Results of the NEOWISE census of comets were recently 
published in the Astrophysical Journal.

Carbon monoxide (CO) and carbon dioxide (CO2) are common molecules found 
in the environment of the early solar system, and in comets. In most circumstances, 
water-ice sublimation likely drives the activity in comets when they come 
nearest to the sun, but at larger distances and colder temperatures, other 
common molecules like CO and CO2 may be the main drivers. Spaceborne carbon 
dioxide and carbon monoxide are difficult to directly detect from the 
ground because their abundance in Earth's own atmosphere obscures the 
signal. The NEOWISE spacecraft soars high above Earth's atmosphere, making 
these measurements of a comet's gas emissions possible.

"This is the first time we've seen such large statistical evidence of 
carbon monoxide taking over as a comet's gas of choice when they are farther 
out from the sun," said James Bauer, deputy principal investigator of 
the NEOWISE mission from NASA's Jet Propulsion Laboratory in Pasadena, 
California, and author of a paper on the subject. "By emitting what is 
likely mostly carbon monoxide beyond four astronomical units (4 times 
the Earth-Sun distance; about 370 million miles, 600 million kilometers) 
it shows us that comets may have stored most of the gases when they formed, 
and secured them over billions of years. Most of the comets that we observed 
as active beyond 4 AU are long-period comets, comets with orbital periods 
greater than 200 years that spend most of their time beyond Neptune's 
orbit."

While the amount of carbon monoxide and dioxide increases relative to 
ejected dust as a comet gets closer to the sun, the percentage of these 
two gases, when compared to other volatile gases, decreases.

"As they get closer to the sun, these comets seem to produce a prodigious 
amount of carbon dioxide," said Bauer. "Your average comet sampled by 
NEOWISE would expel enough carbon dioxide to provide the bubble power 
for thousands of cans of soda per second."

The pre-print version of this paper is available at: http://arxiv.org/abs/1509.08446

The NEOWISE mission hunts for near-Earth objects using the Wide-field 
Infrared Survey Explorer (WISE) spacecraft. Funded by NASA's Planetary 
Science division, the NEOWISE project uses images taken by the spacecraft 
to look for asteroids and comets, providing a rich source of measurements 
of solar system objects at infrared wavelengths. These measurements include 
emission lines that are difficult or impossible to detect directly from 
the ground.


Media Contact

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle at jpl.nasa.gov 

2015-355