A Sedna-like body with a perihelion of 80 astronomical units

Journal name:
Nature
Volume:
507,
Pages:
471–474
Date published:
DOI:
doi:10.1038/nature13156
Received
Accepted
Published online

The observable Solar System can be divided into three distinct regions: the rocky terrestrial planets including the asteroids at 0.39 to 4.2 astronomical units (au) from the Sun (where 1au is the mean distance between Earth and the Sun), the gas giant planets at 5 to 30au from the Sun, and the icy Kuiper belt objects at 30 to 50au from the Sun. The 1,000-kilometre-diameter dwarf planet Sedna was discovered ten years ago and was unique in that its closest approach to the Sun (perihelion) is 76au, far greater than that of any other Solar System body1. Formation models indicate that Sedna could be a link between the Kuiper belt objects and the hypothesized outer Oort cloud at around 10,000au from the Sun2, 3, 4, 5, 6. Here we report the presence of a second Sedna-like object, 2012VP113, whose perihelion is 80au. The detection of 2012VP113 confirms that Sedna is not an isolated object; instead, both bodies may be members of the inner Oort cloud, whose objects could outnumber all other dynamically stable populations in the Solar System.

At a glance

Figures

  1. Sedna and 2012[thinsp]VP113 are clear dynamical outliers in the Solar System.
    Figure 1: Sedna and 2012VP113 are clear dynamical outliers in the Solar System.

    Eccentricity versus perihelion distance for the approximately 1,000 minor planets with well-determined (multi-year) orbits beyond 10au are depicted. There are no known objects with closest-approach distances (perihelia, q) between 55au and 75au, even though such objects would be closer, and should therefore be brighter and easier to detect than Sedna or 2012VP113. This suggests there may be a paucity of inner Oort cloud objects with q<75 au. The perihelia of Sedna and 2012VP113 are much too distant from Neptune (30au) for their existence to be explained by the known mass in the Solar System. All error bars are smaller than the data symbols.

  2. Results from the observational bias simulation.
    Figure 2: Results from the observational bias simulation.

    The simulated inner Oort cloud objects (dots) are shown, along with the simulated detections in our survey (blue crosses) and the most sensitive all-sky survey so far, which re-detected Sedna21 (red crosses) for two different inner Oort cloud object models: our favoured model (a) and a comparison model (b). We have displayed ten simulated survey realizations per survey. The true values for Sedna and 2012VP113 are shown as red and blue circles, respectively, both with error bars much smaller than the plot symbol (there are no error bars associated with all other symbols, which describe simulated data). There is one difference between the two models, the minimum perihelion for the underlying population (75au in a versus 50au in b). Our observational results favour the model in a because both Sedna and 2012VP113 were found within a few au of their perihelion. This indicates that the inner Oort cloud objects may have increasing numbers with increasing distance.

  3. The argument of perihelion for distant objects clusters about 0[deg].
    Figure 3: The argument of perihelion for distant objects clusters about 0°.

    All minor planets with perihelion greater than 30au as a function of semi-major axis are shown. All bodies with semi-major axis greater than the line at 150au show a pronounced concentration near ω0°. Errors on these orbital elements are much smaller than the plotted symbols. This figure appears in histogram form in Extended Data Fig. 1.

  4. Histogram of [ohgr] for minor planets with q[thinsp]>[thinsp]30[thinsp]au.
    Extended Data Fig. 1: Histogram of ω for minor planets with q>30au.

    This is similar to Fig. 3 but in histogram form. The bodies with a>150au are shown as a black line (multiplied by a factor of ten for clarity) and bodies with a<150au are shown as a dotted line. The two distributions differ according to Kuiper’s test with a significance of 99.9%.

  5. The [ohgr] cycling of 2012[thinsp]VP113 in the current Solar System.
    Extended Data Fig. 2: The ω cycling of 2012VP113 in the current Solar System.

