Matter and the universe

Insights from the archives of the solar system

The ROSINA mass spectrometer, developed and built in Bern, studied comet Chury as part of the Rosetta mission from 2014 to 2016. In 2020, several studies based on ROSINA data were published, providing new insights into the comet and on the formation and development of our solar system.

Comets are objects that have evolved very little since the planets were formed. In a sense, they are therefore the archives of the solar system, and determining their composition could also contribute to a better understanding of the formation of the planets.

For over two years, the Rosetta mission of the European Space Agency ESA carried out a detailed examination of the comet 67P/Churyumov-Gerasimenko, called Chury for short (see info box). One of the experiments of the mission was the mass spectrometer ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) which was developed, built and tested under the leadership of the University of Bern and the data of which is still being evaluated.

Interstellar journey of life’s building block

Phosphorus, present in our DNA and cell membranes, is an essential element for life. But how it became available on the early Earth when life appeared here about four billion years ago is something of a mystery.

For the first time, astronomers – among them researchers from the University of Bern – have now been able to show that molecules containing phosphorus, such as phosphorus monoxide, are created in star-forming regions and probably came to Earth with comets. In order to follow the trail of this phosphorus monoxide, researchers combined data from the Bern mass spectrometer ROSINA with data from the giant telescope Atacama Large Millimeter/Submillimeter Array ALMA, operated high on the Chajnantor plateau in the Chilean Atacama desert by the European Southern Observatory (ESO).

Kathrin Altwegg, the principal researcher for ROSINA and co-author of the study published in January 2020, explains: “Comets most probably delivered large amounts of organic compounds to the Earth. The documentation of the trail of phosphorus monoxide strengthens this link between comets and life on Earth.”

Flight through the comet’s dust cloud

A further study based on data from ROSINA, which was also published in January 2020, has found an explanation for why very little nitrogen could previously be accounted for in the nebulous covering of comets: The building block for life predominantly occurs in the form of ammonium salts, the occurrence of which could not previously be measured.

Less than a month before the end of the Rosetta mission, the space probe was just 1.9 km above the surface of Chury as it flew through a dust cloud from the comet. This resulted in a direct impact of dust in the ion source of ROSINA. Thanks to this flight through the dust cloud, it was possible to detect substances that had never been measured before. In particular, the incidence of ammonia, the chemical compound of nitrogen and hydrogen with the formula NH3, was suddenly many times greater. “As a salt, ammonia has a much higher evaporation temperature than ice and is therefore mostly present in the form of a solid in the cold environment of the comet,” explains Katrin Altwegg.

The ammonium salts discovered include several astrobiologically relevant molecules which may result in the development of urea, amino acids, adenine and nucleotides. Kathrin Altwegg says: “This is definitely a further indication that comet impacts may be linked with the emergence of life on Earth.”

Comet’s aurora

In September 2020, a study was published which, also thanks to data from ROSINA, describes a further fascinating phenomenon of Chury.

On Earth, auroras, also called northern lights, have always fascinated people. An international consortium involving the University of Bern has now discovered such auroras in the ultraviolet wavelength range at comet Chury.

This animation shows the key stages of the mechanism by which this aurora is produced © ESA (spacecraft: ESA/ATG medialab)

The researchers were able to prove that in the case of Chury, solar wind electrons are accelerated toward the comet and strike the gas in the coma – the gas around the comet. “Since this process is very high energy, the resulting glow is also highly energized and therefore in the ultraviolet range, which is invisible to the human eye,” explains Martin Rubin, co-author of the study from the Physics Institute at the University of Bern. These UV emissions had in fact been observed earlier at Chury. At that time though it was wrongly assumed that these emissions were caused by particles of sunlight, known as photons, and not in fact by the solar wind electrons, now proved by the recent study.

“The analysis was complicated and required data from various instruments, including ROSINA,” explains Kathrin Altwegg. The study is evidence that our understanding can be deepened and new insights gained by using data from different teams, instruments and computer models. And this years after the end of the active phase of the Rosetta mission in 2016.