Mercury: Crash Course Astronomy #13

Summary

This script explores Mercury, the solar system's innermost and hottest planet, known for its rapid movement and elliptical orbit. Despite its proximity to the Sun, it has a surprisingly long and complex day-night cycle due to a 2:3 spin-orbit resonance. The planet, largely unobservable from Earth, has been studied through space probes revealing a cratered surface, a large iron core, and the unexpected presence of water ice in permanently shadowed polar craters. Its unique characteristics challenge our understanding of planetary dynamics.

Takeaways

• 🌞 Mercury is the closest planet to the Sun and experiences extreme temperatures.
• 🏃 Mercury was named after the Roman messenger god, symbolizing its fast movement in the sky.
• 📡 In 1639, Giovanni Zupi observed Mercury's phases, supporting the heliocentric model of the solar system.
• 🌍 Mercury is the innermost planet and orbits the Sun at an average distance of about 58 million kilometers.
• ⏱️ Mercury completes an orbit around the Sun every 88 Earth days.
• 🌓 The planet shows phases similar to the Moon due to its position relative to the Sun and Earth.
• 🔭 Mercury's observation is challenging due to its proximity to the Sun and small size.
• 🛰️ Space probes like Mariner 10 and MESSENGER have provided significant data about Mercury's surface and composition.
• 🌗 Mercury has a highly elliptical orbit, affecting the intensity of sunlight it receives.
• 🌅 Mercury's day is 59 Earth days long, with a unique 2:3 spin-orbit resonance.
• ⏳ A day on Mercury is very long and peculiar, with the Sun appearing to move backwards in the sky at certain times.
• 💧 Despite its high surface temperatures, there is evidence of water ice in permanently shadowed craters near the poles.

Q & A

What is the closest planet to the Sun and why is it considered 'pretty cool'?

The closest planet to the Sun is Mercury. It is considered 'pretty cool' because, despite its proximity to the Sun and high temperatures, it has a unique set of characteristics such as its quick movement across the sky, phases similar to the Moon, and the presence of water ice in its deep polar craters.

Why does Mercury never appear far from the Sun in the sky?

Mercury never appears far from the Sun in the sky because its orbit around the Sun is much smaller than Earth's, keeping it close to our star. This results in it always being near the Sun's position from our viewpoint.

What significant discovery did Giovanni Zupi make about Mercury in 1639?

In 1639, Giovanni Zupi discovered that Mercury undergoes a complete cycle of phases over time, similar to the Moon. This observation supported the heliocentric model of the solar system, indicating that Mercury orbits the Sun and not the Earth.

What is the average distance of Mercury from the Sun and how does it compare to Earth's distance?

Mercury orbits the Sun at an average distance of about 58 million kilometers, which is roughly a third of the distance between Earth and the Sun.

How long does it take for Mercury to complete one orbit around the Sun?

Mercury completes one orbit around the Sun in approximately 88 days.

Why is it difficult to observe Mercury's surface features from Earth?

Observing Mercury's surface features from Earth is difficult due to its proximity to the Sun, causing it to be low to the horizon and observed through atmospheric turbulence. Additionally, Mercury's small size of about 4900 kilometers in diameter makes it a challenging target for telescopes.

What is unique about Mercury's orbit compared to other planets in our solar system?

Mercury has the most elliptical orbit of any planet in our solar system, ranging from 46 to nearly 70 million kilometers from the Sun. This results in significant variations in the amount of light and heat it receives at different points in its orbit.

How long is a day on Mercury and how does it relate to its year?

A day on Mercury, which is the time it takes for one rotation, is 58.65 Earth days long. Its year, or one orbit around the Sun, is 87.97 Earth days. Interestingly, the ratio of Mercury's day to its year is almost exactly 2/3.

What is the phenomenon where the Sun appears to move backwards in the sky on Mercury?

The phenomenon where the Sun appears to move backwards in the sky on Mercury is due to the combination of its elliptical orbit and the 2:3 spin to orbit ratio. At perihelion, when Mercury is closest to the Sun, its orbital speed is faster than its spin, causing the Sun to appear to move backwards for a few days.

What are the 'rupes' on Mercury's surface and how were they formed?

The 'rupes' on Mercury's surface are cracks that resemble wrinkles on a dried fruit rind. They were formed as the planet's interior cooled and the planet shrank, causing the crust to crack due to compression.

Why does Mercury have a magnetic field despite its slow rotation?

Mercury has a magnetic field due to its large molten iron core, which constitutes a significant portion of its interior. The large core allows for a stronger magnetic field despite the planet's slow rotation.

How is it possible for water ice to exist on Mercury, which is so close to the Sun?

Water ice exists on Mercury in the bottoms of deep craters near its poles, where sunlight never reaches, creating 'cold traps' with temperatures below -170°C. The ice likely comes from comets and asteroids that impacted the planet, and it persists in these craters due to the lack of sunlight.