(136108) 2003 EL61
From Wikipedia, the free encyclopedia
- The correct title of this article is (136108) 2003 EL61. It features superscript or subscript characters that are substituted or omitted because of technical limitations.
| Image:2003EL61art.jpg | |
| Artist's conception of (136108) 2003 EL61 | |
| Discovery A | |
|---|---|
| Discoverer | Ortiz et al. / Mike Brown et al. |
| Discovery date | 2004 December 28 |
| Alternate designations B | none |
| Category | Trans-Neptunian object |
| Orbital elements C | |
| Eccentricity (e) | 0.18874 |
| Semi-major axis (a) | 6484 Gm (43.335 AU) |
| Perihelion (q) | 5260 Gm (35.164 AU) |
| Aphelion (Q) | 7708 Gm (51.526 AU) |
| Orbital period (P) | 104,234 d (285.4 a) |
| Mean orbital speed | 4.484 km/s |
| Inclination (i) | 28.19° |
| Longitude of the ascending node (Ω) | 121.90° |
| Argument of perihelion (ω) | 239.51° |
| Mean anomaly (M) | 198.07° |
| Physical characteristics D | |
| Dimensions | ~ 1960×1518×996 km (~ 1500 km) |
| Mass | (4.2±0.1)×1021 kg |
| Density | 2.6–3.3 g/cm³ |
| Surface gravity | 0.44 m/s² |
| Escape velocity | 0.84 km/s |
| Rotation period | 0.16314 ± 0.00001 d (3.9154 ± 0.0002 h) |
| Spectral class | ? |
| Absolute magnitude | 0.1 |
| Albedo (geometric) | 0.7 ± 0.1 |
| Mean surface temperature | ? K |
(136108) 2003 EL61 (also written (136108) 2003 EL61), is a large (roughly one-third the mass of Pluto) Kuiper belt object discovered by J.L. Ortiz et al. of the Instituto de Astrofísica de Andalucía at Sierra Nevada Observatory (Spain) and Mike Brown's group at Caltech in the United States. The MPC currently gives formal discovery credit to the group of Ortiz et al. Its two moons, rapid rotation, and high albedo due to crystalline water ice on the surface, make it exceptional among the known cubewanos.
Before the discovery of the object was published and designated, the Caltech team used the nickname "Santa", which stems from its discovery just after Christmas, on December 28, 2004, although the Caltech team had acquired images of it starting May 6, 2004. (136108) 2003 EL61 will not be named "Santa"; following IAU guidelines, the object should be named after a deity related to a creation myth.
Contents |
[edit] Discovery controversy
José Luis Ortiz Moreno, an astronomer at the Sierra Nevada Observatory in Spain, and colleagues Francisco José Aceituno Castro and Pablo Santos-Sanz announced the discovery of the object on July 25, 2005, when they re-analysed observations they had made on March 7, 2003. They then scoured older archives (a process known as precovery) and found the object in images dating back to 1955. Ortiz's group announced their discovery on July 27, 2005, and it was published two days later by the MPC.
A Caltech team consisting of Michael E. Brown, Chad Trujillo, and David Rabinowitz had been observing the object for half a year with the 1.3 m SMARTS Telescope, but had not yet made the data public. Brown and his collaborators initially supported giving Ortiz and his group credit for the discovery, but withdrew support when they found reason to suspect that Ortiz may have used discovery data from Brown's team, which had inadvertently been made publicly available on the web.
A week before Ortiz's discovery announcement, on July 20, Brown's team had published an abstract of a report they intended to use to announce the discovery, in which the object was referred to by the internal code name K40506A. Typing this code into internet search engines allowed anyone to find the observation logs of Brown's group, including the observed positions of the object. Third-party web server logs indicated that the page in question had been accessed by an IP address used by computers at the Instituto de Astrofísica de Andalucía where Ortiz's group worked.<ref>Brown, Michael. The electronic trail of the discovery of (136108) 2003 EL61. Retrieved on 2006-08-16.</ref> Brown's group accused Ortiz's group of a serious breach of scientific ethics and asked the Minor Planet Center to strip them of discovery status.<ref>Overbye, Dennis. "One Find, Two Astronomers: An Ethical Brawl", New York Times, September 13 2005. Retrieved on 2006-08-16.</ref>
Ortiz later admitted he accessed the internet telescope logs with the relevant information a day before making his announcement, but denied any wrongdoing.<ref>Hecht, Jeff. "Astronomer denies improper use of web data", NewScientist.com, 21 September 2005. Retrieved on 2006-08-16.</ref>. According to him they did not use the data, other than checking them out of curiosity whether it could be the same object they had found in their 2003 images that same month. This after they realized the object in the abstract by Brown et al. seemed to be an object with similar characteristics. Googling the informal designation mentioned in the abstract, they ended up at the telescope log.
