Our Cosmic Vicinity
Space missions are conducted over years and decades. These missions, their experiments and measurement campaign are truly “Generation Projects”. In this article, I would like to share briefly my personal story, linked with one of the largest unmanned missions: Cassini
The computer I am currently using to write this article… the desk… apartment… city… country… continent… planet… Solar System… Milky Way… Galactic Cluster… Cosmos…
Zooming out from our well known surroundings may be depressing. You realize the vastness and magnitudes of the Universe. At the same time it is astounding what the human mind achieved in the last couple of centuries. Driven by the everlasting curiosity to find not only our cosmic origin, but also our place in the cosmos we are willing to conduct experiments, observations, theoretical work and sending out robotic probes into our planetary neighbourhood.
You may have seen breath-taking pictures from other planets, galaxies and nebulae. You may have heard of “generation projects” trying to reveal nature’s secrets and hidden scientific gems that can be added to our extending knowledge of the cosmos. But how is this scientific work being done? Who are the people and their stories behind it? Here, I would like to share briefly my personal story. My passion and link to space science and how the line of thought is created to tackle a scientific question. Of course I did not dedicate my life to a particular analysis topic. Scientific work is like finding and creating many puzzle pieces that are later (hopefully) used in a larger tessellation. One of these questions was part of my Ph.D. thesis, to extend or continue the work of others. After all, scientists are …
My personal story …
The 1990s’, Elementary school. As a child I was interested in observing nature, but without any particular focus on a certain topic. But in the mid 90s’ it changed.
US-American Alan Hale and Thomas Bopp discovered independently a light speck in their telescopes. Slowly moving over time they determined that it is a yet unknown comet: C/1995 O1, also known as Hale-Bopp.
Hale-Bopp was THE Great Comet at the end of the last millennium, visible with the naked eye during daytime. And during that time I was sitting on the balcony with a new telescope observing this ancient “dirty ice ball” (as comets are being called) with the mind of a kid: I had no idea what it was and where is came from. I was just fascinated by it. My interest and passion for the cosmos was sparking.
Below, you see an image of this tremendous comet… well not the solid body but the resulting tails that emerge from gas and dust ejections:
The next couple of years I focused on astronomy. I read dozens of books and bought regularly science magazines to educate myself with space scientific knowledge that was not taught in school. My goal: studying physics with a focus on astronomy and space science.
2009. I passed my secondary school diploma; the “entrance card” for studying in a University in Germany. The first 5 semesters were the difficult ones: theoretical physics, tons of mathematics, lab work, reports, you name it. But I was able to take my first major space science steps in the last Bachelor’s semester: a semester abroad in the Netherlands at the European Space Agency (ESA). There I worked on some simulations (and also public outreach activities) about so called Near-Earth Objects (short: NEOs). These objects are asteroids, rocky worlds, that encounter or home planet quite closely. Telescopes survey the night sky every day to discover, observe and track carefully these potentially harmful objects. My task was to determine an “observation strategy” for these telescopes to maximize the observational output of an observation night. I loved working on this task and my thesis, because the results were taken into account for an actual application! My thesis was not “just another” paperwork that would catch dust in an old shelf.
One may think that an asteroid impact is a quite abstract topic and great content for a Hollywood movie. But consider that in 2013 a rather small (and unknown!) object with a diameter of only 20 meters (65 feet) entered Earth’s atmosphere above the Russian city Chelyabinsk. A huge explosion a few kilometres above the ground lead to burst windows and injuries. Luckily there were no casualties.
2012. I got my Bachelor’s degree! Time for a new city and experiences since I had to enrol in a Master’s program. The city I chose: Göttingen (central Germany). I was lucky! My new apartment was only 5 “Bike-Minutes” away from the campus. Amazing. But shortly after entering the 7th semester a student job offer was posted in the physic’s department hall: calibration / lab work on a spacecraft instrument. Wow. That’s something for me, I thought! The instrument was the Dust Impact Monitor on-board the spacecraft Rosetta/Philae that flew at that time already to the comet 67P/Churyumov–Gerasimenko. Its time of arrival at the comet: November 2014; and some work needed to be done prior to the landing on the comet’s surface.
