astronomy

S/2021 N 1

S/2021 N 1 is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand S/2021 N 1 rather than just read about it. In short: S/2021 N 1 is the smallest, faintest, and farthest natural satellite or moon of Neptune known, with a diameter of around 16–25 km (10–16 mi). It was discovered on 7 September 2021 by Scott S.

Key takeaways

S/2021 N 1 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect S/2021 N 1 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of S/2021 N 1 from memory before moving on to harder problems.

Reference excerpt

S/2021 N 1 is the smallest, faintest, and farthest natural satellite or moon of Neptune known, with a diameter of around 16–25 km (10–16 mi). It was discovered on 7 September 2021 by Scott S. Sheppard, David J. Tholen, Chad Trujillo, and Patryk S. Lykawka using the 8.2-meter Subaru Telescope at Mauna Kea, Hawaii, and later announced on 23 February 2024. It is an irregular moon, meaning it follows a very wide and elliptical orbit around its planet. It orbits Neptune in the retrograde direction at an average distance of over 50 million km (31 million mi) and takes about 27 Earth years to complete one orbit—the largest orbital distance and period of any known moon in the Solar System.

Discovery S/2021 N 1 was first observed on 7 September 2021 by Scott S. Sheppard and collaborators, during their search for Neptunian irregular moons with the 8.2-m Subaru Telescope at Mauna Kea, Hawaii. Sheppard's team was able to detect this faint moon through the shift-and-add technique, in which they took many long-exposure telescope images, aligned and shifted them to follow Neptune's motion, and then added them together to create a single deep image that would show Neptunian moons as points of light against trailed background stars and galaxies. Applying the shift-and-add technique to very large aperture telescopes like Subaru enabled Sheppard's team to probe deeper than previous Neptunian irregular moon surveys. From September 2021 to November 2023, Sheppard's conducted follow-up observations of S/2021 N 1 using other large-aperture telescopes around the world, which included the 6.5-m Magellan–Baade Telescope at Las Campanas Observatory, the 8.2-m Very Large Telescope at European Southern Observatory, and the 8.1-m Gemini North Telescope at Mauna Kea Observatory to determine the moon's orbit and ensure it would not be lost. S/2021 N 1 and S/2002 N 5, another Neptunian irregular moon discovered by Sheppard's team, were both confirmed and announced by the Minor Planet Center on 23 February 2024, bringing Neptune's number of known moons from 14 to 16.

Orbit

S/2021 N 1 is an irregular moon of Neptune, since it has a distant, highly elliptical, and highly inclined orbit. Irregular moons are loosely bound by Neptune's gravity because of their great distance from the planet, so their orbits are frequently perturbed by the gravity of the Sun and other planets. This results in significant changes in the orbits of irregular moons over short periods of time, so a simple Keplerian elliptical orbit cannot accurately describe the long-term orbital motions of irregular moons. Namely, during an 800-year time span from 1600 to 2400, S/2021 N 1's semi-major axis fluctuates between 49 and 53 million km (30 and 33 million mi), eccentricity between 0.32 and 0.70, and inclination between 129° and 139°. For this reason, proper or average orbital elements are used to describe the long-term orbits of irregular moons more accurately, since these are calculated by averaging out the perturbed orbit over a long period of time. Over an 800-year time span from 1600 to 2400, S/2021 N 1's average semi-major axis or orbital distance from Neptune is 50.7 million km (31.5 million mi; 0.339 AU), with an average orbital period of 27.5 Earth years. S/2021 N 1 has an average orbital eccentricity of 0.50 and an average inclination of 135° with respect to the ecliptic, or the plane of Earth's orbit. Since S/2021 N 1's orbital inclination is greater than 90°, the moon has a retrograde orbit, meaning it orbits in the opposite direction of Neptune's orbit around the Sun. S/2021 N 1's average semi-major axis and orbital period are greater than those of Neptune's moon Neso (49.9 million km; 26.8 yr), which makes S/2021 N 1 hold the record for the largest orbital distance and period of any known moon in the Solar System. For comparison, the planet Mercury has a semi-major axis of 57.9 million km (36.0 million mi; 0.387 AU) from the Sun, which is about 14% larger than S/2021 N 1's average semi-major axis from Neptune. S/2021 N 1's extreme orbital distance is possible thanks to the large size of Neptune's Hill sphere of gravitational influence, which spans about 115 million km (71 million mi; 0.77 AU) in radius. S/2021 N 1's average semi-major axis takes up about 44% of Neptune's Hill radius, although the Jovian moons of the Carme and Pasiphae groups orbit at a greater percentage of their primary's Hill radius. S/2021 N 1 is part of the Neso group, a cluster of distant retrograde irregular moons of Neptune that includes Psamathe and the group's namesake Neso. The moons of the Neso group have orbital elements that are clustered with semi-major axes between 46–51 million km (29–32 million mi), eccentricities between 0.4 and 0.5, and inclinations between 125° and 140°. Like all other irregular moon groups, the Neso group is thought to have formed from the destruction of a larger captured moon of Neptune due to asteroid and comet impacts, which left many fragments in similar orbits around Neptune. S/2021 N 1's orbit exhibits nodal precession with an average period of about 900 Earth years, but it does not exhibit apsidal precession. Instead, the argument of pericenter of S/2021 N 1's orbit periodically librates around 90°, which is a behavior shared by Neso and Sao. This behavior is due to the Kozai–Lidov resonance, where perturbations by the Sun and Neptune are periodic. The Kozai–Lidov resonance causes periodic exchanges between eccentricity and inclination: for example, as S/2021 N 1's orbit becomes more eccentric, its orbit becomes less inclined and vice versa. S/2021 N 1 last passed periapsis, or its nearest point to Neptune in its orbit, in September 2017 at a distance of approximately 27.1 million km (16.8 million mi; 0.181 AU). The moon is moving away from Neptune until it will reach apoapsis, its farthest point from the planet, in March 2032 at a distance of approximately 74.8 million km (46.5 million mi; 0.500 AU). S/2021 N 1 last passed apoapsis in November 2002 at a distance of approximately 76.6 million km (47.6 million mi; 0.512 AU)—the different distance from the next apoapsis is due to perturbations on the moon's orbit.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with S/2021 N 1

Start with the simplest possible case. Write down what S/2021 N 1 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to S/2021 N 1 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about S/2021 N 1 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of S/2021 N 1

In research: S/2021 N 1 appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses S/2021 N 1 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: S/2021 N 1 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 2021, Discoveries by Scott S. Sheppard, Irregular satellites, so understanding it makes those chapters shorter.
In everyday life: Look for S/2021 N 1 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “S/2021 N 1” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study S/2021 N 1 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what S/2021 N 1 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain S/2021 N 1 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is S/2021 N 1 in simple terms?

S/2021 N 1 is the smallest, faintest, and farthest natural satellite or moon of Neptune known, with a diameter of around 16–25 km (10–16 mi). It was discovered on 7 September 2021 by Scott S.

Why does S/2021 N 1 matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study S/2021 N 1?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on S/2021 N 1.