Cometary Aurora May Provide Clues on Solar Wind & Space Weather

The European Space Agency' Rosetta spacecraft was launched in 2004 to observe the comet near Jupiter called comet 67P/Churyumov-Gerasimenko. Although Rosetta's lander Philae landed on the comet in 2014, it was only recently discovered that the comet shared a natural phenomenon with Earth's atmosphere: the northern lights.

The new findings are described in a paper published in the journal Nature Astronomy. Researchers from the United States and Europe collaborated to identify the source of the comet's far-ultraviolet aurora.

On Earth, aurora borealis or the Northern lights are the results of the Sun emitting particles into the system, particularly during solar flares. The particles which are electrically charged emit light after colliding with particles in the Earth's upper atmosphere.

Oxygen hitting solar particles emit red, green, and yellow lights while nitrogen emits blue. Pink, purple, and white are the result of oxygen and nitrogen mixed in the air.

Cometary Aurora

However, the case is not the same on Churyumov-Gerasimenko. Instead of a light show, the ultraviolet light is invisible. The same had been observed on several other comets and some of Jupiter's moons.

Since the nucleus or coma of a comet is darker than charcoal, described the authors, instruments on Earth could detect their emissions. The gas surrounding the coma forms as ice transforms directly into gas, a process called sublimation, as it travels nearer to the Sun.

Observations of the comae in the far-ultraviolet part of the spectrum have revealed that the emissions contain atoms of hydrogen and oxygen. Analyzing the emissions revealed that the gas atoms interact with solar-wind electrons.

The solar-wind electrons, which are charged particles flowing from the sun, are drawn in by the comet's electric field, similar to charged particles arriving on Earth. The interaction results in a cometary aurora.

Instead of emitting colored lights, the solar particles shatter the water molecules to create an ultraviolet glow. Researchers have also reported similar activity of water molecules colliding with sun particles on the moons Europa and Ganymede.

Also, comet 67P lacks a magnetic field, unlike Earth, which is why the Sun's electrons only hit the north and south poles. However, if the comet's properties allowed the invisible aurora to be visible, it would look like a halo surrounding the comet.

Tracking Solar Wind

Marina Galand from Imperial College London describes the comet's glow as one of a kind. "By linking data from numerous Rosetta instruments, we were able to get a better picture of what was going on. This enabled us to unambiguously identify how 67P/C-G's ultraviolet atomic emissions form."

Paul Feldman from Johns Hopkins University explained that the data from Rosetta during "over its two-year visit to the comet have allowed us to rewrite the book on these most exotic inhabitants of our solar system - and by all accounts, there is much more to come."

Galand shared that observing cometary auroras could provide information on the behaviors of the solar wind. Tracking solar wind would then help with space weather forecasts, which are critical since it is the beginning of a new solar cycle.

Read Also: What is the Solar Cycle 25?

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