A Brief Synopsis of my Graduate Research

Alternatively, you can read the full, detailed synopsis here:

A Distant Dwarf Planet Candidate named DeeDee

Mining a new dataset is bound to yield some exciting discoveries, and sure enough, we found some cool things! The discovery near and dear to me was of a new distant dwarf planet candidate that I nicknamed DeeDee (for “distant dwarf”). How distant? 92 astronomical units (Earth-Sun distances, aka “au”) from the Sun, or 2.5x farther than Pluto!

At the time, DeeDee was the second-most distant Solar System object ever discovered. And when we discovered it, we didn’t know how big it was. All we saw was a point of light in the images, but we didn’t know whether that point of light was small and shiny or large and dark. I led a telescope proposal for ALMA to get immediate supplemental infrared data and then led the analysis to calculate DeeDee’s size using the extra data. DeeDee is about 640km in diameter (about the size of Oregon) and reflects about 13% of the light that hits it (like asphalt or a dark roof).

This analysis provided another data point about intermediate-sized bodies in the Kuiper Belt, filling in the complete picture a bit more like filling in a TV screen a few pixels at a time. The discovery also proved that we could discover very distant objects, which is relevant for the next section…

Planet Nine…does it exist or not?

Planet Nine is a proposed, still-hypothetical distant planet beyond Neptune. It’s thought to be about 5 Earth-masses and on a distant, elliptical orbit with an average distance from the Sun of 250au (for context, Neptune is about 17 Earth-masses and orbits the Sun at an average distance of 30au).

Why do some astronomers think it’s there? We haven’t found it directly, so the evidence for its existence is purely mathematical at this point. Based on the fact that the orbits of the most distant trans-Neptunian objects (those that orbit at an average distance of >250au, aka “extreme” TNOs or ETNOs) all appear to be oriented in the same direction, astronomers Mike Brown and Konstantin Batygin predicted that a new planet’s gravitational influence was the culprit.

How do we know that the apparent orbital orientation is real and isn’t just an artifact of where we happen to search and find these objects? Well…we don’t. And this has been a source of debate since Planet Nine’s proposal in 2016. To quantify whether the effect is an artifact, we need a survey simulator — effectively a way to simulate the detection and discovery of thousands of artificial objects in order to understand exactly which types of objects the survey is more/less likely to discover and where.

I built a survey simulator of the Dark Energy Survey in order to statistically test whether Planet Nine’s signature was present in our sample of four extreme TNOs. Unfortunately, a sample size of four is just not big enough to make any conclusive claims, so our sample neither refutes nor confirms Planet Nine. My colleague Kevin Napier has expanded upon my work to include two additional surveys, bringing the sample size to 12, but this still is not a large enough sample to make conclusive claims. Bottom line: we need more data!

Other Kuiper Belt research

Selected Publications

• “Testing the isotropy of the Dark Energy Survey’s extreme trans-Neptunian objects,” 2020, P. H. Bernardinelli, et al (incl. S. J. Hamilton as co-corresponding author), arXiv:2003.08901, Planetary Science Journal, doi:10.3847/PSJ/ab9d80.

• “New Science, New Media: An Assessment of the Online Education & Public Outreach Initiatives of The Dark Energy Survey,” 2018, R. C. Wolf, et al (incl. S. J. Hamilton), arXiv:1804.00591.

• “Evaluating the Dynamical Stability of Outer Solar System Objects in the Presence of Planet Nine,” 2017, J. C. Becker, F. C. Adams, T. Khain, S. J. Hamilton, D. W. Gerdes, et al, arXiv:1706.06609, Astronomical Journal, doi:10.3847/2041-8213/aa64d8.

• “Discovery and Physical Characterization of a Large Scattered Disk Object at 92 AU,” 2017, D. W. Gerdes, M. Sako, S. J. Hamilton, et al., arXiv:1702.00731, Astrophysical Journal Letters, doi:10.3847/2041-8213/aa64d8.

*For complete list, please see NASA ADS.

Research History