Modelling the collision of planets into KIC 8462852 Charlotte Ward - - PowerPoint PPT Presentation

Modelling the collision of planets into KIC 8462852

Charlotte Ward

NASA/JPL-CALTECH

SETI International 1

KIC 846282 showed unusual flux dips in Kepler data

• KIC846282 is a typical F3

main sequence star with no interacting companions.

• Short dips in up to 22% of

flux were observed on timescales of days.

• 3% dimming over the 4.25

years of Kepler data were

• bserved.
• Photographic plates showed

14% dimming since 1890. [1] [2] [3]

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The dimming may be caused by planet consumption

• Transfer of the kinetic energy of the

inspiralled body to the outer layers of the star causes an increase in flux (Metzger et al 2017).

• Kepler observed the subsequent dimming.
• To explain 4 year and 100 year dimming,

Earth mass and subsequent moon mass consumption must be invoked.

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Project goals

Elizabeth Landau, 2017, NASA

• Replicate the mesa star modelling results of

Metzger et al 2017 to show effects of different planetary bodies on star flux.

• Test the Earth and moon collision scenario.
• Investigate short time scale variability of the

star and its sensitivity to assumptions in Metzger et al 2017.

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Inspiral energy is deposited to outer layers of the star

• Deposited energy as a function of radius for

inspiralling body is given by:

• Density vs radius of the star is obtained by

modelling a 1.43 solar mass star on the main sequence with Mesa (Paxton 2011).

• Energy deposited vs radius calculated for Io,

Earth and Jupiter mass planets.

• Extra module in mesa developed to add

inspiral energy to star cells over time.

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Star experiences a rise and slow decay in luminosity

• Results from Metzger et al 2017 showing rise

and decay in luminosity were replicated.

• An Io collision could produce the 4 year

dimming.

• An Earth collision could produce the 100 year

dimming.

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Earth followed by Io collision explains observations

• Metzger et al 2017 suggest than an Earth

mass collision was followed by collision with its moon a few orbits later.

• This would explain 4 and 100 year dimming.
• Simulations showed that Io collision

produced a dip in flux before brightening.

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Planet inspiral causes extreme short term variability

• Simulations suggest 3 order of magnitude

increases in luminosity for Jupiter, 50% increase in luminosity for Io.

• Have such increases in luminosity been
• bserved?

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Timescale over which energy is deposited affects short term brightness

• The short term luminosity is dependent on energy deposition time.
• After 0.5 days the different simulations converge.

Earth Io

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Deposition may occur over ~1 day

• If we consider that energy loss occurs as the planet

transfers energy to particles in the star according to

• We find for inspiral speed:
• It takes 12000 seconds for the planet to reach the

tidal disruption radius

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Summary

• Metzger et al 2017 simulation results were

replicated for inspiralling planetary bodies.

• Earth followed by Io mass collision model

suggested by Metzger et al was confirmed to be feasible.

• Short term variability was shown to be sensitive to

deposition timescales. Longer timescales are proposed.

• Dips in flux were shown to arise from Io masses.

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