Passing stars can perturb the Oort Cloud, triggering comet showers and potentially extinction events on Earth. We combine velocity measurements for the recently discovered, nearby, low-mass binary system WISE J072003.20-084651.2 (“Scholz’s star”) to calculate its past trajectory. Integrating the Galactic orbits of this ~0.15 M⊙ binary system and the Sun, we find that the binary passed within only 52+23−14 kAU (0.25+0.11−0.07 pc) of the Sun 70+15−10 kya (1σuncertainties), i.e., within the outer Oort Cloud. This is the closest known encounter of a star to our solar system with a well-constrained distance and velocity. Previous work suggests that flybys within 0.25 pc occur infrequently (~0.1 Myr−1). We show that given the low mass and high velocity of the binary system, the encounter was dynamically weak. Using the best available astrometry, our simulations suggest that the probability that the star penetrated the outer Oort Cloud is ~98%, but the probability of penetrating the dynamically active inner Oort Cloud (<20 kAU) is ~10−4. While the flyby of this system likely caused negligible impact on the flux of long-period comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.
Two years ago, the Russian government provided a tally: two submarines, 14 reactors — five of which contain spent nuclear fuel — 19 other vessels sunk with radioactive waste on board, and about 17,000 containers holding radioactive waste. The last known dumping occurred in 1993.
Of particular concern are the two submarines, the K-27, which was dumped into the Kara Sea in 1981, and the K-159, which sunk in 2003 into the Barents Sea, while being towed for dismantling. After an expedition to the K-159 last summer, Russian authorities concluded that there was no unusual radioactivity.
“There was no extra radiation from that submarine,” Nils Bohmer, a nuclear expert at the Bellona Foundation, a Norwegian environmental nonprofit, told VICE News. “But later the Russian authorities said that within 10 to 15 years, a decision had to be made whether or not the sub should be lifted.”