NCERT Book Class 7 English (The Alien Hand) Chapter 7 An Alien Hand

Before you read
Have you heard of the Viking Mission to Mars?
The National Aeronautics and Space Administration’s (NASA) Viking
Mission to Mars was composed of two spacecraft, Viking 1 and
Viking 2, each consisting of an orbiter and a lander. The primary
objectives were to obtain images and samples of the Martian surface
and soil and search for any possible signs of life. Viking 1 was launched
on 20 August 1975 and arrived at Mars on 19 June 1976. Viking 2
was launched on 9 September 1975 and entered Mars’ orbit on
7 August 1976.
Besides taking photographs and collecting other science data on
the Martian surface, the two landers conducted three biology
experiments to look for possible signs of life. As of now, there is no
clear evidence of the presence of living microorganisms in the soil
near the landing sites.
Now read the story.

Tilloo and his parents live beneath the surface of a planet
under artificial conditions.
Tilloo has heard and read about the sun and the stars. He
has never seen them.
Tilloo’s father goes to work through a secret passage, and
Tilloo wants to know all about it.