Washington – Comet Lovejoy put up a spectacular show last year as it zoomed past the Sun, but while the visuals were great, the trip selectively altered the production of one form of water in the comet, a new NASA study suggests.
This particular effect wasn’t observed by astronomers before, but a team of astronomers including the W M Keck Observatory on Mauna Kea in the US observed the comet at infrared wavelengths a few days after Lovejoy passed its perihelion — or closest point to the Sun.
The observation was focused on Lovejoy’s water, simultaneously measuring the release of H2O along with production of a heavier form of water, HDO. Water molecules consist of two hydrogen atoms and one oxygen atom. A hydrogen atom has one proton, but when it also includes a neutron, that heavier hydrogen isotope is called deuterium, or the “D” in HDO.
Astronomers calculated the D-to-H ratio — a chemical fingerprint that provides clues about exactly where comets (or asteroids) formed within the cloud of material that surrounded the young Sun in the early days of the solar system. Researchers also use the D-to-H value to try to understand how much of Earth’s water may have come from comets versus asteroids.
The scientists compared their findings from the Keck observations with another team’s observations made before the comet reached perihelion, using both space- and ground-based telescopes, and found an unexpected difference. After perihelion, the output of HDO was two to three times higher, while the output of H2O remained essentially constant. This meant that the D-to-H ratio was two to three times higher than the values reported earlier.
Changes in the water production are expected as comets approach the Sun, but previous understanding suggested that the release of these different forms of water normally rise or fall more-or-less together, maintaining a consistent D-to-H value. The new findings suggest this may not be the case. The research was published in the Astrophysical Journal Letter.