Just over a year ago, the Philae lander arrived on the surface of Comet 67P/Churyumov-Gerasimenko.
It was a tremendous achievement. Humans were on the surface of a comet for the first time - albeit in the form of a robot assistant.
Unfortunately, everything did not go according to plan. The lander was intended to come to rest at a site designated "Agilkia" and was designed to land on relatively soft material. Comet 67P was not soft. The surface was hard rock.
The lander bounced off the surface when the ice screws intended to hold it in place failed to get a grip. The lander had additional systems - a thruster and harpoons - designed to secure it to the surface. They also failed.
Indeed, in some ways, the landing of
Philae was a clear expression of Murphy's Law - if it can go wrong, it will. And yet, Philae touched down and provided a tremendous amount of data until its on-board batteries eventually failed. It managed to complete about 80 per cent of its mission.
During the past year, Philae has tried to get in touch with Rosetta. The orbiter has continued to circle the comet providing a continuous stream of scientific data. It is powered by solar cells which continually bask in sunlight.
The solar panels on the lander, on the other hand, go through a night-and-day cycle as the comet rotates. It was hoped as the comet approached the Sun, these panels would get enough light to power up the lander and in June it did make contact with the orbiter again.
Unfortunately, as the comet approached the Sun, its coma developed and the increased density of particles subliming from the surface decreased the efficiency of the solar panels. Philae is now silent.
Still, the mission can be classified as a tremendous success. Indeed, it is ongoing as the orbiter is still sending information back. A lot was learned by all of the scientists and engineers involved.
In particular, a great deal was learned about the composition of Comet 67P.
Scientists examining the data from the mass spectrometers on the lander have discovered 16 identifiable molecular species on the comet's surface. Some even contain nitrogen giving rise to molecular species that could be building blocks for much more complicated molecules.
In particular, methyl isocyanate, acetone, propionaldehyde, and acetamide were detected for the first time as part of a comet's chemical make-up. These are small organic molecules which form a tool kit for building larger molecular species. Acetone and amides, for example, can lead to the synthesis of nitrogen-containing ring compounds similar to the porphyrin ring found in hemoglobin.
Furthermore, the scientists were able to detect the presence of sugars on the comet's surface. These are formed from formaldehyde by bombardment with solar radiation and appear to be a common constituent of the interstellar medium. Sugars have even been detected in meteorites found in the Antarctic.
Most scientists believe that comets are the remnants of the early solar system. They are leftover pieces that never found their way into joining with the planets. The chemical composition found on the surface of comets is expected to be the same as the proto-planets.
By all accounts, they are rich in the chemical building blocks that lead to more complex molecules supporting the theory that life, or at the very least, complex organic chemistry, might have started in space before it began on Earth.
Visiting a comet isn't the only way to determine the chemical composition, though. At the same time as Rosetta and Philae were investigating Comet 67P, another team was analyzing the chemical composition of the coma from Comet C/2014 Q2 - Lovejoy.
Scientists using the 30-metre radio telescope at Pico Veleta in the Sierra Nevada Mountains of Spain spectroscopically analyzed the chemical composition of the debris being ejected by the comet as it approached the sun.
Spectroscopy examines the characteristic frequencies absorbed and/or emitted by molecules. By examining a sample at multiple wavelengths, it is possible to determine both the chemical composition and concentrations in a sample.
In the case of Comet Lovejoy, most of the same chemicals observed from other comets were found, including some of the same compounds as observed by the Philae lander. In total, 21 organic molecules were detected.
But the most significant discovery was the presence for the first time of ethyl alcohol or ethanol. This is the same alcohol we consume in beer and wine. Indeed, the comet is spewing out alcohol at a rate equivalent to 500 bottles of wine every second.
Further, it is also spewing out glycolaldehyde which is a simple sugar. Yes, the comet is making interstellar ice wine!
Every year technological advances allow us to look further into space with more details increasing the amount of data available.
What we find there tells us much about life on our planet.
