Project Hail Mary

Project Hail Mary by Andy Weir

A man wakes up without knowledge of who he is or what he is doing. His memories gradually filer back in bits. The story unravels with his current condition as well as flashback to the past. We realize that he is on a mission to outer space to save humanity. The others on his mission have died. He previously taught science to children and did research on mysterious "astrophages" on the side. This small organisms can suck enormous amounts of energy from the sun. This will lead to massive global cooling in short order. He is on a mission to space to attempt to find something to counteract this problem to allow humanity to survive. 

In space, he meets another alien whose society is in similar circumstances. The other alien has also had his crew wiped out. As the last member of the crew, they only survived because the astrophages being attended had served as a radiation shield. The two of them join together to try to find a solution. They discover a natural predator to astrophages and then attempt to breed it to properly inhabit the local conditions. There are a number of crisis, but eventually they send a message back to earth. The human is on the way back to earth when he encounters a issue. He realizes this will also endanger the alien, so he goes back to help the alien ship. He ends up helping him and going to the alien planet. There he lives a somewhat comfortable - the aliens are excited to have an extra-terrestrial and help him to adapt.

The book has a positive story of encounter with existential threats. The survival of humanity does depend on a single person making good decisions. The right decisions were made. Earth appeared to survive. He thinks that it was what he did that lead to the success. It was not quite clear to me why both lifeforms seemed to travel to the same area in space to look for a solution. How did they know? And did they think they could really get a message back before the earth totally turned on itself with warfare? It did seem to work, but there did seem to be many close calls.