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Register a new userA magnetic thrust action on small bodies orbiting a pulsar
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Authors
Fabrice Mottez
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We investigate the electromagnetic interaction of a relativistic stellar wind with small bodies in orbit around the star. Based on our work on the theory of Alfven wings to relativistic winds presented in a companion paper, we estimate the force exerted by the associated current system on orbiting bodies and evaluate the resulting orbital drift. This Alfvenic structure is found to have no significant influence on planets or smaller bodies orbiting a millisecond pulsar. %influence on the orbit of bodies around a millisecond pulsar. On the timescale of millions of years, it can however affect the orbit of bodies with a diameter of 100 kilometres around standard pulsars with a period $P sim $1 s and a magnetic field $B sim 10^{8}$ T. Kilometer-sized bodies experience drastic orbital changes on a timescale of $10^4$ years.
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We investigate the electromagnetic interaction of a relativistic stellar wind with a planet or a smaller body in orbit around the star. This may be relevant to objects orbiting a pulsar, such as PSR B1257+12 and PSR B1620-26 that are expected to hold a planetary system, or to pulsars with suspected asteroids or comets. We extend the theory of Alfven wings to relativistic winds. When the wind is relativistic albeit slower than the total Alfven speed, a system of electric currents carried by a stationary Alfvenic structure is driven by the planet or by its surroundings. For an Earth-like planet around a standard one second pulsar, the associated current can reach the same magnitude as the Goldreich-Julian current that powers the pulsars magnetosphere.
Asteroids orbiting into the highly magnetized and highly relativistic wind of a pulsar offer a favourable configuration for repeating fast radio bursts (FRB). The body in direct contact with the wind develops a trail formed of a stationary Alfven wave, called an textit{Alfven wing}. When an element of wind crosses the Alfven wing, it sees a rotation of the ambient magnetic field that can cause radio-wave instabilities. In the observers reference frame, the waves are collimated in a very narrow range of directions, and they have an extremely high intensity. A previous work, published in 2014, showed that planets orbiting a pulsar can cause FRB when they pass in our line of sight. We predicted periodic FRB. Since then random FRB repeaters have been discovered. We present an upgrade of this theory where repeaters can be explained by the interaction of smaller bodies with a pulsar wind. Considering the properties of relativistic Alfven wings attached to a body in the pulsar wind, and taking thermal consideration into account we conduct a parametric study. We find that FRBs, including the Lorimer burst (30 Jy), can be explained by small size pulsar companions (1 to 10 km) between 0.03 and 1 AU from a highly magnetized millisecond pulsar. Some sets of parameters are also compatible with a magnetar. Our model is compatible with the high rotation measure of FRB121102. The bunched timing of the FRBs is the consequence of a moderate wind turbulence. As asteroid belt composed of less than 200 bodies would suffice for the FRB occurrence rate measured with FRB121102. This model, after the present upgrade, is compatible with the properties discovered since its first publication in 2014, when repeating FRB were still unknown. It is based on standard physics, and on common astrophysical objects that can be found in any kind of galaxy. It requires $10^{10}$ times less power than (common) isotropic-emission FRB models.
We investigate the electromagnetic interaction of a relativistic stellar wind with a planet or a smaller body in orbit around a pulsar. This may be relevant to objects such as PSR B1257+12 and PSR B1620-26 that are expected to hold a planetary system, or to pulsars with suspected asteroids or comets. Most models of pulsar winds predict that, albeit highly relativistic, they are slower than Alfven waves. In that case, a pair of stationary Alfven waves, called Alfven wings (AW), is expected to form on the sides of the planet. The wings expand far into the pulsars wind and they could be strong sources of radio emissions. The Alfven wings would cause a significant drift over small bodies such as asteroids and comets.
The aim of the chapter is to summarize our understanding of the compositional distribution across the different reservoirs of small bodies (main belt asteroids, giant planet trojans, irregular satellites of the giant planets, TNOs, comets). We then use this information to i) discuss current dynamical models (Nice and Grand Tack models), ii) mention possible caveats in these models if any, and iii) draw a preliminary version of the primordial compositional gradient across the solar system before planetary migrations occured. Note that the composition of both planetary satellites (the regular ones) and that of the transient populations (NEOs, centaurs) is not discussed here. We strictly focus on the composition of the main reservoirs of small bodies. The manuscripts objective is to provide a global and synthetic view of small bodies compositions rather than a very detailed one, for specific reviews regarding the composition of small bodies, see papers by Burbine (2014) for asteroids, Emery et al. (2015) for Jupiter trojans, Mumma and Charnley (2011) for comets, and Brown (2012) for KBOs.
The masses, atmospheric makeups, spin-orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small, transiting planets have radii of 2.23 (+0.30/-0.25) R_Earth and 3.95 (+0.42/-0.39) R_Earth and orbital periods of 9.55 d and 21.06 d, respectively. A radial velocity (RV) trend of 0.3 +/- 0.1 m/s/d indicates the likely presence of a third body orbiting HD 106315 with period >160 d and mass >45 M_Earth. Transits of this object would have depths of >0.1% and are definitively ruled out. Though the star has v sin i = 13.2 km/s, it exhibits short-timescale RV variability of just 6.4 m/s, and so is a good target for RV measurements of the mass and density of the inner two planets and the outer objects orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin-orbit alignment of small planets through the Rossiter-McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.
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