Steal Across the Sky - 9780765319869

Cam, Lucca, Soledad: three ordinary people chosen by an alien power for reasons no one understands to undertake a journey no one on Earth could have imagined. They, and eighteen other young humans, have been sent by the alien Atoners to distant worlds to observe. To discover the Crime. To see with their own eyes the wrong done to humanity.
At first everyone thought it was a joke. Then they thought it was some kind of viral marketing campaign. The ad had appeared on the Internet:
We are an alien race you may call the Atoners. Ten thousand years ago we wronged humanity profoundly. We cannot undo what has been done, but we wish humanity to understand it. Therefore we request twenty-one volunteers to visit seven planets to witness for us. We will convey each volunteer there and back in complete safety. Volunteers must speak English. Send requests for electronic applications to witness@atoners.com
A few days later, a huge new installation appeared on the moon. The aliens had arrived. And it seemed that they had been here before. They said that they needed to atone for what they had done to humanity ten thousand years ago and that humanity would have to discover for themselves what that great wrong was.
A team of three would be sent to each distant system on a space ship they have no idea how to control. When they arrive, they will discover that humans live on these worlds - and it's up to each of them to make their way in an alien world. They cannot leave until they have discovered the truth.
What they find on these distant planets will change them. The knowledge they will bring back to Earth will change everyone