.jpg) Makemake and its moon S/2015 (136472) 1 (arrow) | |
| Discovery[1] | |
|---|---|
| Discovered by |
|
| Discovery date | 27 April 2015 |
| Designations | |
| MK2 (unofficial nickname)[2] | |
| Orbital characteristics[3] | |
| 22250±780 km[3] | |
| Eccentricity | ≈0 |
| 18.023±0.017 days[3] | |
| Inclination | 83.7° wrtEarth line of sight[3] 63°–87° wrtecliptic (prograde)[1]: 3 |
| Satellite of | Makemake |
| Physical characteristics | |
| ~175 km (4% albedo; best fit)[1]: 4 175–250 km (2–4% albedo)[a] | |
| 87.5 km | |
| Albedo | 0.04 (best fit)[1]: 4 0.02–0.04[1]: 4 |
| 25.0[4] | |
| 7.89±0.04[1]: 3 | |
S/2015 (136472) 1, unofficially nicknamedMK2 by the discovery team,[2] is the only knownmoon of thetrans-Neptuniandwarf planetMakemake.[1][5] It is a dark object about 175 km (110 mi) in diameter, orbiting 22,250 km (13,800 mi) away from Makemake with anorbital period of 18 days.[3] Observations leading to its discovery occurred in April 2015, using theHubble Space Telescope'sWide Field Camera 3, and its discovery was announced on 26 April 2016.[2]
S/2015 (136472) 1 is extremely faint, with anapparent magnitude of 25 invisible light.[4] The satellite is 1,300 times fainter than Makemake, corresponding to amagnitude difference of 7.80.[6][1]: 3
Prior to the discovery of S/2015 (136472) 1, measurements of Makemake'sfar-infraredthermal emission by theSpitzer andHerschel space telescopes showed that the dwarf planet emits more thermal radiation than expected for its size and brightness in visible light.[5] This led astronomers to suspect that Makemake must have extra dark surface area that is contributing to this excess thermal emission.[1]: 3 Makemake does not exhibit significant variations in brightness as it rotates, which leaves the possibilities that some of this dark surface area may either be uniformly distributed on Makemake's surface or is located on satellites orbiting Makemake.[5][1]: 3 [7]: 6 The discovery of S/2015 (136472) 1 lends credibility to the hypothesis that Makemake's excess thermal emission largely comes from satellites with dark surfaces.[7]: 6
Assuming S/2015 (136472) 1 has a uniformly dark surface, the satellite has ageometric albedo or visible lightreflectivity of 2–4%, which makes it as dark ascharcoal.[1]: 3–4 [6] The satellite is exceptionally dark compared to Makemake's geometric albedo of 82%; this may be because the satellite's gravity is too weak to hold on to bright,volatile ices as they sublimate off the satellite's surface into space.[1]: 4 [6] S/2015 (136472) 1 is estimated to have a diameter of 175 to 250 km (109 to 155 mi), based on its geometric albedo and brightness in visible light.[a] Within this range, S/2015 (136472) 1's diameter is most likely 175 km (109 mi) for a geometric albedo of 4%.[1]: 4 If S/2015 (136472) 1 has the same density as Makemake, then it would contribute less than 0.2% of the total system mass.[1]: 4
S/2015 (136472) 1 follows a likelycircular orbit around Makemake with anorbital period of 18 days and asemi-major axis of 22,250 ± 780 km (13,830 ± 480 mi).[3] The satellite's orbit is oriented edge-on from the point of view of Earth-based observatories,[8] meaning that the satellite appears to pass in front of or behind Makemake.[3] This would make the satellite difficult to detect because it would be lost in Makemake's glare most of the time; this is the reason why the satellite was not seen in earlier telescope observations.[1] Although it is ambiguous whether the satellite is orbiting Makemake in theprograde or retrograde direction, the satellite'sorbital inclination with respect to Earth's line of sight suggests that it may have beeneclipsing andocculting Makemake7±2 years before or after January 2018.[3]
As of 2025[update], the satellite has no official name.[9] The designation S/2015 (136472) 1 is the satellite'sprovisional designation, with "S/" indicating satellite, "2015" being the satellite's year of discovery, and "1" being the satellite's order of discovery in that year.[10] "(136472)" is Makemake'sminor-planet number.[11]
The nickname 'MK2' simply meansobject 2 in the Makemake system. A permanent name may be chosen from an associated figure in the mythology of Easter Island.
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| Minor-planet moons | ||
| Ranked by size | ||
