Predictions for the Detection and Characterization of a Population of Free-Floating Planets with K2 Campaign 9

TL;DR

This paper predicts the detection and characterization capabilities of K2 Campaign 9 for free-floating planets, estimating the number of observable events and the potential to measure their masses and parallaxes.

Contribution

It provides the first detailed simulation-based predictions for detecting and measuring free-floating planets with K2C9, including event counts and parameter estimation prospects.

Findings

Between 1.4 and 7.9 events detectable depending on noise levels

Most events will allow parallax measurement or constraints

Masses can be fully measured for up to 0.98 events

Abstract

K2 Campaign 9 (K2C9) offers the first chance to measure parallaxes and masses of members of the large population of free-floating planets (FFPs) that has previously been inferred from measurements of the rate of short-timescale microlensing events. Using detailed simulations of the nominal campaign (ignoring the loss of events due to Kepler's emergency mode) and ground-based microlensing surveys, we predict the number of events that can be detected if there is a population of 1-Jupiter-mass FFPs matching current observational constraints. Using a Fisher matrix analysis we also estimate the number of detections for which it will be possible to measure the microlensing parallax, angular Einstein radius and FFP mass. We predict that between 1.4 and 7.9 events will be detected in the K2 data, depending on the noise floor that can be reached, but with the optimistic scenario being more likely. For nearly all of these it will be possible to either measure the parallax or constrain it to be probabilistically consistent with only planetary-mass lenses. We expect that for between 0.42 and 0.98 events it will be possible to gain a complete solution and measure the FFP mass. For the emergency mode truncated campaign, these numbers are reduced by 20~percent. We argue that when combined with prompt high-resolution imaging of a larger sample of short-timescale events, K2C9 will conclusively determine if the putative FFP population is indeed both planetary and free-floating.