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The near-Earth asteroid (3200) Phaethon is the parent body of the Geminid meteor stream. Phaethon is also an active asteroid with a very blue spectrum. We conducted polarimetric observations of this asteroid over a wide range of solar phase angles α during its close approach to the Earth in autumn 2016. Our observation revealed that Phaethon exhibits extremely large linear polarization: P  = 50.0 ± 1.1% at α  = 106.5°, and its maximum is even larger. The strong polarization implies that Phaethon’s geometric albedo is lower than the current estimate obtained through radiometric observation. This possibility stems from the potential uncertainty in Phaethon’s absolute magnitude. An alternative possibility is that relatively large grains (~300 μm in diameter, presumably due to extensive heating near its perihelion) dominate this asteroid’s surface. In addition, the asteroid’s surface porosity, if it is substantially large, can also be an effective cause of this polarization. (3200) Phaethon is a near-Earth asteroid discovered in 1983 that has large inclination and eccentricity. Here, the authors perform polarimetric observation of Phaethon over a wide range of solar phase angle and report that the asteroid exhibits a very strong linear polarization.

We present time series medium-band (R ∼ 20–40) observations of the third interstellar object (ISO) 3I/ATLAS (C/2025 N1) obtained with the 7-Dimensional Telescope, which enabled spatially resolved monitoring of its gas and dust activity from 2025 July to September. The m400-band image (λc = 400 nm, Δλ ≈ 25 nm) reveals an emergence of a pronounced and spatially extended CN emission at a heliocentric distance of rh < 3 au. This onset is consistently identified across multiple diagnostics, including a break in the light-curve evolution, excess reflectance, inward expansion of annular excess beyond 10,000–20,000 km, growth of the coma half-light radius from ∼11,000 to ∼19,000 km, and a rapid rise in the CN production rate QCN relative to Afρ. We further separate the CN-emitting and dust-scattered components via two-dimensional surface brightness fitting into inner (dust) and outer (gas) components. We find that the outer component preserves a nearly constant profile shape, varying only in normalization, implying a relatively fast expansion of CN-bearing molecules. Together, these results reveal how a transition occurs in the optical from dust-dominated scattering at large heliocentric distances to volatile-driven, gas-dominated activity as 3I/ATLAS enters the inner solar system. The timing and characteristics of the CN activation resemble the volatile enhancement observed in 2I/Borisov, suggesting that both known active ISOs exhibit comparable activation behavior at heliocentric distances of ∼2–3 au.

We conducted contemporaneous optical and near-infrared polarimetric and spectroscopic observations of C/2023 A3 (Tsuchinshan-ATLAS, hereafter T-A) from 2024 October 16 to December 17, covering a wide range of phase angles (20°–123°) and wavelengths (0.5–2.3 μm). We paid special attention to gas contamination in the dust polarization using these data. As a result, we find the maximum polarization degree Pmax=31.21%±0.05 %, 33.52% ± 0.06%, 35.12% ± 0.01%, 37.57% ± 0.01%, and 35.35% ± 0.01% in the Rc, Ic, J, H, and Ks bands, respectively. Although dust polarization shows a red slope at shorter wavelengths and can peak around 1.6 μm, the phase angle at which maximum polarization occurs exhibits less dependence on wavelength ( αmax∼90° –95°). Although only a few historically bright comets, such as West, Halley, and Hale–Bopp, have undergone such extensive dust-polarization observations, our measurements are generally consistent with those of two comets that possibly originated from the Oort Cloud (West and Halley). From these results, we conjecture that the optical properties and growth processes of dust in the presolar nebula, which formed these cometary nuclei, were likely uniform.

Studying small near-Earth asteroids is important in order to understand their dynamical histories and origins as well as to mitigate the damage caused by asteroid impacts on Earth. We report the results of multicolor photometry of the tiny near-Earth asteroid 2015 RN35 using the 3.8 m Seimei telescope in Japan and the TRAPPIST-South telescope in Chile over 17 nights in 2022 December and 2023 January. We observed 2015 RN35 across a wide range of phase angles from 2° to 30° in the g, r, i, and z bands in the Pan-STARRS system. These lightcurves show that 2015 RN35 is in a nonprincipal axis spin state with two characteristic periods of 1149.7 ± 0.3 s and 896.01 ± 0.01 s. We found that the slope of the visible spectrum of 2015 RN35 is as red as asteroid (269) Justitia, one of the very red objects in the main belt, which indicates that 2015 RN35 can be classified as an A- or Z-type asteroid. In conjunction with the shallow slope of the phase curve, we suppose that 2015 RN35 is a high-albedo A-type asteroid. We demonstrated that surface properties of tiny asteroids could be well constrained by intensive observations across a wide range of phase angles. 2015 RN35 is a possible mission-accessible A-type near-Earth asteroid with a small Δv of 11.801 km s−1 in the launch window between 2030 and 2035.

