Does life exist elsewhere in the universe beyond Earth?
Based on our knowledge of the nature of life on Earth and of how it arose about 3½ billion years ago and subsequently evolved to occupy almost every ecological niche on the planet, and on our knowledge of the vastness of the universe, the answer is an almost-certain yes.
But what about life elsewhere in our own backyard – what about life in our own solar system besides Earth? We may well soon know a lot more about this because a spacecraft is speeding towards Europa, a moon of Jupiter, to investigate the suitability of a hidden ocean on this moon to harbour life.
Nasa’s Europa Clipper spacecraft was launched from the Kennedy Space Centre in Florida on October 14th, 2024. The mission is outlined by Nadia Drake in a recent edition of Scientific American.
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Jupiter is the largest planet in the solar system and the fifth planet out from the sun, orbiting the sun at a distance of 5.2 astronomical units (1AU equals the average distance from Earth to sun; 149.6 million kilometres). It is a gas giant with a mass more than 2½ times the combined masses of all the other planets. After the moon and Venus, Jupiter is the third brightest natural object in the sky.
Mars may have harboured life in the past but life on Mars today seems extremely unlikely. Europa is the best bet for a planet/moon in our solar system, apart from Earth, to harbour life. The goal of Europa Clipper’s mission is to learn if Europa is habitable for life as we know it.
[ Is there life on Europa? Nasa probe heads for moon with more water than EarthOpens in new window ]
Most space scientists are convinced that an enormous ocean is packed beneath Europa’s frozen surface, an ocean that may have brewed the raw ingredients of biology for billions of years. Perhaps life has already arisen there. Europa Clipper will arrive in Jupiter in 2030.
Europa Clipper will loop around Jupiter on a course that will carry it by Europa 49 times over four years. Clipper carries nine instruments on board that will study Europa’s chemistry, map the moon’s icy surface, look for water – plumes rising from the surface and search by radar for lakes within Europa’s frozen crust.
Mission scientists are hoping Clipper’s instruments, including world-class cameras and the best mass spectrometer ever flown (it ingests molecules and determines their composition), will survive the onslaught of the intense magnetic fields in this region for long enough to collect plentiful information about the life-harbouring potential of Europa. If the mission is extremely fortunate, Clipper will intercept a water plume and identify signature organic molecules of life.
In 1609 when Galileo Galilei pointed his home-made telescope at Jupiter, he also noticed smaller spots of light. He studied the motions of these spots and deduced they were moons of Jupiter. He named the moons Europa, Ganymede, Io and Callisto.
For a long time, scientists thought that the habitability of other planets for life depends on the planet’s distance from the warming influence of a star. It was also assumed that our outer solar system was a frozen region with very little geological activity.
But Nasa’s 1979 Voyager and its 1995 Galileo spacecraft sweeps by Jupiter found gravitational interaction between Jupiter and its moons have warmed and made them all very geologically active.
Io is extremely volcanic, and Europa seems to exhibit plate tectonics and a salty water sea of unknown depth trapped beneath a frozen surface shell of unknown thickness. It seems that a planet’s or moon’s biological potential does not depend solely on its distance from the sun, and possibly not even on the sun at all, as indicated by the existence of life on Earth around hydrothermal deep ocean vents.
American astronomer Frank Drake wrote a formula in 1961 to estimate the number of civilisations in our Milky Way galaxy with which communication might be possible. Nadia Drake is Frank Drake’s daughter. The Drake Equation includes several factors, including rate of star formation, the fraction of stars that have planets and the numbers of planets that potentially support life.
The equation stimulates scientific thinking about the search for extraterrestrial intelligence (SETI), and Frank Drake is generally regarded as the father of SETI. Europa Clipper’s mission will help to assign meaningful values to some of the SETI equation variables.
William Reville is an emeritus professor of biochemistry at UCC
