Hello,

For everyone who hasn't been studying gravitropism this week that might read this post, the term gravitropism is used to describe the ability of plants to align themselves with Earth's gravitational field. In other words, this is why the roots of plants grow down and the stems and leaves grow upwards.

A lot of people think that gravity is only important on the Earth's surface. This is not true at all. The astronauts orbiting the Earth are still subjected to the Earth's gravitational forces - this is what keeps them in orbit! Being in orbit around the Earth is sort of like constantly falling towards the planet but missing the ground. This is why the astronauts feel weightless. For many years NASA scientists and astronauts have been doing experiments on board the Space Shuttle, the Mir Space Station, and the International Space Station to understand the effects of weightlessness on plant growth.

However, the conditions on the Space Station or a Space Shuttle orbiting the Earth are very different than the conditions on the Moon. The Moon's gravitational pull is only 1/6 that of the Earth's. An astronaut on the Moon therefore would weigh less than they do on the Earth, but they would not be weightless. If you could grow plants on the Moon, the plants would be subjected to the Moon's gravitational force. This is less than the Earth's gravitational force, but it's still a gravitational force.

Like the other Solar Week scientists, I know about basic physics. Some of the Solar Week scientists also specialize in studying the Sun while some of us specialize in studying the Earth's magnetosphere. Beyond explaining that the Moon does have gravity, I'm not really qualified to say how plant growth would be different on the Moon. You might want to try looking around NASA web sites to learn more about growing plants on the Space Station or the Moon. Here are a couple of articles to get you started:

http://science.nasa.gov/h...02/15may_maggrav.htm

http://science.nasa.gov/h...y2001/ast09apr_1.htm