Internal Structure of the 2019 April 2 CME

We present the first analysis of internal coronal mass ejection (CME) structure observed very close to the Sun by the Wide-field Imager for Solar PRobe (WISPR) instrument on board the Parker Solar Probe (PSP). The transient studied here is a CME observed during PSP’s second perihelion passage on 2019 April 2, when PSP was only 40 R ⊙ from the Sun. The CME was also well observed from 1 au by the STEREO-A spacecraft, which tracks the event all the way from the Sun to 1 au. However, PSP/WISPR observes internal structure not apparent in the images from 1 au. In particular, two linear features are observed, one bright and one dark. We model these features as two loops within the CME flux rope (FR) channel. The loops can be interpreted as bundles of field lines, with the brightness of the bright loop indicative of lots of mass being loaded into those field lines, and with the dark loop being devoid of such mass loading. It is possible that these loops are actually representative of two independent FR structures within the overall CME outline.

The dust and gas environment of comet 8P/Tuttle

ABSTRACT Comet 8P/Tuttle has been selected as a possible backup target for the Comet Interceptor mission (ESA). This comet was observed intensively during its previous perihelion passage, in 2008 January. From those observations, important information was obtained about the physical properties of the nucleus and coma. This study focuses on the coma of 8P/Tuttle using visible spectra and images to derive gas and dust production rates. The production rates obtained suggest that this comet can be considered as ‘typical’ concerning the C2/CN and C3/CN ratios, although, depending on the criteria adopted, it could be defined as C3 depleted. NH2 production rates suggest an enrichment of this molecule. Visible and infrared images have been analysed using a Monte Carlo dust tail model. At comparatively large heliocentric distances, the coma is characterized by a dust-to-water ratio around or less than 1. Nevertheless, when the comet approaches perihelion, and the subsolar latitude crosses the equator, the coma dust-to-water ratio increases significantly, reaching values larger than six. Such a high dust-to-gas ratio around perihelion suggests that the nucleus of 8P/Tuttle is also ‘typical’ regarding the refractory content, considering the comparatively high values of that magnitude estimated for different comets.

Solar observations with the Nancay Radioheliograph in support of the Solar Orbiter and Parker Solar Probe missions

<p>The Nancay Radioheliograph is dedicated to imaging the solar corona at decimetre-to-metre wavelengths. The imaged structures are the quiet corona, through thermal bremsstrahlung, and bright collective emissions due to electrons accelerated in quiescent, flaring and eruptive active regions. The instrument produced nearly daily maps of the Sun between 1996 and 2015, at several frequencies in the 150-450 MHz range with sub-second cadence. The observations were stopped in 2015 for a major technical upgrade through the replacement of the correlator and the data acquisition system. They were resumed in November 2020, and at the time of writing the commissioning of the instrument is well underway. This contribution will give a brief overview of the technical changes and present observations at eight frequencies of solar activity since November 2020, including the coronal mass ejection (CME) of December 14 seen in some images of the total solar eclipse, observations conducted during the present perihelion passage of the Parker Solar Probe mission, as well as during periods of interest to the Solar Orbiter mission. The data are freely available, and special products of common visualisation with the space missions will be illustrated.</p>

Component properties and mutual orbit of binary main-belt comet 288P/(300163) 2006 VW139

Context. The binary asteroid 288P/(300163) is unusual both for its combination of wide-separation and high mass ratio and for its comet-like activity. It is not currently known whether there is a causal connection between the activity and the unusual orbit or if instead the activity helped to overcome a strong detection bias against such sub-arcsecond systems. Aims. We aim to find observational constraints discriminating between possible formation scenarios and to characterise the physical properties of the system components. Methods. We measured the component separation and brightness using point spread function fitting to high-resolution Hubble Space Telescope/Wide Field Camera 3 images from 25 epochs between 2011 and 2020. We constrained component sizes and shapes from the photometry, and we fitted a Keplerian orbit to the separation as a function of time. Results. Approximating the components A and B as prolate spheroids with semi-axis lengths a < b and assuming a geometric albedo of 0.07, we find aA ≤ 0.6 km, bA ≥ 1.4 km, aB ≤ 0.5 km, and bB ≥ 0.8 km. We find indications that the dust production may have concentrated around B and that the mutual orbital period may have changed by 1–2 days during the 2016 perihelion passage. Orbit solutions have semi-major axes in the range of (105–109) km, eccentricities between 0.41 and 0.51, and periods of (117.3–117.5) days pre-perihelion and (118.5–119.5) days post-perihelion, corresponding to system masses in the range of (6.67–7.23) × 1012 kg. The mutual and heliocentric orbit planes are roughly aligned. Conclusions. Based on the orbit alignment, we infer that spin-up of the precursor by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect led to the formation of the binary system. We disfavour (but cannot exclude) a scenario of very recent formation where activity was directly triggered by the break-up, because our data support a scenario with a single active component.

