Haumea (2003 EL61) Family
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On September 16, 2009, an astronomer announced at the European Planetary Science Congress that Haumea has a spot on its bright surface that is relatively darker and redder in visible light. Of an unknown size (which may cover as much as an entire hemisphere of Haumea), the spot may be relatively richer in surface minerals and organic materials or may contain a larger fraction of crystalline ice. Haumea's spot may be a scar from a recent impact, where the surface material at the spot may include substances from the impactor that are possibly mixed with material from Haumea's inner layers, or seasonal deposits of surface volatile substances, or some other cause (more from Lacerda's web page on Haumea's spot and from Lacerda et al, 2008).
Haumea (2003 EL61)
Initally nicknamed "Santa" and officially designated as 2003 EL61, a team of astronomers (including Mike Brown, Chad Trujillo, and David Rabinowitz) first discovered the movement of a relatively large planetary body outside the orbit of Neptune just after Christmas, on December 28, 2004. Brown's team had been acquiring and analyzing images of EL61 since May 6, 2004 -- with the 1.3-meter, Small and Moderate Aperture Research Telescope System (SMARTS) -- and had sent abstracts of a report to the American Astronomical Society (AAS) on July 20, 2005 that was intended to support the official announcement of its discovery at an upcoming meeting of the AAS Division of Planetary Sciences. However, the team did not make its data public while waiting to refine Santa's orbital and physical characteristics with additional observations using NASA's Hubble Space Telescope. As a result, controversy subsequently developed over which astronomer team should receive "official" attribution for EL61's discovery (more below).
On September 17, 2008, the International Astronomical Union (IAU) announced that 2003 El61 had been designated a "dwarf planet" and named Haumea (press release). The name of the goddess of childbirth and fertility in Hawaiian mythology, Haumea also represents the element of stone, which is appropriate as observations of Haumea, the trans-Neptunian dwarf planet, indicate that it is probably composed of mostly rock under an icy crust. Of Haumea's two moons, the largest moon has been named Hi'iaka, after the Hawaiian goddess who is said to have been born from the mouth of Haumea and is the matron goddess of the island of Hawai'i; the lesser moon has been named after Namaka, a water spirit who is said to have been born from Haumea's body. (more from Astronomy Picture of the Day).
Haumea is one of the brightest objects in the Solar System beyond the orbit of Neptune, surpassed only by Pluto and Make-make (2005 FY9). According to astronomer Michael Brown's team web page on Haumea, the object is one of the largest in the Edgeworth-Kuiper Belt. It is currently located about 51 AUs from the Sun in an elliptical orbit (e= 0.189) with an inclination of 23.19 degrees but has an average orbital distance (semi-major axis) of about 43.34 AUs. It has two known moons (more below).
The EKO is as much as 930 miles (1,500 kilometers or km) wide -- compared with Pluto's diameter of about 1,400 miles (2,300 km). Although it is not spherical, The IAU has designated Haumea to be a dwarf planet because it is in hydrostatic equilibrium, where its unusual ellipsoidal shape is due to its rapid rotation instead of a lack of gravitational force. It is one of over two dozen EKOs that may have formed closer to the Sun but subsequently were scattered by Uranus and Neptune (called "Centaurs and scattered disk objects") that have been discovered in highly inclined, elliptical orbits extending as far out as 200 AUs.
