Presolar Grains

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. Presolar grains are dust produced by stars that died before the formation of the Earth’s solar system. Stardust grains condense out of cooling gas lost via stellar winds from the surface of low-mass stars and stellar explosions and become a constituent of interstellar medium (ISM). About 4.6 Ga, a molecular cloud in the ISM collapsed to form the solar system, during which some primordial stardust grains from the ISM survived and were incorporated into small bodies formed in the early solar system. Some of these small solar system bodies, including asteroids and comets, escaped planet formation and have remained minimally altered, thus preserving their initially incorporated presolar grains. Fragments of asteroids and comets are collected on Earth as interplanetary dust particles (IDPs) and meteorites. Presolar grains have been found in primitive IDPs and chondrites—stony meteorites that have not been modified by either melting or differentiation of their parent bodies. Presolar grains, typically less than a few μm, are identified in primitive extraterrestrial materials by their unique isotopic signatures, revealing the effects of galactic chemical evolution (GCE), stellar nucleosynthesis, and cosmic ray exposure. Comparisons of presolar grain isotope data with stellar observations and nucleosynthesis model calculations suggest that presolar grains were dominantly sourced from asymptotic giant branch stars and core-collapse supernovae, although there are still ambiguities in assigning the type of star to some groups of grains. So far, various presolar phases have been identified such as corundum, olivine, and silicon carbide, reflecting diverse condensation environments in different types of stars. The abundances of different presolar phases in primitive extraterrestrial materials vary widely, ranging from a few percent for presolar silicates to a few parts per million for presolar oxides. Presolar grain studies rely on the synergy between astronomy, astrophysics, nuclear physics, and cosmochemistry. To understand the stellar sources of presolar grains, it is important to compare isotope data of presolar grains to astronomical observations for different types of stellar objects. When such astronomical observations are unavailable, stellar nucleosynthesis models must be relied upon, which require inputs of (a) initial stellar composition estimated based on solar system nuclide abundances, (b) stellar evolution models, and (c) nuclear reaction rates determined by theories and laboratory experiments. Once the stellar source of a group of presolar grains is ascertained, isotope information extracted from the grains can then be used to constrain stellar mixing processes, nuclear reaction rates, GCE, and the ISM residence times of the grains. In addition, crystal structures and chemical compositions of presolar grains can provide information to infer dust condensation conditions in their parent stars, while abundances of presolar grains in primitive chondrites can help constrain secondary processing experienced by the parent asteroids of their host chondrites. Since the discovery of presolar grains in meteorites in 1980s, a diverse array of information about stars and GCE has been gleaned by studying them. Technological advances will likely allow for the discovery of additional types of presolar grains and analysis of smaller, more typical presolar grains in the future.

Search for possible connections of the h-Virginids meteor shower with near-Earth asteroids

Asteroids and comets are the oldest objects in the Solar System and contain the initial matter that existed at the moment of its formation. By studying those small celestial bodies one may describe the processes taking place at the early stages and conditions of the formation of the Solar System. The study of the genetic relationships (using metrics based on orbital elements) of meteor showers with parent bodies (asteroids and comets) can be used to develop the theory of evolutionary processes that took place at the time of the formation of the solar system. In this work, we have studied the genetic relationships of the small meteor shower of the h-Virginids (HVI) with the near-Earth asteroids of the Apollo group. An author’s multi-factor method is applied, which implies the use of D-criterion by Drummond, metric by Kholshevnikov, Tisserand’s parameter, μ and ν quasi-stationary parameters of the restricted three-body problem, and the analysis of the orbit’s perihelion longitude π. The observational base includes television catalogues meteor orbits that are in the public domain: Meteoroid Orbit Database v2.0 (2010–2012) (CAMS) and the European meteor network EDMOND (2001–2016) catalogues. As a result of this study, the orbit of the h-Virginids (HVI), according to the values of Tisserand’s parameter, was found to be transitional, and thus, it was impossible to identify whether it was of cometary or of asteroid type. Using the author’s method, the asteroids 2001SZ269 and 2014HD19 were distinguished. The 2001SZ269 asteroid was distinguished as a candidate having a possible connection with the h-Virginids’ parent body.

