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Out of This World


The PacMan-shaped hot spot has baffled scientists. Image: NASA/JPL

By David Reneke

Dave Reneke brings news from the space and astronomy communities around the world.

PacMan in the Moon
Were you a closet PacMan player? If the image here looks familiar then you’re going to like this story.

The highest resolution temperature map ever taken of Mimas, one of Saturn's small inner moons, has revealed a surprising pattern on the rocky surface – a PacMan-shaped hot area that scientists are now trying to explain.

Not only did the fly-by of Mimas by NASA’s Cassini spacecraft on 13 February reveal the yellowish computer game shape, it also highlighted the vast Herschel crater that looks like the Death Star from Star Wars. It also revealed a bizarre pattern of unexplained daytime temperatures across this enigmatic 600 km-wide world.

"Other moons usually grab the spotlight, but it turns out Mimas is more bizarre than we thought it was," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena. "It has certainly given us some new puzzles."

One of the biggest questions researchers are asking is what is causing the sudden temperature change on either side of the two straight lines that form PacMan's “mouth”. The warmest region was in the morning, along one edge of the moon's disc, making a sharply defined PacMan shape, with temperatures around –294°F.

The rest of the moon was almost 30° colder. A smaller warm spot, the dot in PacMan's mouth, showed up around the Herschel crater with a temperature of –310°F. The warm spot around Herschel makes sense because the 5 km-high walls trap heat inside the crater, but scientists were completely baffled by the sharp, V-shaped pattern.

Who Speaks for Planet Earth?
The heading comes from an episode of Carl Sagan’s Cosmos but it rams home the importance of those first words and who says them. To use an old science fiction metaphor: “No one individual has the right to speak for us all”.

The question was put to the United Nations recently, and the consensus was that any signal detected would first be verified by several of the world’s largest radio astronomy institutions, confirmed by a specially convened panel of scientists, evaluated on its merits, then answered by the UN on behalf of humanity. But not everyone thinks we should show our hand.

There isn't any greater potential threat to the status quo than the discovery of extraterrestrial life, which is why some people would prefer it if we didn't try. Primed by the old B-grade sci-fi movies of yesteryear, we’ve become indoctrinated to invasion. These fears reveal more about us than any eventual ETs.

Most of the objections to contacting aliens are weak under close examination. We can't suddenly decide to hide after 50 years of pumping radio and television signals into space. As an intelligent species we must make every effort to contact anyone if they’re out there.

So let’s not knock the SETI program for having a go. Just because we haven’t heard from anyone yet doesn’t mean there’s no one there. Lack of evidence is not necessarily evidence of lack.

Let's step aside from our daily concerns for a moment and think about what we might want to say in reply to ET if our words are going on 1000-year journey. Perhaps an informative message would be to actually talk about the defining characteristics of our civilisation. Putting our best foot forward, so to speak.

The payoff is worth it. If we received a signal from another world, regardless of content, it would be undeniably the greatest story in human history. It would finally answer that age-old question: “Are we alone”.

David Reneke is an astronomy educator, writer and broadcaster who represents Australasian Science on more than 60 networked radio stations across Australia. He also produces a range of educational CD-ROMS on astronomy and space exploration for beginners, and runs an astronomy outreach program for schools throughout NSW. Subscribe to David’s free Astro-Space newsletter at