With a spin period of just 3.9 hours, Haumea is the fastest rotating known body in our Solar System larger than 100 kilometers (60 miles) across (David Tytell, Sky and Telescope, April 20, 2006; and (Brown et al, 2005 preprint). Shaped like a rugby or American football because of its fast rotation, Haumea must be as dense as basalt and be made almost entirely of rock or else its very fast spin would have stretched it out even more than it is already. This suggests it has lost most of its low-density icy mantle -- unlike many other known EKOs -- probably due to an ancient cataclysmic collision which could have broken up Haumea's ice mantle, set it reeling, and produced it's two small moons. Probably spherical and 20 percent larger before the collision, Haumea was about about 1,000 miles wide (almost 1,610 km), or about two-thirds the width of Pluto, and made of roughly half ice and half rock, like other EKOs. It is thought to have collided with an object that was perhaps 700 miles wide (roughly 1,130 km) and traveling at nearly 7,000 miles per hour (over 11,000 km per hour). The impact produced at least seven other large icy objects with diameters ranging from 6 to 250 miles (10 to 400 km), and its discovery team have grouped the scattered objects into a family based on their matching gray color and evidence of surface water ice derived from spectral analyses.
The bright pure-ice surface of Haumea and its moons was unexpected. Observations of the primary body made by astronomer Chadwick A. Trujillo and his colleagues revealed the strong spectral signature of crystalline water ice. While crystalline ice forms at temperatures above 110° Kelvins (-163° Celsius), the ambient temperature of space around Haumea is much colder, at below 50° Kelvins. In addition, since crystalline water ice should turn dark and ruddy in less than 100 million years from cosmic rays and micrometeoroid impacts in a process known as space weathering. Given the orbital spread of the EL61 family of fragments, however, the collision that produced them must have taken place billions of years ago. Hence, the object may have experienced resurfacing, perhaps by micrometeorite impacts that convert surface ices to crystalline form by flash-heating.
Spectra of Haumea's outer satellite obtained by astronomers Kristina M. Barkume, Michael E. Brown, and Emily L. Schaller also reveal the signature of almost pure water ice (Barkume et al, 2006). While the observations were too low in resolution to distinguish the type of water ice, it seems that nearly all of the moon is coated in highly reflective frost, like the three moons of Pluto which may also have formed from a violent collision. Hence, the moons of the largest KBOs may differ in origin from those of ordinary KBOs, possibly because their satellite systems formed from the remains of violent impacts instead of by delicate gravitational capture (Noll et al, 2007; Stern et al, 2006 and 2005; and Brown et al, 2005).
José Luis Ortiz Moreno, an astronomer at the Sierra Nevada Observatory in Spain, and colleagues Francisco José Aceituno Castro and Pablo Santos-Sanz claimed to have discovered the object on July 25, 2005. After re-analyzing observations they had made on March 7, 2003 and scouring older archives (a process known as "precovery"), they found the object in images dating back to 1955. Ortiz's team announced their discovery on July 27, 2005, and it was published two days later by the Minor Planet Center (MPC) operated by the International Astronomical Union (IAU), the clearinghouse for such discoveries.
After sending congratulations, Brown's team subsequently found that it had inadvertently published the internal code designation (of K40506A) for their discovery of Santa on July 20, 2005. Apparently, typing this code designation into internet search engines allowed other EKO searchers to find the observation logs of Brown's team (including Santa's observed positions) at a web site containing the observing logs of the SMARTS system, where Professor Brown and his colleagues were using a SMARTS telescope at the Cerro Tololo Inter-American Observatory in Chile to track the object. Dr. Richard W. Pogge (of Ohio State University), who maintains the SMARTS web site, subsequently used third-party web server logs to determine that the web page in question had been accessed eight times from July 26 to 28, 2005 by an IP address used by computers at the Instituto de Astrofísica de Andalucía where Ortiz's team worked, and which the team used to notify the MPC of its discovery of Haumea (see "electronic trail").
Dr. Ortiz subsequently confirmed that he and a student accessed SMARTS telescope logs through the internet and downloaded the relevant information a day before making his announcement for the purpose of confirming whether Santa was the same object. Denying any wrongdoing, Ortiz is said by one account to have conceded that Brown's team discovered Haumea first. On August 14, 2005, Professor Brown wrote an email to Brian G. Marsden, director of the IAU's MPC, which accused Ortiz's team of a serious breach of scientific ethics and asked that the MPC to strip it of discovery status and that the IAU issue a statement condemning their actions (more discussion of the discovery controversy from Dennis Overbye, New York Times, September 13, 2005 and at Wikipedia's page on 2003 EL61).
