New data from NASA’s Microwave Instrument on the Rosetta Orbiter Spacecraft (MIRO) has revealed that the amount of water shedding off of comet 67P/Churyumov-Gerasimenko has been significantly increasing; by the end of the observation period in August, 67P/C-G was shedding 1.2 liters (40 ounces) of water every second, with conditional variations. While the increase isn’t surprising given that the comet is headed for the Sun, getting an up close look at this process will be useful in determining how the comet was formed. MIRO’s principal investigator, Samuel Gulkis, was lead author of the paper, published in a special edition of Science that is dedicated to research from the Rosetta mission.
MIRO is analysing the gases shed off of 67P/C-G, as well as a couple of centimeters under the body’s surface to account for any sublimation that might be occurring there. MIRO is gathering data about ten particular molecules, including water, ammonia, methanol, and carbon monoxide. In addition to measuring temperature, it is also recording the velocity and abundance of the molecules as they are leaving the comet.
"In observations over a period of three months [June through August, 2014], the amount of water in vapour form that the comet was dumping into space grew about tenfold," Gulkis said in a press release. "To be up close and personal with a comet for an extended period of time has provided us with an unprecedented opportunity to see how comets transform from cold, icy bodies to active objects spewing out gas and dust as they get closer to the sun.”
The comet is roughly shaped like a rubber duck, which means that locations are affected differently at different times throughout the comet’s “day”. During that observation time, the researchers were able to determine that the highest amount of activity came from the “neck” of the comet, during the afternoon hours.
"That situation may be changing now that the comet is getting warmer," Gulkis continued. "MIRO observations would need to be carefully analysed to determine which factors, in addition to the sun's warmth, are responsible for the cometary outgassing.”
The team will continue to track the gas pouring off of the comet, as well as where on the comet it is coming from. This will help paint a full picture of how the comet changes as it prepares to make its closest approach to the Sun this August. Additionally, the increased activity could impact Rosetta’s orbit of the comet, which will need to be accounted for. Matters get additionally complicated because the comet isn’t as homogenous as anticipated.
"If we would have just seen a steady increase of gases as we closed in on the comet, there would be no question about the heterogeneity of the nucleus," added Myrtha Hässig from the Southwest Research Institute in San Antonio, who served as lead author on a different paper about the comet’s coma (the shedded dust and gas surrounding the comet) using data from the ROSINA instrument. "Instead we saw spikes in water readings, and a few hours later, a spike in carbon dioxide readings. This variation could be a temperature effect or a seasonal effect, or it could point to the possibility of comet migrations in the early solar system.”
Looking ahead, the researchers will combine data from MIRO and ROSINA in order to better understand how outgassing of comets change over time, which will describe the comet on a very basic level. This will also provide information about how the comet was formed and how it has been evolving since.