Twinkle: a low-Earth orbit, visible and infrared observatory for exoplanet and solar system spectroscopy

<div>The Twinkle Space Mission is a space-based observatory that has been conceived to measure the atmospheric composition of exoplanets, stars and solar system objects. Twinkle’s collaborative multi-year global survey programmes will deliver visible and infrared spectroscopy of thousands of objects within and beyond our solar system, enabling participating scientists to produce world-leading research in planetary and exoplanetary science.</div> <div> </div> <p>Twinkle’s rapid pointing and non-sidereal tracking capabilities will enable the observation of a diverse array of Solar System objects, including asteroids and comets. Twinkle aims to provide a visible and near-infrared (0.5-4.5 micron) spectroscopic population study of asteroids and comets to study their surface composition and monitor activity. Its wavelength coverage and position above the atmosphere will make it particularly well-suited for studying hydration features that are obscured by telluric lines from the ground as well as searching for other spectral signatures such as organics, silicates and CO<sub>2</sub>.</p> <p>I will present an overview of Twinkle’s capabilities and discuss the broad range of targets the mission could observe, including the measurements it will take to support <span class="size">JAXA's Martian Moons eXploration (MMX) mission, demonstrating the broad scientific potential of the spacecraft.</span></p>

Twinkle: a low-Earth orbit, visible and infrared observatory for exoplanet and solar system spectroscopy

<p>The Twinkle Space Mission is a space-based observatory that has been conceived to measure the atmospheric composition of exoplanets, stars and solar system objects. The satellite is based on a high-heritage platform and will carry a 0.45 m telescope with a visible and infrared spectrograph providing simultaneous wavelength coverage from 0.5 - 4.5 μm. The spacecraft will be launched into a Sun-synchronous low-Earth polar orbit and will operate in this highly stable thermal environment for a baseline lifetime of seven years.</p> <p>Twinkle’s rapid pointing and non-sidereal tracking capabilities will enable the observation of a diverse array of Solar System objects, including asteroids and comets. Twinkle aims to provide a visible and near-infrared spectroscopic population study of asteroids and comets to study their surface composition and monitor activity. Its wavelength coverage and position above the atmosphere will make it particularly well-suited for studying hydration features that are obscured by telluric lines from the ground as well as searching for other spectral signatures such as organics, silicates and CO<sub>2</sub>.</p> <p>Twinkle is available for researchers around the globe in two ways:</p> <p>1) joining its collaborative multi-year survey programme, which will observe hundreds of exoplanets and solar system objects; and</p> <p>2) accessing dedicated telescope time on the spacecraft, which they can schedule for any combination of science cases.</p> <p>I will present an overview of Twinkle’s capabilities and discuss the broad range of targets the mission could observe, demonstrating the huge scientific potential of the spacecraft.</p>

A Summary and Update on NASA’s Planetary Defense Program.

<p>NASA and its partners maintain a watch for near-Earth objects (NEOs), asteroids and comets that pass within Earth’s vicinity, as part of an ongoing effort to discover, catalog, and characterize these bodies and to determine if any pose an impact threat. NASA’s Planetary Defense Coordination Office (PDCO) is responsible for:</p><ul><li>Ensuring the early detection of potentially hazardous objects (PHOs) – asteroids and comets whose orbits are predicted to bring them within 0.05 astronomical units of Earth's orbit; and of a size large enough to reach Earth’s surface – that is, greater than perhaps 30 to 50 meters;</li> <li>Tracking and characterizing PHOs and issuing warnings about potential impacts;</li> <li>Providing timely and accurate communications about PHOs; and</li> <li>Performing as a lead coordination node in U.S. Government planning for response to an actual impact threat.</li> </ul><p> </p><p>NASA’s current congressionally-mandated objective is to detect, track, and catalogue at least 90 percent of NEOs equal to or greater than 140 meters in size by 2020, and characterize the physical properties of a subset representative of the entire population. This mandate will likely not be met given current resources dedicated to the task; however significant progress is being made.</p><p>In this paper, we will report on the status of our program and the missions working to support our planetary defense coordination office. In addition, we will provide the latest detections and characterizations results. Our office continues to work diligently with our international partners to achieve our goals and continue to safeguard Earth with the latest technologies available.</p>