A planet in the "habitable zone" a. is close to the central star. b. is far from the central star. c. is the same distance from its star as Earth is from the Sun. d. is at a distance where liquid water can exist on the surface.

Planetary science studies planets, moons, and planetary systems, especially those of our solar system. It's a branch of astronomy but can also intersect with geology and meteorology. Scientists in this field aim to understand how planetary systems form and evolve.
In planetary science, **the habitable zone** is a critical concept. It's the area around a star where conditions might be just right for liquid water. This distance varies depending on the type of star. For example, a hotter star will have its habitable zone further out, while a cooler star will have it closer. The core idea is to find planets where life as we know it could potentially exist.
Understanding planetary atmospheres, surface conditions, and potential water sources are crucial. By studying other planets and their conditions, we can learn more about Earth and the potential for life elsewhere.

Liquid water is essential for life as we know it. It's a solvent, which means it can dissolve a variety of substances, bringing about the chemical reactions necessary for life. Hence, the presence of liquid water is one of the primary criteria for determining whether a planet might be habitable.
**For a planet to have liquid water on its surface, several conditions must be met**:

• The planet must be within the habitable zone of its star to maintain temperatures that allow water to remain in a liquid state.
• There must be an adequate atmospheric pressure to prevent water from evaporating or freezing instantly.
• The planet should have a stable climate to ensure liquid water can be sustained over long periods.

Scientists use advanced techniques to detect signs of liquid water on exoplanets (planets beyond our solar system), such as analyzing the planet's atmosphere for water vapor.

Astronomy is the scientific study of celestial objects, space, and the universe as a whole. It encompasses the observation and analysis of stars, planets, comets, galaxies, and the cosmos.
In the context of the habitable zone, astronomy plays a pivotal role. **Astronomers** use telescopes and other instruments to detect and study planets that orbit stars beyond our solar system, referred to as exoplanets.

• They look for planets in the habitable zone because these provide the best chance of finding liquid water and potentially life.
• Astronomical missions like the Kepler and TESS space telescopes have helped identify thousands of exoplanets, some of which lie in the habitable zone.
• Advanced methods like radial velocity and transit photometry are used to discover these planets and determine their distance from their respective stars.

Understanding the habitable zone in astronomical terms helps scientists narrow down which exoplanets could be candidates for further study in the search for extraterrestrial life.