Our mostly dry planetary neighbors once had lots of water—what does that imply for us?
- Written by The Conversation

We already knew about Venus. We had our suspicions about Mars. Now we’re sure.
Our two closest solar system neighbors once had oceans – planet-encircling, globe-girdling, Earth-like oceans. But waterbearing planets are fragile. Venus didn’t have the right stuff and lost her oceans to...