As I write this on Christmas Day there is a new “star” in the sky. Not a real star, but a rocket launched faultlessly this morning from French Guiana near the equator carrying the James Webb Space Telescope.
On its way to a location one million miles (1.6 million km) away, far beyond the moon, 18 large concave mirrors folded up like origami will open to form one 6.5 m (21 ft) diameter mirror. The giant JWST will peer with red and infrared light at the first galaxies, as they were 13 billion years ago.
Another exciting goal is to search for signs of life on planets around other stars. Imagine you are on the moon during a total lunar eclipse. The sky is dark and starlit but it’s not night. In the sky is a bright red ring casting an eerie red glow on the barren landscape. Within that circle you see only black, but with a telescope you might see some lights and lightning flashes. A strange sight no human has yet seen, but probably within your lifetime someone will. Lunanauts will then experience a total eclipse of the sun, which from their moon base happens about once a year – common because the Earth appears four times bigger than the Sun and an eclipse lasts several hours.
The black disc they would see is the night side of the Earth, the Sun hidden behind it, and the thin red ring is sunlight coming through Earth’s atmosphere. Any people on the disc’s edge would be experiencing a red sunrise or sunset, blue light having been scattered down to make the sky blue.
If lunanauts study the light of that red circle in a spectroscope they will see dark lines at particular wavelengths, like a barcode. These lines correspond to different gases in our atmosphere: nitrogen, oxygen, methane, carbon dioxide, etc. Hopefully they will not see the CO2 still increasing! The atmosphere of any planet can be affected by even primitive life.
Perhaps this is how the JWST will discover life on exoplanets – planets around distant stars. A little starlight passing through their atmospheres as they transit in front of the star would imprint those barcodes, and if JWST can detect them it could analyze the atmospheres of planets thousands of light years away.
Any signs of life? Is our galaxy teeming with even simple life among its billions of planets? We may know in a few years.