To study which one of the following was a spacecraft launched that would be farthest from the Sun and would run exclusively on solar power?
- (a)Jupiter's Trojan asteroids
- (b)Saturn's rings and moons
- (c)Mars' atmosphere
- (d)Kuiper Belt and Oort Cloud
Correct — A, Jupiter's Trojan asteroids. The spacecraft is NASA's Lucy, launched on 16 October 2021 on a twelve-year journey to eight asteroids — two in the main belt and six Trojans, the bodies that share Jupiter's orbit around the Sun, travelling in swarms ahead of and behind the planet. Lucy runs entirely on solar power, and the numbers show how demanding that is at Jupiter's distance: each of its two circular arrays is 7.3 metres across, and even so the spacecraft expects only about 504 watts at its farthest encounter. No previous solar-powered mission had been sent to operate that far out, which is what the stem means by farthest from the Sun. The mission is named after the Lucy fossil, because the Trojans are treated as fossils of planet formation, left over from the material that built the outer planets.
- (b)Saturn's rings and moons — Saturn's rings and moons were the business of Cassini, which reached Saturn in 2004 — and Cassini was powered by radioisotope thermoelectric generators, not by sunlight. At Saturn's distance solar panels are not a practical option, which is the opposite of what this stem describes.
- (c)Mars' atmosphere — Mars atmospheric missions such as MAVEN and India's Mars Orbiter Mission are indeed solar-powered, but Mars is far closer to the Sun than Jupiter's orbit. A spacecraft studying Mars is nowhere near the farthest a solar array has been asked to work.
- (d)Kuiper Belt and Oort Cloud — The Kuiper Belt is the domain of New Horizons, which flew past Pluto in 2015 and Arrokoth in 2019, and it too carries a radioisotope power source. Sunlight out there is far too weak for panels, so no solar mission has ever been sent to the Kuiper Belt or beyond it.
Trojan asteroids occupy the two gravitationally stable Lagrange points of a planet's orbit, sixty degrees ahead of and sixty degrees behind it, where the pull of the Sun and the planet combine to hold small bodies in place. Jupiter has by far the largest known swarms. Because they have sat there largely undisturbed since the outer planets formed, they preserve material from that era, and reaching several of them in one mission tests ideas about how the giant planets migrated early in the Solar System's history. Lucy's targets include Eurybates, Polymele, Leucus, Orus and the binary Patroclus with its companion Menoetius, plus the main-belt asteroids Dinkinesh and Donaldjohanson.
The stem gives two clues and they work together. 'Farthest from the Sun' rules out anything at Mars or nearer, and 'exclusively on solar power' rules out the deep-space missions that rely on nuclear sources — Cassini at Saturn and New Horizons in the Kuiper Belt both did. What is left is a destination far out but not too far, and Jupiter's orbit is exactly that boundary: it is about as distant as solar arrays can still deliver useful power, and only with panels of a size that would have been impractical a generation ago. That is why Lucy's arrays are 7.3 metres across yet yield only around half a kilowatt, roughly what a household appliance draws. Reading the two clues as one constraint answers the question without knowing the mission's name.
- Lucy is a NASA mission launched on 16 October 2021 on a twelve-year journey to eight asteroids.
- Its targets are two main-belt asteroids and six Jupiter Trojans, the bodies that share Jupiter's orbit ahead of and behind the planet.
- Each of its two solar arrays is 7.3 metres in diameter and the spacecraft expects only about 504 watts at its farthest encounter.
- Cassini at Saturn and New Horizons in the Kuiper Belt were both powered by radioisotope thermoelectric generators, not solar panels.
- Trojan asteroids sit at the stable Lagrange points sixty degrees ahead of and behind a planet in its orbit.
- Choosing the Kuiper Belt because it is farthest. Sunlight there cannot power a spacecraft, so the mission described cannot be going there.
- Forgetting that Cassini and New Horizons were nuclear-powered. The stem's word 'exclusively' is doing real work.
- Confusing Trojan asteroids with the main asteroid belt between Mars and Jupiter. Trojans share Jupiter's own orbit.
As a which-mission-studies-what item, as a statements question on how a deep-space probe is powered, or as a match between spacecraft and their destinations.
No directly related past PYQ was found.
- practice — not a real PYQ
Jupiter's Trojan asteroids are found
- (a)in the main belt between Mars and Jupiter
- (b)sharing Jupiter's orbit, about sixty degrees ahead of and behind the planet
- (c)in orbit around Jupiter as its irregular moons
- (d)between the orbits of Saturn and Uranus
Answer(b) sharing Jupiter's orbit, about sixty degrees ahead of and behind the planet — at the stable Lagrange points L4 and L5.
- practice — not a real PYQ
Which one of the following spacecraft was powered by a radioisotope thermoelectric generator rather than by solar panels?
- (a)Lucy
- (b)MAVEN
- (c)New Horizons
- (d)Mars Orbiter Mission
Answer(c) New Horizons — sunlight in the Kuiper Belt is far too weak for panels, so the Pluto mission carried a nuclear power source.