Ever since we discovered that distant galaxies are racing away from us, there has been a heated debate over just how fast the Universe is expanding.

At the beginning of the 21st century, we thought we knew the answer. But now, two very different viewpoints have emerged. And they are dividing the scientific community.

The Sky at Night meets leading astronomers and cosmologists on both sides of the debate. Which team has the right answer? Or could both
teams be right? If so, we may need to rethink everything we think we know about the Universe.

Marsquake! This month's episode follows Insight, NASA's latest mission to the Red Planet, as it goes in search of the secrets buried deep below Mars's surface. By listening for tremors caused by Marsquakes and meteor strikes, scientists hope to reveal how the planet was formed, why its fate was so different from the Earth and whether the planet is dead or alive.

The programme also says a heartfelt goodbye to Opportunity, the rover that explored the surface of Mars for more than 14 years until it was engulfed by a dust storm last year.