An image of Venus, made with data recorded by Japan’s Akatsuki spacecraft in 2016, shows swirling clouds in the planet’s atmosphere.
Credit: PLANET-C Project Team/JAXA

Could there be microscopic life in the clouds of the planet Venus? The idea may seem far-fetched, but in 2020, scientists discovered a tantalizing hint that it could be true, in the form of a strange gas in Venus’s atmosphere.

Venus has been called Earth’s twin. It’s next door to Earth, about the same size as Earth, and covered by an atmosphere of thick, swirling clouds. All of these features made it a tempting target during the early exploration of space. Speculators even imagined dense jungles covering the planet’s surface. When the first landers visited Venus in the 1970’s, however, they revealed a searing environment of 870 °F (465 °C) with pressures 90 times greater than that at Earth’s surface. Clouds of sulfuric acid filled the sky. The search for other life within the solar system quickly shifted to the more temperate Mars.

The new evidence was discovered by an international team of scientists that was actually more interested in exoplanets, planets orbiting distant stars. The team was led by Jane Greaves at Cardiff University in the United Kingdom. Scientists are constantly looking for ways to study exoplanets for signs of alien life. One way is to study the spectra (ranges of light) reflected by exoplanets for clues to chemicals in their atmosphere. One such chemical may be the gas phosphine. On Earth, phosphine is produced by microbes in anaerobic environments—places without oxygen. The gas is short-lived, so to be present in a planet’s atmosphere, it must be replenished continually. So, the presence of phosphine in an exoplanet’s atmosphere could be a sign of ongoing alien life.

The team recorded atmospheric data from Venus in an attempt to establish a benchmark for the spectral signature of an Earth-sized planet without phosphine. To their surprise, their findings indicated that the Venusian atmosphere did contain phosphine. After asking another team of scientists to double-check their results and studying the planet with a more powerful telescope, the evidence of phosphine was confirmed. Scientists do not yet know of a nonbiological way for phosphine to arise on Venus, pointing to the amazing possibility that Venus may harbor microscopic life. If such life exists, it is likely to be found in Venus’s clouds, where conditions are less hellish than those on the surface.

Greaves and her team emphasized that scientists are a long way from determining that there is life on Venus. The authors noted, for example, that sulfur dioxide produces a similar spectral signature to phosphine under certain conditions, raising the possibility that other molecules may mimic phosphine.

January 8, 2020

Late last year, on Dec. 18, 2019, the European Space Agency (ESA) launched the CHEOPS telescope into space, where it will study the composition of exoplanets. Exoplanets, or extrasolar planets, orbit stars other than our sun. The CHEOPS telescope was launched aboard a Russian-made Soyuz rocket from the Guiana Space Center on the northern coast of South America. CHEOPS—pronounced KAY ops—is an acronym for Characterizing Exoplanets Satellite. If the acronym sounds familiar, Cheops was also the Greek name of the ancient Egyptian king Khufu, who constructed the Great Pyramid at Giza.

A Soyuz rocket carrying the ESA’s CHEOPS telescope lifts off from the Guiana Space Center on Dec.18, 2019. Credit: ESA/S. Corvaja

CHEOPS is small for a satellite, measuring just 5 feet (1.5 meters) long. The craft turns within a polar orbit that allows it to fly between night and day. Its back, covered in solar panels, receives continuous sunshine, while the telescope and camera on the other side is always peering into dark, sunless, and limitless space.

This artist’s impression shows CHEOPS with its back to the sun and the telescope pointed into dark space. Credit: ESA/C. Carreau

The CHEOPS mission is not to discover new exoplanets, but rather to learn more about the exoplanets we already know exist. CHEOPS will study exoplanets larger than our own Earth but smaller than the planet Neptune. Scientists want to know if these intermediate sized exoplanets are more like “super-Earths”—large rocky worlds—or “mini-Neptunes”—small gas giants. By studying an exoplanet’s atmosphere, diameter, mass, and other properties, CHEOPS can determine its composition and whether or not it might be able to support life. Astronomers have discovered over 4,000 exoplanets so far, but there are likely hundreds of billions more to be found.

CHEOPS will use the transit method to study exoplanets. It will aim its camera at a star and capture periodic dips in the star’s light output. These dips occur when an exoplanet passes in front of—or transits—a star in relation to CHEOPS’s point of view.

CHEOPS is a stepping stone between the first exoplanet observatories, such as Kepler and COROT, and the powerful observatories of the near future. The United States National Aeronautics and Space Administration (NASA) James Webb Space Telescope (JWST), scheduled for launch in 2021, will be able to determine the gases present in the atmospheres of some exoplanets and even record low detail images of those gases. The European Southern Observatory’s Extremely Large Telescope (ELT) will also be able to image rocky exoplanets and characterize their atmospheres after it is completed in 2025. The ELT is a ground-based observatory being built in the Atacama Desert of northern Chile. Kepler and COROT prepared the way for CHEOPS, and the JWST and ELT will further examine the most promising CHEOPS targets as scientists continue the hunt for extraterrestrial life.

March 18, 2016

ExoMars 2016 hopes to find evidence of life on Mars, the fourth planet from the sun.
Credit: NASA/JPL/Malin Space Science Systems

On Monday, March 14, a rocket blasted off for Mars. The joint mission of the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos) will arrive at the Red Planet in October. When it reaches orbit, ExoMars 2016 will sniff the Martian atmosphere to see if it smells like life.

Mars is the fourth planet from the sun. Today, it is a cold, desolate place. It orbits some 142 million miles (228 million kilometers) away from the sun, about 1 ½ times the distance at which Earth orbits. Its atmosphere is about 100 times less dense than Earth’s. Water exists there only as ice or in small, briny, subsurface streams in the Martian summer. Mars has no global magnetic field to protect it from harmful solar radiation. It is hard to imagine life—even bacteria—eking out an existence in such a place.

