QUESTION:
Do you think that it is possible that Mars was once a planet covered in 
ocean?  Water is found in the Martian poles!

ANSWER from Cathy Davis on December 11, 1996:
This is a question we hope to answer with the Mars Global Surveyor mission
which arrives at Mars on September 12, 1997.  But there is a lot of evidence
(flood channels, islands apparently eroded by water) that suggests that
once Mars had a great deal of water.

ANSWER from the Internet: 
http://quest.arc.nasa.gov/mars/teachers/tg/program1/Act1.3.html
(Live From Mars Teacher's Guide)

In the late 19th Century astronomers peered at Mars through telescopes 
and saw lines stretching across its surface: Giovanni Schiaparelli, 
an Italian, called them "canali" meaning "channels" or "grooves", which 
was translated into English as "canals." Some interpreted these "canals"
as evidence of intelligent life, and even an advanced Martian civilization 
capable of massive, planet-wide engineering projects. 

Now spacecraft have looked close-up at Mars, and we know there are no 
canals built by a Martian Corps of Engineers. But some of the channels 
do have shapes which look much like those we see on Earth. While it's 
tempting to think of them as dried-up river beds, most scientists think 
many of the channels resulted from sudden releases of underground water 
or sudden melting of underground ice, rather than from sustained rainfall 
and enduring rivers.  ...while no rain currently falls, there almost 
certainly has been running surface water in the past.

Now the thin atmosphere on Mars and the planet's deep freeze mean that 
liquid water cannot exist on the surface. But once, during that time 
when volcanoes were active, the planet could have been warm enough for 
liquid water.