September 29, 2015

Mars. (NASA/JPL/Malin Space Science Systems)

The solar system just got a little bit wetter. Yesterday, scientists from the National Aeronautics and Space Administration (NASA) reported that water flows on Mars during warm seasons. They made the finding using a probe called the Mars Reconnaissance Orbiter (MRO).

Mars is the fourth planet from the sun. The planet is one of Earth’s “next-door neighbors” in space. Scientists have long suspected that water flowed on Mars in the distant past. Probes and rovers had found minerals on its surface that only form in the presence of water. Ice had also been discovered on Mars, both at the poles and other places on the planet.

In this illustration of our solar system, Mars is the fourth closest planet to the sun. Scientists have known for a while that Mars had liquid water on its surface at one time, but that Mars still has water at its surface today is an exciting discovery. (World Book illustration by Precision Graphics)

In August 2005, NASA launched the MRO, which arrived in orbit around Mars in March 2006. The craft was designed to study the planet’s structure and atmosphere and to identify potential landing sites for lander and rover missions. Scientists used the MRO’s instruments to observe mysterious dark streaks on Martian hillsides which appear to ebb and flow over time. The streaks darken in the warm season, when temperatures can exceed -10 °F (-23 °C).

The MRO revealed that these dark streaks were caused by liquid water saturated with salts. Salts lower the freezing point of water. This is why people in colder climates salt sidewalks in winter, and why oceans can stay liquid below the freezing point of pure water. In the warmer periods on Mars, the salts allow frozen water to melt and flow just under the surface of the hills. Some of the water wicks to the surface, forming dark spots.

The detection of liquid water on Mars will revitalize the search for current, as well as past, life on the planet. All known life needs liquid water to survive, so its presence on the Red Planet hints that life could possibly exist there today. Scientists are eager to continue the search for life, but also wary: liquid water on Mars will make it easier for organisms from Earth to colonize the planet. If probes land in these areas, bacteria could hitch a ride along with them and spread to the Martian surface, potentially changing or wiping out any native life that might exist there. Thus, space agencies may have to study such areas from a distance.

Other World Book articles

• Red Rover: Curiosity on Mars (a Special report)
• The Search for Water on Mars (a Special report)

December 9, 2014

Data from NASA’s Curiosity rover have revealed fascinating new details about the ancient geology of Mars, including the formation of Mount Sharp (also known as Aeolis Mons) and the abundance of surface water. The findings have also increased the likelihood that Earth may not have been the only planet in the solar system with primitive life billions of years ago.

Curiosity scientists reported that they think they have discovered why a 3-mile- (5-kilometer-) high mountain sits in the middle of Gale Crater, the impact crater where the rover landed in August 2012. Before Curiosity, scientists knew that Mount Sharp, like some mountains on Earth, consists of layer upon layer of sediment (layers of dirt, stone, and other materials laid down over many millions of years. But they did not know how Mount Sharp formed because, unlike Earth, Mars has not been shaped by plate tectonics. One theory was that the mountain formed from material that was thrown up as an asteroid or meteor crashed onto the surface there about 3.5 billion years ago. Another theory suggested that the mountain was “excavated” as sediments were eroded from around the peak. Studies made as Curiosity treks up the mountain now suggest that both wind and water were likely involved in the process.

Patterns of sedimentary deposits in Gale Crater suggests the crater held a lake more than 3 billion years ago, filling and drying in cycles that lasted tens of millions of years. (NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS)

Curiosity scientists think that Gale Crater experienced repeated wet and dry episodes that lasted for millions, or tens of millions, of years. During the wet episodes, rivers carrying water filled with sand and rock flowed over the crater’s rim to the floor, forming one large lake or even several smaller lakes. Over time, the sediments settled out of the water and hardened into layers that may have completely or partially filled the crater. During the dry episodes–when the water in the lakes evaporated–Martian winds sculpted the mountain by blowing away some of the sediment around the rim. Gradually, the mound in the center of the crater grew higher and higher.

Mount Sharp in Gale Crater likely formed from layers of sediment (yellow) carried by wind and by rivers flowing over the crater’s rim (above). The sediments then settled out in the center of the crater, forming rock (brown). Wind then eroded the sedimentary rock around the rim, forming Mount Shap. (NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS)

The existence of surface water–as well as underground water–on Mars for such a long period–perhaps 1 billion years–increases the chances that primitive life may have developed on the planet billions of years ago. In such a stable environment, which could have lasted for some 1 billion years, life could have arisen on the red planet some 3.8 billion years ago, as it did on Earth.

