Overview

• Grade Level: AP Physics 2 / AP Environmental Science (Astronomy) / Earth and Space Science (grades 10-12)

• Time Required: Single class (45 minutes); bell-ringer option (10 minutes); extension (2 additional class periods)

• Historical Period: 1973-1975, the Mariner 10 mission to Venus and Mercury and the Caltech-JPL Mariner 10 imaging team led by Bruce Murray

• Modern Connection: The 4 May 2026 Nature Astronomy paper led by Sebastian Zieba (Harvard-Smithsonian CfA) and Laura Kreidberg (MPIA Heidelberg) reporting the first JWST-derived constraint on the surface composition of a rocky exoplanet (LHS 3844 b), confirming the planet is airless and dark, with a basaltic, Mercury-like surface

Learning Objectives

Students will be able to:

1. Describe the design, trajectory, and key findings of the Mariner 10 mission, including its use of the first interplanetary gravity assist, the three Mercury flybys (29 March 1974, 21 September 1974, 16 March 1975), and the approximately 2,700 photographs returned by its television cameras.

1. Explain in their own words why Mercury's surface preserves a uniquely complete record of inner-Solar-System bombardment history, and identify the Caloris Basin as the largest single impact structure imaged by Mariner 10.

1. Summarise the 2026 Nature Astronomy paper's experimental design, including the JWST MIRI instrument, the multi-phase thermal-emission spectroscopy at 5-12 microns, the 100-plus hours of telescope time, and the surface-vs-atmosphere conclusion.

1. Construct an argument about why the discovery that LHS 3844 b has a Mercury-like surface, fifty-two years after Mariner 10 imaged Mercury itself, represents a methodological shift in exoplanet science rather than just a new data point.

Before Reading

Anticipation Questions

1. The Mariner 10 mission cost approximately ninety-eight million 1973 US dollars and returned the first close-up photographs of Mercury ever obtained. Adjust that for inflation. Is the resulting figure a lot or a little, compared to a 21st-century space mission of similar scope?

1. LHS 3844 b is 48 light-years from Earth. Mercury is 0.3 to 0.5 AU from Earth depending on orbital position. Order these distances on a logarithmic scale. What does it mean for an astronomer to call both of them "close"?

1. Before reading: predict three observations a 21st-century telescope might be able to make about an Earth-sized exoplanet 48 light-years away. Defend each prediction.

Key Vocabulary

• Gravity assist (slingshot): A spacecraft trajectory manoeuvre that uses the gravitational pull of a planet to change the spacecraft's speed or direction without using rocket propellant. Mariner 10 was the first deep-space mission to use one.

• Vidicon camera: A type of television tube used as the imaging detector on early planetary spacecraft, including Mariner 10. Output was analogue, transmitted to Earth over a low-bandwidth radio link.

• Caloris Basin: A roughly 1,500-km-diameter impact crater on Mercury, first imaged by Mariner 10, and one of the largest impact structures in the Solar System.

• Tidally locked: An orbital configuration in which one face of a body always points toward its primary, because rotation and orbital period are equal. The Moon is tidally locked to Earth; LHS 3844 b is tidally locked to its M-dwarf host star.

• M-dwarf: A class of cool, low-mass main-sequence star (spectral class M). LHS 3844 is an M-dwarf and is the most common type of star in the Milky Way.

• Tidal radius (Lagrange point L2): A point in the Earth-Sun system, 1.5 million km outside Earth's orbit, where the Sun's and Earth's gravity balance with the centripetal force; the operational location of the James Webb Space Telescope.

• Mid-Infrared Instrument (MIRI): One of four science instruments on JWST, sensitive in the 5-28 micron wavelength range, used for thermal-emission spectroscopy of cool to warm objects.

• Thermal emission spectroscopy: A measurement of an object's spectrum at infrared wavelengths, where the emission is dominated by thermal radiation rather than reflected starlight. The shape of the spectrum constrains both temperature and surface or atmospheric composition.

• Basalt / basaltic: A common volcanic rock formed by rapid cooling of magma at planetary surfaces, with a characteristic dark colour and low reflectance. The lunar maria are basaltic. LHS 3844 b's spectrum is best matched by basaltic rock.

During Reading

Guided Questions

1. Identify the launch date and the three flyby dates of Mariner 10. Why was the gravity assist off Venus required to reach Mercury?

1. Describe in your own words why Mariner 10's vidicon cameras could only return about 2,700 photographs even though the mission lasted from November 1973 to March 1975.

1. The story states that Mariner 10 found Mercury to be "a thoroughly cratered rock" with no detectable atmosphere. Why does the absence of an atmosphere mean Mercury's surface preserves a "uniquely complete record of inner-Solar-System bombardment history"?

1. Identify the lead and senior authors of the 2026 Nature Astronomy paper. What institutions were involved?

1. The 2026 paper constrains atmospheric pressure on LHS 3844 b to less than 100 mbar at 5-sigma confidence. Convert that to atmospheres. How does it compare with Earth's atmospheric pressure?

After Reading

Discussion Questions

1. Is the comparison between Mariner 10's photographs of Mercury and JWST's spectroscopy of LHS 3844 b a meaningful analogy, or is the difference in technique (close-up images vs distant spectra) too large to support the comparison? Defend your position.

1. (Genuinely debatable.) Mariner 10 cost about $98 million in 1973. JWST cost about $10 billion to build. Adjusting for inflation and the differing science goals, which mission has produced more value per dollar? Pick a position and defend it.

