Exoplanets have become commonplace, and the idea that our Solar System is a unique individual in the vast swath of the Universe is long moot. But for ages, scientists have agonised over the likelihood that other star systems might host life. Each time an announcement has been made which teases the possibility of alien life, it has been swiftly knocked down by later studies. 

The Spitzer Space Telescope

The Spitzer Space Telescope

Until yesterday, when NASA made a stunning discovery by the Spitzer Space Telescope, located over 2 million kilometres away from Earth and at 1.5 times the distance of the Moon. The telescope which began operations last October, spent 500 hours studying one specific star system, known as TRAPPIST-1, just 39 light years away. Here’s what the agency learnt.

1. TRAPPIST-1 consists of a dwarf star that resides in the Aquarius constellation. It was first observed to have 3 rocky planets in 2015 by astronomers and yesterday, scientists announced the discovery of 4 additional planets with a rocky surface. The planets are named 1b to 1h in order of their distance from the star. The star itself is a dwarf, roughly the size of Jupiter and with ultra cool. It has a surface temperature of 2,550K, just half that of the Sun’s surface. 

An illustration of the rough distances of the planets to their star

An illustration of the rough distances of the planets to their star

2. 3 planets, e, f and g, reside in the star’s habitable zone, and are sufficiently exposed to enough X-rays and UV-rays to shape an atmosphere. They are believed to have a vapour atmosphere, while the nearer planets have a hydrogen-based atmosphere. That means that there’s a possibility of a carbon-based life development on the habitable planets. 

3. However, it’s believed that the planets are tidally locked, with the exception of planet h. What that means is only one side of the planets faces the star constantly and is subject to more intense heat than the other. The result is that of severe winds that circle the planets and while life is unlikely to emerge from such conditions, it’s possible at the twilight zones, where day and night meet. 

An artist's impression of what sunrises/sunsets might look like on one of the planets in their twilight zone

An artist’s impression of what sunrises/sunsets might look like on one of the planets in their twilight zone

4. The orbits of the planets are much faster than that of ours. The nearest has an orbit of 1.5 days, while the furthest is estimated at 20 days or so. They are all nearly the size of the Earth, the smallest being just slightly under Venus and the largest a tad larger than us. 

5. The star is metal-rich, which is an unusual property of stars at such a young age – TRAPPIST-1 is only 500 million years old. That’s very irregular as hydrogen-burning stars such as the Sun have virtually no metal elements. That comes in much later as the Sun begins to burn heavier elements. 

Planets in transit, an impression of the seven planets in the TRAPPIST-1 system

Planets in transit, an impression of the seven planets in the TRAPPIST-1 system

6. The orbits being so much closer, the planets in the habitable zones have a much closer view of the star, nearly 10 times the size of the Sun as we see it. However that does not mean they are much warmer, simply because the star is so much cooler. Imagine how stunning that must be like. 

7. Even if TRAPPIST-1 doesn’t contain life, it demonstrates that rocky planets and such systems are far more common than we’ve anticipated. Nearly most, if not all of the nearby star systems we’ve studied host planets. That makes life far more possible than we’ve previously expected. 

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