20 August 2023


Joshua Winn. The Little Book of Exoplanets. Princeton University Press 2023.

In 1971 I took astronomy classes at Manchester University and one of my lecturers was Professor Zdenek Kopal. He was one of the first scientists in the then new age of space exploration trying to find ways to discover if any of the trillions of stars we know to exist had solar systems like our own and if any of those other suns had planets capable of supporting life like the Earth.
Whilst he was an expert in the mathematical ways in which the impact of planets on the movement of its parent star allowed us to surmise those planets existed, he had a bit of a downer on the consequences of alerting any out there capable of harbouring life like our sun does for Earth. Indeed he delighted in smiling wickedly at us sitting there agog saying - ‘If we hear that space phone ringing - don’t answer’.

The thought that unlike on Star Trek - then new on TV - you would not wish to say hello to other intelligent beings capable of looking for companions in the vastness of space - came over as rather odd to me at 19. Until he cogently explained what happened on Earth over the past 1000 years when a more advanced civilisation sailed oceans to discover remote island races or new continents packed with wonder.

It never ended well, Kopal reminded us - for the less advanced people. They either got conquered by better weapons they had never seen before or made slaves to benefit a distant empire. Rarely did it turn into a mutually beneficial relationship. So why would advanced aliens saying hello surveying us with technology we can only dream about be a good thing? We might be better off pretending to metaphorically hide behind the cosmic sofa.

But of course, as Kopal also reminded me, it was too late anyway. Our radio signals had been beaming out their version of all human life for 50 years and TV images had time to travel at the speed of light to many possible planets around countless stars. So staying quiet was even in 1971 an impossibility. If they were searching then they already knew we were here. Indeed it was a widespread view that the highly popular UFO mystery was the result of aliens from one of those worlds coming to say hello but perhaps wisely keeping distance as they noticed how violent we seem to be.

In the decades since I heard his memorable views science has moved on at quite a pace. Especially in the last two decades as we have put even better ‘eyes on the skies’ - including telescopes in orbit away from our thick atmosphere that severely restricts the picture we can see from under that blanket of gases. Even so stars are a very long way from Earth.

Technology is improving all the time and whilst the vast distances involved are why we are as yet some way from taking real photographs of such planets outside our solar system we have found ingenious ways to plot where planets exist and learn the conditions on their surface so we can draw images based on the type of star that is their sun.

The author of this thrilling exploration of humanity’s real life Star Trek knows his stuff as a Princeton astrophysicist and member of NASAs transiting exoplanet survey. Exoplanets being the name of planets detected around stars beyond our sun. The exciting fiction of Star Trek turns out surprisingly right. There are ‘strange new worlds’ around most stars. Solar systems are normal not an exception. And some would probably make Mr Spock’s eyebrows raise a little too.

One circling the star Aldeberan is six times larger than Jupiter - the huge gas giant in our solar system. Others are so far from their sunS that their orbit - which in the Earth’s case is, of course, a year - can only be measured in centuries.

Gradually as we have found more and more the numbers have expanded and the diversity of their characteristics became extraordinary. Including seas of molten rock and ones on the point of being imminently destroyed by their sun.

Astounding stats pepper this fascinating book. For instance that 99.99999999% of planets known to exist within our Milky Way galaxy are circling other stars NOT our sun - which has just 8 since we discounted Pluto as a true planet.

The author carefully charts the ways in which we have learned to ‘discover’ something impossible to see directly with our eyes even using the largest telescope, as the laws of physics are a tough boundary to cross. It is like trying to view a fly on a car headlight miles away. It is only in the last two decades a real search has been made possible, many years after I saw Kopal talk of why he felt they would be out there by the billions and some almost certainly would have life.

Kopal’s only methods in 1971 were mathematics and guesswork. We have in a short blink in the eternity of space-time come a very long way that would have astonished my old university professor. Indeed in the late 90s we knew only of enough definite exoplanets to count on both fingers across millions of suns visible in our night sky. Today that number is in the thousands and we know not only that they exist but hard scientific facts about the conditions on these worlds.

Indeed alongside the normal book index in this fascinating guide to the story of that search is a two page index to planets discussed in the book - with names that are rather less Star Trek - so not Vulcan but forged from the vast numbers of stars to catalogue. So each star has a number assigned and to it and letters added for discovered planets.

For example the not exactly catchy name of planet HD 209458B orbits a distant Sun like star but is a large Jupiter-like gas giant located close enough to the star that its size relative to its Sun causes an eclipse akin to about 1% of a total solar one on Earth by our moon. It passes in front of its sun regularly so as we get eclipses when our moon crosses the path of our Sun this 1% eclipse - called a ‘transit’ - causes light from the star to dim as a measurable part is blocked when this gas giant crosses its solar surface in line to us. Meaning we can reliably not just judge the size and orbit of the planet causing this ‘dimming’ but by tracking the transits measure the elements within the planet’s atmosphere as it makes these tracks past what is to us just a distant star.

This book is full of the thrill of this modern journey of exploration and like the story of our first space voyages - not yet via the Starship Enterprise but remotely bringing the stars and their solar systems into our earthly remit.

We stand on the final frontier of a whole new map of the universe closer than ever to discovering if Star Trek got the other things right and beings like Vulcans and Klingons are actually out there. They may be just a measurement of twinkling light and transits of a star away from discovery.
  • Jenny Randles

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