SCIENCE UPDATE
The Milky Way probably includes billions of solar systems with inhabitable planets. Astronomers have now calculated how many of them have the opportunity to spot us.
New discoveries and updates from the ever-fascinating world of science.
Over the past few decades, astronomers have discovered more than 4000 exoplanets − those orbiting other stars − within our galaxy, the Milky Way. Some of these could harbour life, perhaps even intelligent civilisations which might, like our own, be scanning the stars for signs of life elsewhere.
But how visible would we be when viewed from the outside? Scientists from Cornell University in the United States have looked into this, and they calculate that our world – and the evidence of life on it – could be observed from 1004 known stars located within a distance of 326 light years.
The scientists used similar methods to those used in our own searches in the other direction, seeking exoplanets and evidence of life on those. In most cases, astronomers are able to discover an exoplanet when, as observed from Earth, it moves in front of its star, so the starlight is slightly dimmed. If alien civilisations are to discover our own world, they would need to be located in a direction that allows their line of sight to encounter both the Sun and Earth. Then, if they find us, that line of sight should also allow them to see evidence of life here. The sunlight that passes through Earth’s atmosphere is influenced by the substances present in it, so that analyses of light wavelengths would reveal evidence of life such as oxygen and methane.
We know that 95% of these 1004 stars are so old that life on their planets has had billions of years to evolve. One particularly interesting star is K2-155, located 200 light years away and orbited by an Earth-like planet.
Other candidates could emerge in the decades to come, because the stars’ reciprocal locations change all the time. In 2044 another star with exoplanets, this one only
12 light years away, will be in a position to spot us.