In Brief: Features of the moon
The distinctive features of moon when observed from a telescope or even naked eye are:
- Impact craters
- Lunar craters, large and small, are the result of the bombardment of meteorites on the lunar surface.
- That is why they are called impact craters
- Light-coloured highlands
- Most of the lunar surface constitutes light-coloured highlands.
- About 85% of lunar surface is light-coloured highlands.
- Dark-coloured Maria
- The large dark areas on the lunar surface are called maria (singular form-mare for “sea” in Latin) (see figure below)
- These dark coloured features are the remains of huge lava flows which have solidified to give it a distinctive dark color.
- No Atmosphere
- Moon is too small to have an atmosphere.
- Its surface gravity is so low, (only about 1/6th of that of Earth), that any gas molecules easily escape into space.
- No global magnetic field
- Moon has no global magnetic field because it lacks in substantial amounts of moving molten material in its interior. (Earth’s magnetic field is due to moving iron core)
- However Moon does have weak magnetic fields in certain pockets when the rocks solidified billions of years ago.
In-Focus: Lunar Swirls
- Besides, lunar surface also has another distinctive feature called lunar swirls.
- They look like bright, snaky clouds swirled over the surface of the moon. (See figure)
- Imagine it to look like cream swirled in a cup of coffee.
Origin of lunar swirls
- It is seen that the location of lunar swirls coincide with the location of localized magnetic fields on moon’s surface.
- The localized magnetic fields on the lunar surface are due to magma ejected during volcanic eruptions.
- The localized magnetic fields deflect particles from the solar wind and cause some parts of the lunar surface to weather more slowly.
- This has resulted in bright-and-dark patterns swirling the lunar surface.
- In summary, the localized magnetic fields act like ‘sunscreen’ to regolith on the lunar surface.
- The ARTEMIS mission is NASA’s mission to study effects of solar wind from a lunar orbit.
- ARTEMIS it deployed primarily to observe Moon’s interaction with the solar wind.
Basics: Solar Wind
- Sun’s powerful gravitational attraction keeps most of the gases of the photosphere, chromosphere, and corona from escaping.
- Corona is the outermost region of the Sun’s atmosphere.
- Due to high temperature of corona, its atoms and ions are moving at very high speeds (about a million kilometers per hour).
- As a result, some of the coronal gas escape is called the solar wind.
- The solar wind is composed of electrons and nuclei of hydrogen and helium.
- Each second the Sun ejects about a million tons of material into the solar wind.
- Solar winds engulf the entire solar system including Pluto.
Interaction of solar wind and magnetic field
- Earth is protected from solar winds due to its global magnetic field that acts as a shield.
- The aurora seen at far northern or southern latitudes on Earth are produced when electrons and ions from the solar wind enter our upper atmosphere.
- On lunar surface the localized magnetic fields interact with solar winds to give rise to distinctive lunar swirls.