Approximate location of Comet ISON in our Solar System at the time of the ALMA observations.
Credit: B. Saxton (NRAO/AUI/NSF); NASA/ESA Hubble; M. Cordiner, NASA, et al.
Approximate location of Comet Lemmon in our Solar System at the time of the ALMA observations.
Credit: B. Saxton (NRAO/AUI/NSF); Gerald Rhemann; M. Cordiner, NASA, et al.
The emission from organic molecules in the atmosphere of comet ISON as observed with ALMA.
Credit: B. Saxton (NRAO/AUI/NSF); M. Cordiner, NASA, et al.
The emission from organic molecules in the atmosphere of comet Lemmon as observed with ALMA.
Credit: B. Saxton (NRAO/AUI/NSF); M. Cordiner, NASA, et al.
This rotating 3-D ALMA map shows how HCN molecules are released from the nucleus of comet Lemmon and then spread evenly throughout the atmosphere, or coma. Similar maps revealed that HNC and formaldehyde are produced in the coma, rather than originating from the comet's nucleus. Credit: Visualization by Brian Kent (NRAO/AUI/NSF)
An international team of scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) has made incredible 3D images of the ghostly atmospheres surrounding comets ISON and Lemmon. These new observations provided important insights into how and where comets forge new chemicals, including intriguing organic compounds.
An international team of scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) has made incredible 3D images of the ghostly atmospheres surrounding comets ISON and Lemmon. These new observations provided important insights into how and where comets forge new chemicals, including intriguing organic compounds.
Comets contain some of the oldest
and most pristine materials in our Solar System. Understanding their
unique chemistry could reveal much about the birth of our planet and the
origin of organic compounds that are the building blocks of life.
ALMA's high-resolution observations provided a tantalizing 3D
perspective of the distribution of the molecules within these two
cometary atmospheres, or comas.
“We achieved truly
first-of-a-kind mapping of important molecules that help us understand
the nature of comets,” said team leader Martin Cordiner, a Catholic
University of America astrochemist working at NASA’s Goddard Space
Flight Center in Greenbelt, Maryland.
The critical 3D component
of the ALMA observations was made by combining high-resolution,
two-dimensional images of the comets with high-resolution spectra
obtained from three important organic molecules – hydrogen cyanide
(HCN), hydrogen isocyanide (HNC), and formaldehyde (H2CO). These spectra
were taken at every point in each image. They identified not only the
molecules present but also their velocities, which provided the third
dimension, indicating the depths of the cometary atmospheres.
The
new results revealed that HCN gas flows outward from the nucleus quite
evenly in all directions, whereas HNC is concentrated in clumps and
jets. ALMA’s exquisite resolution could clearly resolve these clumps
moving into different regions of the cometary comas on a day-to-day and
even hour-to-hour basis. These distinctive patterns confirm that the HNC
and H2CO molecules actually form within the coma and provide new
evidence that HNC may be produced by the breakdown of large molecules or
organic dust.
"Understanding organic dust is important, because
such materials are more resistant to destruction during atmospheric
entry, and some could have been delivered intact to the early Earth,
thereby fueling the emergence of life,” said Michael Mumma, director of
the Goddard Center for Astrobiology and a co-author on the study. "These
observations open a new window on this poorly known component of
cometary organics."
“So, not only does ALMA let us identify
individual molecules in the coma, it also gives us the ability to map
their locations with great sensitivity,” said Anthony Remijan, an
astronomer with the National Radio Astronomy Observatory (NRAO) in
Charlottesville, Virginia, and a study co-author.
The observations, published today in the Astrophysical Journal Letters,
were also significant because modest comets like Lemmon and ISON
contain relatively low concentrations of these crucial molecules, making
them difficult to probe in depth with Earth-based telescopes. The few
comprehensive studies of this kind so far have been conducted on
extremely bright comets, such as Hale-Bopp. The present results extend
them to comets of only moderate brightness.
Comet ISON (formally
known as C/2012 S1) was observed with ALMA on November 15-17, 2013,
when it was only 75 million kilometers from the Sun (about half the
distance of the Earth to the Sun). Comet Lemmon (formally known as
C/2012 F6) was observed on June 1-2, 2013, when it was 224 million
kilometers from the Sun (about 1.5 times the distance of the Earth to
the Sun).
"The high sensitivity achieved in these studies paves
the way for observations of perhaps hundreds of the dimmer or more
distant comets,” said Goddard’s Stefanie Milam, a study co-author. “The
findings suggest that it should also be possible to map more complex
molecules that have so far eluded detection in comets.”
This
research was funded by the NASA Astrobiology Institute through the
Goddard Center for Astrobiology and by NASA’s Planetary Atmospheres and
Planetary Astronomy programs.
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The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of Europe, North
America and East Asia in cooperation with the Republic of Chile. ALMA is
funded in Europe by the European Southern Observatory (ESO), in North
America by the U.S. National Science Foundation (NSF) in cooperation
with the National Research Council of Canada (NRC) and the National
Science Council of Taiwan (NSC) and in East Asia by the National
Institutes of Natural Sciences (NINS) of Japan in cooperation with the
Academia Sinica (AS) in Taiwan.
Contacts:
Charles E. Blue, Public Information Officer
Nancy Neal-Jones/Elizabeth Zubritsky
NASA's Goddard Space Flight Center, Greenbelt, Md.
301-286-0039/301-614-5438
