* Astronomy

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RE: (136108) 2003EL61

Blobrana · L

Astronomers have found a mysterious clan of icy objects in the outer solar system, which look much younger than their years.
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Blobrana · L

Some families seem blessed with eternal youth, looking much younger than their years. Now, astronomers have found just such a clan of icy objects in the outer solar system. They appear puzzlingly fresh-faced, despite the fact that they probably formed in a collision more than a billion years ago.
The largest member of the family, a rapidly tumbling blimp-shaped object called 2003 EL61, was discovered in 2005. In 2007, astronomers found five smaller objects travelling in similar orbits. Their paths suggested they all formed a single object that was broken apart in a collision more than a billion years ago.
Now, a team led by David Rabinowitz of Yale University in New Haven, Connecticut, US, reports that the brightness of the large object and four of the smaller ones (the fifth could not be observed) changes little when observed from various points along Earth's orbit.

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Title: Study of the Surface of 2003 EL61: the largest carbon-depleted object in the trans-neptunian belt
Authors: N. Pinilla-ALonso, R. Brunetto, J. Licandro, R. Gil-Hutton, T.L. Roush, G. Strazzulla

2003 EL61 is the largest member of a group of TNOs with similar orbits and 'unique' spectra (neutral slope in the visible and the deepest water ice absorption bands ever observed in the TNb). Studying the composition of the surface of 2003 EL61 provides useful constrains on the origin of this particular group of TNOs and on the outer Solar system's history.
We present visible and near-infrared spectra of 2003 EL61 obtained with the 4.2m WHT and the 3.6m TNG at the Roque de los Muchachos Observatory (Canary Islands, Spain). Near infrared spectra were obtained at different rotational phases covering almost one complete rotational period. Spectra are fitted using Hapke scattering models and constraints on the surface composition are derived.
No significant variations in the spectral slope and in the depth of the water ice absorption bands at different rotational phases are evident, suggesting that the surface of 2003 EL61 is homogeneous. The scattering models show that a 1:1 intimate mixture of crystalline and amorphous water ice is the most probable composition for the surface of this TNO, and constrain the presence of other minor constituents to a maximum of 8%
The derived composition suggests that: a) cryovolcanism is unlikely to be the main resurfacing process responsible for the high presence of water ice on the surface of these bodies; b) the surface is older than 10^8 yr. Any catastrophic event, like the collision suggested to be the origin of this population, had to happen at least 10^8 yr ago; c) the surface of 2003 EL61 is depleted of carbon chains. According to the orbital parameters of this population, this makes it a possible source of carbon-depleted Jupiter family comets.

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Title: High Precision Photometry of Extreme KBO 2003 EL61
Authors: Pedro Lacerda, David Jewitt, Nuno Peixinho

We present high precision, time-resolved visible and near infrared photometry of the large (diameter ~ 2500 km) Kuiper belt object (136108) 2003 EL61. The new data confirm rapid rotation at period P = 3.9155±0.0001 hr with a peak-to-peak photometric range (Delta m_R) = 0.29±0.02 mag and further show subtle but reproducible colour variations with rotation. Rotational deformation of 2003 EL61 alone would give rise to a symmetric lightcurve free of colour variations. The observed photometric deviations from the best-fit equilibrium model show the existence of a large surface region with an albedo and colour different from the mean surface of 2003 EL61. We explore constraints on the nature of this anomalous region set by the existing data.

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Near IR Spectrum of 2003 EL61, adapted from Trujillo et al. (2007). A pure crystalline water-ice model fit and a mix of water ice and HCN ice are overplotted. The locations and approximate widths of the 1.25 m and 1.6 m filters used to monitor the 1.5 m water-ice band depth, as well as the wavelength regions where the Earths atmosphere is opaque, are also shown.

Blobrana · L

Title: Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003 EL61
Authors: D. Ragozzine, M. E. Brown

The collisional family of Kuiper belt object (KBO) 2003 EL61 opens the possibility for many interesting new studies of processes important in the formation and evolution of the outer solar system. As the first family in the Kuiper belt, it can be studied using techniques developed for studying asteroid families, although some modifications are necessary. Applying these modified techniques allows for a dynamical study of the 2003 EL61 family. The velocity required to change orbits is used to quantitatively identify objects near the collision. A method for identifying family members that have potentially diffused in resonances (like 2003 EL61) is also developed. Known family members are among the very closest KBOs to the collision and two new likely family members are identified: 2003 UZ117 and 1999 OY3. We also give tables of candidate family members which require future observations to confirm membership. We estimate that a minimum of ~1 GYr is needed for resonance diffusion to produce the current position of 2003 EL61, implying that the family is likely primordial. Future refinement of the age estimate is possible once (many) more resonant objects are identified. The ancient nature of the collision contrasts with the seemingly fresh surfaces of known family members, suggesting that our understanding of outer solar system surfaces is incomplete.

