Objects in Outer Solar System Liyong ZHOU, Huigen LIU Nanjing - - PowerPoint PPT Presentation

Objects in Outer Solar System

Liyong ZHOU, Huigen LIU

Nanjing University

Outer Solar System

Trans-Neptunian Objects

➢ TNOs, as the remnants from the early stage of the Solar system, their masses, sizes, shapes, material composition and their distribution in space keep important information about the formation and evolution of the Solar system. ➢ The total mass/number of TNOs is about 20-200 times of the main belt

• asteroids. The number of TNOs with diameters greater than 100km is

estimated to be over 100,000. ➢ Up to now, about 2,000 of TNOs have been detected. A large number of TNOs are still unseen.

Orbits of TNOs

(semi-major axis vs. inclination)

Trans-Neptunian Objects

➢Planet Nine???

Nontrivial distribution: ➢Classical TNOs ➢ Resonant TNOs ➢ Scattered TNOs (Centaurs) ➢ In recent years, a new group of TNOs are recognized: Detached TNOs (with very large perihelion distance), implying the existence of a massive object far away in the solar system. ➢ About ¼ TNOs are found on orbits with inclination higher than 20deg.

Levison et al. 2008 (Nice model) Nesvorny et al. 2015 (slow migration model)

➢ Various Models have been proposed to explain their spatial distribution and

• rbits characteristics.

Planet migration, stellar encounter, scattering planet embryo, …..

Trans-Neptunian Objects

Color-inclination relation:

The correlation is strong (ρ = –0.7) and highly significant (>8σ) in the range 0°--34°. The optical colors are independent of inclination below ≈12°. Objects with inclinations >=12° show bluish colors, which are either weakly correlated with inclination or simply homogeneously blue, whereas objects with inclinations less than 12°are homogeneously red.

N.Peixinho et al, 2008

Trans-Neptunian Objects

Models have to be modified to produce such dependence on inclination. Are there any other dependence?

Trans-Neptunian Objects

Color indices of limited number

• f TNOs (red) and NTs(blue)

➢Neptune Trojans (NTs)

The total number and mass of Neptune Trojans are also believed to be above the main belt asteroids. They have peculiar orbits.

➢The basic data, like the light curve, spectral and even photometry data of TNOs and NTs are still quite rare.

Observations of TNOs

Observed NTs, many of them have high inclinations

32 TNOs found by DES (red dots)

➢ The most productive observation up to now, the Deep Ecliptic Survey (completed in 2005), found 662 TNOs in 550deg2 near the ecliptic (β±6.5˚). ➢ Other surveys:

 Pan-STARRS (Diameter 1.8m X 2, FOV~3deg2, <24.5m, δ<-47.5 ˚). Expect to find 20,000 TNOs.  Dark Energy Survey (Diameter 4m, FOV~5deg2, <24m, 5000deg2 around the south galactic cap). Reported 32 TNOs discoveries in an area of 27deg2 (-15 ˚ >β>-45 ˚).  CFHT (Diameter 3.6m, FOV~1deg2, r<24.5m) Outer Solar System Origins Survey, along the ecliptic, 84deg2/year, expect 3-4 TNOs/deg2, measure precisely their orbits.  LSST (Diameter 8.4m, FOV~9.6deg2). Expect to

• bserve 40,000 TNOs in 10 years. Hundreds of

photometry data for each target.

Number of TNOs found (black)

Observations of TNOs

LSST survey. Color indicates the times

• f observation.

Possible Observation in CSS-OS

➢Discovery and Orbit Determination of TNOs and NTs

➢ Discovery - Compared to asteroids (~700,000), TNOs and NTs are still “too few”. ➢ Improvement – TNOs generally have poor accuracy of orbital elements. The apparent motion is less than 4” /h at 40AU, ~70s/pixel, magnitude 25m, three exposures, interval ~10d. ~100TNOs/deg2 near the ecliptic plane (<25m)

➢Photometry and Spectroscopy of TNOs and NTs

➢ Spectroscopy – Information about the surface, thus origin and evolution. ➢ Photometry – Size, shape, detecting binary systems, ring systems. Multi-band Photometry, Spectroscopy, to the limit magnitude Light curve: continuous observation of hours

➢Planet Nine

Detached TNOs implies the existence of Planet Nine m9: 10 Earth masses a9: 400-700 AU q9: 250 AU (Batygin & Brown 2016)

Direct Detection of Planet Nine Vmag：22-28  Big space telescopes is preferred Proper motion: <0.2 arc sec/day Possible regions for Planet Nine （＋ Cassini data） ➢ Green regions：possible ➢ Red regions: impossible ➢ White regions: uncertain Total： 180 x 14～2500 sq. deg.  wide field telescope More constraints from GAIA. Fienga et al. 2016 Observational strategy: sky survey with an interval 10 day to verify the motion of Planet Nine.

Possible Observation in CSS-OS

Niku: a = 36 au, e = 0.3, i = 110° 2008 KV42: a = 41 au, e = 0.5, i = 103° 2016 NM56: a = 74 au, e = 0.9, i = 144° (Chen et el. 2016, ApJL)

Are they really rare?

Possible Observation in CSS-OS

Indirect Detection of Planet Nine – Highly inclined or retrograde TNOs.

Transit follow-ups for TESS

 Requiements of RV follow-ups  Not enough telescopes with high precision spectroscopy  TTV method is a good way to confirm small planet pairs near MMR; Photometry precision <= 1000 ppm (Neptune-sized planets)

Planet detection via Micro lensing

Possible to detect Earth-like planets near HZ;

Data Cadence Requirements: < 3 min; last > 60 min;

OGLE-2005-BLG-390 b: 5.5 Earth Mass around 0.22 Solar Mass star; Semi-major axis~ 2-4.1 AU