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.

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 14, 2014

Yesterday, the robot probe Philae began sending back the first images ever taken from the fractured terrain of a comet. After an awkward landing in which the probe bounced twice, initially back out into space, it stabilized on Comet 67P. It is currently attempting to drill into the surface of the comet. European Space Agency (ESA) scientists hope the tool will be able to capture some samples for analysis in Philae’s on-board laboratories.

An artist’s impression of the probe Philae (front view) on the surface of Comet 67P. (ESA/ATG medialab)

The objective of this ESA mission is to explore the origins of our solar system. Comets are believed to hold materials that are largely unchanged since the formation of the planets 4.6 billion years ago. Scientists speculate that comets delivered water to the early Earth. Others theorize that comets could even have “seeded” Earth with the chemicals needed to start life on the planet.

From the pictures Philae has returned to Earth, the ESA scientists believe it landed in the shadow of a cliff, meaning that the sunlight the probe receives is limited. As a result, its solar panels probably will not keep the battery systems properly charged, cutting short the run of the mission.

ESA’s Rosetta satellite, with its piggybacked Philae lander, was launched in 2004. The pair traveled 4 billion miles (6.4 billion kilometers) to reach Comet 67P, out near the orbit of Jupiter. After a long period of maneuvering into the correct position, Rosetta dropped Philae onto to Comet 67P on November 12.

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/

October 17, 2014

Numerous rovers and orbiting probes will break from their usual observations of Mars on Sunday to watch a comet flyby described by NASA officials as a once-in-a-million-year event. Comet Siding Spring–named for the Australian observatory where it was discovered in 2013–will pass within about 87,000 miles (139,500 kilometers) of the red planet. That’s less than half the distance between Earth and the moon. Siding Spring will zip by Mars at a speed of about 126,000 miles (56 kilometers) per hour at about 2:27 p.m., EDT.

Why are astronomers so excited?  For one, Siding Spring will be the first comet from the far-distant Oort cloud to be studied close up by spacecraft. For another, the comet is making its first-ever voyage through the inner solar system. That means it has never passed by sun and so has never been altered by the sun’s powerful heat and radiation. In other words, the comet looks much the same as it did 4.6 billion years ago, shortly after the formation of the solar system. “This is a cosmic science gift that could potentially keep on giving,” said John Grunsfeld of NASA’s Science Mission Directorate. “This particular comet … will provide a fresh source of clues to our solar system’s earliest days.”

Siding Spring, which has a nucleus (core) from 0.5 to 5 miles (0.8 to 8 kilometers) wide, is a well-traveled comet. Scientists believe it formed somewhere between the orbits of Jupiter and Neptune as the solar system was being born. At that time, many similar objects there were colliding and coming together to form the outer planets (Saturn, Jupiter, Uranus and Neptune). Siding Spring, however, apparently was caught by the gravitation pull of one of these planets and thrown out into the Oort cloud at the outer reaches of the solar system. For billions of years, the comet visited only the outer planets on its trips into the solar system. Then about one million years ago, it was jolted from its orbit–probably by a star passing by the Oort cloud–and started its voyage to the inner solar system.

When imaged by the Hubble Space Telescope on March 11, 2014, Comet Siding Spring was 353,000 miles (568,000 kilometers) from Earth. The coma (dust cloud) surrounding the comet’s nucleus (core) is about 12,000 miles (19,000 kilometers) wide. The comet will take about 1 million years to complete one orbit of the sun. (NASA, ESA, and J.-Y. Li [Planetary Science Institute])

“We can’t get to an Oort Cloud comet with our current rockets. These orbits are very long and extended, at very great velocities,” said Carey Lisse, a senior astrophysicist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “So this comet is coming to us. It’s a free flyby, if you will, and that’s a very fantastic event for us to study.”

Watching for the comet–and observing its effects on the Martian atmosphere–will be various Mars orbiters, including the Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Atmosphere and Volatile Evolution craft. Other observers will be the Hubble, Spitzer, Kepler, and Chandra space telescope. Scientists are particularly interested in what the Mars rovers Curiosity and Opportunity make of the comet. If the Martian atmosphere isn’t too dusty, they could provide the first images of a comet from another planet.

