http://www.universetoday.com/2008/08/18/as...t-near-neptune/

Press Release Images: http://www.astronomy.ohio-state.edu/~dhw/SDSS08/ssfigs.html

http://sphinx.planetwaves.net/2006sq372.htm





Bill

Holy crap!

Unless I miss my guess, 1600AU is a record apogee for any non-cometary object, although this beast is doubtless yet another 'platypus'. Thanks for posting this, Bill.

One may argue, though, that 2006SQ372 is a cometary object

I am sure that if 2006 SQ372 had a perihelion sufficiently close to the Sun, it would develop a cometary tail, due to its volatile-rich composition, and be recognised as a comet. It seems clear that both Sedna and this object are part of the same population as the classical comets, originally part of the Oort Cloud. (The Centaurs, on the other hand, probably originated with the KBOs.) The combination of very large perihelion and aphelion, but with aphelion well short of the classical Oort Cloud, appears to be unique among known objects -- although no doubt there are an enormous number of such objects, which are only now starting to be discovered.

I expect that these objects are considerably more numerous than traditional comets, since their velocities at aphelion do not need to be such that their perihelia are close enough to the Sun to allow for a tail to form (which surely are only a tiny fraction of all likely velocities). What make Sedna so remarkable to me is its great size, compared to the "average" Oort Cloud object, of which 2006 SQ372 is more typical, comparable to a large cometary nucleus. The largest conventional comet nucleus was that of the Great Comet of 1729, which was likely over 100km in diameter, while Hale-Bopp's nucleus was about 40km wide, and P/Halley's nucleus is about 16km by 8km by 8km. 2006 SQ372, at between 45km and 150km in diameter, would be considered a very large, but not unprecedented in size, comet if it were to approach close enough to the Sun to form a tail.

The bottom line to me is that the term "comet" is related to an icy body's forming a coma and tail, rather than to its origins. Even Centaurs have been detected forming a coma, and would be called comets if they are perturbed into a sufficiently close perihelion, but they apparently originate in a different region of the Solar system than do Oort Cloud objects.

I'm not sure why this object is being classed with Sedna. Aphelion distances are not good indicators of origin because aphelia can be raised to arbitrary values (including infinity) by gravitational slingshots with giant planets - provided that the perihelion is low enough for such an encounter to have occurred sometime in the past as seems to be the case here.

Or it's possible that this was a classical Oort Cloud object in a cometary orbit that had its aphelion lowered by a giant-planet encounter -- most likely Neptune, going by its current perihelion. (Question: does 2006 SQ372's orbit intersect or at least come close to that of Neptune's, or is it so highly inclined that it probably never came close enough to Neptune to be significantly perturbed?)

I think that all of these objects -- classical Oort Cloud objects, inner Oort Cloud objects, most comets, plus Sedna and 2006 SQ372, which I understand have aphelia less than those of even the inner Oort Cloud -- originated in the classical Oort Cloud, and some of them were somehow perturbed into observable orbits.

I think so because observations of extrasolar dust disks suggest that they extend for hundreds of AU from the central star, and I have no reason to think that our own system was any different. The dust density would have been so low, and accretion timescales so long, that I expect that there are few if any large objects native to the region -- "large" meaning big enough to gravitationally perturb other objects into cometary orbits. It does seem plausible, however, that a small number of large objects from the Uranus / Neptune region (which also produced the Centaurs, Plutinos and scattered-disk KBOs) may have had their aphelia raised into the Oort Cloud, and in turn perturbed some Oort Cloud objects into cometary orbits.

Yep, it was in the news: 2006 SQ372 is not a dwarf planet, probably an Oort cloud object with a diameter of 96 kilometers

As far as I know it is generally believed that Oort cloud comets are produced by perturbations of the Oort cloud by passing stars, molecular clouds, and galactic tide. This is different from Kuiper belt comets that are indeed disturbed by the giant planets. Intuitively, I doubt that a small number for large objects from the Uranus / Neptune region can perturb enough objects from the Oort cloud. The isotropic distribution of Oort cloud comets may also pose a problem because the large objects would mostly be scattered withing the ecliptic), although I am not sure here because that picture may be too simple.


