The Request: Mars scientists are asking students from around the world to help them understand the red planet. Send in a rock collected by you or your classroom from your region of the world, and we will use a special tool like the one on the rover to tell you what it's made of. Then everyone can compare their rocks to the ones found on Mars.

The Response, from Space.com: An overwhelming response to a global request for rocks has a Mars geologist buried in terrestrial hunks and chunks.

"We're processing them and getting them moved out as quickly as we can, but we're still behind," said Arizona State University geologist Phil Christensen. "It doesn't seem to be letting up. I want to say that the mail carriers have been really tolerant."

Caltech astronomer Mike Brown, who led the discovery, said Sedna's slow rotation rate had him convinced there was an unseen satellite exerting a gravitational tug.

Here's why: Most objects in the solar system that don't have companions complete a rotation, or day, in a matter of hours. There are many examples of fast-spinning asteroids and similarly whirling large, round Kuiper Belt objects. Pluto, on the other hand, has had its rotational period slowed to six Earth-days by its companion, Charon.

Sedna spins on its axis once every 20 Earth-days, or perhaps even more slowly, making the presence of a moon practically inevitable, Brown had thought. So shortly after the discovery, Hubble was pointed at Sedna.

"Much to our surprise, there's no satellite," he told reporters today.

Italian scientists have discovered that the back of the Turin Shroud has the image of a man's face - and possibly his hands - impressed upon it. These findings were published Tuesday 13th April in the Institute of Physics journal, Journal of Optics A. Giulio Fanti and Roberto Maggiolio of Padova University used various image-processing techniques to enhance the faint features that can be seen in photographs of the Shroud (J. Opt. A6 491). This is the first time the reverse side of the controversial relic has ever been studied.

The Turin Shroud is a piece of linen, some 4.4 metres long and 1.1 metres wide, that contains images of the body and face of a man. The Shroud is believed by many to be the cloth Jesus was wrapped in before being buried. Although the front of the Shroud has been extensively studied, its back has remained hidden beneath another piece of linen, which was sewn on by nuns to cover up damage caused by a fire in 1532. However, this protective layer was removed in 2002, allowing the back of the cloth to be photographed.