Which of the following has highly elongated elliptical orbit ?

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Correct — A, Comet. The standard measure of how stretched an orbit is, is eccentricity: 0 is a perfect circle and 1 is a parabola. Earth's orbit has an eccentricity of about 0.017, effectively a circle; Halley's Comet has an eccentricity of 0.967. The consequences of that number are dramatic and are worth carrying as the mental picture of what 'highly elongated' means. Halley comes in to 0.59 astronomical units at perihelion, closer to the Sun than Venus, and swings out to 35.14 au at aphelion, roughly the distance of Pluto, completing the circuit in 74 to 80 years — it last passed perihelion on 8 February 1986 and is next due on 28 July 2061. Its orbit is also retrograde, inclined at 18 degrees to the ecliptic, and it feeds two annual meteor showers, the Eta Aquariids in early May and the Orionids in late October. This elongation is not incidental to what a comet is; it is the reason a comet behaves as it does. A comet is a body of frozen volatiles — Halley's outgassing was measured by the Giotto probe in March 1986 as roughly 80 per cent water vapour with carbon monoxide and carbon dioxide — held with dust in a nucleus barely 15 km long, the 'dirty snowball' Fred Whipple had predicted. It stays frozen and invisible through most of its long orbit and only develops a coma and a tail in the short stretch near perihelion, when solar heating sublimes the ice. A body on a near-circular orbit would either be permanently cooked or permanently frozen and would never behave this way. The other three options fail for two quite different reasons: asteroids do orbit the Sun, but on low-eccentricity, near-circular paths; and a meteor and a meteorite are not orbiting bodies at all, but two later stages in the life of a fragment that has already left orbit.

Why the other options are wrong — (b) The only other option that actually is a body in solar orbit, which makes it the real distractor. But main-belt asteroids move on near-circular, low-eccentricity paths between the orbits of Mars and Jupiter, staying at a roughly constant distance from the Sun — the opposite of the comet's profile. They are also rocky and metallic rather than icy, and never grow a tail.  (c) A meteor is not an object at all but an event — the streak of light produced when a fragment from space enters the atmosphere and burns up. The body itself, before entry, is a meteoroid, ranging from grains up to about a metre across. Since a meteor is a flash lasting a second or two inside the atmosphere, asking about its orbit is a category error.  (d) The third stage of the same sequence: a meteorite is what remains of a meteoroid after it has survived ablation in the atmosphere and reached the ground. It is by definition on the surface of a planet, so it has no orbit either. Meteoroid in space, meteor in the sky, meteorite on the ground is the distinction being tested by including two of the three.

Concept: The small bodies of the solar system are classified by composition and by where they are, and the four words in this option set cover two different classification schemes that students routinely merge. On composition and orbit: asteroids are rocky or metallic planetoids concentrated in the main belt between Mars and Jupiter, on low-eccentricity orbits; comets are icy bodies from the Kuiper Belt beyond Neptune or from the far more distant Oort Cloud, thrown onto long, highly eccentric orbits that bring them briefly into the inner solar system. When a comet nears the Sun its ices sublime to form a coma and a tail, and the tail always points away from the Sun because it is pushed by radiation pressure and the solar wind, not trailed behind the direction of travel. The second scheme is about a single fragment's journey: a meteoroid is a small body in space, often debris shed by a comet or chipped off an asteroid; a meteor is the luminous trail it makes on entering the atmosphere; a meteorite is the piece that survives to the ground. About 25 million meteoroids and micrometeoroids enter Earth's atmosphere every day, totalling roughly 15,000 tonnes a year, and only a tiny fraction of that mass reaches the surface.

State PCS 2024 Q112 — Science & Technology PYQ with Answer

State PCS 2024 Q112 — Science & Technology PYQ with Answer