1. The story argues that the LHS 3844 b paper extends exoplanet science "past the atmospheres a planet might or might not have, to the surface a planet definitely does have." Is "the surface a planet definitely does have" really a stronger claim than atmospheric chemistry? Defend your answer.

1. Bruce Murray went from leading the Mariner 10 imaging team to directing JPL to co-founding The Planetary Society with Sagan. What pattern of scientific career does that represent, and is it still possible in 2026?

1. The story closes with the observation that Mariner 10 is still in solar orbit and will pass near Mercury again in 2049. What does it mean for a piece of scientific equipment to outlive the person who built it?

The Parallel

1. List the structural features that are similar between Mariner 10's 1974 close-up of Mercury and JWST's 2026 spectroscopy of LHS 3844 b. List the features that are different. Which list is longer, and which is more important?

1. The 2026 paper finds that LHS 3844 b is "the same kind of object" as Mercury. What does that phrase mean precisely, and what does it not mean?

1. Could there be an analogous "first close-up of an exo-X" story for another Solar System body that has not yet been observed at a comparable exoplanet? Suggest one (a Venus-like exoplanet, a Mars-like exoplanet, a Titan-like exomoon, an Io-like volcanic body) and defend its scientific motivation.

Activities

Bell-Ringer (10 minutes)

Project two images side by side: a Mariner 10 close-up photograph of a heavily cratered region of Mercury (any of the well-known Caloris Basin frames or rim shots) and a contemporary artist's conception of the dayside of LHS 3844 b as a dark basaltic rocky surface under a red M-dwarf sun. Ask students: "These two images are of different worlds, 48 light-years apart. What makes them comparable?" Have them write two sentences. Use the responses to introduce the lesson.

Single Class (45 minutes)

• 0 to 5 minutes: Bell-ringer recap.

• 5 to 18 minutes: Read the historical half of the story aloud. Students fill out a guided-reading organiser with three columns: "Mariner 10 design and trajectory," "Bruce Murray and the JPL imaging team," "The three flybys and the photographs."

• 18 to 32 minutes: Read the modern half aloud. Students extend the organiser with two more columns: "JWST MIRI instrument and the Zieba-Kreidberg observation" and "What the spectrum says about LHS 3844 b's surface."

• 32 to 42 minutes: Whole-class four-corners discussion of After Reading question 1 (is the Mariner 10 vs JWST analogy meaningful). Students physically move to a corner marked "Yes, the surface is the surface," "Yes, but only because we constrain the atmosphere first," "No, spectroscopy and photography measure too-different things," or "It depends on what you want to do with the information."

• 42 to 45 minutes: Exit ticket. One sentence: "The most useful thing about treating Mariner 10 and JWST as comparable instruments is: ___."

Extension Activity

Exoplanet-spectroscopy essay (3 to 5 pages, two class periods): students pick a published JWST exoplanet paper from 2024-2026 and write a structured essay describing what the paper measured, what the team concluded, and how the team controlled for systematic uncertainties. They cite at least three primary or near-primary sources. They include a paragraph speculating about what kind of follow-up observation would be most useful and which instrument should do it.

Primary Source Connections

• B. C. Murray et al., "Mariner 10 Pictures of Mercury: First Results," Science 184 (12 July 1974), pp. 459-461. Type: first published scientific report from the Mariner 10 imaging team.

• B. C. Murray, "The Mariner 10 Pictures of Mercury: An Overview," Journal of Geophysical Research 80.17 (1975), pp. 2342-2344. Type: synthesis paper. The imaging-team summary.

• B. C. Murray, R. Greeley, and G. Schubert, "Earthlike Planets" (San Francisco: W.H. Freeman, 1981). Type: textbook. The standard graduate textbook on planetary geology from the Mariner-and-Viking era.

• S. Zieba, L. Kreidberg et al., "The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy," Nature Astronomy (4 May 2026). DOI: 10.1038/s41550-026-02860-3. Type: peer-reviewed paper. The main paper at the heart of the modern half.

• The Planetary Society archive (planetary.org). Type: institutional archive. Holds Bruce Murray's papers, oral histories, and the foundational documents of The Planetary Society.

• NASA's Mariner 10 image archive at the Planetary Data System (PDS). Type: data archive. All 2,700-plus Mariner 10 Mercury photographs at full resolution.

Standards Alignment

C3 Framework

• Dimension 1 (Developing Questions): Compelling question: "What does it mean to call a planet 48 light-years from Earth 'the same kind of object' as Mercury, and what does the answer tell us about the development of exoplanet science as a field?" Supporting questions about the role of instruments, the structure of spectroscopic argument, and the relationship between proximity and resolution.

• Dimension 2 (Applying Concepts): Physics (orbital mechanics, gravity assist, infrared spectroscopy, blackbody emission). Geology (impact cratering, basalt, space weathering). History (the institutional structure of US planetary exploration, JPL-NASA-Caltech as an alliance).

• Dimension 3 (Evaluating Sources): The story is accompanied by a populated evidence manifest with twelve verified claims and direct source URLs.

• Dimension 4 (Communicating Conclusions): The structured four-corners discussion and the extension essay both require sustained argumentation and source evaluation.

AP Alignment

• AP Physics 2: Unit 6 (Geometric and Physical Optics) and Unit 4 (Thermodynamics). Thermal-emission spectroscopy, blackbody radiation, the use of infrared light to probe surface temperatures.

• AP Environmental Science / AP Earth and Space Science: Planetary geology, the cratering record as a chronometer, the comparative geology of inner-Solar-System bodies.

• AP Research / AP History of Science: A model case for tracing how a 50-year-old close-up planetary mission and a 21st-century space telescope produce comparable scientific conclusions through different methods.