NEOWISE series of infrared images of comet C/2012 K1 (PanSTARRS) on May 20, 2014. Credit: NASA/JPL
An international team of researchers led by Martin Cordiner of NASA’s Goddard Space Flight Center has conducted measurements of H3OH (methanol) emission from comet C/2012 K1 (PanSTARRS) that could yield invaluable information about cometary compositions and provide insights on the formation of our solar system.
ALMA, thanks to its unprecedented resolution and sensitivity, was previously used to study the distributions of HCN (hydrogen cyanide), HNC (hydrogen isocyanide) and H2CO (formaldehyde) in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON). Now, the facility obtained new information on the distribution and temperature of methanol in the inner coma of comet C/2012 K1 (PanSTARRS). The observations were conducted on June 28-29, 2014, when the comet was very bright (magnitude 8.5), visible through a small telescope and even binoculars, and relatively near Earth at a distance of nearly 2 astronomical units (AU).
“Detection of 12-14 emission lines of CH3OH on each day permitted the derivation of spatially-resolved rotational temperature profiles (averaged along the line of sight), for the innermost 5,000 km of the coma,” the scientists wrote.
C/2012 K1 (PanSTARRS) is an Oort cloud comet discovered on May 17, 2012 using Pan-STARRS telescope located on the island of Maui in Hawaii. The comet came to perihelion on Aug. 27, 2014, 1.05 AU from the sun. Thus, the summer of 2014 offered astronomers a great chance to observe this icy planetesimal in detail.
Comets are believed to be frozen leftovers from the formation of the solar system around 4.5 billion years ago. They are pristine and therefore may hold clues to how the solar system was made. Finding an organic compound like methanol on a comet hints that these icy bodies could have been a source of the complex organic molecules necessary for life.
Methanol, thanks to its abundance in comets and its complex energy level structure is an easily detectable molecule for probing the cometary coma temperature at radio and submillimeter wavelengths. ALMA enabled spatially resolved 2D measurements of the coma’s rotational temperatures. They detected large variations in the methanol rotational temperature in C/2012 K1 over ~1,000 kms (sky-projected distance), likely caused by changes in the coma kinetic temperature, mainly due to adiabatic cooling, and heating through solar irradiation.
The scientists called for further high resolution observations and modelling that could yield better information about the coma thermal physics and molecular excitation, and assist in more accurate determination of cometary compositions. They also also emphasized that there is still a lack of understanding concerning the physical and chemical structure of the near-nucleus cometary coma at distances less than a few thousand kilometers from the nucleus.
http://phys.org/news/2016-02-scientists-methyl-alcohol-emission-comet.htmljCp  http://arxiv.org/abs/1602.03488
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