The ambiguity in who discovered the object stems from the fact that the Caltech group of Brown did not submit their discovery to the Minor Planet Center for a year after detecting it in their images. Standing protocol is that the one who first does submit a report to the MPC with enough positional data for a decent orbit determination, gets discovery credit. This is what Ortiz' group did, thus following correct protocol, using their 2003 imagery, 2005 follow-up imagery, and "precovery" positions from historic archives.
The Minor Planet Center's discovery circumstances database gives the group of Ortiz et al. as the formal discoverers of the object.
On July 29, 2005, shortly after the Ortiz discovery announcement, Brown's group announced the discovery of another Kuiper belt object, Eris, which is more distant and is thought to be larger than the dwarf planet Pluto. The announcement was made earlier than planned, at the urging of the Minor Planet Center, to forestall the possibility of that discovery leaking out as well.
[edit] Size and composition
The only method to estimate the size of a small trans-Neptunian object is its magnitude assuming a value for the albedo. For larger objects, thermal emission can provide a size directly. (136108) 2003 EL61 is exceptional because its two moons provide the means to determine directly the mass of the system from Kepler's third law. The estimated mass is 4.2 × 1021 kg, 28% the mass of the Plutonian system.<ref name="Brown2005"> M. E. Brown, A. H. Bouchez, D. L. Rabinowitz, R. Sari, C. A. Trujillo, M. A. van Dam, R. Campbell, J. Chin, S. Hartman, E. Johansson, R. Lafon, D. LeMignant, P. Stomski, D. Summers, P. L. Wizinowich Keck Observatory laser guide star adaptive optics discovery and characterization of a satellite to large Kuiper belt object 2003 EL61, The Astrophysical Journal Letters, 632, L45 (October 2005) Full text from Caltech</ref> Because (136108) 2003 EL61 rotates roughly once every four hours, faster than any other known body in the solar system larger than 100 km in diameter, it should be distorted into a triaxial ellipsoid. (136108) 2003 EL61 displays large fluctuations in brightness. Although these fluctuations could be due to a mottled surface, it is thought that this fluctuation is due to an elongated shape. Rapid rotation and elongated shape result in constraints on the density (the denser the object, the less elongated), estimated at 2.6–3.3 g/cm³, suggesting substantial non-ice content (compare with Pluto's density of 2.0 g/cm³ and Moon's density of 3.3 g/cm³). These limits on the density, together with the known mass, give another way to constrain the dimensions of the object.<ref name="Rabinowitz2006"> D. L. Rabinowitz, K. M. Barkume, M. E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C. A. Trujillo (2005), Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt, The Astrophysical Journal (2006), 639, Issue 2, pp. 1238-1251 Preprint on arXiv (pdf)</ref> (136108) 2003 EL61 has approximately the diameter of Pluto along its longest dimension, and half that along its shortest. This would make it one of the largest trans-Neptunian objects discovered so far; possibly fourth after Eris, Pluto and arguably (136472) 2005 FY9, larger than Sedna, Orcus, and Quaoar.
The short rotation period of (136108) 2003 EL61 may have been caused by a giant impact, which also created its satellites. (136108) 2003 EL61 may not be the only elongated, rapidly rotating, large object in the Kuiper Belt. In 2002, Jewitt and Sheppard suggested that Varuna should be elongate, based on its rapid rotation (see the references there).
[edit] Surface
Gemini telescope obtained spectra of (136108) 2003 EL61, which show strong water ice features similar to the surface of Pluto's moon Charon. Trujillo,Brown, et al. report crystalline water ice.<ref name="Trujillo 2006">C. A. Trujillo, Brown M.E., Barkume K., Shaller E., Rabinowitz D. The Surface of 2003 EL61 in the Near Infrared. To appear in The Astronomical Journal (2006); Preprint on arXiv (pdf)</ref> Water ice has been reported on many trans-Neptunian objects but typically in the form of amorphous ice. Crystalline ice is unstable on timescales of 10 million years under conditions in the Kuiper Belt. This discovery hints at resurfacing processes producing fresh ice. As surprising as the crystalline form is the inferred amount of ice. Following the report, the surface of (136108) 2003 EL61 appears to be ⅔ to ⅘ pure ice, with the remainder of the surface material of unknown composition.
(136108) 2003 EL61 has an albedo approaching that of pure snow, consistent with crystalline ice on the surface. This very high albedo does not appear to be unique among large TNOs. Recent measurements of Eris imply an even higher (inferred) albedo (0.86) for that object.