I mailed my future supervisor and we arranged an appointment at the institute. But… it was not on the campus. With the bus, train and by feet combined it was 90 minutes away. Science requires sacrificies I thought. And this sacrifice was not enough. The day I went to the institute I planned some extra time. The weather prediction was bad and a snowstorm was heading towards the area of Göttingen. I took the train that was heading to the neighboring town to catch up a bus that would drive directly to the institute. But the snow storm was severe. The train reached its destination with some delay but the buses were cancelled. So I decided to hike the rest 6 km through the snowstorm. Somehow I will find it, I thought. But the conditions worsen and it took me over 2 hours to reach my future institute. Although I planned some time ahead I reached it over 90 minutes late. But my future supervisor was not mad after all. A few months later he joked that he could not reject me at all after the afternoon-snowstorm-meander-hike I took.
Finally, 2014 the Rosetta/Philae spacecraft reached the comet.The lander was deployed, bounced a few times on the surface and we conducted our measurement campaign. The complete team from Germany, Mexiko, Japan and Hungary was sitting together with all other experiment teams in the lander centre in Cologne. Waiting for the confirmed lander deployement. Waiting for the first images from the comet and waiting for the first data to analyse. This week was a blast! An unforgettable experience for me; grateful that I was part of this mission and team.
Take a look at 67P as is was seen by the spacecraft Rosetta. You can clearly see white “jets” and “curtins”: the ejection streams of dust and gas.
In parallel, I worked on my master thesis that was later the fundament of my Ph.D. thesis: Cassini’s Cosmic Dust Analyzer.
… linked with the Cassini mission
The Cassini-Huygens mission; designed, launched and operated collaboratively by the European Space Agency (Huygens) and NASA (Cassini) dates back to the 80s where first design studies were attempted. The objective of Cassini-Huygens was ambitious: Cassini should visit the ring world Saturn, carrying a lander that should land and conduct measurements on Saturn’s mysterious moon Titan. Titan, a world that was completely hidden under a thick layer of clouds and fog, was puzzling. Organic chemistry, a dense atmosphere and other previous observations inspired scientists and engineers to visit this foreign world.
Then, after years of designing, testing and setting everything up Cassini and its piggybacked lander Huygens were launched into space in October 1997. I was 7 years old.
A few years later, in 2004, Cassini reached its destination: Saturn and its vast system of moons. The interplanetary space trip took over 7 years with miscellaneous visits (so called fly-bys) at Venus (twice) or Saturn’s larger gas giant brother Jupiter. 2005, the probe Huygens landed successfully on the moon Titan. Images, data and even sound was recorded and sent back to Earth, revealing Titan’s secrets below its thick cloud. Meanwhile, I was sitting in secondary school, 14 years old (with no clue at all that my life journey would bring me there).
In the next couple of years Cassini orbited Saturn dozens of times. Recorded, stored and sent a huge amount of data. Visited several moons, and helped us to understand this ring world. One of my personal highlights was a scientific paper published by Postberg et al. (2009) who conducted measurements with the Cosmic Dust Analyzer (CDA) in the vicinity of the moon Enceladus, who was known for cryo-vulcanic activities (so … “ice volcanos”). They found mineral components in some ice particles that were ejected by Enceladus. And these minerals lead to a major conclusion: there has to be liquid water below the ice surface of this moon. Liquid water in our Solar System, on a foreign moon, at a distance of 10 times the distance between Earth and Sun. What a discovery! That year, I just finished secondary school and started studying.
