After the 2017 detecton of 1I/’Oumuamua, comet 2I/Borisov has become the second recognized interstellar interloper. Like ‘Oumuamua, Borisov’s measured hyperbolic trajectory and speed as it falls toward the Sun confirm that its origin is from beyond our Solar System. But while detailed observations indicate ‘Oumuamua is a rocky body with differences from known Solar System objects, Borisov is definitely a far wandering comet. Taken on October 12, 2019 this Hubble Space Telescope image of Borisov reveals a familiar looking comet-like activity and concentration of dust around around its nucleus. Not resolved in the image, some estimates suggest the nucleus could be between 2 and 16 kilometers in diameter. At the time of the Hubble image, comet 2I/Borisov was about 418 million kilometers away. Borisov is still inbound though and will make its closest approach to the Sun on December 7 at a distance of about 300 million kilometers (2 Astronomical units).
On July 29, 2011 the Cassini spacecraft’s narrow-angle camera took this snapshot and captured 5 of Saturn’s moons, from just above the ringplane. Left to right are small moons Janus and Pandora respectively 179 and 81 kilometers across, shiny 504 kilometer diameter Enceladus, and Mimas, 396 kilometers across, seen just next to Rhea. Cut off by the right edge of the frame, Rhea is Saturn’s second largest moon at 1,528 kilometers across. So how many moons does Saturn have? Twenty new found outer satellites bring its total to 82 known moons, and since Jupiter’s moon total stands at 79, Saturn is the Solar System’s new moon king. The newly announced Saturnian satellites are all very small, 5 kilometers or so in diameter, and most are in retrograde orbits inclined to Saturn’s ringplane. You can help name Saturn’s new moons, but you should understand the rules. Hint: A knowledge of Norse, Inuit, and Gallic mythology will help.
How do binary stars form? To help find out, ESO’s Atacama Large Millimeter Array (ALMA) recently captured one of the highest resolution images yet taken of a binary star system in formation. Most stars are not alone — they typically form as part of a multiple star systems where star each orbits a common center of gravity. The two bright spots in the featured image are small disks that surround the forming proto-stars in [BHB2007] 11, while the surrounding pretzel-shaped filaments are gas and dust that have been gravitationally pulled from a larger disk. The circumstellar filaments span roughly the radius of the orbit of Neptune. The BHB2007 system is a small part of the Pipe Nebula (also known as Barnard 59), a photogenic network of dust and gas that protrudes from Milky Way’s spiral disk in the constellation of Ophiuchus. The binary star formation process should be complete within a few million years.
Have you contemplated your home galaxy lately? If your sky looked like this, perhaps you’d contemplate it more often! The featured picture is actually a composite of two images taken last month from the same location in south Brazil and with the same camera — but a few hours apart. The person in the image — also the astrophotographer — has much to see in the Milky Way Galaxy above. The central band of our home Galaxy stretches diagonally up from the lower left. This band is dotted with spectacular sights including dark nebular filaments, bright blue stars, and red nebulas. Millions of fainter and redder stars fill in the deep Galactic background. To the lower right of the Milky Way are the colorful gas and dust clouds of Rho Ophiuchi, featuring the bright orange star Antares. On this night, just above and to the right of Antares was the bright planet Jupiter. The sky is so old and so familiar that humanity has formulated many stories about it, some of which inspired this very picture.