My first Magazine Sky & Telescope - 04.2019

NEWS NOTES SOLAR SYSTEM a rare look at the origins of the solar sys- tem. Dynamicists suspect that this body formed directly in the frigid fringe of the solar nebula 4½ billion years ago and has remained largely unchanged ever since. 0.12 The two lobes rotate around as a 0.10 single structure in roughly 15 hours, a relatively slow spin that doesn’t create 0.08 nearly enough centripetal force to ﬂ ing them apart. They’re “soundly bound” in 0.06 a structural sense, notes investigator Jef- frey Moore (NASA Ames), though they’re 0.04 essentially “resting on each other.” 0.02 The larger globe of 2014 MU 69 (dubbed “Ultima”) has roughly three times the 0.00 volume of its companion (“Thule”). They probably consist primarily of ice, but their surfaces are actually quite dark, p Left: This view of 2014 MU 69 combines a de- tailed black-and-white image (140 m per pixel) reﬂ ecting between 6% and 13% of the with a lower-resolution, enhanced-color image weak sunlight striking them. The red- using blue, red, and near-infrared frames. Right: dish hue, thought to arise from complex Overall, the two lobes are roughly as dark as the organic compounds pounded for eons by Moon’s maria, though the “neck” that joins them space radiation, matches that of other is both brighter and less red than elsewhere. low-inclination Kuiper Belt objects. But the narrow “neck” joining the reddish, and mottled with brighter and two globes is both the brightest and darker markings. the least red of the surface seen so far. This “snowman” appearance was This could mean that it has a different expected — that shape had been inferred from a challenging but successful ground- composition, or perhaps it’s where small based effort to record the object’s passage particles have “rolled” down steep slopes toward the object’s center of mass. in front of a star in July 2017 (S&T: Nov. Still to come are observations taken 2017, p. 9). Moreover, astronomers now when the spacecraft passed closest, at a realize that many objects in the “classi- distance of just 3,535 km. Speciﬁ cally, a cal” Kuiper Belt are also binaries. These series of images taken by the Long Range objects, like 2014 MU 69 , lie 40 to 50 astronomical units from the Sun and have Reconnaissance Imager (LORRI), essen- tially a 20.8-cm f/13 telescope, could roughly circular, low-inclination orbits. reveal details on the two lobes’ surfaces This object became New Horizons’ post-Pluto target simply because the space- down to about 17 m across. craft could reach it. Nevertheless, it offers ■ J. KELLY BEATTY First Views of Distant Object “Ultima Thule” AT 5:33 UNIVERSAL TIME on Janu- ary 1st, NASA’s New Horizons spacecraft successfully ﬂ ew past the tiny Kuiper Belt world 2014 MU 69 , better known by the nickname “Ultima Thule” (pro- nounced UL-ti-muh THOO-lee, meaning “beyond the known world”). The highly anticipated event occurred some 6.6 billion km (4.1 billion miles) from Earth and 3½ years after the spacecraft’s his- toric encounter with Pluto in July 2015. In the days and weeks following the ﬂ yby, the slow trickle of observations radioed by the spacecraft’s 15-watt transmitter have morphed 2014 MU 69 from a 26th-magnitude blip barely observable by the Hubble Space Telescope into a tiny, colorful, and intriguing two- lobed object. It’s made of two roundish worlds nestled against each other, with one lobe somewhat larger than the other, and has a combined length of 33 km (21 miles). Both lobes are dark, slightly Astronomers discovered two dying stars spinning out coils of dust 8,000 light-years away. Although the system is ofﬁ cially known as 2XMM J160050.7-514245 (left), its snake-like appearance earned it the nickname “Apep,” after the serpentine god of ancient Egypt. At Apep’s center is a duo of massive Wolf-Rayet stars, which are blowing off their outer layers before they explode as supernovae. (The pair is unresolved at center; to their upper right is a fainter companion star.) The snake-like shape, which stretches almost half a light-year wide, arises as one of the stars carves its way through the other’s stellar wind. While one of the stars blows out material at a swift 3,400 km/s (7.6 million mph), the dusty pinwheel is ex- panding more slowly at only 570 km/s. That star might be launching dual winds, one fast and one slow, a feat indicating that it’s spinning almost fast enough to ﬂ y apart. Apep might be an example of what happens before long-duration gamma-ray bursts, thought to be massive stellar explosions. The results appear in the November 19th Nature Astronomy. ■ JOHN BOCHANSKI 8 A PR I L 2 019 • SK Y & TELESCOPE Dying Stars Make Glowing Serpent

My first Magazine Sky & Telescope - 04.2019 | Page 10