Scientific Crossword

1. The smallest particle of a chemical element that can exist.
4. A celestial body moving in an elliptical orbit round a star.
6. Emitting or relating to the emission of ionizing radiation or particles.
7. All existing matter and space contained into one place.
8. A medicine (such as penicillin or its derivatives) that inhibits the growth of or destroys microorganisms.
10. A pure substance that can't be broken down.
13. Sound or other vibrations having an ultrasonic frequency, particularly as used in medical imaging.
16. The emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles which cause ionisation.
17. Often described as the red planet, it is the fourth planet in the solar system.

2. The regularly repeated elliptical course of a celestial object or spacecraft about a star or planet.
3. A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
4. The process in which green plants convert sunlight into nutrients.
5. The rate per second of a vibration constituting a wave, either in a material (as in sound waves), or in an electromagnetic field (as in radio waves and light).
9. The process in which hot substances rise and cooler substances sink
11. A region of space having a gravitational field so intense that no matter or radiation can escape.
12. The force that attracts a body towards the centre of the earth, or towards any other physical body having mass.
14. A small rocky body orbiting the sun.
15. Seventh planet from the sun, ironically, due to its name, this planet is a gas giant.