Picture This: Falling to a comet

DARMSTADT, GERMANY — Somewhere between the orbits of Mars and Jupiter, a comet is sailing through our solar system at around 55,000 kilometers (more than 34,000 miles) per hour. Today, a robotic lander settled down onto this comet’s surface. It was an amazing feat of engineering for the lander and the Rosetta spacecraft that ferried it there.

The pair launched into space more than 10.5 years ago. Since then, they’ve enjoyed one very long and complicated voyage.

The lander is named Philae (FEE-LAY), after an island in the Nile River. Earlier today, Rosetta released this minifridge-size robotic lander. It fell for hours. Eventually, it touched down on the rocky surface of 67P/Churyumov-Gerasimenko. Philae is now preparing to beam back panoramic photos of this comet’s surface. But it will do more than snap pictures. Philae’s on-board instruments also will explore the chemistry of the dust beneath the lander’s toes.

Stephan Ulamec of the German Aerospace Center in Cologne, Germany, is the Philae project manager. Amid cheers and applause, earlier today, he announced: “We are on the comet!” The European Space Agency’s operations center had just gotten a signal that the lander had successfully made it to the surface.

This marked the first time scientists had set a spacecraft onto the surface of a comet.

The historic landing was more than 20 years in the making. And it didn’t happen without a lot of hand-wringing.

A glitch arose November 10. That’s when the lander didn’t switch on properly, during a first try. Tensions among the Earth-based operations crew grew even greater on the morning of November 12. This is when mission scientists identified a problem with the lander’s thruster system. It was supposed to fire, pushing the probe downward as its foot screws and harpoons attempted to anchor the lander to the surface. Four attempts to correct the thruster failed. Eventually, the team had to clear Philae for launch anyway. And as signs had indicated, the thruster never fired.

For more on Philae’s voyage and what scientists hope to learn from it, check out tomorrow’s follow-up story.

Power Words

comet    A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”

engineering   The field of research that uses math and science to solve practical problems.

harpoon     A spear-like weapon that is thrown to pierce an aquatic animal. It’s barbed or hooked head keeps the weapon attached to the animal. An attached rope can then be pulled in, bringing the animal to a hunter’s boat. A harpoon may also be any latching device that pierces a surface to hold onto it.

orbit  The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

lander  A special, small vehicle designed to ferry humans or scientific equipment between a spacecraft and the celestial body they will explore.

solar system  The eight major planets and their moons in orbit around the sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

thruster  An engine that pushes or drives with force by expelling a jet of fluid, gas or stream of particles.