According to NASA chief scientist Dr Ellen Stofan, in the next twenty years, scientists may very well finally answer whether we are alone in the Solar System and beyond.
This artist’s impression shows the super-Earth exoplanet HD 85512b. This exoplanet is about 3.6 times as massive as the Earth and lies at the edge of the habitable zone around the star, where liquid water, and perhaps even life, could potentially exist. Image credit: ESO / M. Kornmesser / Nick Risinger, skysurvey.org.
“NASA science activities have provided a wave of amazing findings related to water in recent years that inspire us to continue investigating our origins and the fascinating possibilities for other worlds, and life, in the Universe,” Dr Stofan said April 7 during a panel discussion that focused on NASA’s efforts to search for habitable worlds.
Astronomers see the signature of water in giant molecular clouds between the stars, in disks of material that represent newborn planetary systems, and in the atmospheres of giant planets orbiting other stars.
The Solar System’s four gas giants are thought to contain huge quantities of water, and their moons and rings have substantial water ice.
Perhaps the most surprising water worlds are the five icy moons of Jupiter and Saturn that show strong evidence of oceans beneath their surfaces.
Planetary researchers using NASA’s Hubble Space Telescope recently uncovered evidence for a massive subterranean ocean on Ganymede, one of the four Galilean moons of Jupiter and the largest moon in the Solar System.
Europa is thought to have an ocean of liquid water beneath its surface in contact with mineral-rich rock, and may have the three ingredients needed for life as we know it.
Gravity data from NASA’s Cassini spacecraft recently revealed that Enceladus – the sixth-largest of the moons of Saturn – harbors a regional subsurface ocean at depths of 30-40 km. In 2014, scientists discovered more than a hundred active geysers erupting on this icy moon. A March 2015 study suggested Enceladus may have hydrothermal activity on its ocean floor.
NASA’s missions have also found signs of water in craters on Mercury and our moon.
While our Solar System may seem drenched in some places, others seem to have lost large amounts of water.
On Mars, scientists have found evidence that the planet had water on its surface for long periods in the distant past.
In 2012, Curiosity rover discovered an ancient streambed that existed amidst conditions favorable for life as we know it.
More recently, NASA scientists using ground-based telescopes were able to estimate the amount of water Mars has lost over 4.5 billion years.
They concluded that the planet once had enough liquid water to form an ocean, and that the ancient Martian ocean covered a greater portion of the planet’s surface than the Atlantic Ocean does on our planet and held more water than Arctic Ocean.
The story of how Mars dried out is intimately connected to how the planet’s atmosphere interacts with the solar wind. Data from NASA’s solar missions are vital to helping scientists better understand what happened.
This illustration depicts the best-known candidates in NASA search for life in the Solar System. Image credit: NASA.
Researchers think it was too hot in the Solar System’s early days for water to condense into liquid or ice on the inner planets, so it had to be delivered – possibly by comets and water-bearing asteroids.
According to Dr Stofan, NASA’s Dawn mission is currently studying Ceres, which is the largest body in the asteroid belt between Mars and Jupiter. Scientists think Ceres might have a water-rich composition similar to some of the bodies that brought water to the Solar System’s terrestrial planets.
The amount of water in Jupiter holds a critical missing piece to the puzzle of the formation of the Solar System. This gas giant was likely the first planet to form, and it contains most of the material that wasn’t incorporated into the Sun. The leading theories about its formation rest on the amount of water the planet soaked up.
Dr Stofan said that with the study of extrasolar planets, NASA scientists are closer than ever to finding out if other water-rich worlds like ours exist. For example, the Hubble and Spitzer space telescopes recently detected water vapor in the atmosphere of the extrasolar Neptune-like planet HAT-P-11b.
“In fact, our basic concept of what makes planets suitable for life is closely tied to water: every star has a habitable zone, or a range of distances around it in which temperatures are neither too hot nor too cold for liquid water to exist,” Dr Stofan said.
In recent years, NASA’s Kepler Space Telescope has helped scientists discover many potentially habitable exoplanets, such as Gliese 832c, Kepler-438b, Gliese 667 Cc.
