The comet on which scientists recently landed a probe is a fluffy ball of ice, dust and basic organic materials—and it is light enough to float on water, new research shows.

The measurements were taken from an array of instruments aboard the European Space Agency’s Rosetta spacecraft, which is currently in close orbit around a comet known as 67P/Churyumov-Gerasimenko, more than 500 million kilometers (310 million miles) from earth.

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