Data from instruments conducted by the Southwest Research Institute aboard ESA’s Rosetta spacecraft helped uncover unique UV auroral emissions around the irregularly shaped comet 67P. Although these aurors are out of the visible spectra, other aurors have been seen on various planets and moons in our solar system and even around a distant star. Photo credit: Courtesy of ESA / Rosetta / NAVCAM
ESA’s Rosetta mission discovers a unique aurora near comet 67P / Churyumov-Gerasimenko.
Data from instruments at the Southwest Research Institute aboard ESA’s Rosetta spacecraft helped reveal auroral emissions in the far ultraviolet around a comet for the first time.
Aurors are formed on earth when charged particles from the sun follow the magnetic field lines of our planet to the north and south poles. There, sun particles meet atoms and molecules in the earth’s atmosphere and create shimmering curtains of colored light in the sky at high latitudes. Similar phenomena have been observed on various planets and moons in our solar system and even around a distant star. SwRI’s instruments, the Alice Fern Ultraviolet Spectrograph (FUV) and the Ion and Electron Sensor (IES), helped detect these novel phenomena on Comet 67P / Churyumov-Gerasimenko (67P / CG).
“Charged particles from the sun that flow onto the comet in the solar wind interact with the gas surrounding the comet’s icy, dusty core to form the aurors,” said Dr. Jim Burch, Vice President of SwRI, who directs IES. “The IES instrument discovered the electrons that caused the aurora.”
The gas envelope around 67P / CG, known as “coma”, is excited by the sun particles and glows in ultraviolet light, an interaction that is recorded by the Alice FUV instrument.
“At first we thought the ultraviolet emissions from Comet 67P were phenomena known as ‘daylight,’ a process caused by the interaction of solar photons with cometary gas,” said Dr. Joel Parker from SwRI, who runs the Alice Spectrograph. “We were amazed to discover that the UV emissions are aurora, driven not by photons but by electrons in the solar wind that break water and other molecules in a coma and accelerate in the comet’s nearby area. The resulting excited atoms make this distinctive light. ”
Dr. Marina Galand from Imperial College London led a team that used a physics-based model to integrate measurements made by various instruments on board Rosetta.
“That way, we didn’t have to rely on a single set of data from an instrument,” said Galand, lead author of a Nature Astronomy paper that outlines this discovery. “Instead, we could put together a large data set with multiple instruments to get a better picture of what was going on. This allowed us to clearly identify how the ultraviolet atomic emissions from 67P / CG form and to reveal their auroral nature. ”
“I studied the aurors of the earth for five decades,” said Burch. “It is surprising and fascinating to find aurors around 67P that lack a magnetic field.”
After rendezvous with 67P / CG in 2014-2016, Rosetta has provided a wealth of data showing how the sun and solar wind interact with comets. In addition to discovering these comet aurora, the spaceship was the first to orbit the core of a comet, the first to fly next to a comet as it entered the inner solar system, and the first to send a lander to the surface of a comet.
For more about this research:
Reference: “Far-ultraviolet aurora identified on comet 67P / Churyumov-Gerasimenko” by M. Galand, PD Feldman, D. Bockelée-Morvan, N. Biver, Y.-C. Cheng, G. Rinaldi, M. Rubin, K. Altwegg, J. Deca, A. Beth, P. Stephenson, KL Heritier, P. Henri, J. Wm. Parker, C. Carr, AI Eriksson and J. Burch, September 21, 2020, Natural astronomy.
DOI: 10.1038 / s41550-020-1171-7
Other instruments that contributed to this research were Rosetta’s Langmuir Probe (LAP), the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), the Microwave Instrument for the Rosetta Orbiter (MIRO), and the Visible and InfraRated Thermal Imaging Spectrometer (VIRTIS).
Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta’s Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. Airbus Defense and Space built the Rosetta spacecraft. NASA’s Jet Propulsion Laboratory (JPL) manages the US contribution of the Rosetta Mission to NASA’s Science Mission Directorate in Washington under a contract with the California Institute of Technology (Caltech). JPL also built the microwave instrument for the Rosetta Orbiter and houses its lead researcher, Dr. Mark Hofstadter. SwRI (San Antonio and Boulder, Colorado) developed the ion and electron sensor and Alice instrument of the Rosetta orbiter and is home to its principal researchers.
