Baking a Comet
from Gerhard Holtkamp, 16. June 2011, 20:36
What do comets look like up close? If you want to know you can either take a spacecraft and fly there or you can prepare one in your kitchen...
Canadian astronomer Dr.Bill Sherwood has a keen interest in comets. But while other astronomers are content to study pictures or spectra taken by telescopes on Earth or analyse the reams of data generated by spacecraft he likes to put his hands on them. Lacking suitable transportation into space he had an ingenious idea: Prepare one yourself!
Attendants at a special event held at the European Space Operations Centre (ESOC) in Darmstadt on 15-JUNE-2011 celebrating 25 years of cometary science at ESA (looking back at the pioneering Giotto mission and forward to the present Rosetta mission) got a first hand look at how it is done as Dr.Sherwood was "baking" a comet live on stage while the various interviews and presentations took place next to it.
The recipe goes like this: While we do not (yet) know exactly how comets formed we do know the major constituents and also many minor ingredients present with their rough percentages. We also have a good idea about density and some vague ideas about the internal structure.
So start with plenty of water which makes up about 80% of the comet, add a lot of CO2 in the form of dry ice, then put in the other substances we know about like Carbon, Sodium, Ammonia, Nitrogen, Phosphorus, Potassium, Iron, Zinc, Magnesium, Talc, Alcohol and some more complicated organic substances. You may even add a little vinegar as radio astronomers have detected it in comets!
Put all of this in a large plastic bag and knead it like the dough of a cake. Make sure you wear thickly insulated gloves as your hands would freeze due to the dry ice. After about an hour (ideal for doing this presentation in schools to interest students in science) something black and icy and highly porous can be taken out of the plastic bag. The comet is ready. "No two comets ever come out the same - they are all different, just like real comets. Their surface is completely uneven in composition and structure."
Dr.Sherwood had an important advice: "DON'T TRY THIS AT HOME!" If done improperly you risk some minor (or major) explosions. You got to know which kind of dry ice to use (pellet size etc.) and some of the other ingredients might cause problems too. "Traces of this will stick to my hands for some days - enough for sniffers at airport security to give an alarm. I better plan an extra hour for check-in tomorrow on my return flight to Canada..."
Being at room temperature the comets shrank to about half size within two or three hours which shows that they are quite good insulators at least compared to the icecream I take out of my freezer! You can see two comets "baked" three hours apart next to each other in the photograph (the park meter records the time of finish).
I have seen some data on comets before - their composition, their physical properties etc. - but it was only now after seeing up close these "freshly baked" objects which try to give as good an approximation as possible to our current understanding what comets are like that I begin to fully appreciate the difficulties of space missions to comets.
In 2014 the European Rosetta spacecraft will reach comet 69P/Churyumov-Gerasimenko. After studying it out of distance for a few months a small lander called Philae will detach itself from the mother craft and touch down on the surface. I knew before that this is not easy. But now I'm aware that it is actually very difficult and many things can go wrong (expected and unexpected). Should it succeed (which I dearly hope) it will be one of the master pieces of ESOC mission operations.
After Dr.Sherwood showed one of his fresh comets to the panel of experts on stage (the picture shows him next to ESA Director of Human Spaceflight and Operations and Head of ESOC Thomas Reiter) I asked him whether he would consider adding strawberries to the recipe just for taste as we are in the midst of the strawberry season. "That wouldn't be a bad idea but I'm a Canadian so I should go for maple sirup!"
Canadian astronomer Dr.Bill Sherwood has a keen interest in comets. But while other astronomers are content to study pictures or spectra taken by telescopes on Earth or analyse the reams of data generated by spacecraft he likes to put his hands on them. Lacking suitable transportation into space he had an ingenious idea: Prepare one yourself!
Attendants at a special event held at the European Space Operations Centre (ESOC) in Darmstadt on 15-JUNE-2011 celebrating 25 years of cometary science at ESA (looking back at the pioneering Giotto mission and forward to the present Rosetta mission) got a first hand look at how it is done as Dr.Sherwood was "baking" a comet live on stage while the various interviews and presentations took place next to it.
The recipe goes like this: While we do not (yet) know exactly how comets formed we do know the major constituents and also many minor ingredients present with their rough percentages. We also have a good idea about density and some vague ideas about the internal structure.
So start with plenty of water which makes up about 80% of the comet, add a lot of CO2 in the form of dry ice, then put in the other substances we know about like Carbon, Sodium, Ammonia, Nitrogen, Phosphorus, Potassium, Iron, Zinc, Magnesium, Talc, Alcohol and some more complicated organic substances. You may even add a little vinegar as radio astronomers have detected it in comets!
Put all of this in a large plastic bag and knead it like the dough of a cake. Make sure you wear thickly insulated gloves as your hands would freeze due to the dry ice. After about an hour (ideal for doing this presentation in schools to interest students in science) something black and icy and highly porous can be taken out of the plastic bag. The comet is ready. "No two comets ever come out the same - they are all different, just like real comets. Their surface is completely uneven in composition and structure."
Dr.Sherwood had an important advice: "DON'T TRY THIS AT HOME!" If done improperly you risk some minor (or major) explosions. You got to know which kind of dry ice to use (pellet size etc.) and some of the other ingredients might cause problems too. "Traces of this will stick to my hands for some days - enough for sniffers at airport security to give an alarm. I better plan an extra hour for check-in tomorrow on my return flight to Canada..."
Being at room temperature the comets shrank to about half size within two or three hours which shows that they are quite good insulators at least compared to the icecream I take out of my freezer! You can see two comets "baked" three hours apart next to each other in the photograph (the park meter records the time of finish).I have seen some data on comets before - their composition, their physical properties etc. - but it was only now after seeing up close these "freshly baked" objects which try to give as good an approximation as possible to our current understanding what comets are like that I begin to fully appreciate the difficulties of space missions to comets.
In 2014 the European Rosetta spacecraft will reach comet 69P/Churyumov-Gerasimenko. After studying it out of distance for a few months a small lander called Philae will detach itself from the mother craft and touch down on the surface. I knew before that this is not easy. But now I'm aware that it is actually very difficult and many things can go wrong (expected and unexpected). Should it succeed (which I dearly hope) it will be one of the master pieces of ESOC mission operations.
After Dr.Sherwood showed one of his fresh comets to the panel of experts on stage (the picture shows him next to ESA Director of Human Spaceflight and Operations and Head of ESOC Thomas Reiter) I asked him whether he would consider adding strawberries to the recipe just for taste as we are in the midst of the strawberry season. "That wouldn't be a bad idea but I'm a Canadian so I should go for maple sirup!"
