SciTech

Rosetta mission lands Philae probe on comet

On Nov. 12, the European Space Agency landed the Philae probe on a comet’s surface. (credit: ESA–C. Carreau via Flickr) On Nov. 12, the European Space Agency landed the Philae probe on a comet’s surface. (credit: ESA–C. Carreau via Flickr)

In the vastness of space, comets hurtle through our solar system as clouds of dust and ice, producing vibrant tails when heated by the sun. Comets have always intrigued astronomers by making fleeting appearances. Ancient stargazers would only see a particular comet once in a lifetime, and originally believed them to be harbingers of doom.

On Nov. 12, the European Space Agency’s (ESA) Rosetta Mission pushed the limits of scientific exploration by making the first attempt to land on a comet’s surface. Additionally, scientists designed their probe to collect and analyze samples from the comet that could potentially provide insight into the history of our solar system and life in space. Their efforts were generally regarded as a success despite a few issues that have caused the probe on the surface to go into a temporal state of hibernation.

It is an arduous task to first chase down a comet, orbit it as the comet continues on its path in space, and eventually launch a probe from the orbiter to touch down onto the surface.

Launched in March 2004, the Rosetta orbiter carrying the probe Philae made a 10-year journey to reach the comet known as 67p/Churyumov-Gerasimenko. The comet travels in a wide elliptical orbit around the sun beyond the orbit of Neptune. Using a technique known as a gravity slingshot, the Rosetta orbiter utilized the gravitational pull of the Earth and Mars to perform multiple slingshots to provide speed boosts.

During its journey, Rosetta successfully passed by two asteroids — Steins and Lutetia — as planned, and collected further data that scientists could analyze back on Earth. Each successive rotation of the spacecraft around the sun increases the radius of its orbit. Scientists carefully calculated the journey to reach and approach the comet in orbit based on the estimated path of the comet.

Imagine having to coordinate the movement of an object the size of a few refrigerators to line up with the orbit of a cloud of dust and ice hurtling through space at remarkable speeds. Once near the comet, Rosetta uses its sensors to determine the immediate path of the comet and model its motion. When Rosetta was in orbit, scientists used the data they received to plan the ideal launching procedure for landing probe Philae. They calculated a complicated series of maneuvers to position Rosetta within just-one-and-a-half miles from the center of the comet. Previously, the closest encounter with a comet was by a NASA probe in 2004 that came within 150 miles of the comet.

Positioned in the front of the comet away from the debris of the tail, Rosetta pushed Philae out into the vastness of space to control its own destiny. Philae, named after the Philae island in the Nile River, began its lonely seven-hour trip at a speed of around one meter per second toward the surface of the comet.

At this distance from Earth, messages to be transmitted to the probe took too long to allow for any manual intervention. Scientists were forced to rely on the computer programs that they developed ten years ago to analyze the data of the spiraling comet, determine a landing spot, and accurately land there. Rosetta moved away from the comet using its cameras to keep Philae in its field of view so scientists can keep track of its descent.

Landing on a comet is very different from landing on the moon or another planet because of the comet’s non-uniform movement and weak gravitational pull that is 1/1000 of that of the Earth. Scientists were afraid that with a lack of gravity, the probe could hit the surface and immediately bounce off back into space. To prevent this, engineers developed a sophisticated landing gear to absorb momentum and fire harpoons to lock the probe to the surface of the comet.

The probe contains a multitude of instruments for collecting and analyzing the composition of the comet. A drill allows it to dig below the surface and collect a variety of samples while an alpha proton X-ray spectrometer can analyze the chemical composition.

Previous research of comet tails has shown evidence of organic compounds, which may support the idea that life originated in space and was transported on comets.

The harpoon mechanism did not launch correctly, causing the probe to bounce twice before fortunately returning to the surface of the comet. Philae landed in the shadow of a cliff, and cannot get enough sunlight to power its battery. While scientists devise a solution, they have placed Philae in hibernation by turning off all of its instruments. They are optimistic that Philae’s journey is just beginning. Regardless, this mission has been a remarkable achievement and has taught scientists a plethora about comets as we move closer to a more complete understanding of these mysterious objects.