“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” Arthur C. Clarke
A Belgian-led team reported Monday that it's discovered three Earth-sized planets orbiting an ultra-cool dwarf star less than 40 light-years away or some 240 trillion miles away. In astronomical terms, that's pretty close considering our own Milky Way galaxy spans 100,000 light years. It's the first time planets have been found around this type of star — and it opens up new, rich territory in the search for extraterrestrial life.
The ultracool dwarf star, known as TRAPPIST-1, isn't the kind of star scientists expected to be a hub for planets. It's at the end of the range for what classifies as a star: half the temperature and a tenth the mass of the sun. TRAPPIST-1 is red, barely larger than Jupiter and too dim to be seen with the naked eye or even amateur telescopes from Earth.
This star is so close and so faint, astronomers can study the atmospheres of these three temperate exoplanets and, eventually, hunt for signs of possible life. They're already making atmospheric observations, in fact, using NASA's Spitzer Space Telescope. The Hubble Space Telescope will join in next week.
Two of the exoplanets have orbital periods of about 2.4 days and 1.5 days respectively. The third planet has a less well-determined orbital period in the range 4.5 to 73 days.
The inner two planets only receive four times and twice the amount of radiation received by the Earth respectively.
The third outer planet probably receives less radiation that of the Earth receives but its orbit is not yet well known and maybe lying within the habitable zone.