Comet C/2014 Q2 (Lovejoy) was analysed in February 2015, using infrared spectroscopy at the Keck Observatory in Hawaii, shortly after Lovejoy passed its closest approach to the Sun.

Investigators paid particular interest in measuring deuterium (D), an isotope of hydrogen (H) found in water. The measurements of “D-to-H” in cometary water yield the amount of water these icy bodies deliver to Earth’s oceans.

While previous observations of water in most comets have found that it differs from water on Earth in the ratio of hydrogen to deuterium, the Lovejoy investigation reveals a new wrinkle in the scientific understanding of cometary water. The only differences were found in Jupiter family comet 103P/Hartely 2. This difference in the “D-to-H ratio” implied that comets may only have contributed a tiny fraction of Earth’s water, and that it was much more likely asteroids that did the job.

According to a recently published paper, “Ground-based Detection of Deuterated Water in Comet C/2014 Q2 (Lovejoy) at IR Wavelengths” in The Astrophysical Journal Letters, a comet’s D-to-H ratio may vary in its distance from the Sun.

Lead author Lucas Paganini, a planetary scientist at Catholic University of America and the NASA Goddard Space Flight Center. He also is a research assistant at the Goddard Center for Astrobiology, stated, “We did ground-based observations to measure water and heavy water (HDO) and compared to measurements before the comet reached perihelion using space and ground-based telescopes. We also studied the overall chemical composition of comets. Not only water, but we also studied volatiles of importance, like methane and ethane and so forth.”

The main astro-biological implication is the differences in the D-to-H ratios of comets helps explain where the comet was formed, and how water evolves during the lifetime of a comet. This knowledge in turn helps investigators better understand how water collected and travelled in the early Solar System. Water is a key molecule of life, which is why this is one of the key questions that cometary scientists are trying to understand.

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