There are lots of celestial bodies that orbit around the sun, making up the solar system. The planets are the largest among them held by the strong gravitational field of the sun. There are other smaller objects like asteroids, meteors, comets etc in the outer space. Planetoids, asteroids, meteors and comets are minor celestial objects.
There are about 5,00,000 planetoids with many more being discovered every day. Larger planet-like asteroids or minor planets are called planetoids. They are smaller than planets and are small bodies made of rock that comes around the sun positioned in the asteroid belt. The region between Mars and Jupiter is called the asteroid belt. Centaurs are planetoids located between Jupiter and Neptune. Those planetoids at or beyond the Neptune’s orbit is called Trans-Neptunian objects. It was in the year 2001, a spacecraft from NASA landed on the surface of an asteroid for the first time.
The asteroids are found to rotate in periods of 3 to 30 days. There are more than 20000 asteroids that are known. Among them, ‘Ceres’ and ‘Eros’ are the larger ones. The temperature variation during the day and night is very large. For instance, on Eros the temperature during day is 100 degree Celsius and at night it is -150 degree Celsius.