'New' Trans-Neptunian Object 2003 EL61.

[Spaceman Spiff]

d-dit d-dit d-dit d-dit - this just in ... Auntie Beeb is reporting a new, 'large' TNO, see Distant object found orbiting Sun.

I don't know if we've got this one, but if not, I've knocked up this SSC clippette for it based on the Spanish version of the orbit (I can't find the NEAR data, but if someone does, might be interesting to add both orbits and compare measurements from two different teams.

Please note, I've guessed the radius to be 1,500km based on the fact that the normalised magnitude of this TNO is 0.4 compared to 1.6 for Sedna. Therefore I'm also assuming same colour and albedo between the two.

Spiff.

Code: Select all

"2003 EL61" "Sol"
{
  Class "asteroid"
  EllipticalOrbit
  {
    Epoch 2453580.5
    Period 285.33
    SemiMajorAxis 43.3408541
    Eccentricty 0.1887862
    Inclination 28.19395
    ArgOfPericenter 239.53682
    AscendingNode 121.89008
    MeanAnomaly 197.97485 # At 2000 actually.
  }
  Radius 1500
  Albedo 0.55
  Color [ 0.65 0.45 0.35 ]
  Texture "asteroid.jpg"
  BlendTexture true
}


[selden]

See also
http://www.gps.caltech.edu/~mbrown/2003EL61/

It seems to have a satellite, so the mass should be relatively accurate.

[symaski62]

http://www.aas.org/publications/baas/v3 ... 05/786.htm
http://www.aas.org/publications/baas/v3 ... 05/320.htm
http://www.aas.org/publications/baas/v3 ... 05/451.htm


http://cfa-www.harvard.edu/mpec/K05/K05O36.html

17 mag !


^^

[Spaceman Spiff]

Nice work, selden, symaski62,

I'll try and distill this data into a better SSC, including elongated body and moon.

Now onto 2003 UB313...

Spiff.

[lostfisherman]

I hope it doesn't keep it's nickname 'Santa' and 'Santas Little Helper' for it's moon. Everyone should like the Simpsons but that might be pushing things a bit far...
http://en.wikipedia.org/wiki/2003_EL61

[Spaceman Spiff]

Greetings!

OK, I've done an SSC for this TNO including its moon and odd shape. I've reduced the size of it to 1,400km mean diameter (3,000km is maybe a bit too much) and corrected the typo 'Eccentricty' in the orbit definition. The 'odd shape' is modelled by a prolate spheroid, but for a 1,400km sized body that is really amazing. Could it be a contact binary? Again for this size, amazing!

Spiff.

Code: Select all

# 2003 EL61.

# [1] "Bright Trans-Neptunian Object", F.J. Aceituno, P. Santos-Sanz and
# J.L. Ortiz, URL: http://www.iaa.es/~ortiz/brighttno.html. Undated, but no
# later than 27 Jul 2005.
# [2] "Keck Observatory laser guide star adaptive optics discovery and
# characterization of a satellite to large Kuiper belt object 2003 EL61.",
# M.E. Brown (CalTech), A.H. Bouchez (Keck Observatory, CalTech Opt. Obs.), D.
# Rabinowitz (Yale University), R. Sari (CalTech), C.A. Trujillo (Gemini
# Observatory), M. van Dam, R. Campbell, J. Chin, S. Hartman, E. Johansson, R.
# Lafon, D. LeMignant, P. Stomski, D. Summers, P. Wizinowich (Keck Observatory).
# 28 Jul 2005, submitted to ApJ Letters (conditional acceptance).
# [3] "Photometric observations of a very bright TNO with an extraordinary
# lightcurve.", D. Rabinowitz, S. Tourtellotte (Yale University), M. Brown
# (Caltech), C. Trujillo (Gemini Observatory). Poster submitted for 37th DPS
# meeting, 4-9 Sep 1005, Bulletin of the American Astronomical Society, 37 #3.
#