Deep channels descending a crater wall on Mars showing evidence of water. Credit: NASA

For a brief time after it formed some 4.6 billion years ago, however, scientists think that Mars was a warmer, wetter planet, much like Earth. Since scientists think life emerged on Earth shortly after its formation, it is possible that life arose on Mars at this time as well, when conditions were more favorable. If it developed, this early life could have gone extinct as Mars cooled and its atmosphere was blown away by the solar wind. Some of it, however, could have survived, most likely as microscopic organisms living underground. Determining whether Mars has hosted or still hosts life is extremely important in figuring out how common or rare life is in the universe. If it developed twice in the same solar system, the odds are good that it developed elsewhere, too.

ExoMars 2016 consists of two modules: the Trace Gas Orbiter and an entry, descent, and landing demonstrator nicknamed Schiaparelli (after Italian astronomer Giovanni Schiaparelli). The Trace Gas Orbiter will scan Mars’s atmosphere for gases that might indicate the presence of life, such as methane. On Earth, such gases are usually formed as a byproduct of living things.

In addition to looking for possible signs of life in the atmosphere, ExoMars 2016 will pave the way for an even more ambitious future mission. If all goes according to plan, Schiaparelli will be the first successful lander for either the ESA or Roscosmos. (Both have made previous, failed attempts to land a probe on Mars.) With this experience, the ESA and Roscosmos plan to send a large rover to the planet in 2018. This rover will continue to look for signs of past and present Martian life. It will carry a drill able to bore up to 8 feet (2 meters) below the surface. If life is hiding out on Mars, the ExoMars missions just might find it.

November 26, 2014

A remastered image of Jupiter’s moon Europa released by NASA shows, for the first time, how this ice-covered body would appear to the human eye. The image is actually a mosaic of images taken by the Galileo spacecraft in the late 1990′s. The previous version of the image had been strongly enhanced with false color. The new image shows Europa in near-natural color.

Areas of Europa’s surface that appear blue or white contain relatively pure water ice. Reddish and brownish areas include higher amounts of other gases or solids. The polar regions, which are visible at the left and right of the image, are much bluer than the more equatorial latitudes. Scientists suspect this difference is due to differences in the size of the ice grains in these locations. (NASA/JPL-Caltech/SETI Institute)

Although Europa is one of the smoothest bodies in the solar system, its surface features include shallow cracks, valleys, ridges, pits, blisters, and icy flows. However, none of them extend more than a few hundred yards or meters upward or downward. In some places, huge sections of the surface have split apart and separated. The surface of Europa has few impact craters (pits caused by collisions with asteroids or comets). The splitting and shifting of the surface and disruptions from below have destroyed most of the old craters.

Europa is considered one of the likeliest places in the solar system for the existence of extraterrestrial life. Beneath its icy surface is an immense lake of salty liquid water that might be a home for living things.

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)

August 6, 2012

The largest and most advanced robotic laboratory ever sent to another planet made a perfect landing on Mars early Monday morning after a descent so complicated and perilous that mission controllers referred to it as “the seven minutes of terror.” The automobile-sized rover, named Curiosity, touched down at 1:32 a.m. Eastern Daylight Savings Time, capping an 8 ½-month, 354-million-mile (570-million-kilometer) journey from Earth. Its mission is to answer one of the most important questions in planetary science–whether Mars is, or ever has been, capable of supporting microbial life. Mission controllers at NASA’s Jet Propulsion Laboratory erupted into cheers and high-fives as Curiosity set down in Gale Crater, an impact crater that may once have held a lake. Moments after landing, Curiosity beamed back its first photographs of the Martian surface.

One of the first images of Mars taken by Curiosity after landing. (Image credit: NASA/JPL-Caltech)

The rover’s nail-biting landing involved a rocket-powered sky crane, the world’s largest supersonic parachute, and the incredibly precise detonation of 79 explosive devices. A failure at any stage of the descent would have doomed the mission. Curiosity, officially named the Mars Science Laboratory, began its plunge through the Martian atmosphere seven minutes before landing. At an altitude of 7 miles (11 kilometers), the parachute deployed to slow the lab, which was traveling at 13,200 miles (21,243 kilometers) per hour. At precise moments, the heat shield then the parachute and part of the rover’s protective shell broke away, leaving only the rover and its sky crane, which fired its rockets. At about 65 feet (20 meters) above the surface, the crane began lowering the rover using three cables. Once Curiosity touched down, the cables broke away and the crane flew off to crash land away from the drop site.

The rover carries a scientific payload about 15 times as massive as those carried by NASA’s Mars rovers Spirit and Opportunity. Curiosity, which has been described as a self-contained geology laboratory, holds 10 sophisticated instruments, two of which 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.

NASA's Curiosity rover is lowered onto the Martian surface by the sky crane, new technology designed specifically for this mission. (Image credit: NASA/JPL-Caltech)

Curiosity’s prime target is Mount Sharp (also known as Aeolis Mons), a mysterious 3-mile- (5-kilometer-) high mountain in Gale Crater consisting of layers of rock that may have been laid down over billions of years. Although the mountain looks similar to layered mountains on Earth, scientists do not know how it formed because, unlike Earth, Mars has not been shaped by plate tectonics. As the rover scales the mountain, it will analyze the layers in an attempt to discover how Mars, which was once warmer and wetter, became so cold and dry. It will also search for organic (carbon-bearing) molecules necessary for life as we know it. Curiosity is scheduled to explore the surface of the red planet for two Earth years (one Martian year). However, because it is powered by a nuclear generator, its mission may be extend for much longer.

Additional World Book articles:

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