Wednesday, 29 November 2017

Earth-sized Planets Discovered Orbiting Nearby Star

It was around this time last year, when I posted about exoplanets and the possibility of habitable life beyond Earth. Perhaps, then, a year on, is an apt time to revisit this theme and one of my favourite space stories from 2017 – the discovery of exoplanets found orbiting Trappist-1. Trappist-1 is a red dwarf star, located 39 light-years away from Earth in the constellation Aquarius. As such, it is one of our nearest neighbours in the Milky Way.

2015 was the year of the first discovery of Earth-sized planets orbiting Trappist-1 but, early in 2017, astronomers announced the news of additional exoplanets around the star, seven in total. The Guardian first published a story on the discovery in February, with follow-up stories in May and August.

The seven planets are, to date, the largest number of exoplanets found orbiting a neighbouring star, raising hopes that the search for alien life might be within reach using the next generation of astronomical telescopes. Trappist-1 shines with a light 2000 times fainter than our sun, meaning that the planets are more likely to hold liquid water and surface life. Researchers hope to obtain this information within the next decade.

One of the most exciting aspects of the story – alongside the possibility of discovering aliens, or a planet capable of supporting human life – was the incredible orbits of the planets and the prospect of the Trappist-1 star looming large in the sky from the planets’ surface (see illustration below). Because the planets are so much closer to the cool Trappist-1 star, each of their orbits is more compact than those of the planets orbiting our sun – the closest with a very short orbit of one and a half days, the furthest away taking 20 days.

Illustration of the view of Trappist-1 from the fifth planet by Nasa/JPL-Caltech.

These phenomena put me in mind of SF narratives that hinge on inter-world relationships, and the planetary astrophysics underpinning such stories. A famous example is Isaac Asimov’s ‘Nightfall’, a 1941 short story, later adapted into a novel with Robert Silverberg. The action takes place on Lagash, a planet located in a multiple star system with six suns, which keeps it constantly illuminated. The coming of an eclipse is a cause for concern for the planet's scientists, who fear that the general population will be unable to cope with the darkness. However, ultimately, it is the discovery of other stars and planets, which become visible during the eclipse, that sends Lagash's inhabitants into a frenzy.

The double planet (or binary planet) system of Urras and Anarres in Ursula Le Guin’s The Dispossessed is another memorable example, in which the juxtaposition of capitalist Urras and anarchist Anarres functions as a device for Le Guin’s exploration of ‘ambiguous’ utopias. In a variation of this theme, the planet Solaris, in the novel of the same name, orbits a binary star system with one red-coloured and one blue-coloured sun.

Geographies of the double planet system Urras and Anarres.

Finally, returning to our solar system, the Twilight Zone episode, ‘Midnight Sun’, imagines a scenario in which the Earth's orbit has been disturbed, causing it to move slowly towards the sun. In the end, it transpires that this was only a fever dream experienced by the protagonist Norma, and the Earth is in fact, inexplicably, moving further away from the sun.

SF experimentation with different star systems and planetary configurations adds to the other-worldliness of the stories, even while often offering a critical lens on real world issues. The Trappist-1 discovery begins to shed light on just how distant or close such other worlds may be.

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