"2003 EL61 Barycenter" "Sol"
{
  Class "Invisible"
  EllipticalOrbit
  {
    Epoch 2453580.5 # 29.0 Jul 2005.
    Period 285.33
    SemiMajorAxis 43.3408541
    Eccentricity 0.1887862
    Inclination 28.19395 # -0.38521856?° +0.16524998?°
    ArgOfPericenter 239.53682 # +0.91285785?° -0.07597426?°
    AscendingNode 121.89008 # +0.13526717?° +0.98332108?° (sic! -0.98332108?°?)
    MeanAnomaly 202.00430 # Adjusted from 197.97485?° at 2000.0 to orbit Epoch.
  }
}

"2003 EL61" "Sol/2003 EL61 Barycenter"
# Orbit data from [1].
# Mass, radius data from [2].
# Total System mass: (4.2?±0.1)?—10^21kg, or 0.00070 Earth masses.[2]
# Radius ratio: 1:0.22 based on 3.3 mag difference, same albedo. [2]
# Mass ratio: 1:0.010648 based on cube of radius ratio, i.e., same densities.
#
{
  Class "asteroid"
  EllipticalOrbit
  {
    Epoch 2453458.40 # ?±0.02 days
    Period 49.12 # ?±0.03 days
    SemiMajorAxis 527.076 # = (49,500?±400)km ?— ( 0.010648 / ( 0.010648 + 0.989352 ) )
    Eccentricity 0.050 # ?±0.003
    Inclination 234.8 # ?±0.3?°
    ArgOfPericenter 98.6 # ?±0.4?°
    AscendingNode 26.1 # ?±0.4?°
    MeanAnomaly 180 # I.e., moon passes pericentre at Epoch.
  }
# Mass 0.000070 # Earth masses (98.9352% of system).
  Radius 645.5 # Based on absolute magnitude 1.5 mags. less than Pluto, same albedo, adjusting for prolate spheroid.
  Albedo 0.55 # Assumed same as Pluto.
  Color [ 0.65 0.45 0.35 ]
  RotationPeriod 1000000000000
  Obliquity 90 # No data on polar axis. Can't orient.
  EquatorAscendingNode 292.00430 # No data on polar axis. Can't orient.
  PrecessionRate 2206.7838169 # RotationPeriod 3.9152 days from double-peaked light curve[3].
  Oblateness -0.28571 # Major to minor axes = 1.4:1.0.
  Texture "asteroid.jpg"
}

"2003 EL61 I" "Sol/2003 EL61 Barycenter"
# Moon of 2003 EL61.
# Orbit, mass, magnitude data from [2].
# Radius ratio: 1:0.22 based on 3.3 mag primary-secondary difference,
# same albedo. [2]
#
{
  Class "asteroid"
  EllipticalOrbit # Relative to J2000 ecliptic
  {
    Epoch 2453458.40 # ?±0.02 days
    Period 49.12 # ?±0.03 days
    SemiMajorAxis 48972.924 # = (49,500?±400)km ?— ( 0.989352 / ( 0.010648 + 0.989352 ) )
    Eccentricity 0.050 # ?±0.003
    Inclination 234.8 # ?±0.3?°
    ArgOfPericenter 278.6 # ?±0.4?°
    AscendingNode 26.1 # ?±0.4?°
    MeanAnomaly 0 # I.e., moon passes pericentre at Epoch.
  }
# Mass 0.00000075 Earth masses (1.0648% of system)
  Radius 127 # 0.22 of 2003 EL61.
  Obliquity 234.8 # Assume perpedicular to orbital plane.
  EquatorAscendingNode 26.1 # Assume perpedicuklar to orbital plane.
  RotationPeriod 1178.88 # Synchronous rotation 1:1 = 49.12 days.
  Albedo 0.55 # Assumed same as Pluto.
  Color [ 0.65 0.45 0.35 ]
  Texture "asteroid.jpg"
}


[Planet X]

Distant solar system body may be cigar-shaped
16:20 08 September 2005
NewScientist.com news service
Maggie McKee, Cambridge, UK

Mike Brown, Caltech
Chad Trujillo, Gemini Observatory
Dave Tholen, University of Hawaii
One of the three large new bodies discovered recently in the outer solar system is spinning so quickly it has stretched into a cigar shape, according to new observations. If confirmed, the strange shape is sure to fuel the controversy over what constitutes a planet.

