We have been on the constant look out for planets that could support life – or, at least, life as we know it – for as long as we have accepted that the earth is not the centre of the universe. NASA and various other agencies have been looking out for planets that can support life. Over the years scientists and astronomers have discovered at least three thousand exoplanets – planets that orbit some other star in the galaxy.
There are plenty of exoplanets that are Earth-like, meaning that they are believed to have conditions conducive to supporting life as we know it. One such planet even orbits Proxima Centauri, the closest star after the sun (it is only at a distance of four light years). So when it was announced on February 22, 2017 that NASA had discovered seven exoplanets that were supposed to be Earth-like, the reception to the news should have been lukewarm.
It was anything but. The news exploded to the point that Google felt compelled to make a special doodle commemorating the event. NASA said that seven rocky planets, the size of the Earth had been discovered orbiting the dwarf-star Trappist-1, a star in the Aquarius system. The world went crazy. Articles and news items appeared in every journal of note and even some that weren’t (of note).
The Big Deal
So what was the big deal? By all rights, this wasn’t the first time something like this had been discovered. So why was everyone so revved up about this news? Well, apart from the potential for colonization, the Trappist-1 system is such big news because this is where we start getting really serious about a search for alien life.
How it Works
The most common method used to detect planets orbiting a star is by measuring any changes that occur in the light emanating from said star. This means that if the light dims even briefly and by the smallest amount it could mean that a planet was orbiting that star. In our search for life elsewhere, we have assumed that conditions have to be more or less the same as they are in the solar system and so we have focussed our search on stars that at least resemble our sun in terms of size. The assumption was that such stars had the highest chance of having a planet with life on it.
The Trappist-1 system has put paid to all such assumptions. Trappist-1 is a dwarf-star, ultra-cool and only slightly larger than Jupiter in size. The most interesting fact here is that our galaxy is full of such dwarf-stars. In fact, the incidence of such stars is much higher than the incidence of sun-like stars. This means that our chances of finding Earth-like exoplanets have increased exponentially. This also means that our chances of finding life on one such planet have also increased.
What makes it Work?
Of course, the biggest question raised here would be – if the star is so small, how can it help sustain life? Well, the seven planets that make up the Trappist-1 system orbit at distances from the star that could fit within the orbit of Mercury. The proximity of the planets to the star is compensated for by the fact that the dwarf-star is ultra-cool; meaning its brightness is a thousand times less than the brightness of the sun.
These factors allow for three of the seven planets to fall directly in the habitable zone of the star. The term ‘habitable zone’ refers to planets on which it is very likely that water in its liquid form will exist. It is also quite likely that the other four planets could have liquid water depending upon their atmospheric compositions.
In 2018, the James Webb Space Telescope will be launched. This telescope has the ability to measure and determine the chemical composition of the atmospheres on exoplanets. The seven Trappist-1 planets are ideally suited for such observation. Scientists are excited to discover whether any of the planets has an atmospheric composition that includes methane, oxygen or ozone. The presence of even one of these gases could indicate the presence or at least possibility of life on the planet.