October 18, 2016

On September 30, a bright light of science was extinguished in the solar system. That day, the space probe Rosetta crash-landed on the comet it had been orbiting, marking the end of an ambitious mission that paid–and should continue to pay–huge dividends for astronomy.

The European Space Agency (ESA) launched Rosetta on March 2, 2004. Rosetta orbited comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. Scientists think that comets preserve dust, ice, and rock from the solar system’s formation. By gathering data on a comet, therefore, Rosetta helped scientists to learn more about the solar system’s composition and history. Rosetta was named for the Rosetta stone, an inscribed rock that enabled scholars to interpret ancient Egyptian hieroglyphs. Rosetta also carried a small craft named Philae to land on the surface of the comet’s nucleus (core). Philae was named for the Philae obelisk, which also bore inscriptions that helped decipher ancient Egyptian writing.

This artist’s impression shows the European Space Agency (ESA) lander Philae on the surface of comet 67P/Churyumov-Gerasimenko. Philae was released from the ESA probe Rosetta to gather detailed information about the comet’s structure and makeup. Credit: DLR German Aerospace Center

Rosetta overcame many difficulties to provide key insights into the history of the early universe. It was initially planned as a sample return mission to a different comet in collaboration with the United States National Aeronautics and Space Administration (NASA). But because of the tragic loss of the space shuttle Challenger in 1986, NASA pulled out of the Rosetta mission, and the ESA was forced to scale it back. Many years later, in 2002, an Ariane 5 rocket failed shortly after liftoff. Rosetta was scheduled to be carried into space on the next Ariane 5 later that year. The failure grounded the Ariane 5 for many months, and mission scientists changed their target comet to 67P/Churyumov-Gerasimenko.

In 2014, when the lander Philae touched down on 67P, its landing harpoons failed to trigger. The craft bounced high into space and came down on its side in a sunless area of the comet’s nucleus. Scientists worked feverishly to conduct experiments and gather data for 57 hours before the lander’s solar-powered batteries died. Despite Philae’s loss, Rosetta continued orbiting the comet, taking photographs and collecting data. On Sept. 2, 2016, with just weeks left in the mission, Rosetta discovered the wayward Philae in the shade of a small cliff on the comet’s surface.

In spite of all the bumps along the way, Rosetta was a fabulously successful mission. It became the first spacecraft to orbit a comet, and it released the first probe to land on (rather than crash into) a comet. It returned invaluable data about the evolution of comets as they approach the sun and the history of the early solar system. Scientists are only just beginning to draw conclusions from Rosetta’s data.

Rosetta’s collision with the comet was not accidental, but had been planned by mission scientists. The highly elliptical (elongated) orbit of 67P takes it as close as 115 million miles (185 million kilometers) and as far as 530 million miles (850 million kilometers) from the sun. This creates vast and lengthy temperature changes over the course of its six-and-a-half-year orbit. These temperature extremes ravage a spacecraft’s sensors and electronic equipment. As the comet tracked back away from the sun, scientists feared that Rosetta could not survive another hibernation in the icy depths of the outer solar system. Rather than risk it, they decided to send Rosetta out in style, crashing into the comet while collecting as much data as possible. On its final descent, Rosetta studied the comet’s gas, dust, and plasma environment very close to the surface. The probe also took some harrowing high-resolution images as it plunged toward the comet.

Despite the end of Rosetta, ESA has several other important missions in progress. LISA Pathfinder plans to study gravitational waves from space. The Gaia probe is in the process of creating the most detailed map of the galaxy ever. The ExoMars Trace Gas Orbiter is en route to Mars to study the planet’s atmosphere and release a lander in preparation for a future wheeled rover.

December 22, 2014

Earth’s water may not have come from melting comets, according to a paper published in December 2014 by scientists working on the European Space Agency’s Rosetta mission. The Rosetta spacecraft, launched in 2004, went into orbit around P67/Comet Churyumov-Gerasimenko in 2014, landing a small probe on the comet’s nucleus (core) in November.

Most researchers think that the hot, turbulent formation of Earth would have left the early planet dry. Scientist have thus struggled to determine how Earth got its oceans. Most researchers agree that the water was delivered by smaller bodies crashing into the young planet. Such bodies may have been comets or asteroids.

Scientists are still unsure of the source of the water in Earth’s oceans, which cover most of the planet’s surface. This satellite view shows the Indian Ocean, partly bordered by Africa, Asia, and Australia, and below it the Southern Ocean surrounding Antarctica. (NASA/Goddard Space Flight Center and ORBIMAGE/SeaWiFS Project)

Scientists working with an instrument called the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) analyzed water from Comet Churyumov-Gerasimenko to see if it was similar to water found on Earth. Water consists of the elements hydrogen and oxygen. Some of the hydrogen, however, is in a heavier isotope (form) called deuterium. By comparing the ratio of deuterium to ordinary hydrogen in different samples, scientist can tell if the water in each sample is from the same place.

The researchers discovered that the water analyzed by the ROSINA instrument has a higher ratio of deuterium to hydrogen than does Earth’s water. The finding casts doubt that the water on Earth came from comets like Churyumov-Gerasimenko. However, Earth’s water may have come from bombardment by asteroids or from a different population of comets.

November 19, 2014

Philae, the first robot probe to set down on the surface of a comet, detected molecules fundamental to the development of life on Earth in the thin atmosphere surrounding Comet Churyumov-Gerasimenko (67P). The molecules are “organics,” carbon-containing molecules that serve as the chemical building blocks of life as we know it. Philae landed on the comet on November 12 after a 10-year, 310-million-mile (500-million-kilometer) journey from Earth as part of the European Space Agency’s Rosetta mission.

