�鶹������ҳ���

The conditions in space are hostile to life and travelling in spacecraft is difficult and expensive.

So scientists are using different methods to see if there is life on planets other than the Earth.

Space probes can explore other planets without needing astronauts.

Some of the missions undertaken by space probes include:

• Viking 1 and Viking 2 - landed on Mars in the 1970s, took photographs and analysed soil samples
• Mars Global Surveyor - went into orbit around Mars in 1996/1997 and mapped the surface in 3D
• Spirit and Opportunity - two robot vehicles that landed on Mars in 2004
• NASA’s InSight – a Mars explorer that landed on the 26th November, 2018. It is the first robotic explorer to study in-depth the crust, mantle and core of Mars

Life on other planets

The Earth's atmosphere contains about 21 per cent oxygen as a result of photosynthesis by plants and single-celled organisms.

If we found evidence of oxygen in the atmosphere of another planet, it could indicate the presence of life forms.

It is possible to detect oxygen and other gases on other planets by studying the light reflected from planets.

It is thought possible that alien civilisations, capable of transmitting radio signals, may exist.

The Search for Extra-Terrestrial Intelligence (SETI) is a programme that uses radio telescopes to look for non-natural signals coming from space.

Space probes and landers are also looking for extra-terrestrial life.

There are photographs of channels on Mars that may have been created by flowing water.

Landers touch down on planets and take a soil sample, which is then analysed for evidence of life.

• It is estimated there are up to 400 billion stars in our galaxy, the Milky Way.
• There could be 50 billion exoplanets orbiting these stars.
• If even 1% of these were earth-like there are 500 million stars in our galaxy alone capable of supporting life.
• It is estimated that there are at least as many galaxies as there are stars in our galaxy.