DISCOVERY OF A MAKEMAKEAN MOON - Draft Version April 25, 2016 - Preliminary research paper

Aug 25, 2026

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Satellite discovery documentation describing a companion in orbit around the dwarf planet Makemake (136472). The moon, provisionally S/2015 (136472) 1, was detected in Hubble Space Telescope WFC3 imaging from UTC April 27, 2015, at about 7.80 magnitudes fainter. Its near edge-on geometry likely hid it during earlier searches. Limited orbital motion prevents mass determination from discovery data alone; circular-orbit estimates require a period longer than 12.4 days. A “dark moon hypothesis” is proposed to explain thermal-observed dark material, testable with future JWST observations.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages6

Reading Time15 min

AccessFree to download

Abstract

Introduction

Makemake properties and motivation for finding a satellite

Discovery Circumstances

HST program, filters, observing strategy

Visit 1 detections and co-moving behavior

Visit 2 non-detection and sensitivity tests

Implications for the satellite search

Draft version April 25, 2016 Preprint typeset using LATEX style AASTeX6 v. 1.0 DISCOVERY OF A MAKEMAKEAN MOON Alex H. Parker1 and Marc W. Buie Southwest Research Institute 1050 Walnut St., Suite 300 Boulder, CO 80302, USA Will M. Grundy Lowell Observatory, Flagsta↵, AZ, USA. Keith S. Noll NASA Goddard Space Flight Center, Greenbelt, MD, USA. [1](1 aparker@boulder.swri.edu)[ aparker@boulder.swri.edu](1 aparker@boulder.swri.edu) ABSTRACT We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the Hubble Space Telescope’s Wide Field Camera 3 on UTC April 27, 2015 at 7.80±0.04 magnitudes fainter than Makemake. It likely evaded detection in previous satellite searches due to a nearly edgeon orbital conﬁguration, placing it deep within the glare of Makemake during a substantial fraction of its orbital period. This conﬁguration would place Makemake and its satellite near a mutual event season. Insuﬃcient orbital motion was detected to make a detailed characterization of its orbital properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days, and must have a semi-major axis &21,000 km. We ﬁnd that the properties of Makemake’s moon suggest that the majority of the dark material detected in the system by thermal observations may not reside on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform dark surface. This “dark moon hypothesis” can be directly tested with future JWST observations. We discuss the implications of this discovery for the spin state, ﬁgure, and thermal properties of Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites. Keywords: Kuiper belt objects: individual (Makemake)—planets and satellites: detection 1. INTRODUCTION Makemake is the second-brightest known transNeptunian Object (behind only Pluto) and the largest known classical Kuiper Belt Object (KBO) . It has the most methane-dominated spectrum of any known TNO (Licandro et al. 2006 ; Brown et al. 2007 ; Tegler et al. 2008), a very high visible albedo (Lim et al. 2010), a well-deﬁned radius derived from stellar occultations (Ortiz et al. 2012 ; Brown 2013), a well-measured (albeit very small-amplitude) lightcurve that pins its rotational period to 7.771 hours (Heinze & de Lahunta 2009), and polarization properties very similar to Pluto and Eris, but distinct from smaller KBOs (Belskaya et al. 2012) . However, despite this wealth of information, the lack of a known satellite has prohibited the measurement of Makemake’s mass and density. We report the discovery and preliminary characterization of a Makemakean moon in Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) imagery. While the satellite’s orbital properties are only marginally constrained from the discovery data alone, its existence will permit future precise measurement of Makemake’s mass and density given suﬃcient follow-up observations. In the following sections, we describe the discovery circumstances of S/2015 (136472) 1, its photometric properties, and preliminary characterization of its orbital properties. We demonstrate that this moon could account for some or all of the dark material detected in the Makemake system with thermal observations, and discuss po- 2 Figure 1 . All six 725-second images from visit 1, collected over two subsequent HST orbits. The satellite is clearly visible to the North and West of Makemake in every frame. Images have not been cleaned for cosmic rays or otherwise cosmetically enhanced. Black bar is 100 . Ecliptic North is up, Ecliptic East is left. Observation start times are labeled on each image. Over the time spanned by these images, Makemake moved 400 .22 with respect to background s

FAQs

What satellite around Makemake was discovered and how was it detected?

A satellite provisionally designated S/2015 (136472) 1 was detected in Hubble Space Telescope WFC3 imaging data collected on UTC April 27, 2015.

Why might the satellite have been missed in earlier searches?

Its nearly edge-on orbital configuration likely placed it deep in Makemake’s glare for a substantial part of its orbital period.

What does the “dark moon hypothesis” claim, and how can it be tested?

It suggests thermal-observed dark material may come from a uniformly dark surface on S/2015 (136472) 1 rather than from Makemake itself. Future JWST observations can test this directly.

Aug 25, 2026

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