Once a comet is in the inner solar system, it's orbit can be quickly modified by encounters with Jupiter and other planets, and it is impossible to determine the source region for an individual object (e.g. many "dynamically new" comets with aphelia in the Oort cloud have visited the inner solar system before). Statistically, it is still expected that the fraction of Kuiper belt comets is larger for short-period comets than for Oort cloud ones.

Agreed, once an object has undergone a major perturbation by a giant planet there's no longer any way to be sure where it started out. What is a 'classical Oort cloud object' anyhow? Quite possibly they were mostly scattered from the giant planet zone as these bodies 'cleared their orbits'. This scattering would not have been restricted to the ecliptic plane.

But if you group anything with Sedna you have a problem. Sedna has never been anywhere near the giant planets. The discovery of a second object in that category would be major news, but this isn't that news.

Is Sedna too large to have been scattered out into the Oort cloud by the giant planets in the formation period of the solar system, together with the other Oort cloud bodies? Once it reaches a near parabolic orbit, very little disturbance will be necessary for it's orbit to be changed to not to return to the inner solar system.

A quick literature search brings up Matese et al., Earth, Moon and Planets 97, 459-470, 2005. They argue for a trans-neptunian origin of Sedna and it's perihelion been detached by a hypothetical wide binary companion of the sun.

Indeed, it seems to be difficult to explain Sedna's origin if the first (?) attempt at an explanation is that speculative!

There are other objects already known that more closely resemble the newly discovered one:

The following is a quote from a relevant website - I'll add the link in a moment

Two objects, the SDO (87269) 2000 OO67 and the inner Oort cloud object (90377) Sedna, have aphelion distances near 1000 AU; another (2006 SQ372) has aphelion distance near 1900 AU. (Three unusual asteroids have aphelia over 1000 AU: 2002 RN109, 2005 VX3, and 2007 DA61; these may be inactive comets.) A total of 55 TNOs (plus 8 more unusual objects and one Apollo asteroid) have aphelion distances exceeding 100 AU. Relatively few (21) have been discovered with perihelion distances greater than 46 AU, and only three with perihelion distances greater than 47 AU: Sedna at 76 AU, 2004 XR190 at 51 AU, and 2004 VN112 at 47.4 AU. Data thus far suggests than there is indeed a cutoff to the classical TNO population at 47 AU, although the discoveries of Sedna and 2004 XR190 suggest an unrecognized population of much more distant objects (see below).

The link:

http://www.johnstonsarchive.net/astro/tnos.html

In particular, 2000 OO67 seems similar:

2006 SQ372 perihelion: 24.166 AU aphelion: 2010 AU
2000 OO67 perihelion: 20.766 AU aphelion: 1166 AU

(elements according to http://sphinx.planetwaves.net/centaurs.htm)

Sedna remains unique:

2003 VB12 (90377 Sedna) perihelion: 76.262 AU aphelion: 687 AU

Three of the other objects mentioned seem to be more comet-like to me:

2002 RN109 perihelion: 2.690 AU aphelion: 1157 AU
2007 DA61 perihelion: 2.656 AU aphelion: 1034 AU
2005 VX3 perihelion: 4.114 AU aphelion: 2588 AU

This case looks like an extreme scattered-disk object:

2004 VN112 perihelion: 47.413 AU aphelion: 584 AU

Here is a list of objects with aphelia greater than 300 AU, ordered by increasing perihelia, from this site:

1996 PW ------ 2.511 508.865
2007 DA61 --- 2.656 1034.135
2002 RN109 -- 2.690 1157.351
2005 VX3 ----- 4.114 2587.979
2000 OO67 -- 20.766 1082.740
2006 UL321 -- 23.494 498.035
2006 SQ372 - 24.166 1911.722
2005 PU21 --- 29.315 318.487
2001 FP185 -- 34.260 414.172
2007 VJ305 -- 35.144 362
2002 GB32 --- 35.330 394.344
2007 TG422 -- 35.562 928
2003 SS422 -- 39.369 353.510
2000 CR105 -- 44.160 393.832
2004 VN112 -- 47.413 584.366
2003 VB12 --- 76.115 896.093 (Sedna)

From this list, it seems obvious that Sedna remains unique.

Hey, that's a very handy shortlist of 'distant travellers' you've drawn up there.

