Why are we looking for another Earth?

The announcement that an international team of researchers had found a planetary system with 7 “Earth-like” planets orbiting a cool (pun intended) small red star 40 light-years away brought loads of excitement and a series of questions. Have we really found other earths? Are they “habitable”? Do they harbour any kind of life? Could we go there, at least in the future?

I’ll get to these questions shortly. For now, let me hail a few significant aspects of this discovery. First, one of the observatories that participated in the research is in Morocco, near Marrakesh, at a mountainous site called Oukaimeden, at an altitude of 2,700 metres. And indeed, two of the team members are Moroccan, and a third one is Saudi, part of a big collaboration that included a Belgian institution (which provided the telescope in Morocco and other instruments), Nasa with its Spitzer infra-red space satellite, and institutions from the United States, the United Kingdom, France, Switzerland and South Africa.

Secondly, two of the telescopes that contributed observations and data for the discovery, including the one in Morocco, are no bigger than 60 centimetres in diameter.

Thirdly, the star, called TRAPPIST-1 after the Belgian ‘Transiting Planets and Planetesimals Small Telescope’ project, is twenty times more common than our sun but 2,000 times dimmer, representing both an opportunity and a challenge for future searches...

That’s for the main news. However, in the excitement and the rush to communicate to the public the fact that this is a historic discovery, some essential ideas were lost in translation.

Indeed, while the planets were described as ‘Earth-like’, they are not necessarily “like Earth”. The planets have diameters ranging between 76 per cent and 113 per cent of Earth’s diameter, and masses between 0.4 and 1.4 that of our planet. But we know nothing about whether they carry an atmosphere, how thick or how thin and with what gases, what the temperatures are on those worlds, how fast they rotate around themselves, are their axes inclined, do they have seasons, and many factors that really distinguish our planet from the hell-like environment of Venus (which by the above description is also ‘Earth-like’) or the cool but unprotected surface of Mars.

Secondly, when astronomers say that such worlds are ‘habitable’, what they mean is that they orbit their star at distances that make water — if it exists there — potentially liquid. Emphasis on “if it exists” and “potentially”! Water is an easy molecule to form, and we have found it in many different cosmic environments, but whether it will have accumulated anywhere on those planets and remained there is a big open question. Indeed, water can easily evaporate, especially if the atmosphere on a planet is too thin, so finding it there in liquid form is far from guaranteed, even if the planet happens to be in the right ‘goldilocks’, ‘habitable’ zone.

So, to make a long story short, and I don’t mean to disappoint you, dear reader, there is a world of difference between a planet having the size of the Earth and it carrying oceans or even lakes of water, let alone having any form of life.

So why are we are so excited about these planets? Could we possibly go visit them in the future? Sorry, but no. With our present space technologies, that is, spacecraft travelling at 50,000km/h, it would take roughly one million years to get there! And even if we built small boxes that could travel close to the speed of light (a futuristic possibility), they would take decades or centuries to reach there, carrying only tiny cameras and sensors, and still requiring loads of energy to be sent there...

So what are we excited about? Well, this is the most striking planetary system we have ever found; not even the solar system has so many rocky planets. And although we have only found two dozen or so planets of this kind so far, the statistics indicate that in our galaxy alone, there could be over a billion of them. Surely some of them will have life, right? Maybe. But at least the opportunities are there, and generations of researchers will be busy “dissecting” these worlds (from afar, with telescopes and other instruments) to try to find signatures of life, at least the primitive kind and study various issues of planetary science.

So let us look at the bright side now. With small telescopes on high mountains, or for our region large telescopes on mid-altitude mountains, amazing planetary systems can be found, scientific and educational opportunities open up, and everyone can contribute to this fascinating cosmic exploration and adventure.

Future generations will envy us and our children. In our era, humanity is discovering other worlds, amazing varieties of physical and cosmic conditions, and perhaps one day soon the grand prize: the discovery of life on another world. We are taking strides in that direction, and each step has brought wonderful samples. On with the grand adventure!

Nidhal Guessoum is a professor of physics and astronomy at the American University of Sharjah. You can follow him on Twitter at: www.twitter.com/@NidhalGuessoum.