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Most of the major planets in the Solar System support populations of co-orbiting bodies, known as Trojans, at their L4 and L5 Lagrange points. In contrast, Earth has only one known co-orbiting companion. This paper presents the results from a search for Earth Trojans using the DECam instrument on the Blanco Telescope at CTIO. This search found no additional Trojans in spite of greater coverage compared to previous surveys of the L5 point. Therefore, the main result of this work is to place the most stringent constraints to date on the population of Earth Trojans. These constraints depend on assumptions regarding the underlying population properties, especially the slope of the magnitude distribution (which in turn depends on the size and albedo distributions of the objects). For standard assumptions, we calculate upper limits to a 90% confidence limit on the L5 population of $N_{ET}<1$ for magnitude $H<15.5$, $N_{ET}=60-85$ for $H<19.7$, and $N_{ET} $= 97 for $H=20.4$. This latter magnitude limit corresponds to Trojans $sim$300 m in size for albedo $0.15$. At H=19.7, these upper limits are consistent with previous L4 Earth Trojan constraints and significantly improve L5 constraints.
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The only discovery of Earth Trojan 2010 TK$_7$ and the subsequent launch of OSIRIS-REx motive us to investigate the stability around the triangular Lagrange points $L_4$ and $L_5$ of the Earth. In this paper we present detailed dynamical maps on the $(a_0,i_0)$ plane with the spectral number (SN) indicating the stability. Two main stability regions, separated by a chaotic region arising from the $ u_3$ and $ u_4$ secular resonances, are found at low ($i_0leq 15^circ$) and moderate ($24^circleq {i_0}leq 37^circ$) inclinations respectively. The most stable orbits reside below $i_0=10^circ$ and they can survive the age of the Solar System. The nodal secular resonance $ u_{13}$ could vary the inclinations from $0^circ$ to $sim 10^circ$ according to their initial values while $ u_{14}$ could pump up the inclinations to $sim 20^circ$ and upwards. The fine structures in the dynamical maps are related to higher-degree secular resonances, of which different types dominate different areas. The dynamical behaviour of the tadpole and horseshoe orbits, reflected in their secular precession, show great differences in the frequency space. The secular resonances involving the tadpole orbits are more sensitive to the frequency drift of the inner planets, thus the instabilities could sweep across the phase space, leading to the clearance of tadpole orbits. We are more likely to find terrestrial companions on horseshoe orbits. The Yarkovsky effect could destabilize Earth Trojans in varying degrees. We numerically obtain the formula describing the stabilities affected by the Yarkovsky effect and find the asymmetry between the prograde and retrograde rotating Earth Trojans. The existence of small primordial Earth Trojans that avoid being detected but survive the Yarkovsky effect for 4.5,Gyr is substantially ruled out.
To facilitate multimessenger studies with TeV and PeV astrophysical neutrinos, the IceCube Collaboration has developed a realtime alert system for the highest confidence and best localized neutrino events. In this work we investigate the likelihood of association between realtime high-energy neutrino alerts and explosive optical transients, with a focus on core-collapse supernovae (CC SNe) as candidate neutrino sources. We report results from triggered optical follow-up observations of two IceCube alerts, IC170922A and IC171106A, with Blanco/DECam ($gri$ to 24th magnitude in $sim6$ epochs). Based on a suite of simulated supernova light curves, we develop and validate selection criteria for CC SNe exploding in coincidence with neutrino alerts. The DECam observations are sensitive to CC SNe at redshifts $z lesssim 0.3$. At redshifts $z lesssim 0.1$, our selection criteria reduce background SNe contamination to a level below the predicted signal. For the IC170922A (IC171106A) follow-up observations, we expect that 12.1% (9.5%) of coincident CC SNe at $z lesssim 0.3$ are recovered, and that on average, 0.23 (0.07) unassociated SNe in the 90% containment regions also pass our selection criteria. We find two total candidate CC SNe that are temporally coincident with the neutrino alerts, but none in the 90% containment regions, which is statistically consistent with expected rates of background CC SNe for these observations. Given the signal efficiencies and background rates derived from this pilot study, we estimate that to determine whether CC SNe are the dominant contribution to the total TeV-PeV energy IceCube neutrino flux at the $3sigma$ confidence level, DECam observations similar to those of this work would be needed for $sim200$ neutrino alerts, though this number falls to $sim60$ neutrino alerts if redshift information is available for all candidates.
We present the discovery of a long-term stable L5 (trailing) Neptune Trojan in data acquired to search for candidate Trans-Neptunian objects for the New Horizons spacecraft to fly by during an extended post-Pluto mission. This Neptune Trojan, 2011 HM102, has the highest inclination (29.4 degrees) of any known member of this population. It is intrinsically brighter than any single L5 Jupiter Trojan at H~8.18. We have determined its gri colors (a first for any L5 Neptune Trojan), which we find to be similar to the moderately red colors of the L4 Neptune Trojans, suggesting similar surface properties for members of both Trojan clouds. We also present colors derived from archival data for two L4 Neptune Trojans (2006 RJ103 and 2007 VL305), better refining the overall color distribution of the population. In this document we describe the discovery circumstances, our physical characterization of 2011 HM102, and this objects implications for the Neptune Trojan population overall. Finally, we discuss the prospects for detecting 2011 HM102 from the New Horizons spacecraft during their close approach in mid- to late-2013.
The recent discovery of a staggering diversity of planets beyond the Solar System has brought with it a greatly expanded search space for habitable worlds. The Kepler exoplanet survey has revealed that most planets in our interstellar neighborhood are larger than Earth and smaller than Neptune. Collectively termed super-Earths and mini-Neptunes, some of these planets may have the conditions to support liquid water oceans, and thus Earth-like biology, despite differing in many ways from our own planet. In addition to their quantitative abundance, super-Earths are relatively large and are thus more easily detected than true Earth twins. As a result, super-Earths represent a uniquely powerful opportunity to discover and explore a panoply of fascinating and potentially habitable planets in 2020 - 2030 and beyond.
Dark matter could be composed of compact dark objects (CDOs). These objects may interact very weakly with normal matter and could move freely {it inside} the Earth. A CDO moving in the inner core of the Earth will have an orbital period near 55 min and produce a time dependent signal in a gravimeter. Data from superconducting gravimeters rule out such objects moving inside the Earth unless their mass $m_D$ and or orbital radius $a$ are very small so that $m_D, a < 1.2times 10^{-13}M_oplus R_oplus$. Here $M_oplus$ and $R_oplus$ are the mass and radius of the Earth.
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