I've just pencilled in diameters too, and that also divides neatly into 3 classes:

Damocloids with perihelia less than 5 are all smaller than 10 km.
Sedna, perihelion 76, diameter 1500 km.
All the rest, perihelia 20 - 50, diameters in the range 60 - 260 km.

I've been looking at the full list with fascination. There really is a lot that can be pulled from the data. For example, the current definition of a "dwarf planet" includes being sufficiently large that it is in hydrostatic equilibrium. For icy bodies, that is generally thought to mean a diameter equal to or greater than 400km. The above list currently contains 61 objects (not counting Pluto's moon Charon) of that size or greater. By year of discovery:

1930: 1
.
.
.
1995: 1
1996: 3
1997: 1
1998: 2
1999: 2
2000: 4
2001: 3
2002: 11
2003: 10
2004: 8
2005: 7
2006: 2
2007: 5
2008: 1

Mike Brown's team apparently has an additional 30 or more probable dwarf planets under observation, but they have not yet been published.

I have lurking about this forum for a while now; this topic really picqued my interest. I am very intrigued by the exploration of the trans-Neptunian region. I am bemused by the big news of a second "inner Oort cloud" object being found

Attached is a list of the objects have the largest semi-major axes That I have been able to find. I identified the objects from the MPC list of Centaurs and Scattered-Disk Objects and David Jewitt's list of damocloids. All orbital and physical data ( and classification, if available) is from neo.jpl.nasa.gov/orbits. I have included data on a couple of comets for comparison.

For my money, I think 2007 TG422 is a closer twin to Sedna that 2006 SQ372. At least its perihelion is far enough beyond Neptune that it wasn't scattered by it.

Fascinating article on hitching a ride on 2006 SQ372 in The Space Review.

http://www.thespacereview.com/article/1189/1

Welcome Ron and thanks for those posts. Our categorisation of transneptunian objects is obviously in a bit of a mess (not only in the notorious case of Pluto which is currently off-limits here for good reason.) In the end the descriptive categories are the least informative item on that otherwise very informative spreadsheet - and on the full updated list which is indeed a wonderful resource. I'm particularly wary of the term 'inner Oort cloud object'. If I had to choose a naming scheme from scratch I'd probably plump for asteroids, plutoids and sednoids (1 so far), based on perihelion distance, and call something a comet in addition only if and when it is exhibiting cometary behaviour, i.e. growing 'hair'.

Let the numerical data speak for themselves!

Acceleration is only a function of the larger object, so Sedna's mass doesn't really factor in, so long as it's a lot less massive than Uranus (which it is). If it were comparable to Uranus or Neptune, it might have jerked them around. But its actual mass may as well have been the same as a baseball when it comes to playing orbital billiards with the giants.

It makes little sense to me, as if hitching a ride on another object would require less energy than launching a probe in an orbit similar to it...

It should "work" if you don't try to match velocities before you impact it. You might pick up several kps of delta-v that way. All at once.

This is a special case of what's been called "lithobraking." Or perhaps litho-breaking might be a more appropriate term. :-)

--Greg (Sometimes you're the windshield; sometimes you're the bug)

This depends on having a mission ready and waiting to go when a suitable candidate object is found. The problem is spending large amounts of money on something that has an uncertain payoff.

If the objective is to get as far as possible from the Sun in the shortest time, then something like the old TAU mission would be more suitable. TAU was based on nuclear electric propulsion.

I am resurrecting this old thread because a new paper is out:

2006 SQ372: A Likely Long-Period Comet from the Inner Oort Cloud

We report the discovery of a minor planet (2006 SQ372) on an orbit with a perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show that this is a transient orbit and is unstable on a timescale of 200 Myrs. Falling near the upper semimajor axis range of the scattered disk and the lower semimajor axis range of the Oort Cloud, previous membership in either class is possible. By modeling the production of similar orbits from the Oort Cloud as well as from the scattered disk, we find that the Oort Cloud produces 16 times as many objects on SQ372-like orbits as the scattered disk. Given this result, we believe this to be the most distant long-period comet ever discovered. Furthermore, our simulation results also indicate that 2000 OO67 has had a similar dynamical history. Unaffected by the "Jupiter-Saturn Barrier," these two objects are most likely long-period comets from the inner Oort Cloud.