Makemake (dwarf planet)

Makemake

Makemake as seen by the Hubble Space Telescope
Discovery
Discovered by	Michael E. Brown, Chad Trujillo, David Rabinowitz
Discovery date	March 31, 2005
Designations
MPC designation	(136472) Makemake
Pronunciation	/ˌmɑːkiːˈmɑːkiː/ or /en-us-Makemake.oggˌmɑːkeɪˈmɑːkeɪ/[a]
Named after	Makemake
Alternate name(s)	2005 FY9
Minor planet category	dwarf planet, plutoid, TNO (cubewano)[1]
Adjective	Makemakean
Orbital characteristics[2][3]
Epoch January 28, 1955 (JD 2 435 135.5)
Aphelion	7,939.7 Gm (53.074 AU)
Perihelion	5,760.8 Gm (38.509 AU)
Semi-major axis	6,850.3 Gm (45.791 AU)
Eccentricity	0.159
Orbital period	113,183 d (309.88 a)
Average orbital speed	4.419 km/s
Mean anomaly	85.13°
Inclination	28.96°
Longitude of ascending node	79.382°
Argument of perihelion	298.41°
Physical characteristics
Mean radius	750+200−100 km[4] 710 ± 30 km[5]
Surface area	~6,300,000 km²
Volume	~1.5 × 109 km³
Mass	~3 × 1021 kg
Mean density	~2 g/cm³ (assumed)
Equatorial surface gravity	~0.4  m/s²
Escape velocity	~0.75  km/s
Sidereal rotation period	7.771±0.003 hours[6]
Axial tilt	unknown
Albedo	78.2+10.3−8.6 (geometric)[4]
Temperature	30–35 K [d](assuming the same albedo)
Spectral type	B-V=0.83, V-R=0.5[7]
Apparent magnitude	16.7 (opposition)[8][9]
Absolute magnitude (H)	-0.45[3]

Makemake, formally designated (136472) Makemake, is the third-largest known dwarf planet in the Solar System and one of the two largest Kuiper belt objects (KBO) in the classical KBO population.^[b] Its diameter is roughly three-quarters that of Pluto.^[10] Makemake has no known satellites, which makes it unique among the largest KBOs. Its extremely low average temperature, about 30 K (−243.2 °C), means its surface is covered with methane, ethane, and possibly nitrogen ices.^[11]

Initially known as 2005 FY₉ and later given the minor planet number 136472, it was discovered on March 31, 2005, by a team led by Michael Brown, and announced on July 29, 2005. Its name derives from the Rapanui god Makemake. On June 11, 2008, the International Astronomical Union (IAU) included Makemake in its list of potential candidates to be given "plutoid" status, a term for dwarf planets beyond the orbit of Neptune that would place the object alongside Pluto, Haumea and Eris. Makemake was formally classified as a plutoid in July 2008.^{[12][13][14][15]}

Discovery

Makemake was discovered on March 31, 2005, by a team at the Palomar Observatory, led by Michael Brown,^[3] and was announced to the public on July 29, 2005. The discovery of Eris was made public the same day, following the announcement of Haumea two days earlier.^[16]

Despite its relative brightness (it is about a fifth as bright as Pluto),^[c] Makemake was not discovered until well after many much fainter Kuiper belt objects. Most searches for minor planets are conducted relatively close to the ecliptic (the region of the sky that the Sun, Moon and planets appear to lie in, as seen from Earth), due to the greater likelihood of finding objects there. It probably escaped detection during the earlier surveys due to its relatively high orbital inclination, and the fact that it was at its farthest distance from the ecliptic at the time of its discovery, in the northern constellation of Coma Berenices.^[9]

Besides Pluto, Makemake is the only other dwarf planet that was bright enough for Clyde Tombaugh to have possibly detected during his search for trans-Neptunian planets around 1930.^[17] At the time of Tombaugh's survey, Makemake was only a few degrees from the ecliptic, near the border of Taurus and Auriga,^[e] at an apparent magnitude of 16.0.^[9] This position, however, was also very near the Milky Way, and Makemake would have been almost impossible to find against the dense background of stars. Tombaugh continued searching for some years after the discovery of Pluto,^[18] but he failed to find Makemake or any other trans-Neptunian objects.

Name

The provisional designation 2005 FY₉ was given to Makemake when the discovery was made public. Before that, the discovery team used the codename "Easterbunny" for the object, because of its discovery shortly after Easter.^[19]

In July 2008, in accordance with IAU rules for classical Kuiper belt objects, 2005 FY₉ was given the name of a creator deity. The name of Makemake, the creator of humanity and god of fertility in the mythos of the Rapanui, the native people of Easter Island,^[13] was chosen in part to preserve the object's connection with Easter.^[19]

Orbit and classification

Orbits of Makemake (blue), Haumea (green), contrasted with the orbit of Pluto (red) and the ecliptic (grey). The perihelia (q)^[3] and the aphelia (Q) are marked with the dates of passage. The positions on April 2006 are marked with the spheres illustrating relative sizes and differences in albedo and colour.

