Closing in an interplanetary mystery this week on planetary radio. Hi everyone, I'm Matt Kaplan.

Welcome to Public Radio's travel show that takes you to the final frontier,

and sometimes where no physicist has gone before.

Why aren't the pioneer spacecraft where they're supposed to be?

Is there an overlooked prosaic cause?

Or is something wrong with our understanding of the laws of the

universe. An update this week on the pioneer anomaly from JPL scientist John

Anderson. Later Bruce Betts will provide another opportunity to win the new Explorers Guide to

Mars poster as he sizes up the current night sky and other happenings around the solar system.

In our news this week week some astronomers are sizing down

2003 UB 313. The Kuiper belt object affectionately, though not officially,

called Xena by some.

You'll remember Mike Brown of Caltech telling us he believes the faraway sphere was substantially

larger than Pluto.

A lot more data has been gathered since then, enough to make Mike decide at one point that his

planet or planetoid or object, take your pick of terms, might be only barely larger than Pluto.

But hold the phone, a German team says Zena is much larger than Pluto.

There's an article at planetary.org that may help sort out some of the confusion.

And the absolute latest is in Emily

Lochu Wallace blog where she says Mike now accepts the German data.

Also at planetary.org is a detailed update on spirit and opportunity.

They keep going and going and going.

...