Astronaut and Apollo 16 moonwalker John Young was once quoted as saying, “[René] Descartes … said, ‘There’s nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it.’” Well, it appears that Mr. Descartes and Captain Young were right.
Earlier today, on the second anniversary of NASA’s Curiosity rover landing on Mars, the European Space Agency’s (ESA) Rosetta spacecraft rendezvoused with comet 67P/Churyumov–Gerasimenko following a journey a decade in the making. The spacecraft and comet are both now approximately 405 million kilometers (252 million miles) away from Earth, between the orbits of Jupiter and Mars, in what is the first ever “meet up” of its kind. Rosetta and its lander, Philae, will accompany the comet on its journey around the Sun during the next year, through the end of its science mission in December 2015.
Jean-Jacques Dordain, ESA’s Director General, conveyed his excitement over the space agency’s historic milestone: “After ten years, five months and four days traveling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometers, we are delighted to announce finally, ‘we are here.’ Europe’s Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. Discoveries can start.”
Following a scheduled thruster burn (the last of 10 begun in May this year), the ESA announced via social media at 5:35 a.m. EDT, “We have arrived at the comet!” Moments later, the first image from 67P/Churyumov–Gerasimenko following the rendezvous—which found the spacecraft merely 100 kilometers (62 miles) from its target—arrived back on Earth, showing the rugged, unique shape of the comet’s nucleus up close.
ESA’s Rosetta Project Scientist, Matt Taylor, discussed the nucleus’ unusual shape: “Our first clear views of the comet have given us plenty to think about. Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects.”
Other images beamed back have since showed the comet to have a craggy surface, not pocked with craters. Its appearance is unexpected, as the comet was anticipated to have an icy, smooth surface. However, in the last week it was revealed that Rosetta’s visible, infrared, and thermal imaging spectrometer (VIRTIS) has shown the comet to have a temperature of approximately -70 degrees Celsius, 20 to 30 degrees warmer than expected—explaining the distinct lack of ice.
This latest discovery about the comet’s appearance comes after other news that has taken scientists by surprise. NASA’s Microwave Instrument for Rosetta Orbiter (MIRO), one of the NASA’s three instruments aboard Rosetta (the other two include an ultraviolet spectrometer called Alice, and the Ion and Electron Sensor, or IES) detected “huge amounts of water outgassing,” which was discussed in a previous AmericaSpace article written by Leonidas Papadopoulos.
Papadopoulos wrote on June 30: “ … In the current point in its orbit, approximately 362 million miles (583 million km) from the Sun, midway between Mars and Jupiter, 67P/Churyumov–Gerasimenko was expected to be less active. Yet Rosetta’s MIRO instrument has been constantly detecting excessive amounts of water vapor streaming from the comet ever since it first detected the water signatures in early June, from a distance of 217,480 miles (350,000 km) away. Scientists have calculated that the amount of the observed water outgassing is the equivalent of two small glasses of water spewed out into space every second.” Scientists will further investigate why this phenomenon is happening. In addition, the comet’s Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) saw activity in the comet’s “coma” (a comet’s signature dusty tail) flare up, and then die down.
Today’s rendezvous comes following a journey of 10 years, which saw Rosetta take a series of three gravity-assist flybys of Earth and one of Mars. Rosetta was originally intended to launch in January 2003, and was slated to rendezvous with comet 46P/Wirtanen in 2011. However, during that time an Ariane 5 launch failure grounded the fleet of rockets, and the launch was pushed back—which meant Rosetta would not be able to meet the previously targeted comet in time. At long last, Rosetta was launched on March 2, 2004, from the Guiana Space Centre in Kourou, French Guiana. Following the flybys of two planets (and two asteroids), it went into a lengthy (31-month-long) hibernation period. In January, Rosetta was famously “woken up” and was found to be in excellent health, despite its long rest.
Alvaro Giménez, ESA’s Director of Science and Robotic Exploration, underscored the history and length of planning surrounding Rosetta and its mission: “Today’s achievement is a result of a huge international endeavor spanning several decades. We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come.”
Today’s success by the ESA expands on the space agency’s heritage of achievement in the field of cometary science. Rosetta’s “grandfather,” Giotto, made history in 1986 when it became the first spacecraft to approach a comet’s nucleus (it flew by then-returning Halley’s Comet). Giotto returned still-spectacular images of the comet, and the mission has been hailed as a high point in ESA’s history. The International Cometary Explorer (ICE), launched in 1978 and also known as ISEE-3, was a joint effort by NASA and the ESA. ICE became the first spacecraft to “chase” a comet, passing through the tail of comet Giacobini-Zinner in 1985. This spacecraft recently entered the news again when it was “re-awakened” after a sabbatical of 17 years.
While mission controllers work on circularizing Rosetta’s orbit around 67P/Churyumov–Gerasimenko, images and data coming from the spacecraft’s instruments will lead the way in determining a landing site for Rosetta’s “brother”—its lander, Philae. The ESA announced that by late August scientists hope to have identified at least five possible landing sites for a November touchdown. Philae’s landing will be the first time a spacecraft has ever touched down upon a comet’s surface. It is hoped data from the lander will shed some light into how the Solar System—and, perhaps, our planet—was formed. Sylvain Lodiot, ESA’s Rosetta spacecraft operations manager, emphasized how today’s success is only a stepping stone for a greater purpose.
“Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land,” Lodiot related.
Today’s historic achievement by the ESA just shows that there are secrets still to reveal about our cometary neighbors in the Solar System. In November, with Philae’s landing, space watchers and scientists alike will discover there is “nothing so hidden” about comet 67P/Churyumov–Gerasimenko, despite time and distance.