Research
Earth Trojans (ETs)
Trojans asteroids orbit near a planet's L4 or L5 Lagrange points, meaning they have the same orbit as the planet and always stay just ahead of or behind it. We know that other planets have Trojan asteroids; for example, we have discovered over 7000 Jupiter Trojans! However, we have only found one Earth Trojan (ET) so far: 2010 TK7. Despite several dedicated searches for new Earth Trojans, this population is clearly poorly constrained. A better understanding of this population is important as Earth Trojans can give unique insight into the early stages of our Solar System since numerical simulations suggest that Earth Trojans could be primordial. Since Earth Trojans also have nearly the same orbit as Earth, they would also be good targets for future probe missions (if we can find them first!). Two probes, OSIRIS-REx and Hayabusa, have already passed through the Trojan regions on their way to their target asteroids.
Unfortunately, the ET population is difficult to study. The geometry of their orbit means that, as viewed from the Earth, they are always near the Sun. This means that you can only observe them near sunrise and sunset, when the sky is still quite bright.
Using 1 hour after sunset on June 16, 2018, we conducted a search for L5 Earth Trojans using DECam at CTIO. In this hour we were able cover 24 sq. deg. of the sky towards L5. Unfortunately, we did not find any new ET candidates. However, from this non-detection, we were able to place the most stringent upper limits on the L5 Trojan population to date. Our limits suggest there could be ~100 ETs ~300m in size yet to be discovered. Whether or not ETs that small could have stable orbits remains an open question.
Shift and Stack (SandS)
Observing very faint solar system objects can be difficult. In particular, moving objects streak in long exposures, making them even harder to detect. To fix this, each exposure can be shifted by the rate of motion for a solar system object and then coadded (Shift and Stack). With this method, stars are streaked while the solar system objects (moving at the right speed) are point sources, allowing you make use of longer exposure times and detect much fainter objects.
Shift and Stack can be used for many different datasets, to obtain greater depth. In particular, this is the strategy for the DEEP. At the University of Michigan, we are currently developing a pipeline to process this data; I have been working specifically on the Shift and Stack component.
I am also using this strategy for a new L5 ET search with DECam (NOAO 2019B-0319, Markwardt et al.). With 8 hours total (1 hour after sunset for 8 nights), we were able to cover 60 sq deg towards L5. With Shift and Stack, we should be able to find objects about 1.5 magnitudes fainter than our previous survey.
We are currently processing this data.
Neptune Trojans (NTs)
In 2018, Jewitt identified the “The Trojan Color Conundrum”, namely that Neptune’s Trojan asteroids (NTs) had no ultra-red members, unlike the the nearby Kuiper Belt. Since then, numerous ultra-red NTs have been discovered, seemingly resolving this conundrum (Lin et al. 2019; Bolin et al. 2023, Markwardt et al. 2023). This seems to indicate that NTs are indeed similar in color to Kuiper Belt Objects, which are suspected to be the NT source population. However, the existence of ultra-red NT alone is not enough to say whether or not these two color distributions are consistent with having come from the same underlying population.
With our g'r'i'z' observations using the IMACS instrument on the Magellan Baade telescope, we were able to study the optical color distribution of a large portion of the NT population in on self consistent survey. From these results, we found that the colors of NTs are significantly more similar to TNOs as compared to JTs (which are lacking ultra-red members). These results are statistically more significant than previous comparisons. This result suggest that it is likely that NTs did come from the same source population as Kuiper Belt Objects, suggesting a common origin.
