Acids spark lively debate

LEARNING of even the possibility of extraterrestrial life is a topic that has fascinated people for a very long time.

Even as long ago as the 17th century, French author Bernard le Bovier de Fontenelle wrote a famous book titled Entretiens sur la pluralité des mondes (Conversations on the Plurality of Worlds), in which a philosopher discusses the possibility of life other than on the Earth.

However, such thoughts go back much further: even some of the ancient Greeks considered the idea of life among the stars.

I found it interesting recently to read of some thoughts on amino acids, presented in a paper by a group of researchers led by Ngoc Truong at Cornell University in the United States.

Amino acids are building blocks of protein, which makes up a significant portion of our bodies. Indeed, they can be well described as building blocks of life itself. They are organic compounds, meaning they are composed of combinations of carbon, hydrogen, oxygen and nitrogen.

It is important to realise

that the presence of amino acids does not necessarily indicate the presence of life itself, and that of the hundreds of amino acids, only 20 form proteins.

In their recent paper, the researchers comment that of the 14 amino acids that they have studied, all of them would almost completely decompose in hydrothermally active oceans over a fraction of the age of the solar system.

Therefore, detection of these amino acids in such environments today would indicate that these are not what are called “primordial’’ substances — that is, compounds that have been around for billions of years. Instead, they would be an indication of more recent formation. In particular they point out that the detection of two of these, aspartic acid and threonine, would be a very strong indication of a modern origin, and would therefore be a key finding about organic chemistry in such environments.

The significance of hydrothermally active oceans is that in relatively modern times we have realised that such environments do exist on other worlds. By “worlds’’, here, I am specifically referring to two of the moons of the outer planets: Jupiter’s moon Europa, and Saturn’s moon Enceladus.

The existence of these moons has been known for a long time. Jupiter’s four largest moons, including Europa, have been known since Galileo Galilei and others pointed their primitive telescopes to the planet in the early 17th century.

Saturn’s moon Enceladus was discovered in 1789 by William Herschel, who eight years earlier had also discovered the planet Uranus.

Astronomers of centuries ago could not possibly have envisaged what we would find using spacecraft: that both of these moons probably have subsurface oceans.

In 2014, NASA’s Cassini spacecraft showed that Enceladus displays plumes of water and other material erupting from underneath the ice in its southern regions. Europa’s subsurface ocean was inferred much earlier, in particular using measurements made by the Galileo spacecraft in the 1990s, but also from earlier Voyager images and theoretical considerations.

We would certainly like to know a lot more about the content of the oceans underneath the surfaces of these icy moons. Future spacecraft missions to Europa, in particular, are being planned, and research of the type that Truong and his colleagues are performing here on Earth will link in well with measurements that can be made billions of kilometres from home.

This type of work reminds me of a similar situation with regard to Mars. If there is methane on Mars — its presence was announced some years ago, but it is still uncertain — it cannot have been there long, because it would break down in the Martian atmosphere. Its detection would mean that it is currently being produced, though whether this would be of biological or volcanic origin would still be an open question.

There is so much more that we need to learn, and we have the capability to do so. Meanwhile, you can see both Jupiter and Saturn in our current evening sky.

Jupiter is the brilliant yellowish-white object seen low in the east in the early evenings.

Saturn, also prominent but less bright than Jupiter, rises about 7pm and is clearly visible above the eastern horizon by about an hour later.

We live in exciting times.