The European Space Agency’s Rosetta Mission will come to an end tomorrow, when the spacecraft will land on the comet it was launched to study in 2004. The craft reached the comet, called 67P/Churyumov–Gerasimenko, in August of 2014, landing a tiny robotic probe on the surface. The probe, called Philae, was the first craft to ever complete a ‘soft’, or non-destructive, landing on the surface of a comet.

Since the landing in the summer of 2014, Rosetta has relayed information back to Earth regarding the comet’s shape and composition. Scientists were surprised at some of the findings. The composition of the comet turned out to be extremely porous, with empty space making up over 70 percent of the volume. According to Bjorn Davidsson, a Rosetta scientist based at Nasa’s jet propulsion laboratory, “When you see these beautiful images of the comet you should not think of it as rock. It’s something like spun sugar or cotton candy – something very, very fluffy.”

Professor Monica Grady, who is a space scientist at the Open University who works on of Philae’s gas and dust detectors, recalled her surprised when she first saw detailed surface imagery. She said “You’d expect them to be dusty and eroded, not these startling landscapes. You try to interpret things in terms of what we know on Earth, like glaciers or river valleys, but that’s just not happened on the comet. We need to work out how these landscapes formed. And certainly no one expected it to be duck-shaped.”

As it turned out, the comet includes two segments connected by a sort of neck, leading many scientists to describe the shape of the comet as duck-like. The comet includes a ‘body’, about two miles across, as well as a smaller ‘head’, with a diameter of about one mile. A 2015 study from the journal Nature suggests that the comet may have formed as the result of two objects colliding.

With comet 67P moving towards Jupiter’s orbit, and away from the sun, Rosetta’s solar power supply is dwindling. The craft has been left with just enough energy to land on the comet next to its probe, Philae. Rosetta will transmit a final image, taken from 15 kilometers away from the comet, before landing and turning off its transmitter. Though they will never know what happens to the craft from there, mission controllers are hoping for a successful soft landing, near the Philae probe.

According to the ESA’s space operations manager, Andrea Accomazzo, “We could have abandoned it in space or let it bounce off the comet and just switched it off. It wouldn’t have created any problem. Landing it is more a psychological thing.”

Observations by the Rosina instrument, Rosetta’s mass spectrometer, detected chemicals in the “coma” surrounding the comet that may have been the basic chemical components of life on earth.  This included glycine, an amino acid, as well as phosphorous, which is a main component of DNA.

These findings support the idea that comets helped to deliver some of the necessary ingredients for the formation of life on Earth.

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