Monitoring polarization in comet 46P/Wirtanen

ABSTRACT We measure the degree of linear polarization of comet 46P/Wirtanen during two months, embracing the perihelion passage in 2018 December with phase angles ranging from α = 18.1° to 46.4°. The polarimetric response PQ obtained resembles what was previously found in comet C/1975 V1 (West). This suggests 46P/Wirtanen belongs to a group of comets with high maximum positive polarization. In the first half of 2019 February, we conducted BVRI photometry of 46P/Wirtanen and found either neutral or blue colour of its dust, which is in good accordance with measurements of C/1975 V1 (West). While aperture-averaged polarimetry of 46P/Wirtanen reveals a nearly zero polarization PQ at the lowest phase angle α = 18.1°, simultaneous imaging polarimetry suggests that the negative polarization (PQ &lt; 0) arises in a region of within 5000 km of the nucleus, where the negative polarization could be as strong as PQ = −(1.44 ± 0.15) per cent. This observation suggests the existence of the circumnucleus halo and that the coma is populated by at least two types of dust particles. One of those reveals a low positive polarization at side scattering and high negative polarization near backscattering. Both polarimetric features are simultaneously produced by weakly absorbing Mg-rich silicate particles. Another type of dust produces solely positive polarization that could be attributed to carbonaceous particles. This composition of 46P/Wirtanen coma appears to be similar with what was previously found in comet C/1975 V1 (West).

The relationship between comet C/1853 G1 (Schweizer) and the γ-Aquilids and 52 Herculids meteor showers

ABSTRACT We modelled several discrete parts of the meteoroid stream originating in comet C/1853 G1 (Schweizer). In a given model, the orbit of this parent comet was integrated in time backwards for a chosen period (10 000, 20 000, 40 000, or 80 000 yr) and, then, a cloud of 10 000 test particles was assumed to be ejected from the nucleus at the moment of the nearest comet’s perihelion passage. This set was subsequently integrated forward, up to the present. The showers related to the comet were predicted on the basis of the dynamical properties of the particles moving in orbits that approached close to the orbit of the Earth at the present. An uncertainty of the comet’s nominal orbit and its possible consequences on the predicted showers was estimated with a simultaneous following of a set of cloned orbits. We confirmed the proposed relationship between the comet and the γ-Aquilids, #531. Furthermore, our study yielded an indication that comet C/1853 G1 could also be the parent body of another shower, 52 Herculids, #605. We also found the real shower corresponding to the γ-Aquilids in three video data bases used. The 52 Herculids were identified in one of these data bases.

Constraints on the spin-pole orientation, jet morphology, and rotation of interstellar comet 2I/Borisov with deep HST imaging

ABSTRACT We present high resolution, deep imaging of interstellar comet 2I/Borisov taken with the Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) on 2019 December 8 UTC and 2020 January 27 UTC (HST GO 16040, PI: Bolin) before and after its perihelion passage in combination with HST/WFC3 images taken on 2019 October 12 UTC and 2019 November 16 UTC (HST GO/DD 16009, PI: Jewitt) before its outburst and fragmentation of 2020 March, thus observing the comet in a relatively undisrupted state. We locate 1–2 arcsec long (2000–3000 km projected length) jet-like structures near the optocentre of 2I that appear to change position angles from epoch to epoch. With the assumption that the jet is located near the rotational pole supported by its stationary appearance on ∼10–100 h time frames in HST images, we determine that 2I’s pole points near α = 322 ± 10° and δ = 37 ± 10° (λ = 341° and β = 48°) and may be in a simple rotation state. Additionally, we find evidence for possible periodicity in the HST time-series light curve on the time-scale of ∼5.3 h with a small amplitude of ∼0.05 mag implying a lower limit on its b/a ratio of ∼1.5 unlike the large ∼2 mag light curve observed for 1I/‘Oumuamua. However, these small light-curve variations may not be the result of the rotation of 2I’s nucleus due to its dust-dominated light-scattering cross-section. Therefore, uniquely constraining the pre-Solar system encounter, pre-outburst rotation state of 2I may not be possible even with the resolution and sensitivity provided by HST observations.

Dynamical and physical features of Perseid meteoroids from Tajikistan fireball network observations

ABSTRACT We present the results of a study of the dynamical and physical properties of large-sized Perseid meteoroids based on optical observations. Photographic observations of the Perseid meteor shower were carried out during the maximum of its activity in 2007–2011 using the Tajikistan fireball network. Multistation images of 29 Perseids recorded during this period were processed. The atmospheric trajectories, velocities, radiants, orbits, photometric masses and densities of the meteoroids were determined using the astrometric and photometric reduction of fireball images. The initial masses of meteoroids that produced fireballs range from several to 20 g. The observed light-curves of the Perseids and the mean bulk density of most meteoroids of ~0.4 g cm−3 are typical for cometary matter. According to the radiants, velocities and orbits, the captured Perseids are related both to the annual component of the stream and to the dust trail ejected by the parent comet 109P/Swift–Tuttle during its last perihelion passage in 1992.