Chris McKay explains how Mars could become habitable

They will also discovered why watching comet Hale Bopp zoom away is exciting astronomers.

The European Astrofest 99 conference and exhibition in London brought together professional and amateur astronomers. It also attracted some top scientists, like Nasa's Chris McKay.

Nasa's top eclipse expert is at Astrofest 99

He has just returned from the Antarctic, where he is using bacteria found in the harsh environment as a model for researching life on Mars. He explained how humans could turn a frozen planet into a garden of Eden.

"We think that Mars had a past with life, so that leads us to wonder if it could have a future with life," McKay told the BBC.

The first step would be to raise the temperature by adding tiny amounts of greenhouse gases to the atmosphere. Then planting plants from cold parts of the Earth would do the rest. He admitted it would take hundreds of years to complete.

Steven Young, Managing Editor of Astrofest sponsor Astronomy Today added: "There are ethical questions of should we be playing around with the environment of other planets. Friends of the Solar System, or whatever pressure groups will exist, would have something to say about it."

Chasing comets

Comet Hale Bopp may have passed out of sight but it is still very much in mind for Dr Alan Fitzsimmons of Queens University Belfast. He explained why astronomers still very much have their eye on the comet.

Dr Alan Fitzsimmons explains why he is still watching comet Hale Bopp

" We learned a lot from Hale Bopp when it was visible from Earth but we never got a good view of the heart of the comet," Dr Fitzsimmons said.

This was because the heat of the sun caused the icy mass to melt and gases and dust streamed away from the core, obscuring the view.

As the comet recedes to the outer reaches of the solar system, it cools and the gases and dust dissipate. This leaves a clear view.

"The we can see how large it is and what effect travelling through the solar system had," said Dr Fitzsimmons.

Eclipse expert

Also at Astrofest 99 was Fred Espenak, Nasa's most eminent eclipse scientist. He has spent over 20 years chasing eclipses to every corner of the world.