The object, temporarily dubbed 2003 EL61, lies about 51 times farther away from the Sun than the Earth does, in a ring of rocky bodies called the Kuiper Belt. It was discovered in July 2005 by a team of Spanish researchers, who used its apparent brightness to estimate that it might be larger than Pluto.

But just a day after that group announced its find, another team led by Mike Brown of the California Institute of Technology in Pasadena, US, reported that it had also been studying the object and had discovered a small moon orbiting around it. The moon's orbit revealed the larger object's mass, which allowed researchers to estimate its width at about 70% that of Pluto, or 1600 kilometres.

Now, however, more observations with a consortium of small telescopes in Chile suggest the object may actually be about 2000 km ?€“ at least in one dimension. The suggestion comes from observations that reflected sunlight from 2003 EL61 varies greatly in brightness in a pattern that repeats once every three to four hours.

The team says more light is reflected when the longer side of the object is facing the Sun, while less bounces off when the shorter sides are pointed that way. 2003 EL61 appears to be about twice as long as it is wide - and shorter still in height. "It takes the shape of a short, flattened cigar," says team member Chad Trujillo, an astronomer at the Gemini Observatory in Hawaii, US.

Spotty steel
But Dave Tholen, an astronomer at the University of Hawaii, US, says the difference in light readings could also be explained if the object appeared mottled and did not reflect sunlight evenly across its surface. He points that mottled neighbour Pluto actually shows the second-largest such ?€?albedo variation?€

[ElChristou]

Greetings!

OK, I've done an SSC for this TNO including its moon and odd shape...

Many Tx for the work. Question: the orbits for those bodies are not drawn on my config... normal or not?

[Malenfant]

So does it still have a moon, or were they mistaken about that and they were actually seeing the elongrated shape?

[Spaceman Spiff]

Question: the orbits for those bodies are not drawn on my config... normal or not?

Somewhat normal, if you select either one of the asteroids and not the barycentre.

If I select the 2003 EL61 Barycentre and have orbits on (including for 'asteroid'), I see the barycentre's orbit around the sun and the small moon's orbit around the barycentre, but not the main body's orbit around the barycentre. That's because the SemiMajorAxis for the main body is smaller than its radius, so its orbit around the barycentre is entirely contained within the main body, and you can't see it. If I select either the main body or the small moon instead, the orbits of the baryentre and small moon disappear. So it seems to me the way Celestia is working, you have to select the barycentre to see any of the orbits, and you can only see all these orbits at once.

So does it still have a moon, or were they mistaken about that and they were actually seeing the elongrated shape?

Yes, it still has that moon. That moon is 49,000 km away, well outside the 2,000km longest dimension proposed for 2003 EL61 main, and it has been observed separately.

I defined the main body as the prolate spheroid as mentioned in the New Scientist article, though Grant Hutchison thought this less likely against alternatives of spotty albedo or contact binary. I note that if the main body was two equal massed 1,000km diameter bodies almost touching, the orbital period would be about 3-4 hours...

Spiff.

* EDIT: deleted [It's perhaps something to do with that I set each body orbiting a barycentre of class 'invisible' of undefined radius.] I wish there was 'strikethrough' font so that I can show what I changed...

[Malenfant]

I wish there was 'strikethrough' font so that I can show what I changed...

Put the original data in a 'comment'?

[Spaceman Spiff]

No, the SSC is OK and I shan't change that (unless the double contact asteroid model proves more likely).

I meant I wish I could show my edits better in my posts when I correct myself. There is an edit button against each post one sent when one logs in, allowing you to edit earlier posts

Spiff.