Many scientists believe that life on Earth arose from organics that formed simple compounds, which then combined with one another to form the complex structures associated with living things. According to one theory, organic molecules or compounds may have arrived on Earth in meteorites or comets. Scientists have discovered several organic compounds in a number of carbon-rich meteorites called carbonaceous chondrites. In addition, organics were also among the samples collected and returned to Earth by the U.S. spacecraft Stardust from Comet Wild 2 in 2004.

The lander Philae (left) sits on the surface of Comet 67P in a photo taken by a camera on the Rosetta orbiter. (ESA/Rosetta/Philae/CIVA)

Philae, which is equipped with 10 scientific instruments, collected information for some 60 hours before mission scientists sent it into hibernation. The lander did not function as long as scientists had hoped because it landed in the shadow of a cliff, which blocked sunlight from its solar panels. While active, Philae also determined that the comet’s surface is covered by layer of dust 4 to 8 inches (10-20 centimeters) thick. Beneath the dust is very hard water ice. The ice is so hard that the lander’s drill had difficulty breaking through to collect a sample. Before it set down, Philae recorded the temperature on the comet’s surface as -243 °F (-153 °C). Rosetta scientists hope that as 67P and the orbiting Rosetta satellite make their way toward the sun, the solar batteries on Philae will recharge, allowing the lander to resume its on-site study of the comet.

Additional World Book articles:

• Comet (a Research Guide)
• Space exploration

For additional information about the Rosetta missions, see: http://rosetta.esa.int/

November 12, 2014

The European Space Agency (ESA) made space flight history today by deploying a landing craft to the surface of a comet. The Philae lander took only minutes after separating from its mother ship, the Rosetta spacecraft, to reach the nucleus (solid core) of Comet Churyumov-Gerasimenko. To prevent the lander from simply bouncing off the low-gravity comet into space, Philae immediately fired two harpoons into the surface. A small thruster also ignited to keep the lander grounded. However, scientists think the anchors that hold it to the surface failed to work properly, and they are investigating.

Rosetta, which was launched by the ESA in March 2004, traveled 3.7 billion miles (6 billion kilometers) through the solar system to meet up with comet 67P/Churyumov-Gerasimenko (nicknamed Chury). The probe used a series of fly-bys past Earth and Mars to increase its speed during the chase—Chury travels at a speed of around 34,000 miles (55,000 kilometers) per hour. During the lengthy journey, the probe was put into “hibernation” for for some 2.5 years to save energy.

The Rosetta spacecraft appears in a selfie with Comet 67P/Churyumov–Gerasimenko in October 2014, made using a camera on the Philae lander. At that point, Rosetta was about 10 miles (16 kilometers) from the surface of the comet. (ESA)

Scientists at the ESA’s flight center in Darmstadt, Germany, woke Rosetta in January 2014 for the last leg of its journey. In August, ESA scientists fired thrusters to maneuvered it into orbit around the comet. In August, Rosetta became the first spacecraft to rendezvous with a comet. (Other missions have rendezvoused with asteroids and meteors.) Once in orbit, Rosetta began to photograph and map the comet’s surface, mainly to choose a landing site for Philae. Rosetta will continue to study the comet as it orbits the sun.

Philae carries 10 instruments for studying Chury, including a drill to taking samples from below the surface. Scientists are particularly interested in learning about the chemical makeup of the comet and its structure. Comets are leftover debris from the formation of the solar system about 4.6 billion years ago. As such, their primitive material holds valuable clues about the formation of the planets and moons. The solar-powered lander Philae was expected to continue its investigations for at least a week.

More than 10 space missions have been launched to study comets. NASA’s Deep Impact spacecraft intentionally crashed an impactor into Comet Tempel 1 in 2005. In the mid-2000′s, the Stardust space probe collected and returned to Earth particles it captured by flying close to Comet Wild. However, until Rosetta, no mission had touched down on a comet.

Additional World Book articles:

• Comet (a Research Guide)
• Space exploration

For additional information about the Rosetta missions, see: http://rosetta.esa.int/

August 6, 2014

A photo of comet 67P/Churyumov-Gerasimenko taken by Rosetta on August 3, 2014, from a distance of around 180 miles (285 kilometers). (Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.)

A space probe launched in March 2004 has successfully met up with the comet it was sent to study. Ten years ago, the European Space Agency (ESA) launched the Rosetta probe, which has traveled 3.7 billion miles (6 billion kilometers) through the solar system to meet up with comet 67P/Churyumov-Gerasimenko (nicknamed Chury). The probe used a series of fly-bys past Earth and Mars to increase its speed during the chase—Chury travels at a speed of around 34,000 miles (55,000 kilometers) per hour. During the lengthy journey, the probe was put into “hibernation” for for some 2.5 years to save energy. Scientists at ESA’s flight center in Darmstadt, Germany, woke Rosetta in January for the last leg of its journey.

This morning, ESA scientists fired thrusters to stop Rosetta and maneuvered it into orbit around the comet; Rosetta will orbit Chury for the next 15 months. The probe will photograph and map the surface of the comet. Rosetta also carries a lander, Philae, which will be launched in November onto the comet’s surface. (Philae is an island in Egypt where an Egyptologist discovered an obelisk that was used in conjunction with the Rosetta Stone to decipher Egyptian hieroglyphics.) The lander carries a drill that will be used to take samples from below the surface.

Additional World Book articles:

• Comet (a research Guide)
• Space exploration