This object moves — fetching its current position…
Score breakdown
· 4 badges
33 pts · Uncommon
Uncommon34 pts → Rare
Centaur: adrift between the giants+20
Retrograde orbit+8
Kuiper-belt object+5
Catalogue designation only+0
Total score33
1 more point to reach Rare.
Badges
❄️Kuiper-belt object· +5
⏪Retrograde orbit· +8
🔢Catalogue designation only
🦌Centaur: adrift between the giants· +20
✨ Trivia
Hard to believe
🔄Against the traffic. It goes round the Sun backwards, against the direction every planet and almost everything else travels.
What it actually is
🛸Its orbit family. A centaur, wandering between the orbits of Jupiter and Neptune on a path nothing can stabilise. Half asteroid and half comet, and gone from this orbit within a few million years.
🌞Closest approach. At its nearest it comes within 3.28 AU of the Sun — inside the orbit of Jupiter.
🔁One lap. A single orbit around the Sun takes it about 78.2 years.
🥏How far it roams. Its orbit swings between 3.28 and 33.3 AU from the Sun.
Sense of scale
🧱Sense of scale. In everyday terms it is roughly 0.2× the height of Mount Everest.
Standing on it
🦘Don't jump. Escape velocity here is only around 0.83 m/s. A determined jump would launch you off it and into your own orbit around the Sun.
By the numbers
📐Estimated size. Nobody has measured its size directly. Assuming it reflects light like a typical asteroid, its brightness implies something roughly 1.4 km across.
Properties
aphelion au
33.31
designation
2025 XX21
eccentricity
0.8209
full name
(2025 XX21)
h mag
17.07
inclination
168.21
mean motion deg day
0.0126
moid au
2.3
name
2025 XX21
number only
yes
orbit class
CEN
perihelion au
3.276
semi major au
18.29
About 2025 XX21
2025 XX21 is an uncommon kbo. It swings within 3.276 AU of the Sun at perihelion.
A centaur, wandering between the orbits of Jupiter and Neptune on a path nothing can stabilise. Half asteroid and half comet, and gone from this orbit within a few million years.
How to see it
Like any astronomical target, 2025 XX21 is best seen from a dark site away from city lights, and when it is above the horizon depends on your latitude and the time of year. Because it moves against the background stars, the live position panel on this page tracks where it is right now. The visibility panel above works out tonight's viewing window for your saved location.
Why 2025 XX21 is an uncommon kbo
2025 XX21 scores 33 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 1 point would lift it into a rarer tier.
That score comes from 4 science badges — Kuiper-belt object, Retrograde orbit, Catalogue designation only and Centaur: adrift between the giants — each earned for a real, measurable property of the object. Rarity on Spacedle is never random: the more remarkable an object's astrophysics, the more badges it collects, the higher it scores, and the rarer it ranks.