Congratulations, European Space Agency, you’ve made history! After departing from the Rosetta orbiter this morning, touchdown of the robotic lander, Philae, onto Comet 67P/Churyumov-Gerasimenko was confirmed at 16:05 GMT. This is a momentous occasion for space exploration as it marks the first time that a spacecraft has ever landed on the surface of a comet. Hooray!
The idea behind this mission is to globally characterize 67/C-G. Scientists are keen to learn more about comets such as this because these cosmic objects are “time capsules” of the early solar system, holding important clues about the ingredients that went into constructing it some 4.5 billion years ago. Some have even hypothesized that comets may have delivered water for Earth’s oceans, and others believe that comets may have seeded our planet with the chemistry needed to kick-start life.
Although they managed it, landing on the comet was never going to be a walk in the park, let alone attempting this audacious mission while relying on vintage technology. The Rosetta mission was dreamt up in the ‘80s, but it was not until 1993 that the $1.6 billion (€1.3 billion) project was approved and construction of the crafts could be initiated. That means the probes were fabricated using some systems that were undoubtedly invented in the 1980s, making the mission’s accomplishments even more remarkable. Not only that, but 67/C-G’s jagged and boulder-covered surface is unforgiving, and there’s very low gravity on the icy object.
Rosetta’s rocky voyage began in 2004 after two ditched launch attempts. It took a decade to reach the comet in August this year, a journey that covered six billion kilometers (3.75 billion miles) of our inner solar system.
After catching up, the probe spent three months rendezvousing with the cosmic snowball, preparing for today’s momentous touchdown attempt as the comet races towards the sun half a billion kilometers (300 million miles) away from Earth. Of course, it’s had everyone involved on tenterhooks. Following a series of white-knuckle inducing Go/NoGo decisions that began at 19:00 GMT last night, the final Go was excitedly announced at 07:35 GMT today despite a problem onboard Philae.
During routine health checks, it was discovered that the active descent system couldn’t be activated. The absence of a working thruster on top of the lander meant that the ESA had to be fully reliant on harpoons to secure the robot’s position at touchdown. Nonetheless, at 08:35 GMT Philae successfully separated from the orbiter, marking the first stage of the robot’s seven-hour descent to the comet’s surface. Radio contact with the descending probe was established a couple of hours later, which meant that controllers could receive photos taken during the lander's descent. During the plunge, Philae also took measurements of the magnetic field and the environment around the "dirty snowball."
Here's an image of Philae's descent taken by Rosetta's Osiris instrument:
Now securely in place, Philae will study the comet’s internal structure using radio waves and will also drill into its surface to learn about its chemistry, for example its water and carbon content.