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Blobrana · L

In the outer reaches of the solar system, there is an object known as 2003 EL61 that looks like and spins like a football being drop-kicked over the proverbial goalpost of life.
Still awaiting a more poetic name, 2003 EL61 largely escaped the media hubbub during last year's demotion of Pluto, but new findings could make it one of the most important of the Kuiper-belt objects for understanding the workings of the solar system. In this week's Nature, the original discoverer of the body, Mike Brown, announces with his colleagues that an entire family of bodies seems to have originated from a catastrophic collision involving 2003 EL61 about the time Earth was forming.

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Blobrana · L

In a solar system of heavenly bodies, scientists have discovered an ugly duckling -- an oblong-shaped rock in the vicinity of Pluto that may one day light up Earth's sky as a giant comet.
The rock, known as 2003 EL61, is one of the strangest objects in the solar system. It is shaped like an American football and completely rotates every four hours.

"Out in space there is this crazy thing spinning end to end that is as big as Pluto" - Mike Brown, a professor of planetary astronomy at the California Institute of Technology who discovered the object two years ago.

Brown and colleagues at Caltech believe it got its odd shape after a collision with another object about 4.5 billion years ago that sent chunks of the rock scattering, creating two moons and a lot of space debris.

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Kuiper-belt Object Was Broken up by Massive Impact 4.5 Billion Years Ago, Study Shows
In the outer reaches of the solar system, there is an object known as 2003 EL61 that looks like and spins like a football being drop-kicked over the proverbial goalpost of life.
Still awaiting a more poetic name, 2003 EL61 largely escaped the media hubbub during last year's demotion of Pluto, but new findings could make it one of the most important of the Kuiper-belt objects for understanding the workings of the solar system. In this week's Nature, the original discoverer of the body, Mike Brown, announces with his colleagues that an entire family of bodies seems to have originated from a catastrophic collision involving 2003 EL61 about the time Earth was forming.
Brown and his team base their assumptions on similar surface properties and orbital dynamics of smaller chunks still in the general vicinity. They conclude that 2003 EL61 was spherical and nearly the size of Pluto until it was rammed by a slightly smaller body about 4.5 billion years ago, leaving behind the football-shaped body we see today and a couple of moons, as well as many more fragments that flew away entirely.

"Some of these chunks are still in orbit around the sun and very near the orbit of 2003 EL61 itself. The impact made a tremendous fireball, and large icy chunks of the big object split off and went flying into space, leaving behind a huge ice-covered rock spinning end over end every four hours. It spins so fast that it has pulled itself into the shape of an American football, but one that's a bit deflated and stepped on" - Mike Brown, a professor of planetary astronomy at the California Institute of Technology.

A significant part of the finding is that the collision occurred in a region of space where orbits are not very stable.

"In most places, things go around the sun minding their own business for 4.5 billion years and nothing happens. But in a few places, though, orbits go crazy and change and eventually objects can find themselves on a trajectory into the inner solar system, where they would be what we would then call comets."

As a consequence, many of the shards probably made their way to the inner solar system, and a few have undoubtedly hit Earth in the past. The study thus provides new ideas about how the solar system evolves, and how comets fit into the big picture.
Brown adds that 2003 EL61 will put on quite a show in about a billion years, if anyone is still around to enjoy it.

"It's a long time to wait, but 2003 EL61 could become by far the largest comet in eons. It will be something like 6,000 times brighter than Hale-Bopp a few years ago."

The other authors of the paper are Kristin Barkume, Darin Ragozzine, and Emily Schaller, all graduate students in planetary science at Caltech.

Caltech News Release

Astronomers have caught their first glimpse of the innards of an icy asteroid 7.5 billion kilometres away in the Kuiper belt region of the outer solar system.
Mike Brown of the California Institute of Technology in Pasadena and his team discovered that five small Kuiper belt objects were travelling in similar orbits to 2003 EL61, the third-largest KBO ever found. The discovery hinted that the five pieces are fragments that split off after an ancient collision.
Such families of objects are common in the asteroid belt between Mars and Jupiter, but this is the first one seen out in the Kuiper belt. Brown's team found that the fragments all had a similar colour and proportion of water ice to 2003 EL61. This makes their association even more likely.
The fragments each reveal surfaces that were once internal regions of the original object. By analysing the subtle differences in composition between the fragments, astronomers can figure out the internal structure of the original body, in effect putting it back together, like archaeologists reconstructing a smashed pot.

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