Additional World Book articles:

• Mars Pathfinder
• Phoenix [spacecraft]
• Space exploration (Probes to Mars)
• The Search for Water on Mars (a Special Report)

January 27, 2014

Opportunity, the hardy Mars rover that was expected to operate for just 90 days, has marked its 10th anniversary on the red planet. Even more amazingly, the rover, part of the Mars Exploration Rover Mission, is still revealing new information about Mars. NASA launched Opportunity and its twin, Spirit, in 2003 to study the history of water on the red planet. Their  90-day mission, which began in 2004, turned out to be merely a warm-up. Both rovers continued to gather information without any major setbacks for more than five years.

While traversing Mars, the rovers found evidence of ancient hot springs and thermal vents, the first meteorite ever discovered on another world, and rocky spheres created from water-bearing minerals. With Spirit, Opportunity also took the first photos of Earth-like clouds in the Martian sky from the planet’s surface. In early 2009, Spirit became permanently trapped in a bed of loose soil. NASA ended that rover’s mission in 2011. But Opportunity rolled on. The rover has now clocked up about 24 miles (38.7 kilometers) and taken 170,000 photographs.

Opportunity on Mars, in an artist's illustration. (Courtesy NASA/JPL-Caltech)

The rover’s latest discoveries involve rocks dated to about 4 million years ago, the oldest ever discovered by the rover. Opportunity’s analysis of the rocks has provided more evidence for than the surface of Mars was once  warmer and wetter than scientists had thought. Moreover, the rocks formed in water that was less acidic—and thus, more hospitable to microbial life—than the rocks analyzed previously by the rover.

Additional World Book articles:

• Mars Pathfinder
• Mars Science Laboratory
• Space exploration
• The Search for Water on Mars (a special report)

December 19, 2013

The Mars Science Laboratory, nicknamed Curiosity, has made a number of remarkable discoveries since it landed on Mars in the summer of 2012. The most recent feather in the rover’s cap is the discovery of a primordial lake within Gale Crater, the landing site of the small vehicle. Unlike previous evidence of liquid water on the planet, this new finding, in an area called Yellowknife Bay, hints of water similar to the liquid fresh water found on Earth. The new discovery paints the surface of Mars as a much more inviting environment for life as we know it to form. The water in the lake appears to have been both long standing and neither too acidic or alkaline for life as we know it.

The lake seems to have been relatively large and may have remained on the planet for thousands of years, if not more. Furthermore, the water seems to have been present around 3.5 billion years ago, about the same time scientists think life began on Earth. The discovery of the lake also reinforces the findings that what look to be stream beds, channels, deltas, and other landforms on the planet were created by water and are exactly what they appear to be.

The possible extent of an ancient lake inside Gale Crater is shown in an illustration superimposed on a satellite photo. The possible extent of the lake was estimated by mapping ancient lake and stream deposits and recognizing that water flowed from the crater rim into the basin (arrows). The water would have pooled in the linear depression created between the crater rim and Mt. Sharp (center of crater). The area’s history likely included the coming and going of multiple lakes of different sizes as climate conditions evolved. (NASA/JPL-Caltech/MSSS)

The most thrilling discovery to come from the exploration of the planet would surely be the discovery of life, whether the life existed in the past or is currently still thriving. Although the planet has since dried out and the atmosphere nearly vanished, some scientists believe the planet could still harbor life under the planet’s surface. Further exploration is needed to confirm this hope. There has even been talk for many years of the possibility that life on Earth was carried here by meteorites that originated on the Martian surface. Many meteorites came from Mars. Did they they carry some of the building blocks for life to Earth? Did they actually carried life itself as tiny passengers?

Additional World Book articles:

• Probing the Planets (a special report)
• The Search for Water on Mars (a special report)
• Space exploration 2011 (a Back in Time article)
• Space exploration 2012 (a Back in Time article)

May 23, 2013

Opportunity, the hardy Mars rover that has been exploring the red planet since 2004, has now driven farther on an extraterrestrial body than any other American rover. On May 15, Opportunity set a record of 22.220 miles (35.760 kilometers) after finishing a 263-foot (80-meter) drive along the rim of Endeavour Crater. The previous record was set by United States astronauts Eugene Cernan and Harrison Schmitt in December 1972 on the moon. The two astronauts, members of the Apollo 17 mission to the moon, drove a lunar roving vehicle, also known as a moon buggy, 22.210 miles (35.744 kilometers) across the lunar surface. If Opportunity continues to exceed expectations—the rover was designed for only a 90-day mission—it will soon break the all-time off-world distance record of 23 miles (37 kilometers). That record was set on the moon in 1973 by the remote-controlled Lunokhod 2 rover launched by the Soviet Union (now Russia).

