A New Planet in the Outer Solar System?

Michael “Migo” Mueller Rijksuniversiteit Groningen, Kapteyn Astronomical Instute

6th Quantum Universe Symposium Groningen March 2016

Planets move relave to stars: ἀστήρ πλανήτης ~ wandering star 5 planets are visible to the naked eye

February 5, 2016. Photo by Greg Hogan 5 planets are visible to the naked eye

February 5, 2016. Photo by Greg Hogan Pre Copernicus: Post Copernicus: Planeten Saturn

Jupiter

Mercury Venus

Earth Mars

1 AU Post Copernicus: Planeten Saturn

Jupiter

Mercury Venus

Earth Mars

1 AU ~ 1.5e27 fm First discovery of a planet: William Herschel discovers Uranus (1781)

Herschel was actually studying stellar parallax, found a moving object (“comet”) serendipitously. First discovery of a planet: William Herschel discovers Uranus (1781)

Herschel was actually studying stellar parallax, found a moving object (“comet”) serendipitously.

Previous observers had seen Uranus, but failed to recognize its apparent moon (or resolvable size). Uranus

Saturn

Jupiter Enter classical mechanics / perturbaon theory

1766—1786: Laplace and Lagrange pioneer what we now call ‘perturbaon theory’ to explain planetary moon. Enter classical mechanics / perturbaon theory

1766—1786: Laplace and Lagrange pioneer what we now call ‘perturbaon theory’ to explain planetary moon. 1840s: problems with Uranus

Le Verrier: mismatch between Uranus’ predicted and observed posions. Soluon: add an extra planet! Predicts posion and mass of new planet.

U. Le Verrier 1846: Urbain Le Verrier predicts a planet. Johann Galle discovers it • within hours of receiving Le Verrier’s leer • within a degree of the predicted posion

J. Galle, Sternwarte Berlin

U. Le Verrier, obs. Paris 1846: Urbain Le Verrier predicts a planet. Johann Galle discovers it • within hours of receiving Le Verrier’s leer • within a degree of the predicted posion

J. Galle, Sternwarte Berlin

U. Le Verrier, obs. Paris Neptune

Uranus

Saturn

Jupiter Mercury’s perihelion precession

Leading order (secular) perturbaon theory: Interacon term doesn’t depend on angular variables à argument of perihelion changes at constant rate (apsis precession)

U. Le Verrier Mercury’s perihelion precession

Le Verrier (1859): mismatch between predicted and observed perihelion precession of Mercury • Venus: ~280”/100yr • Jupiter: ~150”/100yr • Other planets: ~100”/100yr • Total predicted: ~530”/100yr

• Observed: ~570”/100yr

Is there another planet interior to Mercury?

U. Le Verrier Mercury’s perihelion precession

• Observed: ~570”/100yr

Is there another planet interior to Mercury?

NO!

U. Le Verrier Mercury’s perihelion precession

• Observed: ~570”/100yr

General Relavity explains the small discrepancy. Mercury’s perihelion precession

• Observed: ~570”/100yr

General Relavity explains the small discrepancy. Another outer planet? Small residuals in posions of Uranus and Neptune.

Percival Lowell

Lowell Observatory, Flagstaﬀ 1930: Clyde Tombaugh discovers Pluto

Clyde Tombaugh: 23 years Pluto

Neptun Pluto’s exponenal mass loss

Lowell’s predicon

At discovery

First diameter measurement

Discovery of moon Charon

M. Standish, 1993: new mass measurement of Neptune (by Voyager) explains orbits of Uranus and Neptune. Pluto is not needed (yet present) Pluto’s exponenal mass loss

Lowell’s predicon

At discovery

First diameter measurement

Discovery of moon Charon

M. Standish, 1993: new mass measurement of Neptune (by Voyager) explains orbits of Uranus and Neptune. Pluto is not needed (yet present)

2016: discovery of a new planet adverzed in press. Batygin & Brown, 2016 Frequently referred to as “Planet X”, we’ll call it P9.

M. Brown K. Batygin M. Brown K. Batygin 2016: discovery of a new planet adverzed in press. Batygin & Brown, 2016

M. Brown K. Batygin

Sedna has siblings! (on similarly detached orbits) • Sedna et al. (green) display conspicuous clustering. • Perihelion precession should randomize orbits, this happens in Kuiper belt (red).

1000 AU Also, same orientaon relave to eclipc plane.

Above eclipc Below eclipc Also, same orientaon relave to eclipc plane.

Likelihood of both things happening coincidentally: 0.007% ~ 3.8σ Batygin & Brown: A new distant planet stabilizes these orbits (and destabilizes others). N-body simulaons over 4 Gyr:

t=-4.0E9 yr N-body simulaons over 4 Gyr:

t=-3.0E9 yr N-body simulaons over 4 Gyr:

t=-2.0E9 yr N-body simulaons over 4 Gyr:

t= now

What do we know about Planet 9?

• We have not seen it, yet. What do we know about Planet 9?

• We have not seen it, yet. • We do know where to look, and the search is on! What do we know about Planet 9?

• We have not seen it, yet. • We do know where to look, and the search is on! • Orbit • Perihelion ~ 200 AU • Aphelion ~ 1,200 AU • Period 10,000—20,000 yr • Inclinaon ~ 20 deg (!) • Mass • 5—10 * Earth ~ 0.5 * Neptune • Composion • Ice giant? How come we haven’t seen it, yet?

aphelion

perihelion faint

çè

Bright

P9 isn’t parcularly faint, but the sky is big. Orbital phase unknown! Near perihelion, we’d probably have seen P9. But it could easily be hiding elsewhere. Even at aphelion, P9 is easily detectable with dedicated telescope obs. xkcd.com/1633 The search is on!

Two strategies • Direct detecon of P9; survey of orbit should take ~5 yr • Try and ﬁnd more Sednas (similar or dissimilar orbits?) Conclusions

It’s hard to make predicons, especially about the future (aributed to Niels Bohr)

• 1846, Neptune: right predicon, planet found.

• 1930, Pluto: wrong predicon, found something unexpected.

• 2016, P9: convincing predicon. The planet, if it exists, should be found in the next few years. Telescope me well spent.

• If P9 exists: why? A highly inclined, detached planet is diﬃcult to ﬁt in. If not: how else can we explain Sednas?

It stays interesng!