Additional World Book articles:

• Exploring the Outer Solar System (a Special Report)
• When Worlds and Comets Collide (a Special Report)

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

July 26, 2013

A new image of Comet ISON taken by the Hubble Space Telescope is giving the public a tantalizing preview of what the deep-space traveler may look like when it makes its maiden voyage around the sun in late November. Some astronomers think the comet could outshine the full moon, rivaling the display put on by the Great Comet of 1860. That comet could be seen during daylight hours without a telescope. However, other researchers caution that the comet could fizzle, the way Comet Kohoutek did in 1973. So-called sungrazing comets like ISON often break up or boil during their perilously close passage by the sun. ISON will zip by the solar surface at a distance of only 724,000 miles (1.16 million kilometers). The comet might not even make it that far, given the hazards of travel through the Main Belt (also known as the Asteroid Belt) and inner solar system. One thing is certain, though–the comet will not crash into Earth.

An image of Comet ISON taken when it was 363 million miles (584 million kilometers) from the sun is actually a mosaic of images that simulates the way the comet would look if we could see with the same resolution as Hubble. NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Comet ISON was discovered in September 2012 by Russian astronomers while it was between the orbits of Jupiter and Saturn. It is named for the International Scientific Optical Network, a group of observatories in 10 countries. At this point, the nucleus of the comet is is less than 3 miles (5 kilometers) in diameter, though its dusty head is much larger—about 3,100 miles (5,000 kilometers) across. Its tail is an amazing 186,400 miles (300,000 kilometers) long, thanks to the prodigious amount of carbon dioxide escaping from the comet each day. Infrared observations made by American scientists using the Spitzer Space Telescope revealed that 2.2 million pounds (1 million kilograms) of carbon dioxide are “fizzing” away from the “soda-pop” comet daily. ISON is also shedding 120 million pounds (54.4 million kilograms) of dust.

Astronomers believe Comet ISON began its journey toward the sun from the Oort cloud, a cluster of comets, smaller objects, and perhaps even planets in the outermost region of our solar system. Scientists believe comets preserve leftover ice, rock, and dust from the solar system’s formation. As such, they provide valuable information about the history and composition of the solar system.

Additional World Book articles:

• Halley’s comet
• Meteor
• Stardust
• When Worlds and Comets Collide (a special report)

Jan. 27, 2012

An asteroid–a 36-foot (11-meter) space rock named 2012 BX3–hurtled past Earth today, coming as close as 37,280 miles (60,000 kilometers). “It’s one of the closest approaches recorded,” noted Gareth Williams, associate director of the Minor Planet Center at Cambridge, Massachusetts. “It makes it in to the top 20 closest approaches, but it’s sufficiently far away . . . that there’s absolutely no chance of it hitting us.” Scientists believe that asteroids are chunks of material left over from the formation of the solar system. The gravitational pull of the planet Jupiter probably prevented these pieces from coming together to form a full-sized planet. Some asteroids may represent the nuclei (cores) of comets that are no longer active.

The asteroid Ida and its tiny moon Dactyl appear in a photograph taken by the U.S. spacecraft Galileo. Dactyl may be a piece of Ida that broke away during a collision with another asteroid. NASA/JPL/Galileo Project

The atmosphere protects Earth from most asteroid strikes. Air friction causes an asteroid smaller than about 160 feet (50 meters) in diameter to disintegrate before it can reach the surface and cause damage. Larger asteroids can impact the environment of the entire globe. The impact of an asteroid with a diameter of around 0.6 mile (1 kilometer) would kick large amounts of dust into the atmosphere. The dust would block sunlight, which would cool the air for many months. One such strike occurred 65 million years ago on Mexico’s Yucatan Peninsula. Many scientists think environmental damage caused by the collision led to a mass extinction. The extinction eliminated huge numbers of species, including the dinosaurs.

Additional World Book articles:

• Dawn
• Eros
• Vesta
• When Worlds and Comets Collide (a special report)
• What Has Caused Mass Extinctions (a special report)