Rosetta-Philae Probe: How Humans Touched Down on a Comet for the First Time

Tuesday marks the tenth anniversary of a huge astronomical milestone: the first and only time we have landed on a comet.
The Rosetta probe’s lander Philae landed on Comet 67P/Churyumov-Gerasimenko on 12 November, 2014, after a decade spent travelling nearly 4 billion miles through space.
Having left Earth in 2004, Rosetta approached the orbit of Comet 67P/Churyumov-Gerasimenko on its looping path in and out of the asteroid belt, before finally entering into orbit around the comet itself in August 2014.
“Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface,” Jean-Jacques Dordain, the European Space Agency’s director general at the time, said in a statement just after the landing.
“With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future.”
Upon reaching the comet in August 2014, Rosetta orbited and mapped its surface, looking for a suitable landing spot. After a smooth-looking patch, later named Agilkia, was chosen as the landing location, the Philae lander was deployed on November 12 of that year, marking the very first time a man-made object landed on a comet—a feat that has not yet been repeated.
Philae’s landing was challenging: it bounced several times after the initial touchdown due to its anchoring harpoons failing to deploy. During these bounces, its instruments were operating, collecting data about each bounce location and the properties of the comet’s gas and dust as it soared overhead to its next location. Some landing sites had much softer surface textures than others, with one contact with a boulder revealing the object to be more porous than cappuccino froth.
Eventually, Philae landed at its final touchdown site, named Abydos, which was unfortunately in a shaded area, limiting its ability to recharge with solar power.
Despite these difficulties, Philae managed to send valuable data back to Earth before its batteries ran out.
Philae “listened” to the seismic properties of the comet, and measured the temperatures of the comet’s surface, finding it fluctuated between -292 degrees F to 293 degrees F across the comet’s 12.4 hour day. Scientists also gained insights into the comet’s composition, learning that it contained organic molecules that had never before been found in comets—including methyl isocyanate, acetone, propionaldehyde and acetamide—and was largely made of ice and dust, giving clues about the origins of water and organic compounds in our solar system.
The lander fell into hibernation only 64 hours after separation from Rosetta, but had managed to complete some 80 percent of its planned scientific data collection even in this short time. Philae was briefly heard from in summer 2015, but could not be reactivated.
“The data collected by Philae and Rosetta is set to make this mission a game-changer in cometary science,” Matt Taylor, ESA’s Rosetta project scientist, said in a 2014 statement.
The Rosetta mission concluded in 2016 when the spacecraft was intentionally crash-landed on the comet, gathering data up until the end.
“Just as the Rosetta Stone after which this mission was named was pivotal in understanding ancient language and history, the vast treasure trove of Rosetta spacecraft data is changing our view on how comets and the Solar System formed,” Taylor said in 2016.
“Inevitably, we now have new mysteries to solve. The comet hasn’t given up all of its secrets yet, and there are sure to be many surprises hidden in this incredible archive. So don’t go anywhere yet—we’re only just beginning.”
Rosetta blazed a trail for future comet exploration missions, one of which will be the upcoming Comet Interceptor mission, planned to launch in 2029, which hopes to visit a long-period comet visiting our Solar System for the very first time.
Additionally, there are some future missions planned to asteroids—the Hera spacecraft will head back out to the Dimorphos system in the wake of the DART mission and its alteration of the asteroid’s orbit, while the Rapid Apophis Mission for Space Safety (Ramses) mission will investigate the asteroid 99942 Apophis during its flyby of Earth in 2029.
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