UK Researchers received "rich" data from the Philae lander just before its power died.
Scientists say they detected what might be complex carbon compounds on the surface of the comet the craft landed on two weeks ago.
The results are from the Ptolemy instrument, which is a miniaturised on-board laboratory.
The detection of carbon supports a view that comets may have brought key chemicals to Earth to kick-start life.
The team leader, Prof Ian Wright, told BBC News: "We can say with absolute certainty that we saw a very large signal of what are basically organic (carbon) compounds.
"There is a rich signal there. It is not simple. It is not like there are two compounds; there are clearly a lot of things there - a lot of peaks. Sometimes a complicated compound can give a lot of peaks."
The "peaks" refer to the graph produced by the Ptolemy instrument of the different molecules it detected. The result is in line with initial observations made by a similar German-led instrument on Philae.
In an exclusive interview with BBC News, Prof Wright explained that Ptolemy had gathered huge amounts of scientific data. Normally a quiet, understated man, he was marginally better at containing his enthusiasm than his co-worker and wife, Prof Monica Grady, who jumped for and then wept with joy and relief when Philae landed.
Prof Wright told me: "I am as excited now as I was a couple of weeks ago. It's tremendous!"
"For years, I've been giving public lectures about what we plan to do. Now we have some data and it's: Wow! This is what scientists do this stuff for."
Much of the data gathered by Ptolemy was collected on the fly. Shortly after the Rosetta spacecraft was activated in January, Prof Wright and his team saw the opportunity to analyse the comet's tail as the spacecraft approached.
"It is not something we had planned to do, but it became obvious that it was something we could do."
The early data suggests that the composition of the gases changed as the spacecraft got closer to the comet.
Prof Wright also explained that Philae's bouncy landing suited his experiment. Among Ptolemy's capabilities is the ability to analyse gases and particles around it, and so it was pre-programmed to sniff its environment shortly after landing.
Pictures from Rosetta show that the first landing created a dust cloud, providing Ptolemy with a feast of data.
But Philae's bouncy landing and eventual resting place in the shade meant that it would not be able to recharge its solar powered batteries. The Ptolemy team had a few hours to rethink its scientific programme and upload a much curtailed set of experiments to the instrument.
Fuelled by the drama of the landing, and feeling the weight of history on their shoulders, all the various Philae instrument teams spent the night feverishly working to make the best use of the precious few days of operating life that the lander had left.
The hardest moment for the Philae team was having to abandon plans to analyse material drilled from underneath the comet's surface. Overall, programme managers deemed that there was only sufficient battery power to drill for one sample, rather than two as was originally planned. A collective decision was therefore made that any sample should be analysed by the German-led COSAC instrument - not Ptolemy.
It is unclear whether the drill successfully managed to get a sample to COSAC.
But mission planners did grant the UK team Philae's last ounce of strength to operate Ptolemy's oven, to heat up all the debris that had collected inside the instrument to 200C and analyse the gases that came off.
Prof Wright confirms that this experiment was successfully carried out and that the results could give an indication of the composition of the carbon and nitrogen on the comet. These results may in turn help piece together what happened in the early years of the Solar System when the planets were forming.
The team wishes that Ptolemy could have carried out its full mission, but Prof Wright says the group is delighted with the results it has obtained. It also has the optimistic possibility of Philae coming back to life in the weeks ahead as the comet moves closer to the Sun and lighting conditions improve at the landing site.
"If you ask me whether we have done all we could have done, the answer is 'no'. But I remain optimistic that the thing may come back to life and we will get the chance to do those things," he said.