Opportunity (NASA/JPL-Caltech)

Opportunity and its twin, Spirit, were sent to Mars in 2003 as part of the Mars Exploration Rover Mission to study the history of water on the red planet. Their original 90-day mission turned out to be merely a warm-up. Both Spirit and Opportunity continued to gather information  without any major setbacks for more than five years. In early 2009, Spirit became permanently trapped in a bed of loose soil. NASA ended that rover’s mission in 2011. But Opportunity is still exploring.

Opportunity examines one of its major discoveries--the first meteorite found on a world other than Earth. (NASA/JPL-Caltech/Cornell University)

While traversing Mars, Opportunity found the first meteorite ever discovered on another world and rocky spheres created from water-bearing minerals. With Spirit, Opportunity also took the first photos of Earth-like clouds in the Martian sky from the planet’s surface and disovered convincing evidence that water once flowed across the Martian surface.

Additional World Book articles:

• Mars Pathfinder
• Mars Science Laboratory
• Space exploration
• The Search for Water on Mars (a special report)

November 1, 2012

The first analysis of Martian soil by the rover Curiosity has revealed minerals remarkably similar to those found near volcanoes in Hawaii. NASA scientists reported that the soil contained significant amounts of feldspar, pyroxene, and olivine, minerals typically associated with volcanic eruptions on Earth.

The analysis was the first by the rover’s Chemistry and Mineralogy Instrument (CheMin), one of 10 sophisticated scientific instruments aboard Curiosity, the most advanced robotic laboratory ever sent to another planet. Mineral analysis is vital to the rover’s mission, determining whether Mars is, or ever has been, capable of supporting microbial life.

A graph based on an analysis of a soil sample from Mars reveals minerals commonly found in volcanoes in Hawaii. (NASA/JPL-Caltech/Ames)

Curiosity picked up the soil from a site named Rocknest. A sieve in CheMin filtered out all particles larger than 0.006 inch (150 micrometers), about the width of a human hair. The remaining particles were bombarded with X rays to determine their particular internal structure. According to NASA scientists, the minerals are much younger than the water-worn pebbles photographed by Curiosity in September. Those pebbles provided direct evidence that a deep, fast-moving stream of water once flowed across Gale Crater, the rover’s landing site. The soil minerals apparently had only a limited exposure to water and date from a “transition time” when the crater was changing from a wet to a dry environment.

Olympus Mons, a shield volcano, on Mars is the largest volcano in the solar system. (NASA)

Mars has some of the largest volcanoes in the solar system. The highest peak in the solar system is the Martian mountain Olympus Mons (Latin for Mount Olympus). It rises about 16 miles (25 kilometers) above the surrounding plain to a height about three times that of Mount Everest, the highest point on Earth. Olympus Mons, which is more than 370 miles (600 kilometers) in diameter, is a shield volcano, like the volcanoes on Hawaii. Shield volcanoes have slopes that rise gradually. They form from eruptions of lava that can flow for long distances before becoming solid.

Additional World Book articles:

• Hawaii Volcanoes National Park
• Mars Exploration Rover Mission
• Mars Pathfinder
• Phoenix (spacecraft)
• Space exploration (Probes to Mars)
• The Search for Water on Mars (a Special Report)

X-ray diffraction, commonly used on Earth

Determines minerals’ internal structure by recording how their crystals interact with X rays

September 28, 2012

Rounded pebbles photographed by Curiosity, NASA’s newest Mars rover, are direct evidence that a deep, fast-moving stream of water once flowed across Gale Crater, the rover’s landing site, scientists announced on September 27. Curiosity scientists said the pebbles had been eroded and smoothed out while being carried down a stream or river that ran for perhaps 25 miles (40 kilometers) across the Martian surface. “This is the first time we’re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it,” said science co-investigator William Dietrich of the University of California, Berkeley. The pebbles are too big to have been blown to the site by the wind. By comparing the size and shape of the Martian pebbles to pebbles found in streambeds on Earth, Curiosity scientists determined that the water on Mars was moving about 3 feet (0.9 meter) per second with a depth somewhere between ankle and hip deep. The largest and most advanced robotic laboratory ever sent to another planet, Curiosity is designed to answer one of the most important questions in planetary science–whether Mars is, or ever has been, capable of supporting microbial life.

