WISE & NEOWISE Cannot Find Planet Nine

A 3pi Search for Planet Nine at 3.4 microns with WISE and NEOWISE

Authors:

Meisner et al

Abstract:
The recent 'Planet Nine' hypothesis has led to many observational and archival searches for this giant planet proposed to orbit the Sun at hundreds of astronomical units. While trans-Neptunian object searches are typically conducted in the optical, models suggest Planet Nine could be self-luminous and potentially bright enough at ~3-5 microns to be detected by the Wide-field Infrared Survey Explorer (WISE). We have previously demonstrated a Planet Nine search methodology based on time-resolved WISE coadds, allowing us to detect moving objects much fainter than would be possible using single-frame extractions. In the present work, we extend our 3.4 micron (W1) search to cover more than three quarters of the sky and incorporate four years of WISE observations spanning a seven year time period. This represents the deepest and widest-area WISE search for Planet Nine to date. We characterize the spatial variation of our survey's sensitivity and rule out the presence of Planet Nine in the parameter space searched at W1 less than 16.7 in high Galactic latitude regions (90% completeness).

Hunting for Planet Nine With Wise & NEOWise

Searching for Planet Nine with Coadded WISE and NEOWISE-Reactivation Images

Authors:

Meisner et al

Abstract:

A distant, as yet unseen ninth planet has been invoked to explain various observations of the outer solar system. While such a 'Planet Nine', if it exists, is most likely to be discovered via reflected light in the optical, it may emit much more strongly at 3−5μm than simple blackbody predictions would suggest, depending on its atmospheric properties (Fortney et al. 2016). As a result, Planet Nine may be detectable at 3.4μm with WISE, but single exposures are too shallow except at relatively small distances (d9≲430 AU). We develop a method to search for Planet Nine far beyond the W1 single-exposure sensitivity, to distances as large as 800 AU, using inertial coadds of W1 exposures binned into ∼1 day intervals. We apply our methodology to ∼2000 square degrees of sky identified by Holman & Payne (2016) as a potentially likely Planet Nine location, based on the Fienga et al. (2016) Cassini ranging analysis. We do not detect a plausible Planet Nine candidate, but are able to derive a detailed completeness curve, ruling out its presence within the parameter space searched at W1<16.66 (90% completeness). Our method uses all publicly available W1 imaging, spanning 2010 January to 2015 December, and will become more sensitive with future NEOWISE-Reactivation releases of additional W1 exposures. We anticipate that our method will be applicable to the entire high Galactic latitude sky, and we will extend our search to that full footprint in the near future.

Finding Metal Rich Asteroids With WISE/NEOWISE

How to find metal-rich asteroids

Authors:

Harris et al

Abstract:

The metal content of asteroids is of great interest, not only for theories of their origins and the evolution of the solar system but, in the case of near-Earth objects (NEOs), also for impact mitigation planning and endeavors in the field of planetary resources. However, since the reflection spectra of metallic asteroids are largely featureless, it is difficult to identify them and relatively few are known. We show how data from the Wide-field Infrared Survey Explorer (WISE)/NEOWISE thermal-infrared survey and similar surveys, fitted with a simple thermal model, can reveal objects likely to be metal rich. We provide a list of candidate metal-rich NEOs. Our results imply that future infrared surveys with the appropriate instrumentation could discover many more metal-rich asteroids, providing valuable data for assessment of the impact hazard and the potential of NEOs as reservoirs of vital materials for future interplanetary space activities and, eventually perhaps, for use on Earth.