As of 2009, Makemake is at a distance of 52 astronomical units (7.78×10⁹ km) from the Sun,^[8][9] almost as far from the Sun as it ever reaches on its orbit.^[11] Makemake follows an orbit very similar to that of Haumea: highly inclined at 29° and a moderate eccentricity of about 0.16.^[20] Nevertheless, Makemake's orbit is slightly farther from the Sun in terms of both the semi-major axis and perihelion. Its orbital period is nearly 310 years,^[2] more than Pluto's 248 years and Haumea's 283 years. Both Makemake and Haumea are currently far from the ecliptic—the angular distance is almost 29°. Makemake is approaching its 2033 aphelion,^[9] while Haumea passed its aphelion in early 1992.^[21]

Makemake is classified a classical Kuiper belt object,^[1][b] which means its orbit lies far enough from Neptune to remain stable over the age of the Solar System.^[22][23] Unlike plutinos, which can cross Neptune's orbit due to their 2:3 resonance with the planet, the classical objects have perihelia further from the Sun, free from Neptune's perturbation.^[22] Such objects have relatively low eccentricities (e below 0.2) and orbit the Sun in much the same way the planets do. Makemake, however, is a member of the "dynamically hot" class of classical KBOs, meaning that it has a high inclination compared to others in its population.^[24] Makemake is, probably coincidentally, near the 11:6 resonance with Neptune.^[25]

Physical characteristics

Brightness, size, and rotation

Makemake (apmag 16.9)

Makemake is currently visually the second brightest Kuiper belt object after Pluto,^[17] having a March opposition apparent magnitude of 16.7^[8] in the constellation Coma Berenices.^[9] This is bright enough to be visible using a high-end amateur telescope. Makemake's high albedo of roughly 80 percent suggests an average surface temperature of about 30 K.^[d][4] The size of Makemake is not precisely known, but the detection in infrared by the Spitzer space telescope and Herschel Space Telescope, combined with the similarities of spectrum with Pluto yielded an estimate of the diameter from 1,360 to 1480 km.^[5] This is slightly larger than the size of Haumea, making Makemake possibly the third largest known Trans-Neptunian object after Eris and Pluto.^[20] Makemake is now designated the fourth dwarf planet in the Solar System because it has a bright V-band absolute magnitude of −0.45.^[3] This practically guarantees that it is large enough to achieve hydrostatic equilibrium and become an oblate spheroid.^[13]

Spectra and surface

In a letter written to the journal Astronomy and Astrophysics in 2006, Licandro et al. reported the measurements of the visible and near infrared spectrum of Makemake. They used the William Herschel Telescope and Telescopio Nazionale Galileo and showed that the surface of Makemake resembles that of Pluto.^[26] Like Pluto, Makemake appears red in the visible spectrum, but significantly less red than the surface of Eris (see colour comparison of TNOs).^[26] The near-infrared spectrum is marked by the presence of the broad methane (CH₄) absorption bands. The methane is observed also on Pluto and Eris, but its spectral signature is much weaker.^[26]

Spectral analysis of Makemake's surface revealed that methane must be present in the form of large grains at least one centimetre in size.^[11] In addition large amounts of ethane and tholins may be present as well, most likely created by photolysis of methane by solar radiation.^[11] The tholins are probably responsible for the red color of the visible spectrum. Although evidence exists for the presence of nitrogen ice on its surface, at least mixed with other ices, there is nowhere near the same level of nitrogen as on Pluto and Triton, where it composes more than 98 percent of the crust. The relative lack of nitrogen ice suggests that its supply of nitrogen has somehow been depleted over the age of the Solar System.^[11][27][28]

The far-infrared (24–70 μm) and submillimeter (70–500 μm) photometry performed by Spitzer and Herschel telescopes revealed that the surface of Makemake is not homogeneous. While the majority of it is covered by nitrogen and methane ices and has the albedo ranging from 78 to 90%, there are small patches of dark terrain with the albedo of only 2 to 12%, which comprise 3–7% of the surface.^[5]

Atmosphere

The presence of methane and possibly nitrogen suggests that Makemake could have a transient atmosphere similar to that of Pluto near its perihelion.^[26] Nitrogen, if present, will be the dominant component of it.^[11] The existence of an atmosphere also provides a natural explanation for the nitrogen depletion: since the gravity of Makemake is weaker than that of Pluto, Eris and Triton, a large amount of nitrogen was probably lost via atmospheric escape; methane is lighter than nitrogen, but has significantly lower vapor pressure at temperatures prevalent at the surface of Makemake (30–35 K),^[d] which hinders its escape; the result of this process is a higher relative abundance of methane.^[29]

Lack of satellites

No satellites have been detected around Makemake so far. A satellite having a brightness 1% of that of the primary would have been detected if it had been at the distance 0.4 arcseconds or further from Makemake.^[17] This contrasts with the other largest trans-Neptunian objects, which all possess at least one satellite: Eris has one, Haumea has two and Pluto has three. From 10% to 20% of all trans-Neptunian objects are expected to have one or more satellites.^[17] Since satellites offer a simple method to measure an object's mass, lack of a satellite makes obtaining an accurate figure for Makemake's mass more difficult.^[17]

See also

Notes

References

External links

• MPEC listing for Makemake
• AstDys orbital elements
• Orbital simulation from JPL (Java) / Ephemeris
• Press release from WHT and TNG on Makemake's similarity to Pluto.
• Makemake chart and Orbit Viewer
• Precovery image with the 1.06 m Kleť Observatory telescope on April 20, 2003
• Makemake as seen on 2010-02-18 UT with the Keck 1
• Makemake of the Outer Solar System APOD July 15, 2008
• Simulation of Makemake (2005 FY₉)'s orbit

Makemake Classification Planet · Dwarf planet · Definition of planet · 2006 definition of planet · Kuiper belt · Trans-Neptunian object Discovery Mike Brown · Reflecting telescope · Mount Palomar Observatory Other topics Tenth planet

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