The rounded pebbles found on Mars (left) are similar to rocks transported and cemented together by water on Earth (right). Some of the rocks are several inches (centimeters) wide. (NASA/JPL-Caltech/MSSS and PSI)

The pebbles were found in two tilted conglomerates named Hottah and Link. Conglomerates are rounded pebbles embedded in a fine-grained material. Scientists described Hottah as looking like a “jack-hammered … slab of city sidewalk.” The conglomerates lie about halfway between the north rim of Gale Crater and Mount Sharp, the rover’s ultimate destination. From the many channels found at the base of the rim, the scientists determined that the water flows may have lasted for thousands, even millions of years. “A long-flowing stream can be a habitable environment,” said Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena.

Scientists have long believed that water apparently has existed near the surface of Mars over part of the planet’s history. Evidence collected by spacecraft has suggested that liquid water apparently carved Mars’s large channels, smaller valleys, and young gullies. Scientists also concluded that vast quantities of ice exist within about 3 feet (1 meter) of the surface near the south pole and perhaps near the north pole. They also theorized that water is probably present beneath the surface today, kept liquid by Mars’s internal heat.

The water in the ancient streambed found by Curiosity likely flowed into Gale Crater from a channel called Peace Vallis. As the water flowed over the rim of the crater, it created an alluvial fan, a fan-shaped deposit of layered gravels, sands, silts, and other materials. Curiosity's landing site is marked by a cross in the black oval. (NASA/JPL-Caltech/UofA)

Additional World Book articles:

• Mars Exploration Rover Mission
• Mars Pathfinder
• Phoenix (spacecraft)
• Space exploration (Probes to Mars)
• The Search for Water on Mars (a Special Report)

A new Mars rover named Curiosity lifted off for the red planet atop an Atlas 5 rocket from Cape Canaveral in Florida on November 26. The rover’s mission is to answer one of the most exciting questions in planetary science–whether Mars is, or ever has been, capable of supporting microbial life. The rover is scheduled to land on Mars in August 2012, after spending 8 ½ months traveling some 354 million miles (570 million kilometers) through space.

A channel on Mars that may have been carved by flowing water appears in this photograph from the European Space Agency's Mars Express orbiter. Images taken by the orbiter showed evidence of water on Mars both now and in the planet's past. Photo courtesy European Space Agency.

Officially named the Mars Science Laboratory, the car-sized rover carries a scientific payload about 10 times as massive as those carried by NASA’s three previous Mars rovers. Curiosity, which has been described as a self-contained geology laboratory, holds eight sophisticated instruments powered by a nuclear generator. Two of the instruments were provided by Spain and Russia. Unlike earlier rovers, Curiosity will be able to gather samples of rock and soil, process them, and then distribute them to on-board instruments. The rover is set to land in Gale Crater, near the foot of a 3-mile- (5-kilometer-) high mountain whose lower layers contain minerals that formed in water.

Scientists are anticipating the complex process of getting Curiosity onto the Martian surface as “six minutes of terror.” When Curiosity is about 1 mile (1.7 kilometers) above the surface, a rocket-powered platform called the “sky crane” will drop from the protective shell holding the rover. After flying Curiosity to Gale Crater, the sky crane will lower the rover by tether.

Additional World Book articles:

• Mars Pathfinder
• Phoenix [spacecraft]
• Space exploration (Probes to Mars)
• The Search for Water on Mars (a Special Report)

Dark streaks running down the walls of several craters on Mars may be evidence of water flowing across the surface of the red planet during the Martian spring and summer. The discovery of the streaks, in images taken by NASA’s Mars Reconnaissance Orbiter, was reported by scientists at the University of Arizona. Since the mid-1900′s, scientists have gathered a great deal of evidence suggesting that water flowed over the Martian surface in the distant past.

Channels on Mars (NASA)

The finger-like streaks, which ranged from 1.6 to 16 feet (0.5 to 4.8 meters) wide, were seen in seven craters in various parts of Mars. All were on steep slopes facing the equator. Observed over three Martian years, the streaks appeared in late spring, grew and shifted during the summer, and disappeared in the fall. Some of the streaks grew as much as 600 feet (183 meters) over two Earth months.

The Arizona scientists said that though the streaks may have been caused by frozen carbon dioxide or even rock slides, their best explanation is salty water. However, they noted that they would not be able to confirm that water created the streaks without actually testing samples of the soil in the craters.

The scientists said that the surface of Mars is so salty that any water flowing there would certainly also be salty. The salty nature of the water may help explain its existence on the surface. Salt lowers the freezing point of water, so it can remain a liquid at temperatures colder than 32 °F (0 °C). The scientists doubted that life could exist in such a salty liquid.

Additional World Book articles:

• Astrobiology
• Extremophile
• Space exploration
• Astronomy 2008 (Back in Time article)
• Space exploration 2005 (Back in Time article)
• Space exploration 2006 (Back in Time article)