A near-Sun Solar System Twilight Survey with LSST (1812.00466v1)

Abstract: We propose a LSST Solar System near-Sun Survey, to be implemented during twilight hours, that extends the seasonal reach of LSST to its maximum as fresh sky is uncovered at about 50 square degrees per night (1500 sq. deg. per lunation) in the morning eastern sky, and surveyable sky is lost at the same rate to the western evening sky due to the Earth's synodic motion. By establishing near-horizon fence post picket lines to the far west and far east we address Solar System science use cases (including Near Earth Objects, Interior Earth Objects, Potentially Hazardous Asteroids, Earth Trojans, near-Sun asteroids, sun-grazing comets, and dormant comets) as well as provide the first look and last look that LSST will have at the transient and variable objects within each survey field. This proposed near-Sun Survey will also maximize the overlap with the field of regard of the proposed NEOCam spacecraft that will be stationed at the Earth's L1 Lagrange point and survey near quadrature with the Sun. This will allow LSST to incidently follow-up NEOCam targets and vice-versa (as well as targets from missions such as Euclid), and will roughly correspond to the Earth's L4 and L5 regions.

• The paper proposes a novel twilight survey with LSST to extend observations of near-Sun, low solar elongation objects.
• It details an innovative strategy that covers 50 square degrees per night with repeat visits, enabling rapid confirmation of moving objects.
• The survey targets key populations such as Earth Trojans, NEOs, and near-Sun asteroids, aiming to improve Solar System inventories and risk assessments.

A Near-Sun Solar System Twilight Survey with LSST

The paper "A Near-Sun Solar System Twilight Survey with LSST" presents a comprehensive proposal for a specialized survey by utilizing the Large Synoptic Survey Telescope (LSST) during twilight hours. This approach seeks to extend the observational reach of LSST to the maximal seasonal limits, particularly focusing on the near-horizon regions in both the eastern morning and western evening skies. These twilight periods represent an underutilized observational window, granting the opportunity to explore a variety of Solar System science objectives that are not achievable during the typical observational cadence of the LSST Wide-Fast-Deep (WFD) survey.

Scientific Objectives

The primary focus of this survey is on Solar System small bodies at low solar elongation angles, which are often inaccessible during normal survey operations. The paper identifies several key populations for investigation, including Near Earth Objects (NEOs), Interior Earth Objects (IEOs such as Atira asteroids), Earth Trojans, Near-Sun asteroids, Sun-grazing and dormant comets. These populations reside in dynamic regions near the Sun, which are traditionally challenging for ground-based surveys due to adverse observational conditions, such as high airmass and increased sky brightness at twilight.

Of particular interest are Earth Trojans, hypothetical objects that could be in stable orbits around Earth's L4 and L5 Lagrange points. The paper argues that discovering such objects would significantly enhance our understanding of the Solar System's inventory, as well as provide prospective candidates for spacecraft missions due to their low relative velocities to Earth. Additionally, IEOs and potentially hazardous asteroids (PHAs) are of immense interest due to their impact risks and unique orbital characteristics.

Moreover, the survey aims to discover and monitor near-Sun asteroids subjected to intense thermal conditions that may lead to physical transformations such as disruptions through thermal fracture. Sun-grazing comets, often observed by space-based solar telescopes, are another focal point; the survey could potentially capture these comets' inbound trajectories before their catastrophic encounters with the Sun.

Observational Strategy

The proposed observational approach entailed harnessing twilight sessions to survey approximately 50 square degrees of sky per night. This strategic survey method effectively extends visible sky by utilizing the time and sky not covered by the standard LSST cadence. The observational method proposed includes repeating visits to track moving objects efficiently, achieving same-night confirmations and cross-night linkages for moving object processing. The inclusion of this near-Sun survey within the LSST's operational timeline represents an innovative use of twilight time, enhancing discovery rates and allowing for rapid follow-up observations.

Collaborative Implications

The proposed survey aligns well with upcoming space missions like NEOCam, stationed at the Earth's L1 Lagrange point, and provides opportunities for complementary follow-up observations that may benefit from data synergy between LSST and these dedicated spacecraft missions. The observational overlap with the fields of view of Euclid and other missions could foster collaborative observational campaigns, enhancing the overall scientific returns on Solar System research.

Future Directions

Assuming successful implementation, the results of this survey have the potential to contribute valuable datasets that could refine models of the Solar System's small body populations, especially those that remain poorly constrained. The dataset generated could eventually serve as a significant resource for future exploratory missions, impact risk assessments, and theoretical studies on the compositional and dynamical evolution of these celestial objects.

In summary, the proposed near-Sun Solar System twilight survey with LSST capitalizes on an innovative observational strategy that addresses specific gaps in current astronomical surveys of the Solar System. By embracing the challenges of twilight observations, this approach leverages the unique capabilities of the LSST to produce valuable insights and contribute significantly to the inventory of the Solar System's small-body populations.