    We note that over the course of 500Myr, the argument of perihelion ω moves uniformly across all values. All inner Oort cloud Objects (Table 1) and other distant objects (Extended Data Table 2) are expected to exhibit this behaviour on differing timescales, so the observation that all are restricted to ω near 0° is inconsistent with the current dynamical environment in the Solar System. Because these are simulated plots, there are no error bars associated with data points.

  6. The libration of [ohgr] for 2012[thinsp]VP113 with an assumed object five times the mass of Earth at 210[thinsp]au.
    Extended Data Fig. 3: The libration of ω for 2012VP113 with an assumed object five times the mass of Earth at 210au.

    2012VP113 librates about ω = 0° for most of the duration of the Solar System. This behaviour could explain why the two inner Oort cloud Objects (Table 1) and all objects with semi-major axes greater than 150au and perihelia greater than Neptune’s (Extended Data Table 2) have ω0°. The choice of mass and orbit of the perturber is not unique. Many possible distant planetary bodies can produce the pictured Kozai resonance behaviour, but the currently known Solar System bodies cannot. These are simulated plots, so there are no error bars associated with data points.

Tables

  1. Model parameters for the q[prime] = 5 inner Oort Cloud observational bias and population study
    Extended Data Table 1: Model parameters for the q′ = 5 inner Oort Cloud observational bias and population study
  2. Orbital elements of extreme Solar System bodies
    Extended Data Table 2: Orbital elements of extreme Solar System bodies
  3. Colours of 2012[thinsp]VP113
    Extended Data Table 3: Colours of 2012VP113

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Author information

  1. These authors contributed equally to this work.

    • Chadwick A. Trujillo &
    • Scott S. Sheppard

Affiliations

  1. Gemini Observatory, 670 North A‘ohoku Place, Hilo, Hawaii 96720, USA

    • Chadwick A. Trujillo
  2. Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington DC 20015, USA

    • Scott S. Sheppard

Contributions

C.T. created the moving object detection program for image analysis, developed the discovery statistic simulations, and is the principal investigator of the NASA grant supporting the project. S.S. obtained the telescope time, planned and performed the observations, analysed the data (including the colour measurements) and estimated the inner Oort cloud object orbital evolution using the Mercury integrator.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: Histogram of ω for minor planets with q>30au. (84 KB)

    This is similar to Fig. 3 but in histogram form. The bodies with a>150au are shown as a black line (multiplied by a factor of ten for clarity) and bodies with a<150au are shown as a dotted line. The two distributions differ according to Kuiper’s test with a significance of 99.9%.

  2. Extended Data Figure 2: The ω cycling of 2012VP113 in the current Solar System. (102 KB)

    We note that over the course of 500Myr, the argument of perihelion ω moves uniformly across all values. All inner Oort cloud Objects (Table 1) and other distant objects (Extended Data Table 2) are expected to exhibit this behaviour on differing timescales, so the observation that all are restricted to ω near 0° is inconsistent with the current dynamical environment in the Solar System. Because these are simulated plots, there are no error bars associated with data points.

  3. Extended Data Figure 3: The libration of ω for 2012VP113 with an assumed object five times the mass of Earth at 210au. (96 KB)

    2012VP113 librates about ω = 0° for most of the duration of the Solar System. This behaviour could explain why the two inner Oort cloud Objects (Table 1) and all objects with semi-major axes greater than 150au and perihelia greater than Neptune’s (Extended Data Table 2) have ω0°. The choice of mass and orbit of the perturber is not unique. Many possible distant planetary bodies can produce the pictured Kozai resonance behaviour, but the currently known Solar System bodies cannot. These are simulated plots, so there are no error bars associated with data points.

Extended Data Tables

  1. Extended Data Table 1: Model parameters for the q′ = 5 inner Oort Cloud observational bias and population study (177 KB)
  2. Extended Data Table 2: Orbital elements of extreme Solar System bodies (194 KB)
  3. Extended Data Table 3: Colours of 2012VP113 (123 KB)

Additional data