Comet secrets revealed

Upon touching down on Comet 97P, Philae began immediately to collect data to send back to Earth via Rosetta orbiting above the comet. The Rosetta lander also continued to collect data from her suite of instruments. Rosetta Mission engineer Warwick Holmes explains some of the early findings from the Rosetta Mission data.

Point of interest

One of the instruments on board both the Rosetta and Philae spacecraft is a gas chromatograph. To understand how this instrument works, watch Dr Katja Riedel on measuring gas concentrations

Transcript

WARWICK HOLMES

First thing we discovered is the comet is very light. It has half the density of water, so if the comet was on the sea, it would float.

Then we started looking very carefully to try and understand what are some of these strange features? Well, one thing we noticed were these large cylindrical holes that looked like a well that had been dug straight down into the comet. Strange, what on earth is that? So then we did a bit more image processing, and we found that, here in the middle, you can see there is some venting going on. We realised that these were basically vent holes where the volatile chemistry inside the comet, when it gets close to the Sun, it blasts out like a fire hose. So these were the active sites where the venting that creates the tail of a comet seems to be coming from.

And again, we see another vent hole, but this time with this sort of oozing remnant, which is molten gas, which then solidified into a liquid and then froze solid again.

Looking sideways into one of these wells, we notice there are what we call goosebumps on the side. It looks like lots of little golf balls on the surface, and this seems to be one of the theories of how comets formed. They’re formed by lots of little golf balls sticking together. And there’s another theory, which is an aggregated layer theory, but we saw both, in fact, so both theories are in fact correct.

We collected some dust particles out using the orbiter – dust is being blown off – and we could catch those, and then we analysed the dust particles. So even if we didn’t get onto the surface, we could still analyse the material of the comet. And we blast this with an indium beam, and we can get a spectrum showing what materials there are – sodium, magnesium and all the what we call refractory elements that go into making the comet.

And here we have the gas chromatography. This is showing the gases we found. So there’s oxygen, methane, water vapour, carbon monoxide, carbon dioxide. And then we do some mass spectroscopy. And what did we find? Well, we found a lot of smelly, disgusting chemicals. We had acetylene, alcohol, ammonia, amino acids, hydrogen sulphide, methane, formaldehyde. Every single one of these smells disgusting. And that’s unfortunately the truth of the comet, we’re made – the water and the carbon chemistry that made us all – it’s not like, you know, they say in the nursery rhyme, girls are made of sugar and spice and everything nice. Well, it’s not true, we’re made of smelly comets, OK?

The Science Learning Hub would like to acknowledge the following for their contribution to this resource: Warwick Holmes Lecture video footage courtesy of the University of Waikato All additional images of Comet 67P courtesy of ESA – European Space Agency