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ABSTRACT We present the characteristics of interstellar comet 3I/Asteroid Terrestrial-impact Last Alert System (ATLAS), discovered on 2025 July 1 by the ATLAS. The comet has eccentricity $$\simeq$$6.1 and velocity at infinity $$\simeq$$57 km s−1, indicating an interstellar origin. We obtained B, V, R, I, g, r, i, and z photometry at Kottamia Astronomical Observatory, Palomar Observatory, and Apache Point Observatory on 2025 July 2, 3, and 6. We measured colour indices B–V = 0.98 $$\pm$$ 0.23, V–R = 0.71 $$\pm$$ 0.09, R–I = 0.14 $$\pm$$ 0.10, g–r = 0.84 $$\pm$$ 0.05, r–i = 0.16$$\pm$$0.03, i–z = –0.02$$\pm$$0.07, g–i = 1.00$$\pm$$0.05, and a spectral slope of 16.0 $$\pm$$ 1.9 $${{\ \rm per\ cent}}$$/100 nm. We estimate the comet’s dust cross-section within 10 000 km to be 184.6 $$\pm$$ 4.6 km$^2$, assuming a 0.1 albedo. 3I/ATLAS’s coma has full width at half-maximum $$\simeq$$ 2.2 arcsec and A(0$$^\circ$$)f$$\rho$$ = 280.8 $$\pm$$ 3.2 cm. We estimate 3I/ATLAS is ejecting $$\mu$$m to mm dust at $$\sim$$0.01–1 m s−1, with a mass-loss of $$\sim$$0.1–1.0 kg s−1.
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This content will become publicly available on April 6, 2027
The shape and spin state of (275677) 2000 RS11 from ground-based radar and optical observations
ABSTRACT Near-Earth asteroid (275677) 2000 RS$$_{11}$$ was observed over 5 d in March 2014 with both the Arecibo (2380 MHz, 12.6 cm) and Goldstone (8560 MHz, 3.5 cm) planetary radar systems. The continuous-wave spectra and delay-Doppler images collected revealed a sub-km-sized object with a strongly bifurcated shape. We used these radar observations, in combination with seven optical light curves collected in 2014 and one light curve from 2023, to create a comprehensive shape and spin-state model for RS$$_{11}$$. We find a rotation period of $$P = (4.445\pm 0.001)$$ h around a pole of $$\lambda = (225\pm 80)^{\circ }$$ and $$\beta = (-80\pm 9)^{\circ }$$ relative to the plane of the ecliptic. The shape of RS$$_{11}$$ is unusual in that it does not resemble many of the other near-Earth asteroids modelled with ground-based radar. Whilst RS$$_{11}$$ consists of a largely spherical, smaller lobe attached to an elongated, larger lobe via a narrow neck, the smaller lobe is not aligned with the long axis of the larger lobe, but is closer to the larger lobe’s shortest principal axis. In combination with a large concavity observed on the outer face of the larger lobe, this may point to an unusual formation or event in the object’s past. We estimate that RS$$_{11}$$ has a geometric albedo of $$p_v = (0.16 \pm 0.06)$$ and a radar albedo $$0.08\lt \eta _{\rm OC}\lt 0.16$$. Analysis of its gravitational environment reveals that for standard S-type asteroid densities, we would not expect rotational instability and it is possible for RS$$_{11}$$ to be a low tensile strength rubble-pile asteroid.
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- Award ID(s):
- 2303858
- PAR ID:
- 10699474
- Publisher / Repository:
- Monthly Notices of the Royal Astronomical Society
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 548
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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