The Cosmic Dust Analyzer. Talking about “Cosmic Dust” leads always to some kind of chuckles… yeah, yeah I know, dust at home, you need to vacuum it etc. I have heard all jokes during my thesis time, but let me tell you this: cosmic dust is an amazing topic. These tiny particles contain so much information about their origin, formation, and allow one to derive tremendous conclusions (like the liquid water discovery). Having a scientific deep dive into cosmic dust, the Cassini mission, its results and the CDA would lead to a book, and not a proper sized Medium article. But let me try to explain the physics behind the CDA quickly and take a close look at the instrument’s image:
CDA’s most prominent sub-system was the Dust Analyzer whose most apparent feature was the large opening of around 50 cm (around 1.6 feet). Imagine it as a tube with a wall at the end. Dust particles with a size of the width of a hair fly into this instrument with several (!) kilometers / miles per second. They impact the wall, and disintegrate into their molecular and atomic components. These components are then detected and distinguished in a device called “time of flight spectrometer”. Besides their chemical composition, the Dust Analyzer was also capable of determining their charge, size, impact velocity and other properties.
Where we (the Solar System) are heading
We few years later, between 2015 and 2019, after finishing my Bachelor’s and Master’s degree I got the chance to work on the Cosmic Dust Analyzer (CDA) directly at the CDA team that was located in Stuttgart. One of my tasks was to create and code some new methods to derive the dynamics of these dust particles (so where did they come from? What was the shape of their flight path around Saturn? Are there any correlations with the rings? And so on).
During my studies one paper was published that caught my attention: In 2016 Altobelli et al. (2016) found a few dust particles that were so fast that they must have come from outer space. And with outer space I do not mean the Solar System, but our stellar neighbourhood; coming from other Solar Systems or very distant gas or dust regions. How did Altobelli et al. now that? Well, previous space missions found a region in the sky where dust and gas comes from (with a very high speed). Similar like … a headwind. Imagine our cosmic vicinity like our Earth’s atmosphere during a windless summer day. You do not feel any wind coming from any direction. But if you take a walk, or ride with your bike you feel the wind blowing into your face. You are moving relatively to this calm atmosphere. This analogy applies to our Solar System: We are surrounded by interstellar dust and gas clouds and we move with respect to these clouds. The result: a “cosmic headwind” that can be measured. This wind and the movement of our Sun with respect to our star-neighbours can be seen below:
The CDA was pointing to this headwind direction from time to time and et voilà: we caught some of these galactic particles that revealed us the nature and composition of our cosmic neighbourhood!
Taking these information into account I used my algorithms and code to determine the “headwind” direction of our Solar System. Furthermore, I compared it with previous results to see whether the results are feasible. After all: they made perfect sense and the “headwind” direction of our Solar System did not change over the last decades!
My resulting science image (shown below, credit by me) is a little bit more complex than the illustration that was shown above, however there is one main message: CDA’s result (Albin et al. (2016)) corresponds nicely to a previous publication by Landgraf et al. (2000). Do not bother about the confusing nature of scientific images and papers. A scientific deep dive is something for a future article.
So… that’s it?
Describing my personal journey, Cassini’s story, CDA’s scientific discoveries and a fraction of my thesis is only a very, very tiny light spot in a huge scientific laser show. Hundreds of scientists work on miscellaneous topics and the “breathtaking” ones are occasionally shown and explained in the mass media. So didn’t I discover something completely new and overwhelming? That’s for others to judge. Maybe, some other students and researchers will work on the data, algorithms and code heritage I left behind. Since, science is nothing but …
Thomas
Literature
Postberg, F., Kempf, S., Schmidt, J. et al. Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus. Nature 459, 1098–1101 (2009). https://doi.org/10.1038/nature08046
N. Altobelli, F. Postberg, K. Fiege, M. Trieloff, H. Kimura, V. J. Sterken, H.-W. Hsu, J. Hillier, N. Khawaja, G. Moragas-Klostermeyer, J. Blum, M. Burton, R. Srama, S. Kempf, E. Gruen. Flux and composition of interstellar dust at Saturn from Cassini’s Cosmic Dust Analyzer. Science 352, Issue 6283, pp. 312–318 (2016). DOI: 10.1126/science.aac6397