Asteroid systems such as binaries and pairs are indicative of the physical properties and dynamical histories of small solar system bodies. Although numerous observational and theoretical studies have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC15 in 2022 December to investigate its surface properties. The rotation period of 2010 XC15 is possibly a few to several dozen hours and the color indices of 2010 XC15 are derived as g − r = 0.435 ± 0.008, r − i = 0.158 ± 0.017, and r − z = 0.186 ± 0.009 in the Pan-STARRS system. The linear polarization degrees of 2010 XC15 are a few percent at the phase angle range of 58°–114°. We found that 2010 XC15 is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC15 and 1998 WT24 are of common origin (i.e., an asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC15 and 1998 WT24 was transported from the main belt through the ν 6 resonance or Hungaria region.

Large terrestrial bodies in our solar system like the Earth, Mars, Mercury, and the Moon exhibit geologically complex surfaces with compositional heterogeneity. From past studies using large telescopes and spacecraft, it was shown that asteroids with diameters larger than 100 km also show surface heterogeneity at hemispheric scales, while on smaller objects, such features remain to be detected. Here, we investigate candidates for surface heterogeneity in a sample of 130 main-belt asteroids using multiepoch spectroscopic data from the MIT–Hawaii Near-Earth Object Spectroscopic Survey, which has been observing asteroids for about 20 yr using a self-consistent observation technique. Twelve conservative candidates with spectra more than 3σ apart from each other at 2.4 μm and 52 optimistic candidates for surface heterogeneity are detected. These candidates include eight objects already reported as being heterogeneous. Our study suggests that the size boundary between small homogeneous asteroids and larger heterogeneous objects, if it exists, is lower than 100 km. A-type asteroids have a higher proportion of heterogeneous candidates than other asteroids. This may be because olivine, which is the main surface constituent of these objects, reacts more efficiently to space weathering with respect to pyroxene, such that a similar range of surface ages will translate into a wider range of optical-to-near-infrared spectral slopes in the case of A-type bodies.

Chronic circadian disruption due to shift work or frequent travel across time zones leads to jet‐lag and an increased risk of diabetes, cardiovascular disease, and cancer. The development of new pharmaceuticals to treat circadian disorders, however, is costly and hugely time‐consuming. We therefore performed a high‐throughput chemical screen of existing drugs for circadian clock modulators in human U2OS cells, with the aim of repurposing known bioactive compounds. Approximately 5% of the drugs screened altered circadian period, including the period‐shortening compound dehydroepiandrosterone (DHEA; also known as prasterone). DHEA is one of the most abundant circulating steroid hormones in humans and is available as a dietary supplement in the USA. Dietary administration of DHEA to mice shortened free‐running circadian period and accelerated re‐entrainment to advanced light–dark (LD) cycles, thereby reducing jet‐lag. Our drug screen also revealed the involvement of tyrosine kinases, ABL1 and ABL2, and the BCR serine/threonine kinase in regulating circadian period. Thus, drug repurposing is a useful approach to identify new circadian clock modulators and potential therapies for circadian disorders. Synopsis Chronic circadian misalignment has long term consequences on our health and leads to increased risk of developing diabetes, cardiovascular disease and cancer. Using a drug repurposing approach, dehydroepiandrosterone (DHEA) was identified as an important circadian clock modulator. Approximately 5% of the screened drugs altered circadian period. DHEA shortened circadian period in cells and tissues. When fed to mice, DHEA shortened circadian period and significantly reduced jet‐lag. ABL1/2 tyrosine kinases and BCR serine/threonine kinase are involved in regulating circadian period. Drug repurposing is a useful approach to identify new circadian clock modulators. Graphical Abstract Chronic circadian misalignment has long term consequences on our health and leads to increased risk of developing diabetes, cardiovascular disease and cancer. Using a drug repurposing approach, dehydroepiandrosterone (DHEA) was identified as an important circadian clock modulator.

