FC - Mercury_lecture_ArthurBriaud

Forty Q&A flashcards summarising Mercury’s physical characteristics, orbital dynamics, interior structure, surface geology, and the key findings from Mariner 10 and MESSENGER, along with upcoming BepiColombo exploration.

What is Mercury’s average distance from the Sun?

About 0.39 AU (≈ 58 million km).

Why is Mercury difficult to observe from Earth with the naked eye or small telescopes?

Its elongation from the Sun never exceeds ~28°, so it stays close to the horizon and is lost in twilight glare.

How does Mercury’s diameter (~4,880 km) compare to the Moon and Mars?

Slightly larger than the Moon (~3,480 km) and smaller than Mars (~6,790 km).

What is the maximum daytime surface temperature on Mercury?

Approximately +430 °C.

What is the minimum nighttime surface temperature on Mercury?

Approximately –190 °C, leading to a temperature range of about 630 °C.

Relative to its total mass, which planet contains the most iron?

Mercury.

What is Mercury’s mean density and what does it imply about its interior?

≈ 5,425 kg m⁻³, implying a large iron-rich core about 85 % of Mercury’s radius.

Mercury’s large core generates what planetary feature despite its small size?

An intrinsic dipole magnetic field.

What two components combine to create Mercury’s magnetosphere?

The planetary magnetic field and the solar wind.

Which elements detected in Mercury’s exosphere are sputtered off the surface by the solar wind?

Sodium, potassium, calcium, and magnesium.

What is Mercury’s orbital eccentricity, and how does this affect solar input?

e ≈ 0.2056; the planet receives roughly twice as much solar energy at perihelion as at aphelion.

State Mercury’s 2:3 spin-orbit resonance.

Mercury rotates three times on its axis for every two orbits around the Sun.

How long is a Mercury sidereal day and a Mercury solar day?

Sidereal day ≈ 58.646 Earth days; solar day ≈ 175.9 Earth days.

Why are longitudes near 0° and 180° called Mercury’s “heat poles”?

They face the Sun at each perihelion, receiving the highest cumulative solar heating.

What unexplained orbital phenomenon of Mercury helped confirm General Relativity?

The extra 43 arcseconds per century of perihelion precession predicted by Einstein (not explained by Newtonian gravity alone).

Why is Mercury’s axial tilt (obliquity) extremely small?

Strong solar tidal forces and stabilization by the 3:2 spin-orbit resonance damped its tilt over billions of years.

What are forced longitudinal librations of Mercury?

Small periodic oscillations in Mercury’s rotation rate caused by solar gravitational torques acting on its slightly asymmetric shape.

Name two factors that control the amplitude of Mercury’s forced librations.

Orbital eccentricity (e) and the equatorial moment-of-inertia difference (B − A).

What is the objective of the Peale experiment for Mercury?

To determine whether Mercury’s outer core is molten by combining gravity-field coefficients (C20, C22) with measurements of obliquity and libration amplitude.

Which gravity coefficients are most relevant for probing Mercury’s interior shape in the Peale experiment?

C20 (polar flattening) and C22 (equatorial asymmetry).

Which three spacecraft have visited or are en route to Mercury?

Mariner 10 (flybys 1974-75), MESSENGER (orbiter 2011-2015), and ESA/JAXA’s BepiColombo (arrival 2026).

What year was NASA’s MESSENGER spacecraft launched, and when did it enter Mercury orbit?

Launched 3 August 2004; orbital insertion 18 March 2011.

List at least four of MESSENGER’s seven science instruments.

MDIS, MLA, GRNS, XRS, MAG, MASCS, EPPS.

What two cameras make up the Mercury Dual Imaging System (MDIS)?

A monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC).

What is the ranging precision and maximum range of the Mercury Laser Altimeter (MLA)?

≈ 30 cm precision with a maximum range of ~1,500 km.

Describe MESSENGER’s mapping orbit around Mercury.

Near-polar (~82°), highly elliptical (e ≈ 0.74), 12-hour period enabling close periapsis passes for high-resolution data.

How many orbits did MESSENGER complete before impacting Mercury?

Over 4,000 (≈ 4,100) orbits.

What interior property of Mercury did large libration amplitudes measured by MESSENGER confirm?

The presence of a molten (liquid) outer core decoupled from the solid mantle.

What major volatile substance was confirmed in permanently shadowed polar craters on Mercury?

Water-ice deposits.

Give one piece of evidence that Mercury experienced significant tectonic activity in the past.

Kilometre-thick volcanic plains and extensive thrust-fault scarps (lobate scarps).

What do lobate scarps on Mercury indicate about the planet’s geologic evolution?

Global contraction of the crust as the interior cooled and shrank.

What are ‘hollows’ on Mercury and what is their proposed origin?

Young, irregular, flat-floored depressions likely formed by volatile loss or sublimation-driven, possibly volcanic processes.

How large is the Caloris impact basin, and why is it scientifically important?

≈ 1,550 km in diameter; shows volcanic infill, multi-ring structure, and provides clues to lithospheric thickness and thermal history.

Name one key difference between the Beethoven and Caloris basins.

Beethoven is older, more eroded, and lacks clear concentric rings compared to Caloris.

Approximately how long is Mercury’s ‘great valley’ formed by global contraction?

More than 1,000 km long (about 400 km wide and 3 km deep).

Which volatile element, detected by MESSENGER, is unusually abundant on Mercury’s surface?

Sulfur (and other volatiles like sodium).

How much stronger is sunlight at Mercury compared with Earth?

Up to about 10 times more intense.

What radar technique was first used from Earth to measure Mercury’s librations?

Interferometric radar ‘disco-ball’ observations using Arecibo and other antennas to detect phase differences in surface echoes.

What is the numerical ratio describing Mercury’s spin-orbit resonance?

3 rotations for every 2 orbits (3:2).

State the length of a Mercury year.

Approximately 87.976 Earth days.

When is ESA/JAXA’s BepiColombo mission scheduled to arrive at Mercury?

December 2026, with science operations beginning January 2027.