[edit] Orbit
(136108) 2003 EL61 is classified as a classical trans-Neptunian object with an orbit common for large cubewanos: the perihelion is close to 35 AU and significantly inclined. The diagram shows a view of its orbit in yellow, (Pluto in red, Neptune in grey) and position (as of April 2006). The object passed its aphelion (Q) in 1991, and is currently more than 50 AU from the Sun.
The inclination of its orbit (~28° to compare with 17° for Pluto) and its current position, far from the ecliptic where most of the early surveys took place, combined with a slow mean motion explain why (136108) 2003 EL61 was only discovered recently, in spite of its magnitude.
[edit] Moons
Two small satellites have been discovered orbiting (136108) 2003 EL61.
[edit] S/2005 (136108) 1
S/2005 (2003 EL61) 1 (provisional designation; nicknamed "Rudolph" by the Caltech team), renamed S/2005 (136108) 1 once its primary was numbered, was the first satellite discovered around (136108) 2003 EL61. It orbits once every 49.12 ± 0.03 days with semimajor axis 49,500 ± 400 km and eccentricity 0.050 ± 0.003[1]. Mutual occultations of the moon and the primary, as seen from Earth, occurred in 1999 and will not occur again until 2138.
Only the total mass of the system is known, but assuming the moon has the same density and albedo as the primary, the mass of the satellite is 1% of the mass of (136108) 2003 EL61 and it has a diameter of ~310 km. <ref>http://www.johnstonsarchive.net/astro/tnoslist.html</ref>
[edit] S/2005 (136108) 2
S/2005 (2003 EL61) 2 (provisional designation), later renamed S/2005 (136108) 2, is the smaller inner satellite of (136108) 2003 EL61. The object has been nicknamed "Blitzen".[citation needed]
Its discovery was announced on November 29, 2005. It was found 39,300 km away and, with the assumption of a circular orbit, it orbits the primary in 34.1 ± 0.1 days, and is inclined 39 ± 6° from the larger moon.
The measured brightness implies a diameter 12% that of (136108) 2003 EL61, ~170 km, assuming similar albedo.
[edit] External links
- NASA visualization of the orbit
- Updated data
- Minor Planets Mailing List entry reporting the discovery
- MPEC listing for 2003 EL61
- Space.com story: Large new world discovered beyond Neptune
- New Scientist story: New world found in outer solar system
- BBC story: Distant object found orbiting Sun
- Astronomers Discover "10th Planet" - Sky & Telescope article describing the discovery of (136108) 2003 EL61 and 136199 Eris.
- Michael Brown's webpage
- New Scientist story: Distant solar system body may be cigar-shaped
- BBC story: Record spin rate for cosmic body
- news @ nature.com story: Cosmic 'cigar' spins at astonishing pace; Pluto's neighbour has a very unexpected shape, 9 September 2005.
- New York Times story: "One find, two astronomers", September 13, 2005.
- S.C. Tegler, W. Grundy, W. Romanishin, G. Consolmagno, K. Mogren, F. Vilas: Optical Spectroscopy of the Large Kuiper Belt Objects 136472 (2005 FY9) and 136108 (2003 EL61). Preprint
[edit] References
<references/>
| Large trans-Neptunian objects |
| Kuiper belt: Orcus | Pluto (Charon) | Ixion | 2002 UX25 | Varuna | 2002 TX300 | 2003 EL61 | Quaoar | 2005 FY9 | 2002 AW197 |
| Scattered disc: 2002 TC302 | Eris | 2004 XR190 | Sedna |
| See also Triton, astronomical objects and the solar system's list of objects, sorted by radius or mass. For pronunciation, see: Centaur and TNO pronunciation. |
| Small Solar System bodies |
|---|
| Vulcanoids | Near-Earth asteroids | Main belt | Jupiter Trojans | Centaurs | Damocloids | Comets | Trans-Neptunians (Kuiper belt · Scattered disc · Oort cloud) |
| For other objects and regions, see: asteroid groups and families, binary asteroids, asteroid moons and the Solar system For a complete listing, see: List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names. |
| Minor planets | ||
|---|---|---|
| Previous minor planet | (136108) 2003 EL61 | Next minor planet |
da:2003 EL61 de:2003 EL61 es:(136108) 2003 EL61 fr:(136108) 2003 EL61 it:(136108) 2003 EL61 hu:2003 EL61 nl:2003 EL61 ja:2003 EL61 no:2003 EL61 pl:2003 EL61 pt:2003 EL61 ru:Санта (2003 EL61) sk:2003 EL61 fi:2003 EL61 sv:2003 EL61 zh:小行星136108
