In 2005, SPICAM (http://www.cnes.fr/web/CNES-fr/1951-spicam.php) onboard the satellite of the European Space Agency spacecraft Mars Express (http: //sci.esa .int / March-express /) observes ultraviolet radiation of the red planet. By alignment maneuvers that can not be done too often, it also allows to observe the emissions of the atmosphere of Mars, on the black sky. But whenever Mars Express flew over a magnetic anomaly, ie an area where the crustal magnetic field is intense, SPICAM reveals that the atmospheric UV radiation is increasing.
Jean-Loup Bertaux, SPICAM’s "Principal Investigator" has little doubt that it is the solar wind electrons that excite the atmospheric carbon dioxide and creates auroras similar to our Northern Lights. With Olivier Witasse, my PhD student at the time (now space mission responsible at ESA), we confirm by calculation that it is due to auroral electron energies of about 500 eV. The article is published in Nature in 2005: we discovered the Martian aurora. However, as they occur in wavelengthes invisible to the human eye, is receives low mediatic coverage.
In parallel, the scientific community is tackling a Martian mystery: About three and a half billion years ago, the atmosphere was at least 2 bars - the minimum required to maintain liquid water under carbon dioxide - while today that the water is gone, the atmosphere of Mars is a hundred times more tenuous than the Earth’s. In the past décade, we could draw a likely scenario. First, an escape called "catastrophic", due to a constant bombardment of asteroids, to volcanic eruptions at scales unknown on Earth. Then, over the millennia, a mild but permanent rape due partly to the solar wind, and partly to the solar radiation. It’s the American Janet Luhmann and the French François Leblanc who demonstrated the mechanism of the solar wind, and my team explained that of the solar radiation (Lilensten et al., 2013).
NASA wants the experimental evidence for these mechanisms, and launches the MAVEN spacecraft in 2013 (http://www.nasa.gov/mission_pages/maven/main/index.html). The results are not yet published, and teams are working on them. But already MAVEN confirmed in January 2015 the ultraviolet auroral observations we made ten years earlier.
Between 2007 and 2013, our teams continue comparing SPICAM data and our model, and in parallel, I created the first Planeterrella. A scientific controversy developped around the electronic energies causing auroras: 500 eV or more? To clear up this controversy, I decided to put carbon dioxide into my auroral demonstrator. For this, I created a gas inlet in its third version. But David Bernard, my PhD student, has a better idea: just put a CO2 ice bread in the vacuum chamber. By sublimation under the effect of the vacuum, the gas will remain in slight overpressure and prevent air from entering.
We perform the experience in April, 2015.
Nous équipons la Planeterrella avec un spectromètre à fibre optique / We equip the Planeterrella with an opitc fiber spectrometer (crédit David Bernard / Jean Lilensten, IPAG).
And to our surprise, we see blue auroras. We are stunned.
La Planeterrella simule une planète type Mars. La photographie du haut a servi dans la publication scientifique, et a été reprise sur des millions de sites internet. The Planeterrella simulates a fake Mars. The upper photography was published in the scientific paper, and has been copied in over millions of websites. (Credit: David Bernard / Jean Lilensten, IPAG / UGA / CNRS)
Back in our lab, some bibliography tells us that this radiation due to the CO2 Fox-Duffenbak-Barker band is well known from spectroscopists. Simply, we were ignorant.
The following week, we ask Mathieu Barthélemy to repeat the experience with us and check point by point the full experimental process. The results are confirmed. There was with us a young schoolgirl, third course, Camille. I ask her not to talk about what she saw, and she will keep her word, even to her parents!
En haut, David dans la Planeterrella, après notre première manipe. En bas, notre équipe grenobloise (David à gauche, Mathieu au centre, Jean à droite). (Credit Camille Infante, IPAG)
To complete his thesis, David introduced the atomic data from the FDB band in my ionospheric code. He first simulates the Planeterrella: his calculation corresponds to the observations. He then calculates the light intensity on Mars. But for this we need to know the energy of electron precipitations in the night side, above the magnetic anomalies.
During Europe’s largest geophysical meeting, the general assembly of the EGU in early May 2014, I meet Andrea. She is a young researcher from ESA, who analyzed the Venus Express data (http://www.esa.int/Our_Activities/Space_Science/Venus_Express), the Mars Express clone that observes Venus. Her data on Venus can be easily extrapolated to Mars and David can finish his calculations: the Martian aurora are visible to the naked eye. In addition to the blue emission at 140 km, auroras are green and, above, red (160 kilometres).
I then asked my two friends and former PhD students, Cyril (now researcher at Aalto University, Finland) and Guillaume (now a researcher at NASA) to check our calculations and measurements. They confirm them on all points.
We are ready to write the article. We send it to Planetary and Space Science. The two anonymous referees of the article approve its publication, but not without discussion: for one of them, the fact that auroras are visible with the naked eye does not matter, since there is no human on Mars, and since our scientific instruments are more sensitive than our eyes. For us it is very important: science is not devoid of emotion, and knowing that astronaut on the red soil of Mars could observe, looking up, blue, red and green lights seems important.
Trois interprétations par les co-auteurs de l’article scientifique, montrant à quoi les aurores martiennes bleues doivent ressembler, vues par le rover de la NASA Curiosity, à proximité des anomalies magnétiques de Mars. En réalité, ce bleu se mêle de vert, et au dessus se trouve une couche rouge! Three interpretations by the co-authors of the scientific article, showing how the blue Martian aurora should look like, as seen by the NASA rover Curiosity, near the magnetic anomalies on Mars. In reality, it mixes blue and green emissions, and above stands a red layer! Photomontage NASA/JPL-Caltech/MSSS and Cyril Simon Wedlund (Aalto Univ.)/ / David Bernard (IPAG - CNRS - IUT Montpellier)
Finally, the publication date is announced: 26 May 2015. NASA and CNRS prepare press releases as well as the Aalto University, and the research center in Hungary, where Andrea has found a permanent position.
Immediately, the news runs around the Web. NASA posts it on its cover page. It does not take more than that to attribute the discovery to NASA, much to our amusement. The sites multiply, the news becomes viral...
A Net search on "blue aurora March" quickly gives thousands, and soon hundreds of thousands of references in French and German, up to two millions in English and more in Spanish. What amuses us most is that the three artist views of David and Cyril are everywhere and very quickly become "the first pictures of the blue aurora at Mars taken by NASA". Some even manage to make movies out of them...