In 2005, the Brown team also discovered that Haumea has two small satellites, which were nicknamed "Rudolph" -- found on January 28th -- and "Blitzen" -- announced on November 29th (Brown et al, 2006; and 2005). The larger Hi'iaka (formerly Rudolph) was the first moon to be discovered on January 28, 2005 by observations at the Keck Observatory. It has a possible diameter of about 217 miles or 350 km -- assuming an albedo or surface brightness similar to Haumea -- and around one percent of Haumea's mass. Namaka (formerly "Blitzen"), the smaller moon, has a diameter of around 106 miles or 170 km and has only about 0.2 percent of the primary's mass. The inner moon, Namaka, has a 34.7-day non-circular orbit at an average distance of 62,300 miles (or 39,000 km) of with in inclination of 39 +/- 6 degrees, while the brighter, outer companion Hi'iaka has a 49.1-day, nearly circular orbit (e= 0.05) at a distance of 15,300 miles (or 9,500 km) with an inclination of 235 degrees that is affected by the smaller satellite. The orbits of both satellites are tilted to each other by about 40 degrees.
When Alaska-sized, Haumea (2003 El61) collided with another Pennsylvania-sized object (Alaska and Pennsylvania are large governmental units of the United States), it scattered debris across the Solar System as well as created two moons that persisted to modern times. In 2006, three EKOs smaller than Haumea were found in orbits very similar to its elongated and slanted orbit (Barkume et al, 2006). On March 14, 2007, the discovery team (including Michael E. Brown, Kristina M. Barkume, Darin Ragozzine, and Emily L. Schaller) announced that two additional objects with very similar coloration and proportion of water ice had been found following Haumea in its orbit around the Sun (Brown et al, 2007; and Kenneth Chang, New York Times, March 20, 2007).
These findings suggest that the five smaller bodies are fragments of the icy mantle of Haumea that were ejected after an ancient collision. While 35 collisional families of objects have been found in the Main Asteroid Belt, this family of objects is the first to be found in the Edgeworth-Kuiper Belt. Since each of the fragments have surfaces that may have once been internal regions of the original object, astronomers hope to ascertain the internal structure of the original colliding bodies by analyzing the subtle differences in composition between the fragments (Barkume et al, 2006; and New Scientist, March 14, 2006). Although only five fragments had been found by March 2007, the total number of objects eventually found in the Haumea collisional family may rise to the hundreds or even thousands in coming decades.
Spectroscopic measurements (with the 10-meter Keck II Telescope at Mauna Kea, Hawaii) have revealed that the five objects found thus far -- the largest of which is around 250 miles or 400 km across -- have the same unusual surface properties as Haumea, consisting of nearly pure water ice crystals. In total, the five bodies appear to have around one tenth of the total amount of material blasted off proto-Haumea, and while some of the rest probably evaporated into space, smaller fragments are probably still in the vicinity awaiting discovery.
On October 14, 2008, astronomers Emily L. Schaller and Mike Brown announced confirmation of two more fragments (2003 UZ117 and 2005 CB79) of Haumea ancient collision in the outer Solar System, at the 40th annual meeting of the Division for Planetary Sciences of the American Astronomical Society. Although dispersed throughout the Edgeworth-Kuiper belt, the new pieces still share some orbital characteristics with Haumea (and its collisional family), including unusually bright, pure icy surfaces. In addition, a team of astronomers (Pedro Lacerda, David Jewitt, and Nuno Peixinho) also announced his observation of subtle color changes when Haumea rotates which suggest that the dwarf planet sports a dark, red spot on its surface left over from a big impact scar (more from Govert Schilling, New Scientist, October 15, 2008; Schaller and Brown, 2008; Ragozzine and Brown, 2007; and Lacerda et al, 2008).
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