September 10, 2018

One planet in our solar system might be a little wetter than we previously thought. A team of Italian scientists recently found evidence that a lake of liquid water most likely exists on Mars, buried deep beneath the planet’s southern polar ice cap. The team published its findings on July 25, 2018, in the journal Science.

Italian scientists recently found evidence of what they believe to be a liquid water lake beneath the southern polar ice cap of Mars, the fourth planet from the sun. Credit: NASA/JPL/Malin Space Science Systems

Mars is a very cold place. On average, the surface of the planet is about -80 °F (-60 °C). As on Earth, however, the poles are even colder. Both poles of Mars feature permanent caps of water ice that are more than 1 mile (1.6 kilometers) thick. In addition, the southern cap has a roughly 25-foot (8-meter) thick permanent covering of frozen carbon dioxide. The northern cap has a diameter of about 625 miles (1,000 kilometers), and the southern cap has a diameter of about 220 miles (350 kilometers). In the Martian winter, the caps expand as layers of carbon dioxide frost condense from the atmosphere.

Images such as this one, showing curved depressions in Mars’s Utopia Planitia region, prompted the search for subterranean water with ground-penetrating radar. Credit: NASA/JPL-Caltech/Univ. of Arizona

The team of scientists analyzed data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), an instrument aboard the European Space Agency (ESA) probe Mars Express. Mars Express has been studying the surface of Mars since 2004. MARSIS is a ground-penetrating radar device. Ground-penetrating radar can detect underground features and objects beneath rock and ice. The radar waves reflect off liquid water, however, and for years MARSIS has returned many images with this tell-tale reflection beneath the planet’s south pole. At last, after ruling out other possibilities, the scientists concluded that the radar had found a triangular lake basin about 12 miles (19 kilometers) wide and 1 mile (1.6 kilometers) deep.

The Martian lake might be similar to Lake Vostok and other subglacial lakes on Earth. Lake Vostok, the largest lake in Antarctica, lies beneath 2.5 miles (4 kilometers) of ice, has been isolated for 35 million years, and has temperatures below the normal freezing point of water. But life still likely exists there. If life exists on Mars, it could likely be found in such subglacial lakes. The odds of finding life there are still long, however. The Martian lake would be dozens of degrees below the normal freezing point of water and filled with salts toxic to life on Earth.

As scientists pinch and probe Mars for life, they are also eager to search for life beneath other planetary ice in our solar system. Europa and Enceladus, moons of Jupiter and Saturn, have warm oceans beneath their icy exteriors, and present the best possible chances for extraterrestrial life. The search for life will involve drilling through ice, however, an incredibly complex task even here on Earth. Engineers will have to design a remotely operated drilling system that can withstand the stresses of launch, spaceflight, and landing; drill through massive layers of ice using only batteries or nuclear power; and capture, analyze, and return data to Earth—quite a list! The testing for such a drilling system will begin on our own planet’s subglacial lakes.

April 4, 2014

The discovery of a plume of water vapor shooting from the surface of Enceladus in 2005 provided the first clue that this tiny moon of Saturn might hold liquid water. Now, radar surveys of Enceladus have revealed strong evidence of a subterranean sea with at least as much water as Lake Superior, the largest body of fresh water on Earth. The sea, which is buried beneath about 20 miles (32 kilometers) of surface ice, is centered on the moon’s south pole. But it may actually extend much farther, perhaps across the entire moon. Lined by a rocky floor, the sea may be as much as 5 miles (8 kilometers) deep.

The radar surveys that detected the sea were conducted by scientists working with the Cassini space probe, which has been in orbit around Saturn since 2004. Cassini has flown close to Enceladus several times. Each pass has allowed scientists to use the gravitational pull of the moon on the probe to help map the moon’s internal structure.

Geysers of water vapor and ice erupt from Saurn's moon Enceladus. (Cassini Imaging Team, SSI, JPL, ESA, NASA)

The discovery of the sea puts Enceladus in a select group of extraterrestrial bodies in the solar system that likely hold liquid water. These include Mars and Jupiter’s moons Callisto, Europa, and Ganymede. Since 2005, Cassini scientists have confirmed that the water vapor from Enceladus’s plumes contains carbon and nitrogen, two essential chemical elements for life as we know it. Could there be life there? Planetary scientist Jonathan Lunine, a member of the study team, said the presence of the sea makes Enceladus “a very attractive potential place to look for life.” In recent years, Enceladus and Europa had become space scientists’ favorite destinations for space missions seeking signs of extraterrestrial life in the solar system. However, due to funding limitations at NASA, only one mission has been approved–to Europa. This new evidence may help get a mission to Enceladus back on the drawing board.

Additional World Book articles:

• Cassini, Giovanni Domenico
• Satellite
• Space exploration
• Close Encounters with Saturn (a Special Report)
• Probing the Planets (a Special Report)

May 31, 2013

A large asteroid that is swinging past Earth today is bringing along a surprise companion–a moon. Asteroid 1998 QE2 will make its closest approach to Earth at a comfortable distance of 3.6 million miles (5.8 million kilometers) at 4:59 p.m. Eastern Daylight Savings Time. That distance is about 15 times as far as the orbit of Earth’s moon, so there’s no chance that the asteroid could crash into us.

Scientists have been tracking the asteroid since its discovery on August 19, 1998, by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research program in Socorro, New Mexico. Radar images of the asteroid suggest that it is about 1.7 miles (2.7 kilometers) in diameter. The moon is an estimated 2,000 feet (600 meters) across, more than 15 times the length of a football field. Only about 16 percent of asteroids larger than 655 feet (200 meters) in diameter belong to systems with two or more objects.

A series of radar images show asteroid 1998 QE2 as it appeared when it was about 3.75 million miles (6 million kilometers) from Earth. The small white dot at lower right in the images is the asteroid's moon. (NASA/JPL-Caltech/GSSR)

Scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, began observing the asteroid and its moon on May 29 using two radar telescopes—the Deep Space Network antenna at Goldstone, California, and the Arecibo Observatory in Puerto Rico. The radar observations, which will continue until June 9, will allow the scientists to determine the size and shape of the asteroid and its moon and to study the objects’ surface features. The first radar images of the asteroid revealed dark areas that may be impact craters or another kind of depression in the surface.

NASA’s Near-Earth Object Program identifies and tracks comets and asteroids that move around the sun near Earth’s orbit. These comets and asteroids are called near-Earth objects or NEO’s. The major role of the program is to determine if any NEO’s could strike Earth. By the end of 2008, the program had discovered and tracked more than 90 percent of the NEO’s larger than 0.62 mile (1 kilometer). The program is now focusing on finding 90 percent of NEO’s larger than 450 feet (140 meters). As of mid-2013, the program had found 9,858 NEO’s. At least 860 of them have a diameter of approximately 0.62 mile.

Additional World Book articles:

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