420356 Praamzius

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420356 Praamzius
Discovered byK. Černis
R. P. Boyle
Discovery siteVatican Advanced Technology Telescope
(Mount Graham Obs.)
Discovery date23 January 2012
MPC designation(420356) Praamzius
Named after
(Lithuanian mythology)[3]
2012 BX85
TNO (cubewano)[4]
(near-3:5 resonance)
Orbital characteristics[2]
Epoch 2017-Sep-04 (JD 2458000.5)
Uncertainty parameter 3
excite_mean = 0.053[4]
Observation arc13.08 yr (4,778 days)
Aphelion43.030 AU
Perihelion42.528 AU
42.779 AU
279.81 yr (102,199 days)
0° 0m 12.633s / day
Physical characteristics
Mean diameter
200 km (assumed)[5]
20.8–25.2; mainly 21.0-22.0

420356 Praamzius, provisional designation 2012 BX85, is a trans-Neptunian object and possible dwarf planet in the Kuiper belt, approximately 200 kilometers in diameter.[2][5] It was discovered on 23 January 2012, by astronomers Kazimieras Černis and Richard Boyle with the Vatican's VATT at Mount Graham Observatory in Arizona, United States. The object was named after the chief god Praamžius from Lithuanian mythology.[3]

Eccentricity at different Epochs
Epoch Eccentricity
2015-05-01 0.0019
2016-07-31[3] 0.0032
2017-09-04[2] 0.0058
2021-09-01 0.013
Barycentric 0.0078


Praamzius is a cold Classical Kuiper belt object with both a low orbital eccentricity and a low orbital inclination.[4] With an eccentricity of 0.00324 (epoch 2016),[3] Praamzius has one of the lowest eccentricities of any trans-Neptunian object (TNO), and a more circular orbit than any major planet (including Venus, the least eccentric planet at 0.007). But at different epochs Praamzius will have slightly different eccentricities due to the position of the planets. A 10 million year simulation of the orbit shows the eccentricity (emax) does not get greater than 0.03.[4]

Its orbital radius is near, but not actually on the 3:5 resonance with Neptune, with both period and radius being slightly too large to achieve an exact 3:5 ratio. This could be due to any of several reasons, e.g. their apparent relationship being merely coincidental and Praamzius a typical non-resonant cubewano instead of resonant, or an artefact of librating cycle centred on 3:5 and currently on the longer/wider limb of its oscillation around that, or due to it exhibiting some more exotic resonance such as 7:12, 10:17 or 17:28 which are better fits for its observed track.

However, it is difficult to yet determine which of these is true, as although Praamzius has a comparatively good observational record (with more than 200 confirmed professional sightings over nearly 14 years), with an otherwise decent Uncertainty Parameter of U = 2, or a mere 4.4 to 19.6 arcseconds of drift expected per decade, its great orbital distance and long period mean each of its approximately 28-decade orbits accumulate 0.034 to 0.153 degrees of potential error. Whilst still a very small amount, and unlikely to cause any difficulty with predicting target areas for future imaging or the object's position for probe rendezvous, it is enough to make nearly all of the above scenarios possible (the exception being a non-librating 7:12 resonance; however, it would only require minor, long term libration for 7:12 to become realistic).

The apparent resonance even depends on what source data and calculation methods are employed - the best fit for the given orbital periods within a 25,000 year cycle time, 44:75, is still imperfect and exhibits a final error of more than 1.5 Earth years for the final conjunction (approx 0.5%, or 2 degrees of arc). If we instead use the two bodies' respective semi-major axes, i.e. their mean orbital radii as the basis for calculation, and purely Keplerian 2-body equations (ignoring interference by all other bodies), the decimal ratio returns 1.699943. This is actually close enough to 1.7 that a 10:17 resonance can be considered a credible possibility, not only with U=2, but even in the looser reaches of a notional "U=-1" band, 4.4x more accurate than the usual "U=0" gold standard and about 85x more than band 2. However, appearing to be dead centre is no guarantee of accuracy when the uncertainty IS actually that great, so either of the other explanations could still be correct.


Initial discovery was from images acquired on 23 January 2012 at VATT, on Mount Graham, Arizona using a 1.8 meter reflecting telescope;[1] precovery observations from VATT and the Sloan Digital Sky Survey dating back to 31 December 2002 have been accepted by the Minor Planet Center.[3] The object has been repeatedly tracked through January 2016, mostly by VATT with some supporting observations by Las Campanas Observatory. 420356 Praamzius is one of the most recently discovered minor planets to receive a numeric designation, confirming it as a distinct body with a well determined orbit. This is due to the large number of observations since and indeed before its discovery: about one every 23 to 24 days on average from 2002 to 2016, and as many as one per 10 days in the period between discovery and assignment alone. Precovery images refined the orbit even more.

Physical characteristics[edit]

There is little useful data available from which to make more than the most basic estimates of its size and surface age. However, analysis of precovery observations in the visible spectrum between 2002 and 2007 show that it may be amongst the reddest objects in the Solar System, being more than 1.5 magnitudes fainter in the G (green) filtered versus the R (red) filtered images, which may offer some clues about its composition and origin.[citation needed] This is expected from a fairly small "orbitally unexcited" cold Classical Kuiper belt object as they are generally mostly red. The cold populations distance does not vary from the Sun very much so their surfaces are older, more irradiated, and covered in tholins. Assuming an albedo of 0.20, it would be roughly 200 km in diameter.[5] Praamzius is likely too small to be a dwarf planet. There is a chance it accreted in basically the same orbit it has today.


This minor planet was named after Praamžius (an epithet of Dievas), the Lithuanian mythological god of the sky, peace, and friendship.[3] The official naming citation was published by the Minor Planet Center on 22 February 2016 (M.P.C. 98717).[6]


  1. ^ a b "MPEC 2012-B100: 2012 BX85". IAU Minor Planet Center. 2012-01-30. (K12B85X)
  2. ^ a b c d e "JPL Small-Body Database Browser: 420356 Praamzius (2012 BX85)" (2016-01-30 last obs.). Jet Propulsion Laboratory. Archived from the original on 2015-02-02. Retrieved 7 September 2017.
  3. ^ a b c d e f "420356 Praamzius (2012 BX85)". Minor Planet Center. Archived from the original on September 7, 2017. Retrieved 7 September 2017.
  4. ^ a b c d Marc W. Buie. "Orbit Fit and Astrometric record for 420356". SwRI (Space Science Department). Retrieved 2018-02-12.
  5. ^ a b c d Brown, Mike. "How many dwarf planets are there in the Solar System". Retrieved 2 February 2015.
  6. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 7 September 2017.

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