We present independent polarimetric observations of the interstellar object 3I/ATLAS, including the first near-infrared polarimetric measurements. Using imaging polarimeters, we measured the degree of linear polarization from the visible RC band (0.64 μm) to the near-infrared Ks band (2.25 μm), and investigated its dependence on solar phase angle (polarization phase curve, PPC) and wavelength (polarization color curve, PCC). We confirm that the PPC of 3I/ATLAS differs significantly from those of typical solar system comets, showing an unusually large polarization amplitude. This PPC shows no significant change in the RC band across perihelion passage, despite the perihelion lying within the water snow line. This indicates that the unusual polarimetric behavior of 3I/ATLAS is unlikely to be driven by transient volatile activity, but instead reflects intrinsic optical properties of refractory dust particles. The PCC increases with wavelength over 0.6–1.2 μm and peaks at 1.5–2.0 μm, suggesting that the dominant scattering units are dust aggregates composed of submicron-sized monomers, broadly consistent with interstellar dust and solar-system cometary aggregates. Taken together, our results indicate that 3I/ATLAS preserves polarimetric properties characteristic of a primitive cometary planetesimal formed in another planetary system, with a refractory dust composition that differs from that typically observed among solar system comets, despite sharing a similar size scale of the aggregate building blocks.

Dust emission was detected on main-belt asteroid 596 Scheila in 2010 December and was attributed to the collision of a few-tens-of-meters projectile on the surface of the asteroid. In such an impact, the ejected material from the collided body is expected to mainly come from its fresh, unweathered subsurface. Therefore, it is expected that the surface of 596 was partially or entirely refreshed during the 2010 impact. By combining spectra of 596 from the literature and our own observations, we show that the 2010 impact event resulted in a significant slope change in the near-infrared (0.8–2.5 μm) spectrum of the asteroid, from moderately red (T type) before the impact to red (D type) after the impact. This provides evidence that red carbonaceous asteroids become less red with time due to space weathering, in agreement with predictions derived from laboratory experiments on the primitive Tagish Lake meteorite, which is spectrally similar to 596. This discovery provides the very first telescopic confirmation of the expected weathering trend of asteroids spectrally analog to Tagish Lake and/or anhydrous chondritic porous interplanetary dust particles. Our results also suggest that the population of implanted objects from the outer solar system is much larger than previously estimated in the main belt, but many of these objects are hidden below their space-weathered surfaces.

From 2025 August 1 to August 15 UT, the SPHEREx spacecraft observed interstellar object 3I/ATLAS. Using R = 40–130 spectrophotometry at λ = 0.7–5 μm, lightcurves, spectra, and imaging of 3I were obtained. From these, robust detections of water gas emission at 2.7–2.8 μm and CO2 gas at 4.23–4.27 μm plus tentative detections of 13CO2 and CO gas were found. A slightly extended H2O coma was detected, and a huge CO2 atmosphere extending out to at least 4.2 × 105 km was discovered. Gas production rates and 1σ errors for H2O, 12CO2, 13CO2, and CO were Qgas = 3.2 × 1026 ± 20%, 1.6 × 1027 ± 10%, 1.3 × 1025 ± 25%, and 1.0 × 1026 ± 25%, respectively. Coaddition of all λ = 1.0–1.5 μm scattered light continuum images from 3I produced an image with high signal-to-noise ratio consistent with an unresolved source. The lightcurve of scattered light showed ≲15% variability over the observation period. The absolute brightness of 3I at 1.0–1.5 μm is consistent with a nucleus of <2.5 km radius surrounded by a 100 times brighter coma. The 1.5–4.0 μm continuum structure shows a strong spectral feature commensurate with water ice absorption seen in Kuiper Belt objects and distant comets. The observed cometary behavior of 3I, including its preponderance of CO2 emission, lack of CO output, small size, and predominance of large icy chunks of material in a flux-dominant coma, is similar to the behavior of short-period comet 103P/Hartley 2, the ”hyperactive, strongly thermally processed comet” flyby target of the NASA Deep Impact Extended mission in 2010. This correspondence suggests that interstellar objects can be significantly thermally processed before ejection into the interstellar medium, and by comparison to 1I and 2I, this processing can be widely variable in its physical outcome.