← INDEX — FIG. 00 — 18 MARCH 2011, 00:45 UTC 0.387 AU · 47.36 km/s

SCORCH
MERCURY: MESSENGER AND BEPICOLOMBO

Mercury is the closest planet to the Sun and the least explored rocky planet.

BEGIN — CHAPTER 01 →

CH.01 / 09 — THE HARDEST PLANET TO STOP AT

Falling toward the Sun only makes you faster

A spacecraft falling toward the Sun arrives far faster than Mercury.

Mercury's total is about 13.9 km/s.

HOHMANN TRANSFER + MINIMUM CAPTURE

a = (r_⊕ + r_p)/2 · v = √(μ_☉(2/r − 1/a)) · v_∞ = |v_transfer − v_planet| · Δv_capture = √(v_∞² + 2μ/r) − √(2μ/r)

Circular, coplanar orbits.

CH.02 / 09 — THE FIRST VISITOR

Mariner 10 and Colombo's billiard shot

Mariner 10 used Venus to reach Mercury in 1974.

Colombo found a 176-day orbit that returned Mariner 10 to Mercury twice more.

CH.03 / 09 — SIX FLYBYS AND ONE BURN

MESSENGER: six and a half years of braking

MESSENGER flew past Earth once, Venus twice and Mercury three times.

On 18 March 2011 a 0.86 km/s burn put MESSENGER into orbit.

BRAKING INTO MESSENGER'S 12-HOUR ORBIT

a = (μ T²/4π²)^1/3 · v_p = √(μ(2/r_p − 1/a)) · Δv = √(v_∞² + 2μ/r_p) − v_p

μ = 22,032 km³/s².

ARRIVAL SPEED v∞—

CH.04 / 09 — THE SUNSHADE

370 °C in front, room temperature behind

Sunlight at Mercury is 4.6–10.6 times Earth's.

MESSENGER's sunshade was predicted to reach 370 °C.

EQUILIBRIUM TEMPERATURE OF A SUNLIT PLATE

S(r) = S_⊕ (1 AU / r)² · α S = ε σ T⁴ ⇒ T = (α S / ε σ)^1/4

A flat plate facing the Sun.

DISTANCE FROM THE SUN—

ABSORB / EMIT RATIO α/ε—

CH.05 / 09 — THE 3:2 SPIN–ORBIT RESONANCE

A day that lasts two years

Mercury spins three times for every two orbits.

A Mercury day lasts 176 Earth days.

SOLAR DAY FROM SPIN AND ORBIT

1/T_solar = 1/T_spin − 1/T_orbit · T_spin = ⅔ T_orbit ⇒ T_solar = 2 T_orbit

T_orbit = 87.969 days.

EARTH DAYS ELAPSED—

CH.06 / 09 — WHAT MESSENGER FOUND

Ice on the planet nearest the Sun

MESSENGER found water ice in permanently shadowed polar craters.

MESSENGER ended by impact on 30 April 2015.

CH.07 / 09 — TWO ORBITERS, NINE FLYBYS

BepiColombo: the long way round

BepiColombo launched in 2018: two orbiters and an ion-driven transfer module.

Orbit insertion is planned for 21 November 2026.

Dates: Beyond Earth, NASA, ESA, JAXA.

CH.08 / 09 — LEGACY: FIFTY YEARS OF SLOWING DOWN

From a radar echo to two orbiters

The hard part is stopping.

CH.09 / 09 — REFERENCES

SCORCHMERCURY: MESSENGER AND BEPICOLOMBO